Cold weather idle 4000 rpm why?

Hi all,

Where do I start in diagnosing this problem (electrical, fuel, coolant)? 2002 VFR800 idles too fast during cold weather at a specific warming-up temperature range/condition, but is fine when cold starting or when fully warmed up.

At warm/operating temps, the idle is perfect and I verified the idle adjusts properly when I turn the idle knob.

At cold startup regardless of outdoor temps, again the bike starts and idles properly. But it doesn't stay that way during cold weather (say below freezing/40 degrees) before the engine has fully warmed up.

When the weather is near or below freezing, the idle rises to 4000 rpm as the engine is warming up. The high idle won't decrease when I adjust the idle knob. But once the engine is fully warm, the rpms return to normal and respond to idle adjustment.

This problem doesn't happen when the weather is warmer, say above 40 degrees F.

I have a new battery, put in new spark plugs, put in new K&N air filter ($38 new on Amazon deal!), and re-mapped the Power Commander III using cozye's map. The problem has not changed before or after these fixes.


I've heard of an IAT sensor and a wax unit that seem to affect cold air operation. Is one or the other more likely to be the culprit, since the bike is fine when fully cold or fully warm? Or could this be related to a bad thermostat - during a test ride I noticed my coolant temp would drop below 140 degrees F with fairings off, but it was about 35 degree weather and very windy so maybe that's an unrelated problem compared to the momentary high idling issue?

More info on bike:
2002 VFR800, bought used from owner in CA. Has staintune exhaust, O2 eliminators and PCIII non-USB. Though I installed the K&N, the high-idle problem happened before that on stock air filter and continues on the K&N. Previous owner was running a bad map that was too rich and fouled the plugs (they were black/tar-covered and wet, smelling of gasoline) and also caused tarlike buildup on the stock air filter. Could there be tarlike buildup inside the cylinders that is simulating a rich condition during warmup by giving off gas during the transition from cold to warm after startup? That is too crazy but just throwing it out there). I've also noticed over the past couple of years a random smell of warmed plastic coming from the bike. It's not like burning plastic, but as if plastic is warming up and giving off a smell. I chalked that up to the staintune pipes warming up under the fairings/seat since they don't have heat shields, but maybe this is an electrical issue related to the odd high-idle condition?

Edit: Solved Turns out the fast idle wax unit was clogged, preventing coolant from flowing through the passage of the wax unit. Clearing out the passage solved the problem. The problem was exacerbated by a stuck-open thermostat. After replacing the thermostat and unclogging the fast idle wax unit, the bike warms up quickly, no fluctuating RPMs, even in below-freezing (20s and teens degree F) temperatures.

Aaron S. Ward, on 26 December 2010 - 02:27 PM, said:

Hi all,

Where do I start in diagnosing this problem (electrical, fuel, coolant)? 2002 VFR800 idles too fast during cold weather at a specific warming-up temperature range/condition, but is fine when cold starting or when fully warmed up.

At warm/operating temps, the idle is perfect and I verified the idle adjusts properly when I turn the idle knob.

At cold startup regardless of outdoor temps, again the bike starts and idles properly. But it doesn't stay that way during cold weather (say below freezing/40 degrees) before the engine has fully warmed up.

When the weather is near or below freezing, the idle rises to 4000 rpm as the engine is warming up. The high idle won't decrease when I adjust the idle knob. But once the engine is fully warm, the rpms return to normal and respond to idle adjustment.

This problem doesn't happen when the weather is warmer, say above 40 degrees F.

I have a new battery, put in new spark plugs, put in new K&N air filter ($38 new on Amazon deal!), and re-mapped the Power Commander III using cozye's map. The problem has not changed before or after these fixes.


I've heard of an IAT sensor and a wax unit that seem to affect cold air operation. Is one or the other more likely to be the culprit, since the bike is fine when fully cold or fully warm? Or could this be related to a bad thermostat - during a test ride I noticed my coolant temp would drop below 140 degrees F with fairings off, but it was about 35 degree weather and very windy so maybe that's an unrelated problem compared to the momentary high idling issue?

More info on bike:
2002 VFR800, bought used from owner in CA. Has staintune exhaust, O2 eliminators and PCIII non-USB. Though I installed the K&N, the high-idle problem happened before that on stock air filter and continues on the K&N. Previous owner was running a bad map that was too rich and fouled the plugs (they were black/tar-covered and wet, smelling of gasoline) and also caused tarlike buildup on the stock air filter. Could there be tarlike buildup inside the cylinders that is simulating a rich condition during warmup by giving off gas during the transition from cold to warm after startup? That is too crazy but just throwing it out there). I've also noticed over the past couple of years a random smell of warmed plastic coming from the bike. It's not like burning plastic, but as if plastic is warming up and giving off a smell. I chalked that up to the staintune pipes warming up under the fairings/seat since they don't have heat shields, but maybe this is an electrical issue related to the odd high-idle condition?



An IAT sensor is simply a simple thermometer that takes the temperature of the incoming air for the ECU to do proper fueling. The fueling system on a motorcycle is much more simple compared to what you would find on a modern car, and if our bikes even have an IAT, I can't imagine it would be causing your problems.

The wax unit is in place so that your bike will idle faster while cold, in order to warm up to proper temperature more quickly. Since your problem is related to cold idle RPM, I would start here. To replace you'll have to take off or raise the gas tank, take out the airbox, and possibly even remove the throttle bodies (if so, you'll need a really long philips screwdriver). It isn't terribly hard to do, but is time consuming. The only thing to watch out for is to make sure you mark which hose goes where as you're taking stuff off.

This is just a guess on my part, and I would wait to see what others on here have to add.


Regarding your thermostat, it is possible that your thermostat is stuck open, but that could also be the natural effect of air cooling your engine. If you do have to remove the throttle body, then you might as well change the thermostat, too, while you have the bike apart.

Another thought, if the idle is normal when the engine is warm, your fuel mileage isn't noticeably off, and everything seems normal, you may want to just leave it. Idling high won't hurt anything (other than you won't be able to ride around a parking lot until your bike is warm) if that is the only concern.

Back when my bike was new , it was kept on the back porch, in cold weather the bike would start up at 2,000 rpm, if you tried to move the bike before a temp reading, it would shoot to 4,000 ppm idle.

That was in the first few thousand miles, but I dont believe it does that any more, it fixed itself, My prefernce is to wait until the bike gets a temp reading, and that pretty much offers a no issue ordeal.

But this is all wax solenoid issue related , so might try not moving the bike till get a temp reading

Other wise look towards that wax unit sounds like its working though other than that one end of the spec, just an adjusment needed.

Definately sounds like the wax unit causing what you're talkin bout. I think this is normal operation though by the way you describe it, just like my 03 does when she's really really cold. As long as the idle drops back down around 2k once she starts to warm up and them down to normal (maybe slightly higher than normal) idle once fully warmed up you should be ok. I will go consult my manual to see if it says what specific RPM's it should run with the wax unit operating.

All I could find with regards to the fast idle wax unit was where it is and how to replace it. I did find the instructions for setting idle speed though:

[image: Posted Image]

The wax unit operates a plate, and its that plate to adjust. I would be very reluctant to adjust it.

Reason being after I stopped having the 4000 rpm shoo in cold winter, in the hot summer on cold starts the bike wouldnt idle high enough. But I cured that with running 1400 rpm idle. but it works great in the winter now

Really Id not take it out of neutral till you get a temp reading and see what that does, adjusting you may create other issues later on. But no the standard idle adjustment has no effect on the wax unit.

Aaron S. Ward, on 26 December 2010 - 02:27 PM, said:

during a test ride I noticed my coolant temp would drop below 140 degrees F with fairings off, but it was about 35 degree weather and very windy so maybe that's an unrelated problem compared to the momentary high idling issue?



Your coolant shouldn't be that low. It shouldn't go below 168-170 no matter how cold it is. The thermostat isn't closing. I had this on my 2000. Not the idle you describe but the cool temps. I would start there and since you are under the throttle bodies anyway i would change both the thermostat and the wax unit.

gpd211, on 26 December 2010 - 06:19 PM, said:

Your coolant shouldn't be that low. It shouldn't go below 168-170 no matter how cold it is. The thermostat isn't closing. I had this on my 2000. Not the idle you describe but the cool temps. I would start there and since you are under the throttle bodies anyway i would change both the thermostat and the wax unit.


In theory this is right, since the thermostat is fully closed at these temperatures, and the coolant is just circulating in the engine. However, it's impossible for the bike not to be air and oil-cooled. The affect of 35 degree wind without fairings might account for some of this.

To be sure you can go for another cold ride, keep the engine temp below 160 (just for this test, of course) and feel the coolant line running from the engine block to the radiator, if it is hot, your thermostat is circulating coolant when it shouldn't be and needs to be replaced.

Ah thanks for the great info everyone! I'll allow the bike to show a temperature before riding off and see if that helps, otherwise I'll pick up a wax unit. I saw it at partsfish.com, but any suggestions for other online vendors for honda parts so I can compare prices?

Thanks Ryanme17 for the advice to feel the coolant line when the temp is below opening temperature - I was frustrated that I thought there wasn't an easy way to "test" the thermostat but I overlooked your elegant solution, no disassembly required.

Aaron S. Ward, on 27 December 2010 - 12:08 AM, said:

Ah thanks for the great info everyone! I'll allow the bike to show a temperature before riding off and see if that helps, otherwise I'll pick up a wax unit. I saw it at partsfish.com, but any suggestions for other online vendors for honda parts so I can compare prices?

Thanks Ryanme17 for the advice to feel the coolant line when the temp is below opening temperature - I was frustrated that I thought there wasn't an easy way to "test" the thermostat but I overlooked your elegant solution, no disassembly required.



before you start spending money on parts, sync your starter valves and clean up the little starter valves, linkages and wax unit plunger with some carb cleaner. sounds like the linkage is hanging up a bit.

at least, that is what i would do.

My 2007 has been doing the same thing and I don't even touch the right bar till I see a temp. In temperatures 42 or below the idle sits approx 3500-4000 till I get a temp of 95. Then stays between 2000-2500 till 120 or so. I then start riding and don't have a problem at all with the bike, though my temp gets up into the 210 range usually half to work because I am going traversing hilly side streets in the suburbs of Tokyo at 20-40kph.

My understanding is at those low temps it's revving higher to heat up an for a reason and it's not an issue.

DIMford, on 27 December 2010 - 05:21 AM, said:

My understanding is at those low temps it's revving higher to heat up an for a reason and it's not an issue.
+1.

4k rpm idle during warm-up sounds very high to me. I don't think my '04 ever goes over 2k rpm during warm-up even after sitting subfreezing temps for hours. :huh:

A couple of years ago my bike exhibited a similar high idle all of a sudden. Turned out I was low on coolant. After topping up and burping the system, problem went away and has not returned.

DIMford, on 27 December 2010 - 05:21 AM, said:

My 2007 has been doing the same thing and I don't even touch the right bar till I see a temp. In temperatures 42 or below the idle sits approx 3500-4000 till I get a temp of 95. Then stays between 2000-2500 till 120 or so. I then start riding and don't have a problem at all with the bike, though my temp gets up into the 210 range usually half to work because I am going traversing hilly side streets in the suburbs of Tokyo at 20-40kph.

My understanding is at those low temps it's revving higher to heat up an for a reason and it's not an issue.


Thanks for the further information on RPM behavior during warmup - looks like my bike is not consistent with yours. I wonder if this is due to the faulty thermostat only, or if it's due to a faulty thermostat and faulty wax unit.

Just did more testing, started the bike and allowed it to warm up such that it was idling properly. Conditions were approx 30 degrees F weather, inside a garage with the door open to protect from the wind.

Conclusions
1. Faulty thermostat
2. Need new wax unit too? During warmup, RPMs include some periods of "oscillating"/"bouncing" between two different RPMs (see details below)
3. IAT sensor - symptoms/test procedure unknown for cold temps

Bad thermostat - coolant prematurely began to noticeably warm up inside the tubes and radiators about 1 minute after startup, before any temperature reading showed on the dash and before the RPMs increased from 1500 to 4000

RPM/temp behavior - after about 1.5-2 minutes of warming up, the RPMs rose to 4000 and stayed constant for about a minute and the temperature reading showed up around 90 degrees and rising very slowly (bad thermostat). After about another minute of warming, at around 100 degrees or so, the RPMs rose to 4500 and then fluctuated between 4000 and 4500 for about another minute. Temp reading continued to steadily increase. Let the bike sit and continue warming. After around 2-4 minutes near 160 degrees the RPMs dropped back down to steady 4000. Another minute or two later the RPMs continued to drop, with another phase of RPM fluctuation between 4000 and 3500 for about a minute. The temp reading hit 200 degrees, and then the RPMs leveled off at steady 3500, temp was around 205, and RPMs finally and smoothly decreased down to 1500 idle indicating the bike was warm and ready, operating normally. Before this test, I've always ridden the bike off when the temps were not showing, so I've never observed this strangeness.

I blipped the throttle several times during the warmup and it did not seem to affect the RPM behavior, including the oscillating phases.

The oscillating phases where the RPMs varied over a 500 RPM range were very strange. It was as if a ghost were sitting there revving my engine, but only within 500 RPM variance and only for two limited warming phases of a minute or so each time during the ~10 minute warmup. I can't imagine this behavior being caused only by a faulty thermostat, so I will replace both the thermostat and the wax unit unless someone knows that it's possible for this behavior to be caused only by a bad thermostat in 30 degree cold weather?

IAT sensor - Also, does anyone know what the symptoms are when the IAT sensor is bad, or how to diagnose it? My service manual mentions the sensor in a spec table at pg. 5-3 and says:
"Intake air temperature sensor resistance (at 20C/68F): 1 - 4 KOhms
Even if I verify my IAT sensor is within spec at 68 degrees F, that's not helpful to me because my performance is good when the weather is 68 degrees F. What should the resistance for the IAT sensor be at freezing cold temps? What are the symptoms when the IAT sensor goes bad at cold temps? If my IAT sensor checks out at 68F, I guess I'll just assume it works properly at 30 degrees F and not worry about it.

I've ordered only a new thermostat/o-ring and will put those in and see if the idle issue goes away with the new thermostat installation. I don't mind if I have to go back and take apart the bike again and order a new wax unit - but if I had bought a new wax unit now, before trying the thermostat, it would bother me not knowing whether the old wax unit was bad or not. I can't bring myself to "just replace it" unknowingly.

I just wish there was an easy way to test a wax unit on the bike so I could confirm whether it works or is broken. Seems like my wax unit is operating as intended, but is being thrown off by the too-cold temps that don't warm up at the rate they should due to faulty thermostat.

I've heard of cases where a coolant air bubble in the wax unit caused erratic warmup symptoms. Not sure if this has anything to do with your problem, but you can add it to your list of things to try in addition to cleaning/lubing the linkages.

Aaron S. Ward, on 28 December 2010 - 12:09 AM, said:

I've ordered only a new thermostat/o-ring and will put those in and see if the idle issue goes away with the new thermostat installation. I don't mind if I have to go back and take apart the bike again and order a new wax unit - but if I had bought a new wax unit now, before trying the thermostat, it would bother me not knowing whether the old wax unit was bad or not. I can't bring myself to "just replace it" unknowingly.

I just wish there was an easy way to test a wax unit on the bike so I could confirm whether it works or is broken. Seems like my wax unit is operating as intended, but is being thrown off by the too-cold temps that don't warm up at the rate they should due to faulty thermostat.



You can block one of the rads with card board, it would be usable to get the heat up.

DIMford, on 27 December 2010 - 05:21 AM, said:

My 2007 has been doing the same thing and I don't even touch the right bar till I see a temp. In temperatures 42 or below the idle sits approx 3500-4000 till I get a temp of 95. Then stays between 2000-2500 till 120 or so. I then start riding and don't have a problem at all with the bike, though my temp gets up into the 210 range usually half to work because I am going traversing hilly side streets in the suburbs of Tokyo at 20-40kph.

My understanding is at those low temps it's revving higher to heat up an for a reason and it's not an issue.


Interesting, my bike never went to 4,000 rpm on a cold start in freezing weather, unless I put it in gear, then it would sky rocket to 4 grand and stay there until it warmed. But I had to move it from the back porch to the front driveway while it wamoed up.

It been in a warm garage last few years and never sees freezing start up conditions.

But like you I don touch anything till I see a temp read

I rode around well into winter with cardboard taped over both of my radiators a few years back. It wasn't the same as a working thermostat, but it worked well enough for a short time.

It really is a big job to get to the wax unit and thermostat. If it was me I would just replace them both since they are in the same general area and it is so much work to get to them. It's not really hard work, there's just a lot of stuff to take off. If you do it, a shop manual (printed off of from here: http://www.vfrdiscus...service-manual/ ) can be helpful.

Also, the idea of burping the coolant system really well to make sure there are no air bubbles messing with the wax unit is definitely worth a try. I have no idea why that would cause that, but I've also heard (and had completely forgotten until now) that it can.

Ryanme17, on 28 December 2010 - 11:15 PM, said:

I have no idea why that would cause that, but I've also heard (and had completely forgotten until now) that it can.



Wax unit is in a higher position in the engine. Air travels up in a liquid, this holds true inside of an engine also. If you have an air bubble around any sensor that is supposed to be immersed in fluid the temp will not read the same, in fact because air is an insulator, it should read quite a bit lower. I've had the same problem with cars, hard to track down when it's just a small ammount of air and there's no bleeder too!!

Aaron S. Ward, on 28 December 2010 - 12:09 AM, said:

Seems like my wax unit is operating as intended, but is being thrown off by the too-cold temps that don't warm up at the rate they should due to faulty thermostat.


Hmmm... I dunno. Bad thermostats are a fairly common problem, but I can't recall the idling strangeness you describe being mentioned in any of the "my bike never warms up" threads. I guess my thought is that if the thermostat is bad, the other issues might not even be related. But then again, my forum-memory is pretty poor.

On the plus side, if it is just a kinked hose/air bubble/stuck linkage/etc you may very well fix it inadvertently while jacking with the thermostat. I would replace that and then button up the bare minimum to get her back running again, and see what changes. Good luck.

Thanks for all the input - waiting on delivery of thermostat, will post results when installed.

Aaron S. Ward, on 29 December 2010 - 11:22 PM, said:

Thanks for all the input - waiting on delivery of thermostat, will post results when installed.


Hi Aaron,

I am experiencing exactly the same with my VFR800 A5 VTEC (2006 - wonder if it is actually a 2005 model - how can I find out?).

In the cold weather we are experiencing at the moment in the UK (about 0 degrees Celcius) starting my bike will have it idle at ~2,400 RPM until the temperature reaches 60-70 degrees Celcius after which it shots up to 4,000 RPM. Hugely annoying and embarrassing as I often find myself in congested traffic when it happens (if it happens on the motorway - who cares?).

What I have uncovered so far (from this and other fora):

• Some suggest it can be caused by an air bubble/blockage in the cooling system pipes that should warm the fast idle wax unit.
  
• Another suggestion is to lubricate all the linkages on the FI system and if needed give the SV pistons a good soak of WD40 (through the small orifices next the throttle intakes) � perhaps they need to be re-synced as well?
  
• And lastly I have heard people blame the thermostat.

My bike has been stall for 2 years (in a garage), so I would not be surprised if some of the moving parts needs a bit of lubricate and exercise, but I am very keen to hear about what you have found out since your last post?

Thanks and happy riding :-)

/Lars

i only had the issue, when putting the bike in gear before getting a temp reading, in real cold weather. Once a temp reading was displayed I never had any high rpm idle high issue.

Course its beeen 80,000 mile or more since I had this scenario, it cured itself for some reason, maybe it because my wax unit isnt gettign as cold. But I learn dont put the bike in gear in real cold weather until you get a temp reading if you can help it.

Sounds like you have a stronger issue possibly

I replaced the thermostat but have suspended further re-assembly so that I can verify whether the fast idle wax unit is faulty.

Anyone know about the flow characteristics of a disconnected wax unit at below freezing temps? I'm talking about what to expect concerning whether free flow is allowed at the coolant inlet and outlet on the wax unit, in addition to whether the metal plunger is immobile etc.

I couldn't flush the old coolant out of the wax unit because it seemed like flow was clogged or prevented by a backflow valve or something, but maybe that is the intended behavior when disconnected?

I did one test: I hooked up a tube and squeeze bulb to one of the nipples and tried to force air into the wax unit to push the coolant out. I couldn't force ANY air to flow into the coolant connector that I tested, but I think I was stupidly testing the "outlet" nipple/connector. Maybe that's normal for that connector/nipple, if there is a backflow prevention valve in the wax unit to prevent backflow of coolant. I didn't get a chance to test the other nipple yet, silly me.

However, I was expecting the wax unit to freely allow fluids to flow in and/or out of either coolant connectors? I tested when the wax unit was below freezing temps, maybe that locks down coolant flow? Some coolant was sitting inside the inlet/outlet, which i expected to blow out using the tube I connected, but it wouldn't budge so I couldn't flush old coolant out of the wax unit when I tried that one nipple/connector (which I think is the "outlet" that may be intended to prevent the kind of test I performed).

So, anyone have any insights on the wax unit? I'll try to flush the coolant out of it using the other nipple/connector later tonight. It's still connected to the velocity stacks, but I may still put it in boiling water to see if that unclogs things. I'd like to know if a functional wax unit should prevent free-flow of coolant in any direction when it is at freezing temps? I noticed some contaminants when I pulled out the old/stuck thermostat, perhaps they have accumulated inside the wax unit and may be dislodged by simmering the wax unit in water over a slow flame.

Lars, on 21 January 2011 - 10:46 AM, said:

Aaron S. Ward, on 29 December 2010 - 11:22 PM, said:

Thanks for all the input - waiting on delivery of thermostat, will post results when installed.


Hi Aaron,

I am experiencing exactly the same with my VFR800 A5 VTEC (2006 - wonder if it is actually a 2005 model - how can I find out?).

In the cold weather we are experiencing at the moment in the UK (about 0 degrees Celcius) starting my bike will have it idle at ~2,400 RPM until the temperature reaches 60-70 degrees Celcius after which it shots up to 4,000 RPM. Hugely annoying and embarrassing as I often find myself in congested traffic when it happens (if it happens on the motorway - who cares?).

What I have uncovered so far (from this and other fora):

• Some suggest it can be caused by an air bubble/blockage in the cooling system pipes that should warm the fast idle wax unit.
  
• Another suggestion is to lubricate all the linkages on the FI system and if needed give the SV pistons a good soak of WD40 (through the small orifices next the throttle intakes) � perhaps they need to be re-synced as well?
  
• And lastly I have heard people blame the thermostat.

My bike has been stall for 2 years (in a garage), so I would not be surprised if some of the moving parts needs a bit of lubricate and exercise, but I am very keen to hear about what you have found out since your last post?

Thanks and happy riding :-)

/Lars


Have you tested your thermostat to verify it prevents flow to the radiator below ~160 degrees F? You can feel the hose leading to the radiator, or the radiators themselves, to verify that they don't get warm as the bike warms up. Once it reaches the temp when the thermostat opens, only then should the hose/radiator feel warm.

If your thermostat is bad like mine, and you are getting the odd behavior from the wax unit, perhaps you are simply confirming this odd behavior is normal for wax units when the thermostat is bad. It's unlikely that we both have a bad thermostat and a bat wax unit. Unless of course we both had lots of contaminants in our coolant that clogged both the thermostat and the wax unit :). But I don't know what kind of coolant was in my bike, because I bought it used and never flushed it until now after the thermostat stuck open. The coolant was clean, though I found some build-up inside the metal housing of the thermostat enclosure.

Ryanme17, on 26 December 2010 - 10:12 PM, said:

To be sure you can go for another cold ride, keep the engine temp below 160 (just for this test, of course) and feel the coolant line running from the engine block to the radiator, if it is hot, your thermostat is circulating coolant when it shouldn't be and needs to be replaced.

Aaron S. Ward, on 21 January 2011 - 06:12 PM, said:

Have you tested your thermostat to verify it prevents flow to the radiator below ~160 degrees F? You can feel the hose leading to the radiator, or the radiators themselves, to verify that they don't get warm as the bike warms up. Once it reaches the temp when the thermostat opens, only then should the hose/radiator feel warm.



Great idea! Whereever did you get it?! :biggrin:
(Just teasing, this was actually good to clarify)

The fast idle wax unit was simply clogged. No valving or anything to affect directional flow in the wax unit. It's a straight-through path for the coolant to flow. Seems the coolant warms the wax idle unit by conduction through the metal. I don't think the coolant circulates through the large cylinder portion - I think the large cylinder portion is just to contain the wax/spring/plunger system that is indirectly heated by coolant flowing through the inlet/outlet.

I believe that whatever clogged the wax unit was also responsible for clogging the thermostat causing it to get stuck open. The coolant passage in the wax unit was easy to unclog, so I hope there isn't some other hidden problem with it.

I played with the wax unit a bit, and found that when cold, I could pull the plunger out and feel the spring tension pulling it back. I tested to see if plunging would suck in fluid from the passages, but it did not seem to affect the flow at all. When warm (using boiling water at 212 deg F.) the plunger was frozen in place and would not move at all when I pulled on it. I didn't see any movement of the plunger on its own when I put the wax unit in the boiling water, so I'm not sure what happens when fast idle activates. Perhaps there is some plunger movement that happens but I wasn't paying close enough attention to verify before/after lengths.

Anyway, I will report my results when I assemble everything. I think fixing the thermostat and unclogging the wax unit will eliminate my problems.

Aaron S. Ward, on 23 January 2011 - 05:43 PM, said: The fast idle wax unit was simply clogged. No valving or anything to affect directional flow in the wax unit. It's a straight-through path for the coolant to flow. Seems the coolant warms the wax idle unit by conduction through the metal. I don't think the coolant circulates through the large cylinder portion - I think the large cylinder portion is just to contain the wax/spring/plunger system that is indirectly heated by coolant flowing through the inlet/outlet. I believe that whatever clogged the wax unit was also responsible for clogging the thermostat causing it to get stuck open. The coolant passage in the wax unit was easy to unclog, so I hope there isn't some other hidden problem with it. I played with the wax unit a bit, and found that when cold, I could pull the plunger out and feel the spring tension pulling it back. I tested to see if plunging would suck in fluid from the passages, but it did not seem to affect the flow at all. When warm (using boiling water at 212 deg F.) the plunger was frozen in place and would not move at all when I pulled on it. I didn't see any movement of the plunger on its own when I put the wax unit in the boiling water, so I'm not sure what happens when fast idle activates. Perhaps there is some plunger movement that happens but I wasn't paying close enough attention to verify before/after lengths. Anyway, I will report my results when I assemble everything. I think fixing the thermostat and unclogging the wax unit will eliminate my problems. The way the fast idle wax unit SHOULD work is as follows: When hot, the plunger should expand When cold, the plunger should be shrunk, and it will pull on the air bypass valves, effectively opening them up The idle speed adjustment is ONLY relevant for a hot engine. When the engine is cold, the idle adjustment screw does not even touch the throttle assembly at all! The idle speed control pushes on a plate which also opens the air bypass valves. So, if the fast idle wax unit is opening the air bypass valves, then adjusting the idle screw will do NOTHING AT ALL because the plate which it pushes on is being pushes by the fast idle wax unit. So, when the engine is hot, the wax expands and stops pulling on the air bypass valves. This then allows the idle adjustment plate to seat against the idle speed adjustment rod (it's a threaded rod obviously!), and that's what sets the idle speed for a hot motor. So, if your cold engine idle is high and the idle speed screw doesn't do anything, it means your fast idle wax unit is gummed up or just plain faulty. It will come down eventually due to heat soak (heat from the engine) softening the wax as opposed to the hot coolant passing through the base of it. This is the same reason why in summer the fast idle wax unit doesn't do anything - the ambient temperature is high enough to keep the wax soft.

kaldek, on 23 January 2011 - 06:32 PM, said:

The way the fast idle wax unit SHOULD work is as follows:

• When hot, the plunger should expand
  
• When cold, the plunger should be shrunk, and it will pull on the air bypass valves, effectively opening them up
  
• The idle speed adjustment is ONLY relevant for a hot engine. When the engine is cold, the idle adjustment screw does not even touch the throttle assembly at all!

The idle speed control pushes on a plate which also opens the air bypass valves. So, if the fast idle wax unit is opening the air bypass valves, then adjusting the idle screw will do NOTHING AT ALL because the plate which it pushes on is being pushes by the fast idle wax unit.
So, when the engine is hot, the wax expands and stops pulling on the air bypass valves. This then allows the idle adjustment plate to seat against the idle speed adjustment rod (it's a threaded rod obviously!), and that's what sets the idle speed for a hot motor.

So, if your cold engine idle is high and the idle speed screw doesn't do anything, it means your fast idle wax unit is gummed up or just plain faulty. It will come down eventually due to heat soak (heat from the engine) softening the wax as opposed to the hot coolant passing through the base of it. This is the same reason why in summer the fast idle wax unit doesn't do anything - the ambient temperature is high enough to keep the wax soft.


The wax unit will be under tension when it is cold with a contracted plunger because the starter valves are spring-loaded to apply a pull against the plunger when the plunger is cold/retracted. In that video, the plunger was fully extended and thus no spring force on them, so when he pulled on the starter valves, he only put some air/slack between the plunger and the starter valve linkage. But the setup in the video seems to show that when warm/extended, there is no spring force "tug-of-war" between the plunger and the starter valves.

I'll re-test my wax unit by applying a pulling force to the cold/retraced plunger as I boil it, so I can see what happens and whether that changes the results before the heat/warming eventually locks the plunger in place. The "locked" state when warm seems to be confirmed by this video - the plunger doesn't retract at all when the starter valves are opened/closed by hand.

The video gives a good idea of what kind of distance I should see the plunger when fully extended, and maybe a slight pull on the plunger during warm-up will replicate that result (simulating installed conditions). I can't find any information on a testing procedure to verify proper movement/throw of the plunger. When cold, I could definitely pull the plunger out farther and felt a spring pulling the plunger back into the wax unit. Maybe the trick to proper testing is to apply a force to the plunger when it is contracted, as it would be when installed in the bike, and as the plunger reaches full extension the applied pulling force should be decreased accordingly.

After replacing the thermostat and unclogging the fast idle wax unit, the bike warms up quickly, no fluctuating RPMs, even in below-freezing (20s and teens degree F) temperatures.

It was very easy to unclog the fast idle wax unit - just a straight-through passage. Not necessary to take the wax unit off the bike to unclog the wax unit, although I took it off for testing purposes.

[image: View Post]Aaron S. Ward, on 14 February 2011 - 12:08 AM, said:

After replacing the thermostat and unclogging the fast idle wax unit, the bike warms up quickly, no fluctuating RPMs, even in below-freezing (20s and teens degree F) temperatures.

It was very easy to unclog the fast idle wax unit - just a straight-through passage. Not necessary to take the wax unit off the bike to unclog the wax unit, although I took it off for testing purposes.



There ya go, the way its supposed to be. How did the wax unit get clogged in the first place? Wax unit clogging, Thermos chemically welding? whats the common denominator


HOndas coolant YUMMMY

[image: View Post]spud786, on 14 February 2011 - 12:23 AM, said:

[image: View Post]Aaron S. Ward, on 14 February 2011 - 12:08 AM, said:

After replacing the thermostat and unclogging the fast idle wax unit, the bike warms up quickly, no fluctuating RPMs, even in below-freezing (20s and teens degree F) temperatures.

It was very easy to unclog the fast idle wax unit - just a straight-through passage. Not necessary to take the wax unit off the bike to unclog the wax unit, although I took it off for testing purposes.



There ya go, the way its supposed to be. How did the wax unit get clogged in the first place? Wax unit clogging, Thermos chemically welding? whats the common denominator


HOndas coolant YUMMMY


There was debris in the coolant to the point it was accumulating grey gunk which I think also caused the thermostat to fail, or is a result of the thermostat failing - I don't know the history of the coolant as I bought the bike used. I removed all visible gunk from inside the bike's thermostat housing and coolant overflow, then flushed the system with a full load of distilled water before draining and adding new coolant.

[image: View Post]Aaron S. Ward, on 24 January 2011 - 12:19 PM, said:

In that video, the plunger was fully extended and thus no spring force on them, so when he pulled on the starter valves, he only put some air/slack between the plunger and the starter valve linkage.

He = Me. I'm the guy who made the video. :)