"You see but you do not observe," as Sherlock Holmes would surely have said to me.
I've become quite expert at adjusting the VFR800 starter valves - again and again - seeing the vacuum gauges but not observing what they were telling me..
The Honda book says the starter valve vacuum difference is 20mm. My gauges told me that the non-adjustable SV valve (#4) was actually 10mm but I had been ignoring the reading on the gauge and setting the other three valves the same as #4, i.e. all four SVs to 10mm.
It turns out that #4 is adjustable and quite easily so. It even has the same little locating detents as the other three SVs.
SV #4 has a couple of flat sides on it and a 3/8" open-end wrench fits perfectly. I wound it out and then out some more until the gauge read 20 mm. (I calibrated all four gauges using my brake-bleeder vacuum tool first). Then I did the SV adjustment for the 5th time but to 20 mm.
Finally, smooth as silk - just like a real motorcycle; no more snatchy throttle.
My bike is stock standard. Stock pipes, no mods to PAIR Valves or O2 sensors and all anti-pollution gear is connected and working, No Power Commander, everything by the book.
Well as the cheap gauges pictured, which I also use, are not great quality, I only use 2. First I sync both to read exactly the same on the reference cylinder, then l leave one on reference & move the other to the other 3 cylinders in turn, until the throttle is super smooth, then return to the reference to confirm its still reading exactly. Best way I've found.
Snatchy low end throttle is my only real complaint on this engine, 2004
That was my biggest complaint too. Over the years I've had a Blackbird, a Fireblade 929 and a CBR600RR and none had a snatchy throttle like the VFR800 - they all worked fine (all with anti-pollution stuff connected). I hated the VFR fuelling so much that I was very close to selling the bike but now I think I'll keep it.
Firstly, the 20mmHg difference is an allowable tolerance between the setting of all three starter valves referenced to number 4.
Secondly, assume you mean that your number 4 reference starter valve was only 100mmHg (not 10mmHg). 100mmHg seems very low and is about half the vacuum I have experienced for number 4 (see attached photos). Suggest this has been previously tampered with.
Thirdly, assume you have set the reference valve number 4 to 200mmHg. Fortunately, this is a ball park figure which could work well to balance the others to, as the manual mentions that the MAP (Manifold Absolute Pressure) at Idle is between 200 - 250mmHg
Searching through the service manual there appears to be no vacuum value stated for the Reference Starter Valve - and possibly for good reason as it is factory set and no doubt the reading would vary depending on your local conditions being, temperature, barometric pressure and altitude. Number 4 should not be messed with and the others balanced to it at an idle speed of 1200rpm and at normal operating temperature. In your case it appears someone has previously messed with it.
Attached are two post adjustments done on a 2007 and 2009 VFR - note the difference between the reference number 4 valves for both bikes which were NOT adjusted, first bike 200mmHg and second bike 240mmHg. Also the 20mmHg allowable difference tolerance is shown between two major graduations, so both bikes are well within spec. Both bikes had no fuelling issues in the low throttle band after adjustment.
Hope this clears the air a bit. Glad you got your bike working well.
Grom this thread is older but you sucked me in anyway.
Can't speak for the 7th gen but on prior bikes the 4th cylinder was glued or locked in place. If they do the same on the 7th gen then the fact that it is movable is support for what Grum said that it had been altered.
To Grom's point note that the tolerance is 20 mm but your gauge in mm has an extra zero so your absolute setting is 20 cm. So the setting is 20 cm +- 20mm. Maybe you just mis-typed which is easy to do, but I thought I'd point it out because I originally had a similar misunderstanding.
Does this apply to fifth gens? My throttle is snacthy at low rpms. I've never done anything with starter valves in about 140,000 miles of fifth gens.
Hi MaxSwell.
After 140,000 miles I would say a Starter Valve Synch is looooooooong overdue. Having it checked and adjusted could well sort out your low throttle issues as this is just the area where starter valve synch is critical, at the very low throttle opening range.
Yes make sure and use the 5th gen manual. The 5th gen has staggered vacuums while the 6th gen has identical settings per cylinder.
MaxSwell, I bet $1 that your bikes have had the idle adjusted, yes? As it ages the cylinder vacuums diverge from the spec and the idle gets rougher and goes down. The rider may begin stalling thinking that they aren't gassing it enough at the stoplight or that the idle is too low, and thus adjust the idle up.
Once you tune the starter valves the idle will shoot up and you'll see when done the final step is adjusting the idle back down to 1200. The new idle is smoother and more powerful, much easier to tool around the parking lot with little or no throttle and partial clutch. And most if not all of the on/off behavior of the throttle will be gone.
Yes, whatever problems are left can be corrected with fuel controllers. But tuning the bike is a critical first step. Speaking of which, if you have a Power Commander now, it may be over-fueling in order to compensate. I was able to tune my PC before I could get the starter valves tuned so I know. At 3700 RPMs, partial throttle, 35 mph, the engine shakes. Increase fuel in that area and the engine shake goes away. But the vacuum variance is still there and throttle response is still snatchy. Thus when the starter valves are tuned, the fuel should be re-adjusted, most likely leaned out in the partial throttle areas.
Thanks Knight! My eyes have been opened. Yes I've adjusted idles in the past. Now I've got something critical to do to improve things. Is there a particular measuring device I should purchase?
BTW: The 140,000+ miles were spread across five fifths. Only one, my first, had 100,000+ mi.
I am just about to tune my bike. Valves were spot on and I have removed the pair plumbing and flapper hose. Once I get it all buttoned up with new gaskets and plugs I will attempt my first sync with a PC 3 inplace.
This is what I am waiting for from Amazon. I didnt want to go with the cheaper gauges, $194.38 CAN shipped
Maxredline, would you mind adding to that post the make and model of that kit? Did you pick it over another similar item or were there few choices? The reason I ask, as I browse Amazon I don't see 4-gauge kits.
I rely on mechanics for now, so others can chime in, but it seems the 4-column single manometers that some here use have a lot of negative feedback. They seem to be a real compromise over separate gauges. And at $100 for a 4-column vs. $200 for 4-gauges, the latter seems to be a no-brainer. No?
This is what I am waiting for from Amazon. I didnt want to go with the cheaper gauges, $194.38 CAN shipped
Knight
Maxredline, would you mind adding to that post the make and model of that kit? Did you pick it over another similar item or were there few choices? The reason I ask, as I browse Amazon I don't see 4-gauge kits.
I've been contemplating doing the starter valve sync on my 6th gen. That's not a job I've ever done before. I eventually found similar units on Amazon by searching for "carburetor synchronizer" -- which surprised me since the 6th gen doesn't have, you know, like... carburetors. I guess the tool and underlying concepts are the same even though the hardware being inspected isn't. The things I learn reading VFRD!
This is what I am waiting for from Amazon. I didnt want to go with the cheaper gauges, $194.38 CAN shipped
Knight
Maxredline, would you mind adding to that post the make and model of that kit? Did you pick it over another similar item or were there few choices? The reason I ask, as I browse Amazon I don't see 4-gauge kits.
Thank you very much. What a convoluted name they labelled this item with. The kit is $129.50 USD, which seems inexpensive, but once again I see very mixed reviews.
Some things do not change. Sales and marketing people don't know that fuel injection is here, or that fuel injected vehicles have vacuum to adjust? These should be labelled "vacuum gauge", with some of the detail in the sub-header so people understand that they are sized and scaled for automotive systems.
It is 2015. Our ability to process data is infinitely greater than just a decade ago. Cannot consumer goods be labelled better?
Knight, I would consider the sync tubes if I could find glass with mercury at a reasonable price but I did not. I found tubes that were plastic that had fluid that would go bad within a year or that just required maintanence that I did not want to have to deal with in a tool.
The guages I have bought first of all don't look cheap. They could very well be cheap but the reviews of people who bought them were postive including a mechanics shop. I really don't have much info on them but when I receive them in March I will post up for you.
I found another place that sells them. Check out the page and look at the cheaper set....you decide 8)
I have a set of the Carbtune vacuum gauges with the 4 tubes and the metal sliders and I also have access to a set of digital vacuum gauges and a set of motion pro mercury tubes ( no longer available to buy ) that my good mate owns as he has a workshop
Now when we did a comparison with both sets attached to one bike via a "T" connector as on both #1's then both #2's connected and soon
The readings were almost the same well within the allowable differences less than 2mmhg between the 2 sets of gauges
We also tested the Carbtune the same way with a set of mercury gauges and same result
So maybe I got lucky and got a good set but they have served me well and seem to be more than accurate than some would have you believe
The secret to a good balance of carbs /starter valves / throttle bodies is patience ,a good airflow over the motor so the temp stays reasonably constant and allowing the motor to settle after a quick blip of the throttle after making small adjustments
I make some money out of fixing bikes and general servicing and I get to see the mess people make when they don't know how to do the job they are attempting or how to use the tools .........It can be a real eye opener
I bought the MotionPro SyncPro which is a manometer design but using a non-mercury fluid, and this has served me well on my 5th Gen and VTR1000F for the last two years. I've had no issue with fluid loss, and I do like the calibration step that ensures all tubes are balanced before starting.
My only niggle is that the scale is not mm mercury, just evenly spaced markings. For a synch where you want all cylinders equal, that's fine, but for the 5th gen that calls for staggered vacuums it is not obvious how much one should stagger the readings by. I hooked up a vacuum gauge from my vacuum brake bleeder (which is a marked in mm Hg) and deduced that the markings on the SyncPro are reasonably close to 10mm Hg.
Yeah I'm puzzled by that one too. I always believed that a good even balance was essential for smooth idling on an inline four, and that if the balance was out you could get rattles/vibes from the crank speeding up and slowing down. The VFR does have a a very uneven firing order compared to a conventional flat-plane in-line four, and I wondered if the vacuum level offset was to encourage some crank speed variation to make up for the gaps in the firing order. If so....why isn't the same thing specified in the 6th or 8th gen bikes, or 2nd-4th gen carbed bikes? Which would force me to conclude that, as the 5th gen is the first FI model, the vacuum stagger is intended to compensate for something in the FI system that they were unable to tune out in the software.
Anyone have the Common Service Manual? I think it has a comment about this, but mine is currently away. I thought it said the variance is due to different exhaust runner lengths, but we really shouldn't rely on my memory. The relative pressure from intake to exhaust is important methinks, if in fact it differs by cylinder.
Knight, the manual and other good things are on the download page, gotta love that!
I initally thought about the exhaust lenghts also but I really don't know anything about their length.Terry's explanation sounds interesting reguarding the firing order.
Once I get all my gaskets and put my viffer back together I will first go by the manual and if I don't like the sync I try the vacuum even.
Knight, the manual and other good things are on the download page, gotta love that!
I initally thought about the exhaust lenghts also but I really don't know anything about their length.Terry's explanation sounds interesting reguarding the firing order.
Once I get all my gaskets and put my viffer back together I will first go by the manual and if I don't like the sync I try the vacuum even.
I found (?) one Honda Common Service Manual in the downloads but it is circa 1988. I presume starter valves began with the fuel injection. (?)
Yes, you should see some idle difference and can decide for yourself the settings to keep. A neat method would be iterative tuning. Tweak one way, then the other, re-measure idle, rinse repeat. Would need a machine to do that repeatedly among the 3 valves though, and an extremely accurate tach would be desirable to measure incremental changes. But I dream...
The answer to the question: Why does the 5th gen Service Manual specify a slightly lower vacuum pressure on the starter valves for cylinders #3 and #4?
Because cylinders #3 and #4 experience slightly better exhaust scavenging. The 5th gen exhaust system is a 4 into 2 into 1 type. The 4 into 2 section of the exhaust is as follows: Cylinders #1 and #2 are merged and cylinders #3 and #4 are merged. Then these two merges proceed to the 2 into 1 section merge then on to the exhaust pipe.
The difference in exhaust scavenging effect between the #1 and #2 merge set and the #3 and #4 merge set is caused by the 90 degree "V" engine configuration. The 90 degree V causes the firing order to be (shown in 90 degree increments) is: 1-0-3-0-0-2-0-4, which means that cylinder #1 fires only 90 degrees after cylinder #4. This close-coupled exhaust pulse causes the #3 and #4 merge set to experience better scavenging than the #1 and #2 merge set.
GreginDenver The answer to the question: Why does the 5th gen Service Manual specify a slightly lower vacuum pressure on the starter valves for cylinders #3 and #4?
Because cylinders #3 and #4 experience slightly better exhaust scavenging. The 5th gen exhaust system is a 4 into 2 into 1 type. The 4 into 2 section of the exhaust is as follows: Cylinders #1 and #2 are merged and cylinders #3 and #4 are merged. Then these two merges proceed to the 2 into 1 section merge then on to the exhaust pipe.
The difference in exhaust scavenging effect between the #1 and #2 merge set and the #3 and #4 merge set is caused by the 90 degree "V" engine configuration. The 90 degree V causes the firing order to be (shown in 90 degree increments) is: 1-0-3-0-0-2-0-4, which means that cylinder #1 fires only 90 degrees after cylinder #4. This close-coupled exhaust pulse causes the #3 and #4 merge set to experience better scavenging than the #1 and #2 merge set.
OK, so why does the 6th gen have all equal levels? It too is a 90° V4.
OK, so why does the 6th gen have all equal levels? It too is a 90° V4.
Ok... (in spite of your use of "OK" as a conversational qualifier) I'll give you some thoughts on why the 5th gen exhaust and 6th gen exhausts might have different scavenging characteristics (this will be nothing definitive, just pointing to differences that may individually or together result in different exhaust scavenging characteristics between the 5th gen and 6th gen):
1. Unless I'm mistaken (my only hands-on experience with VFRs is the '99 5th gen I just bought) the routing of the 5th gen and 6th gen exhausts is slightly different. I can't provide you with exact measurements but the Honda engineers seem to have made subtle changes in the the routing of the 6th gen exhaust system and it's fair to assume that they may have done this to change the overall length of the piping into each of the two primary "Y" merges which could easily change the way the engine is scavenged.
2. Each of the 6th gen primary "Y" merges have an oxygen sensor protruding into them. I know from working with and configuring fuel injection systems that installing an O2 sensor can cause a change in the way an exhaust system scavenges, specifically affecting the gas velocity and how quickly that velocity drops between exhaust pulses (the Delta-V).
3. The 6th gen has a catalytic converter installed in the position where the 5th gen has a "clean flowing" 2-into-1 merge joint. If I had to point a finger at any particular item in the 6th gen exhaust that might affect exhaust gas scavenging it would be this item. From working with track cars about 30 years ago I can tell you that taking a catalytic converter out of a crossplane V8 engine's exhaust will significantly change the individual cylinder's exhaust scavenging, making 2 of the cylinders, one in each bank, run leaner (can't remember which 2 though).
Overall I'd guess that the difference you're pointing out, the fact that the 6th gen Service Manual directs you to set all of the Starter Valves to identical vacuum while the 5th gen has a different vacuum specification, is merely a side-effect of the Honda engineering team working hard to overcome the addition of emissions equipment (catalytic converter and O2 sensors) with a goal of delivering horsepower and torque ratings for the new (at the time) 6th gen that compared favorably with the (outgoing) 5th gen (it certainly would have negatively affected sales volume if the 6th gen produced less horsepower/torque than the 5th gen). As they did what was necessary to compensate for the negative effects of the catalytic converter and O2 sensors they ended up with the (purely side-effect) result that equal vacuum settings on all 4 of the Starter Valves gives the 6th gen engine its best idle and off-idle throttle characteristics.
Thank you for a highly detailed hypothesis. Much appreciated. You surely have gone to great lengths.
It wasn't my intention to challenge or refute you, just thinking out loud as I've always wondered why they are different and I understood you had put it down exclusively to the 90°V4.
I used to own a 98-99 5th gen VFR, came from factory non-catted, at the same time I owned a 6th gen (obviously catted)... There is also a catted 5th gen 00-01. If I'm not mistaken the workshop manual does not give different baseline values for catted and non-catted 5th gens.
I believe I read on here years ago that Hispanic Slammer opted for synching his 5th gen as per 6th with maybe a small twist... Not sure, my memory fails me... He swore it felt and behaved better.
Thank you for a highly detailed hypothesis. Much appreciated. You surely have gone to great lengths.
It wasn't my intention to challenge or refute you, just thinking out loud as I've always wondered why they are different and I understood you had put it down exclusively to the 90°V4.
I used to own a 98-99 5th gen VFR, came from factory non-catted, at the same time I owned a 6th gen (obviously catted)... There is also a catted 5th gen 00-01. If I'm not mistaken the workshop manual does not give different baseline values for catted and non-catted 5th gens.
I believe I read on here years ago that Hispanic Slammer opted for synching his 5th gen as per 6th with maybe a small twist... Not sure, my memory fails me... He swore it felt and behaved better.
Food for thought!
I think I've found the evidence we're looking for:
I was reading through my copy of the 19980-2001 Honda VFR800 Service Manual and when I got to Chapter 21, which is titled "Technical Features", I found a surprisingly detailed description of the bike's PGM-FI system. On page 21-10 the Service Manual description of the PGM-FI system there's an explanation of how the ECM (the Engine Control Module, located in the tail of the bike) operates. Specifically, page 21-10 shows three-dimensional graphs of each individual cylinder's MAP signal (Manifold Absolute Pressure) during low RPM operation. Here's a screen-shot of the page:
[image: Screen Shot 2017-01-01 at 8.48.31 AM.png]
You can see from this screen-shot that at low RPM the individual cylinders experience different amounts of vacuum (and as a result they each require a different level of fueling from their respective injector: No. 1 INJ, No. 2 INJ, No. 3 INJ, No. 4 INJ). I still can't explain exactly why the Service Manual procedure for Starter Valve Adjustment on page 5-68 tells us to adjust (to "drop") the vacuum on cylinders No. 3 and No. 4 but I'm pretty sure that this is the basis for it.
Ok... (in spite of your use of "OK" as a conversational qualifier) I'll give you some thoughts on why the 5th gen exhaust and 6th gen exhausts might have different scavenging characteristics (this will be nothing definitive, just pointing to differences that may individually or together result in different exhaust scavenging characteristics between the 5th gen and 6th gen):
1. Unless I'm mistaken (my only hands-on experience with VFRs is the '99 5th gen I just bought) the routing of the 5th gen and 6th gen exhausts is slightly different. I can't provide you with exact measurements but the Honda engineers seem to have made subtle changes in the the routing of the 6th gen exhaust system and it's fair to assume that they may have done this to change the overall length of the piping into each of the two primary "Y" merges which could easily change the way the engine is scavenged.
2. Each of the 6th gen primary "Y" merges have an oxygen sensor protruding into them. I know from working with and configuring fuel injection systems that installing an O2 sensor can cause a change in the way an exhaust system scavenges, specifically affecting the gas velocity and how quickly that velocity drops between exhaust pulses (the Delta-V).
3. The 6th gen has a catalytic converter installed in the position where the 5th gen has a "clean flowing" 2-into-1 merge joint. If I had to point a finger at any particular item in the 6th gen exhaust that might affect exhaust gas scavenging it would be this item. From working with track cars about 30 years ago I can tell you that taking a catalytic converter out of a crossplane V8 engine's exhaust will significantly change the individual cylinder's exhaust scavenging, making 2 of the cylinders, one in each bank, run leaner (can't remember which 2 though).
Overall I'd guess that the difference you're pointing out, the fact that the 6th gen Service Manual directs you to set all of the Starter Valves to identical vacuum while the 5th gen has a different vacuum specification, is merely a side-effect of the Honda engineering team working hard to overcome the addition of emissions equipment (catalytic converter and O2 sensors) with a goal of delivering horsepower and torque ratings for the new (at the time) 6th gen that compared favorably with the (outgoing) 5th gen (it certainly would have negatively affected sales volume if the 6th gen produced less horsepower/torque than the 5th gen). As they did what was necessary to compensate for the negative effects of the catalytic converter and O2 sensors they ended up with the (purely side-effect) result that equal vacuum settings on all 4 of the Starter Valves gives the 6th gen engine its best idle and off-idle throttle characteristics.
And has kindly been pointed out to me by CandyRed on VFRW, the 8th gen exhaust configuration is completely different again. I wonder which configuration is "best"?
Ciao,
End of thread · 38 posts recoveredWayback Machine snapshot 2 Jul 2017