After owning my '93 3rd gen for 6 years and putting only 40,000 km on it in that time, I have noticed that it is not pulling as it used to. Recently I had a carb problem that my mechanic resolved by drilling out the seats and upsizing the needles to fatter ones. My regular mechanic has in the last 5000km rebuilt the top end, balanced the carbs and replaced all fluids. So I thought this would be a good oppurtunity to put the unifilter in and get it dynotuned.
I got a phone call from the dyno shop telling me that I had only made 53 (!) hp, this is after a service and a clutch change. "come pick it up and check the exhuast out".
It has a staintune slip on and a high-flow unifilter and has standard jetting but is still running slightly rich. It runs through the revs without hesistation and idles well, however it feels fluffy and slightly flat. Funny thing is that the exhuast feels cold coming out of the pipe and my right ankle no longer feels hot. Pulled the slip on off and it is clean inside with no scaling or sooty plates, and after blowing the collector with an air compressor, not much oily soot came out.
I'm buggered if I know what is wrong. Its going back tomorrow to be torn down and checked -sounds expensive.
So - given a 17 year old 750F with 60,000km indicated on the odomoter (and the condition and log book would suggest that this is correct) what figures should I expect? I know they made 98.5 bhp out of the factory, so given the age counteracted by the low kilometres and improved breathing I reckon I should have 80+ hp at the rear wheel? Can anyone who has run a dyno on their bike confirm this?
If the bike was running well for 40,000k I can't understand why you'd modify the carbs. Unless the carb mods occurred when you added the pipe and maybe a less restrictive air filter?? He didn't "drill out the seats" he drilled out a vacuum passage that allows the vacuum diaphragm to pull the slide earlier, which also pulls the tapered needle out of the main jet earlier, all in an effort to increase the fuel flow. K&N used to sell a kit that did just this. I think your problem is an overly rich condition, which also explains why your ankle stays cool. You had the "top end rebuilt"?? Why? Those motors usually go 3-4 times farther than your mileage before anything even starts to wear out. Sounds to me like your mechanic enjoys working on your bike (and wallet) maybe just a bit too much. Anyway, to me it sounds like your bike is running rich. If the problem was ignition, surely you could tell the bike had a dead cylinder just by listening to the idle. How's the gas mileage? If it's not as good, "there's your sign". Should be a simple task to use an exhaust sniffer to determine your actual A/F ratio at various RPM's. You'll soon find the problem. I'd bet the carb needles are set too high, and the synch is off. Carb synchronization is critical if you want to maximize the motors output. Also,have the valves adjusted by someone with the proper tools and experience when the motor is dead cold. It needs to sit overnight at least before the valves get adjusted. To be frank, it doesn't sound to me like the guy tuning the bike knows the motor very well. I'd look for a mechanic that's more experienced with tuning these motors. Best of luck to you, you just need a good tuning. Garry
[image: View Post]SEBSPEED, on 24 August 2010 - 05:13 AM, said:
I can't imagine why it would have needed a top end rebuild?
Sounds like you've lost spark to one or more spark plugs, and/or they bolloxed up the carb rebuild.
+ 1 on what Sebastian said, sounds lik at least on of your rear cylinders is not firing. Maybe one front and one rear, or *seriously* weak firing all the way around...
My 90 got dynoed with 76k miles on it, and with a tuner doing the carbs it got to about 93BHP. I did however get about 53 lb-ft of torque. Are you sure he said HP? Those figures are straight from a dynojet 100...still have the readout!
[image: View Post]racerman, on 24 August 2010 - 08:23 AM, said:
If the bike was running well for 40,000k I can't understand why you'd modify the carbs. Unless the carb mods occurred when you added the pipe and maybe a less restrictive air filter?? He didn't "drill out the seats" he drilled out a vacuum passage that allows the vacuum diaphragm to pull the slide earlier, which also pulls the tapered needle out of the main jet earlier, all in an effort to increase the fuel flow. K&N used to sell a kit that did just this. I think your problem is an overly rich condition, which also explains why your ankle stays cool. You had the "top end rebuilt"?? Why? Those motors usually go 3-4 times farther than your mileage before anything even starts to wear out. Sounds to me like your mechanic enjoys working on your bike (and wallet) maybe just a bit too much. Anyway, to me it sounds like your bike is running rich. If the problem was ignition, surely you could tell the bike had a dead cylinder just by listening to the idle. How's the gas mileage? If it's not as good, "there's your sign". Should be a simple task to use an exhaust sniffer to determine your actual A/F ratio at various RPM's. You'll soon find the problem. I'd bet the carb needles are set too high, and the synch is off. Carb synchronization is critical if you want to maximize the motors output. Also,have the valves adjusted by someone with the proper tools and experience when the motor is dead cold. It needs to sit overnight at least before the valves get adjusted. To be frank, it doesn't sound to me like the guy tuning the bike knows the motor very well. I'd look for a mechanic that's more experienced with tuning these motors. Best of luck to you, you just need a good tuning. Garry
Thanks Garry. Actually he did redrill out the seat - the reason he did this was because it was ovalled... refer this thread.
http://www.vfrdiscus...t-in-atomizers/
Its running on all 4 cylinders no missfires.
A/F averages around the low 12s.
My normal mechanic (he's the guy who did the valve clearances and the carb work) has a pretty reasonably priced and often knocks something off the bill if it took him longer than he expected... my judgement is that he is not trying to gouge me to make money.
Anyways, Its back at the dyno shop now getting torn down. Hope they sort it out quickly, as its costing me $80 aussie dollars an hour!
Oh, heres the dyno sheet. Not good power. Its so strange that it is running well and not making power.
take a spay bottle of water.. or a squirt bottle ..let you bike idle. spray your pipes near the head.. the water should vaporize on the spot.. of it runs down.. you know its sold..ergo.no spark. :fing02:
[image: View Post]Jmmymc750, on 24 August 2010 - 08:27 AM, said:
[image: View Post]SEBSPEED, on 24 August 2010 - 05:13 AM, said:
I can't imagine why it would have needed a top end rebuild?
Sounds like you've lost spark to one or more spark plugs, and/or they bolloxed up the carb rebuild.
+ 1 on what Sebastian said, sounds lik at least on of your rear cylinders is not firing. Maybe one front and one rear, or *seriously* weak firing all the way around...
My 90 got dynoed with 76k miles on it, and with a tuner doing the carbs it got to about 93BHP. I did however get about 53 lb-ft of torque. Are you sure he said HP? Those figures are straight from a dynojet 100...still have the readout!
Hmmm... I'm using high octane 98+ BP Ultimate maybe the burn rate is too slow????
Or maybe weak spark from plug leads?
Food for thought.
Thanks for the Dyno numbers, thats great information.
do a LEAK DOWN test!!
it will tell you if you have any leaks in your cylinders..
your mechanic SHOULD have done this after he did the valve job.. i have a feeling he messed up on the shims.
[image: View Post]gll429, on 24 August 2010 - 04:55 PM, said:
do a LEAK DOWN test!!
it will tell you if you have any leaks in your cylinders..
your mechanic SHOULD have done this after he did the valve job.. i have a feeling he messed up on the shims.
Yeah, right on brother. I'm with you on that one - definitely time for a compression AND leakdown test.
Don't let them get away with doing just one - they gotta do BOTH.
Your engine is running too rich. This would explain the loss of power yet smooth running of the engine. Go back to stock jetting and either replace the drilled slides or refill the holes that were drilled. My experience with jet kits is that at best they are too rich. Your stock jetting with 1/2 turn more out on the pilot adjustment will give you the best performance. I would guess your mileage is poor now too with the jetting as is.
[image: View Post]samaki, on 25 August 2010 - 10:47 PM, said:
Your engine is running too rich. This would explain the loss of power yet smooth running of the engine. Go back to stock jetting and either replace the drilled slides or refill the holes that were drilled. My experience with jet kits is that at best they are too rich. Your stock jetting with 1/2 turn more out on the pilot adjustment will give you the best performance. I would guess your mileage is poor now too with the jetting as is.
Hi samaki,
It has stock jetting, and the slids have not been drilled.
The carbs had needles replaced and seats drilled to correct the worn seats which was causing massive overfuelling at low revs. The link to that discussion is above if you are interested.
Yes it is slightly rich - but not enough to lose half the power. Something else is at play :(
The bloke at the dyno shop reckons its probably a vacuum / throttle problem in the carbs. Its back to the dyno today and hopefully they will discover what the problem is!
I'm not getting something here. please help. what is "drilling the seats"?, and if they were worn and overfueling, how does drilling them make them not worn and ristrict fuelling?
The only thing I drill on a carb is the brass cover that hides the mixture screw.
[image: View Post]timmythecop, on 26 August 2010 - 08:38 PM, said:
I'm not getting something here. please help. what is "drilling the seats"?, and if they were worn and overfueling, how does drilling them make them not worn and ristrict fuelling?
The only thing I drill on a carb is the brass cover that hides the mixture screw.
Please get me up to speed on this one.
Thanks :beer:
Seats drilled out to make them back to round and fatter needles installed.
[image: View Post]RedViffer93, on 01 September 2010 - 12:54 AM, said:
[image: View Post]timmythecop, on 26 August 2010 - 08:38 PM, said:
I'm not getting something here. please help. what is "drilling the seats"?, and if they were worn and overfueling, how does drilling them make them not worn and ristrict fuelling?
The only thing I drill on a carb is the brass cover that hides the mixture screw.
Please get me up to speed on this one.
Thanks :beer:
Seats drilled out to make them back to round and fatter needles installed.
Steve
I think they should have brazed them shut, then drilled them back to oem size.
Putting it simply, someone is yanking your chain. I just stripped and cleaned the carbs on my '93 52,000mile bike (84,000km). When I screwed up the jetting and airbox, it pulled 95.2rwhp. That was at 14.5 fuel to air.
I'm now in the mid 12s (bit rich, 13 is bang on) and I'm now pulling 97.5rwhp @ 10670rpm with a slightly modded airbox, UNI filter, pattern exhaust, race can and decent jetting. Peak torque is 57.4ft.lbs (77.5Nm) @ 8167rpm
All this on BP 98 RON.
The thread is here:
http://www.vfrdiscus...__1#entry729398
As you can see, I'm pulling 54.7hp at only 6000rpm. Also, the bike should pull all the way to redline, with the peak power at between 10.5k and 11k. If it's dropping off like yours, and firing on all cylinders, I can only assume that your valves aren't closing or you're only getting 1/2 throttle.
You'd have pitted valves on all cylinders, a roll of toilet paper in the collector and a mouse nest in the airbox for the 750 to pull only 53hp at your mileage (60,000 is only 40,000 miles).
Also, there should have been nothing much wrong with the carbs at 60,000 km. The idea that someone has drilled something out and then put fatter needles in fills me with dread. It wouldn't have been the seats because they can't really wear (the needle seats in the slide). Also, it's usually the needles that wear with use from my experience, not the hole in the carb body. If it was the hole, the correct solution as already mentioned, would have been to braize and re-drill.
Ride away from your local shop as fast as 53hp will take you. Take it to someone (friend with some mechanical skill will do), pull the carbs, return them to stock and then use a Factory Pro kit to fine tune if you want. If I was closer, I'd come over and do it myself. I'm not a mechanic, just a military helicopter driver with a habit of playing with engines and I hate to see a fellow V4er being seen off.
Just so you know, when I bought my '93 in 2005, I asked the local Honda dealer what to look for in a 750. I was told bluntly, "condition". I asked about mileage and was told, "irrelevant". When I asked why, they said a dealer in Southhampton had just rebuilt an engine for a dispatch rider for only the second time. The bike had 417,000 miles on it (675,000km). In that time it'd had plugs, oil and cam shims done and little else (engine related) and had managed something like 212,000 miles before the first rebuild and 205,000 before the second.
I'd be willing to bet that your carb problem was nothing too huge and a good clean and re-assembly would have put you back at 90+ at the rear wheel. However, that doesn't earn a mechanic much as a set of carbs can be pulled, cleaned and re-installed in about 2 hours (by me, an enthusiastic amateur).
Sorry, a couple more things. Overfuelling at low revs isn't the needles, it's the pilot (idle) jets and fuel screws. Strangely enough, the transition from the idle circuit to the needle (4-5000 rpm ish) is affected by the main jet and then the needle has the major influence from 5-6000rpm up to the top end where the main jet once again dominates.
If the carbs are returned to stock and you're getting full throttle, the valves aren't closing (poor shim job). Either way, your mechanic owes you one and should fix the problem for free and let you ride his VFR1200 while you wait.
When you get it back, it should be pulling stock + a bit until you're well over 160,000km. 95 or 98 octane will make bugger all difference other than you might run cooler with 98 and maybe suffer less from blocked idle jets due to higher grade fuel often having some extra cleaning additives in it.
Your engine doesn't have a self tuning ECU with knock sensor and all that gubbins so it can't take advantage of the higher octane unless you bump up the compression, advance the timing etc.
[image: View Post]tdchonda1, on 24 August 2010 - 07:39 AM, said:
You might want to try to see if all cylinders are firing.
You can use a laser pointer temp gun, aim at the headers right where it comes out of the engine.
just an idea.
What should the header temps be at the head? I know its more about comparing different cylinders in this case, but I was just wondering what temp range they should all be within.
[image: View Post]RedViffer93, on 16 September 2010 - 02:02 AM, said:
OK I think the consensus is that the drilling that has been done by the previous mechanic has caused this...
I can't find a another mechanic in Brisbane who wants to know about this! I keep getting told "Time to buy a new bike, 60,000 is a lot of K's"
Frustrating....
tell them they dont know crap about bikes and your vfr will out live them.
you need i can buy the tools you need at harbor freight and ship them to you.. may be able to find a good stock set of carbs too.
then walk you through a valve job.. have you donte a compression test yet? down load a manual? you CAN fix this bike. :fing02:
[image: View Post]gll429, on 16 September 2010 - 02:10 AM, said:
[image: View Post]RedViffer93, on 16 September 2010 - 02:02 AM, said:
OK I think the consensus is that the drilling that has been done by the previous mechanic has caused this...
I can't find a another mechanic in Brisbane who wants to know about this! I keep getting told "Time to buy a new bike, 60,000 is a lot of K's"
Frustrating....
tell them they dont know crap about bikes and your vfr will out live them.
you need i can buy the tools you need at harbor freight and ship them to you.. may be able to find a good stock set of carbs too.
then walk you through a valve job.. have you donte a compression test yet? down load a manual? you CAN fix this bike. :fing02:
thanks mate, I am going to try to do the compression test this weekend myself. Will let you know how I go. I'm pretty cranky with bloody mechanics right now!