'03 misfires between 5000-7000rpm on cylinders 2 or 3. Help!

[TheFleshRocket]

This is a spin-off of my thread about jet size with the UFO 4-2 exhaust. http://www.vmaxforum.net/showthread.php?t=34504

My Vmax is an '03 with almost 19K miles on it. I got it a couple hundred miles ago from a previous owner who hadn't ridden it much in the past year. It's got the UFO Streetpro 4-2 exhaust, 170 mains, needles set at 3 notches out from the pointy side, and a K&N.

Ever since getting the bike, it has had a misfire between 5000-7000rpm.

Below 5000rpm, the bike runs mostly great. (Occasionally whacking open the throttle will result in a hiccup before the bike starts pulling.) Idle is decent--at least as good as it was on my old '98.

From 5000-7000RPM, the bike will stutter and misfire. I can hear the misfire through the right-side "muffler" (I use the term muffler loosely, as this thing is bloody loud!) which means that it must be misfiring on cylinders 2 or 3. (The left front and right rear cylinder, which I call 1 and 4, exit through the left muffler. The left rear and right front cylinder, which I call 2 and 3, exit through the right muffler.)

It doesn't matter if I'm light on the throttle, medium, or WOT--it will misfire between 5-7K. Once it clears 7K, the misfire seems to disappear and the bike pulls strongly to redline.

The problem is more noticeable when the bike is cool than when it's up to operating temp, but the problem never goes away, no matter how hot the bike gets.

Having the choke engaged seems to have no effect on the misfire.

All of the diaphragms are in great shape--no rips, tears, holes, etc. The #1 cylinder diaphragm was a bit sticky in its travel, so I gave it a once-over with some 0000 steel wool, and now it seems to slide as easily as the other three.

I have run Seafoam (about 4oz) in each tank of gas.

I've pulled the carbs off the bike and cleaned them using the shotgun method. The previous owner had overoiled the K&N, so I got a fair amount of brown gunk out of some of the holes when shooting carb cleaner through them. I ended up going through three bottles of carb cleaner, but when I was done, what came out of the holes appeared to be clean.

The carb innards all appear very clean--no scale, build-up, etc. The floats all seem to move smoothly, although I did not measure them when I had the carbs off.

I've synched the carbs twice--before pulling the rack and cleaning them, and after. Sync is just about spot-on.

This morning, I did the peashooter cleaning. I literally went through an entire can of Seafoam, trying to be as thorough as possible. I made a decent smoke show while idling and also while riding the bike afterward, but it had no effect on the misfire.

I've ensured that the carbs are securely screwed to the boots and that the airbox is securely screwed to the carbs. This bike is in overall great shape, and nothing appears to be worn or dry-rotted.

There does seem to be a slight exhaust leak. It's mostly noticeable under light throttle or under trailing throttle (slowing down but with the throttle still slightly open). Instead of your typical psst psst psst exhaust leak, this one sounds like wheeet wheeet wheeet.... wheet wheet... wheet.. wheet wheet. I'm *assuming* it's unrelated, as I can't imagine how a tiny exhaust leak could cause a significant misfire.

I haven't checked the plugs or ignition system yet, but I figured since the characteristics seem to point towards a fuel issue, not a spark issue. I'll probably pull the plugs tomorrow and either replace them (if they're obviously worn) or at least swap 1-2 and 3-4 to see if that has any effect on which cylinder sounds like it's misfiring.

Any input would be appreciated. Thanks!

 

[jwood]

This is a spin-off of my thread about jet size with the UFO 4-2 exhaust. http://www.vmaxforum.net/showthread.php?t=34504

My Vmax is an '03 with almost 19K miles on it. I got it a couple hundred miles ago from a previous owner who hadn't ridden it much in the past year. It's got the UFO Streetpro 4-2 exhaust, 170 mains, needles set at 3 notches out from the pointy side, and a K&N.

Ever since getting the bike, it has had a misfire between 5000-7000rpm.

Below 5000rpm, the bike runs mostly great. (Occasionally whacking open the throttle will result in a hiccup before the bike starts pulling.) Idle is decent--at least as good as it was on my old '98.

From 5000-7000RPM, the bike will stutter and misfire. I can hear the misfire through the right-side "muffler" (I use the term muffler loosely, as this thing is bloody loud!) which means that it must be misfiring on cylinders 2 or 3. (The left front and right rear cylinder, which I call 1 and 4, exit through the left muffler. The left rear and right front cylinder, which I call 2 and 3, exit through the right muffler.)

It doesn't matter if I'm light on the throttle, medium, or WOT--it will misfire between 5-7K. Once it clears 7K, the misfire seems to disappear and the bike pulls strongly to redline.

The problem is more noticeable when the bike is cool than when it's up to operating temp, but the problem never goes away, no matter how hot the bike gets.

Having the choke engaged seems to have no effect on the misfire.

All of the diaphragms are in great shape--no rips, tears, holes, etc. The #1 cylinder diaphragm was a bit sticky in its travel, so I gave it a once-over with some 0000 steel wool, and now it seems to slide as easily as the other three.

I have run Seafoam (about 4oz) in each tank of gas.

I've pulled the carbs off the bike and cleaned them using the shotgun method. The previous owner had overoiled the K&N, so I got a fair amount of brown gunk out of some of the holes when shooting carb cleaner through them. I ended up going through three bottles of carb cleaner, but when I was done, what came out of the holes appeared to be clean.

The carb innards all appear very clean--no scale, build-up, etc. The floats all seem to move smoothly, although I did not measure them when I had the carbs off.

I've synched the carbs twice--before pulling the rack and cleaning them, and after. Sync is just about spot-on.

This morning, I did the peashooter cleaning. I literally went through an entire can of Seafoam, trying to be as thorough as possible. I made a decent smoke show while idling and also while riding the bike afterward, but it had no effect on the misfire.

I've ensured that the carbs are securely screwed to the boots and that the airbox is securely screwed to the carbs. This bike is in overall great shape, and nothing appears to be worn or dry-rotted.

There does seem to be a slight exhaust leak. It's mostly noticeable under light throttle or under trailing throttle (slowing down but with the throttle still slightly open). Instead of your typical psst psst psst exhaust leak, this one sounds like wheeet wheeet wheeet.... wheet wheet... wheet.. wheet wheet. I'm *assuming* it's unrelated, as I can't imagine how a tiny exhaust leak could cause a significant misfire.

I haven't checked the plugs or ignition system yet, but I figured since the characteristics seem to point towards a fuel issue, not a spark issue. I'll probably pull the plugs tomorrow and either replace them (if they're obviously worn) or at least swap 1-2 and 3-4 to see if that has any effect on which cylinder sounds like it's misfiring.

Any input would be appreciated. Thanks!

I would guess the vboost is still intact and functional? Do you hear the servo cycle when the key is initially turned on?

 

[TheFleshRocket]

Vboost appears to be functioning normally. During one of my troubleshooting sessions, I installed a Tboost.

With the Vboost off, the problem is most noticeable.

With the Vboost set to come on at the stock RPM (5500 or so), the problem is less noticeable but still pretty obvious.

With the Vboost set to come on at 3000rpm, the problem persists but is the least noticeable.

Since presumably the Vboost richens up the mixture, that also suggests that one of the carbs (again, presumably 2 or 3--right rear or left front) are running lean.

 

[jwood]

Try unplugging the vboost in the open position during the servo cycle... My bike does the same thing between 5 and 7 thousand rpm.. I now run open vboost 100% of the time with no issues! With the setup you have stated, I believe you need the VBOOST open 100% of the time...

 

[thor_eyerdhal]

Worst when cold could be a lean issue..

Try to raise the needles.

 

[TheFleshRocket]

I raised the needles from #4 to #3 and that helped a little bit, so it does seem to be a lean issue. But I feel like raising the needles isn't the "right" fix since one particular cylinder is misfiring. IE I shouldn't richen up all of them since only one is lean.


'99 VFR800, '08 1125R, '06 1050, '91 F2, '03 DRZ400

 

[TheFleshRocket]

Try unplugging the vboost in the open position during the servo cycle... My bike does the same thing between 5 and 7 thousand rpm.. I now run open vboost 100% of the time with no issues! With the setup you have stated, I believe you need the VBOOST open 100% of the time...

I think 100% Vboost is just masking the problem.


'99 VFR800, '08 1125R, '06 1050, '91 F2, '03 DRZ400

 

[jwood]

I think 100% Vboost is just masking the problem.


'99 VFR800, '08 1125R, '06 1050, '91 F2, '03 DRZ400

I don't think so, your 170 main is way to big to require it NOT to be open.. give it a try....DynoJet states the same (open vboost) with their stage 7 kit, UFO also states the same (open the vboost) the only difference with your set up from mine is your 170 main and 3rd clip, mine is a 165 on the 4th clip and vboost open.. No issues here..

 

[TheFleshRocket]

With the Tboost set to open at half RPM, it will be completely open well before 5000rpm, when the misfire begins. How would having the Vboost open at idle make the behavior any different at 5000 rpm?

Also, the Vboost all the time doesn't take into account that the misfire pretty clearly only affects one of the cylinders.


'99 VFR800, '08 1125R, '06 1050, '03 Vmax, '03 DRZ400

 

[jwood]

With the Tboost set to open at half RPM, it will be completely open well before 5000rpm, when the misfire begins. How would having the Vboost open at idle make the behavior any different at 5000 rpm?

Also, the Vboost all the time doesn't take into account that the misfire pretty clearly only affects one of the cylinders.


'99 VFR800, '08 1125R, '06 1050, '03 Vmax, '03 DRZ400

May need to check your vboost that it is open 100% of its travel, it may need adjustment..

I think my next step would be to check the slides again on that side... A sticky slide in a carb will do exactly as your describing as well as the carbs not being seated all the way, a small air leak around the rubber carb gaskets is another...

Just trying to help...

 

[TheFleshRocket]

Yeah, one of the carb slides was hanging up, but it was in the #1 cylinder which isn't misfiring. I went over it with some 0000 steel wool. I might as well do the other three slides too.


'99 VFR800, '08 1125R, '06 1050, '03 Vmax, '03 DRZ400

 

[Lew L]

I had a slide hang up recently---- bike ran like poop but didn't seem to pop or misfire. maybe check the spark plug wires, boots and coil connections( for corrosion).
Good luck, Lew

 

[Traumahawk]

What are the condition of the plugs? I had a plug misfire... I couldnt track down the cause either until at night. The plug had a carbon track down the side...and was grounding out. I could see the spark on the side of the plug.

 

[TheFleshRocket]

Plugs look good.

I swapped the front and rear right side plugs (3 and 4). I also switched the front and rear left side plugs (1 and 2).

I cleaned off all four slides with the 0000 steel wool. I then swapped the 3 and 4 slides and the 1 and 2 slides.

Since 1 and 4 exit on through the left side muffler and 2 and 3 exit through the right side, I figured if the slides or plugs were at fault, the misfire would go from the right muffler to the left muffler.

It didn't--the misfire is exactly the same as before I changed that stuff.




'99 VFR800, '08 1125R, '06 1050, '03 Vmax, '03 DRZ400

 

[thor_eyerdhal]

Swap coils and wires..

 

[wildweasel_pt]

Like said check wires and connectors by swapping them around. If the problem follows the wires it is either that wire, connector, coil or cap, can also be a faulty TCI as TCIs are time dependent, the coils need time to charge up so when the TCIs start to go south the first symptom is spark fail at high revs. What i mean with this is that the coil doesn't have time to charge up properly and that can result on a weak or no spark at all, this all depends on how the transistors are working inside the TCI.

According to your latest post by swapping plugs the problem remained in the same cylinder so the plug is not the problem, if after misfiring the plug is black and wet, then the problem should not be the carbs as well. With this i guess the problem seems to be electrical. See if what i said above can help you track the problem.

Another thing you can do is to remove the airbox and run the bike with the box removed so you can see the slides work. Rev it and see if they all act equal. Check any issue of the mechanical parts on the air duct through the carbs. Are the carbs properly synced? No leak on the intake rubbers? high revs means high vacuum that can cause some air to be pulled inside the manifold through a crack and lean it out causing the fail. check rubbers and the sync plugs and the VBoost crossover rubbers as well (8 in total)

 

[TheFleshRocket]

Swapping coils and wires seemed like a good idea--right up until I did some reading about the front coils. There have been some descriptive terms for getting the front coils removed, and most of them involve foul language.

During my most recent test ride yesterday, I noticed the following:

If I'm just cruising along in third below 5000rpm and open the throttle, the misfire between 5000-7000rpm is very noticeable.

If I run the bike up through the gears, starting in first gear below 5000rpm, the misfire is very noticeable between 5-7K in first, a bit less noticeable in second, and even less noticeable (though still clearly present) in third.

That leads me to think that it's a sticky slide that gets more and more open as I run the bike up through the gears. However, when I look at the slides with the airbox off, all of them appear to move the same. Unfortunately, the bike will not rev past 4000rpm with the airbox cover off, so there's no way for me to actually watch the slides and see if they're working smoothly at 5-7K RPM.

On a side note, if I do a COP conversion, will that effectively replace all of the ignition components that could be causing this problem. IE if I do COPs and the bike still misfires, will it pretty much definitely be a fuel issue at that point?

 

[TheFleshRocket]

Carbs have been synced and intake rubbers are all in good shape and firmly attached so I doubt there are any leaks there. Sync plugs (the little rubber caps) all seem to be firmly seated and not dry-rotted or anything.

Haven't checked the Vboost crossovers yet.

 

[Traumahawk]

On a side note, if I do a COP conversion, will that effectively replace all of the ignition components that could be causing this problem. IE if I do COPs and the bike still misfires, will it pretty much definitely be a fuel issue at that point?

Yes....you would be replacing all of the electrical components that could be causing the misfire.

 

[wildweasel_pt]

Don't need to remove the coils just swap caps and wires and connectors in order to maintain firing order. The reason for the misfire to seem to be less noticeable on third gear might have to be with the moving inertia of the bike due the gear ratio? Don't understand why you can't rev it above 4k without airbox?
I've read somewhere that theres a wire that goes from the VBoost controller to the TCI so that misfire range may have something to do as well but this is just a WAG. The VBoost entering in action may also be the culprit but you can't check it visually.