Low speed missing/popping

[1stmax97]

I recently bought a 97 vmax. Just got out friday and drove it to work for the first time. It didn't run very good. At any speeds below 50 MPH when cruising one cylinder is missing and popping. Only when cruising, if I get on the throttle it disappears. Also it doesn't matter what the temperature of the engine is, it does it just as bad cold as hot. So I?m thinking coil. I checked the resistance and they are all good. I let it idle and put a temp gauge on all the spark plug boots. The right front plug was colder than the others. So I figured that was the cylinder that was missing. First I try swapping spark plugs wires, and the cylinder is still cold. So I try swapping the front spark plugs and it moves to the left front cylinder. I think ok it must be the plugs. Put in four new plugs and it runs excellent. Better than it ever has no missing or popping and runs really smooth. Well for about 70 miles anyways. Then it started doing the exact same thing again. Only now its on the left front cylinder. I checked the wires to make sure they were tight, pulled out the plugs, they look good. I also re checked the resistance on the coils and its good. What the hell could it be??:bang head:

 

[Buster Hymen]

I recently bought a 97 vmax. Just got out friday and drove it to work for the first time. It didn't run very good. At any speeds below 50 MPH when cruising one cylinder is missing and popping. Only when cruising, if I get on the throttle it disappears. Also it doesn't matter what the temperature of the engine is, it does it just as bad cold as hot. So I?m thinking coil. I checked the resistance and they are all good. I let it idle and put a temp gauge on all the spark plug boots. The right front plug was colder than the others. So I figured that was the cylinder that was missing. First I try swapping spark plugs wires, and the cylinder is still cold. So I try swapping the front spark plugs and it moves to the left front cylinder. I think ok it must be the plugs. Put in four new plugs and it runs excellent. Better than it ever has no missing or popping and runs really smooth. Well for about 70 miles anyways. Then it started doing the exact same thing again. Only now its on the left front cylinder. I checked the wires to make sure they were tight, pulled out the plugs, they look good. I also re checked the resistance on the coils and its good. What the hell could it be??:bang head:

I'm more inclined to think it is a carb issue and not an electrical issue. These carbs are notorious for plugged jets. Start with some Seafoam and then search for shotgun and peashooter in the carb forum.

 

[davidon]

Concur...clean pilot jets out..look for stickies on how to do it

 

[richwrench]

Agreed - carb issue. But I say pull em' & clean em' - it's 12 years old ! These carbs are very fussy about dirt & out-of -sync issues.

 

[1stmax97]

Bought some sea foam and put half of it in my tank. Runs way better now. Missing is gone except a slight miss at idle. Im going to run this tank and then run another tank of seafoam. I may also try the peashooter thing. I would pull the carbs except I just bought it and want to ride it, not work on it! Maybe over the winter I will tear them down but for right now I would like to get it running good enough to ride. The guy I bought it from told me he tore them apart and cleaned them last year. Im thinking he didn't do a very good job. Thanks for the help.

 

[dannymax]

Try some BG 44K, add 1/3 can at each of your next three fill-ups. I've had good results with this product.

It's about $20/can but well worth it IMO.

 

[gleno]

I recently bought a 97 vmax. Just got out friday and drove it to work for the first time. It didn't run very good. At any speeds below 50 MPH when cruising one cylinder is missing and popping. Only when cruising, if I get on the throttle it disappears. Also it doesn't matter what the temperature of the engine is, it does it just as bad cold as hot. So I’m thinking coil. I checked the resistance and they are all good. I let it idle and put a temp gauge on all the spark plug boots. The right front plug was colder than the others. So I figured that was the cylinder that was missing. First I try swapping spark plugs wires, and the cylinder is still cold. So I try swapping the front spark plugs and it moves to the left front cylinder. I think ok it must be the plugs. Put in four new plugs and it runs excellent. Better than it ever has no missing or popping and runs really smooth. Well for about 70 miles anyways. Then it started doing the exact same thing again. Only now its on the left front cylinder. I checked the wires to make sure they were tight, pulled out the plugs, they look good. I also re checked the resistance on the coils and its good. What the hell could it be??:bang head:

DO THIS FIRST: Badly out of synch carbs will also create the the symptom you have described. Resynching your carbs may cure the problem.

If this doesn't work then ...

Missing and popping (especially popping) when cruising and decelerating are symptomatic of an air leak on the intake manifolds or carbs.

Check to see that the rubber intake boots are correctly seated, have no cracks and the clamps are tightened.

If these are good check to make sure you have no intake leaks where the lower aluminium intake manifolds attach to the heads. Check the Allen head screws holding the intake manifolds onto the heads for tightness. The o-rings on the base of these can compress over time and leak.

A torn or holed diaphram in the coasting enrichment circuit of the carbs will also cause popping and missing. Same goes for the CV slide diaphrams.

 

[1stmax97]

DO THIS FIRST: Badly out of synch carbs will also create the the symptom you have described. Resynching your carbs may cure the problem.

If this doesn't work then ...

Missing and popping (especially popping) when cruising and decelerating are symptomatic of an air leak on the intake manifolds or carbs.

Check to see that the rubber intake boots are correctly seated, have no cracks and the clamps are tightened.

If these are good check to make sure you have no intake leaks where the lower aluminium intake manifolds attach to the heads. Check the Allen head screws holding the intake manifolds onto the heads for tightness. The o-rings on the base of these can compress over time and leak.

A torn or holed diaphram in the coasting enrichment circuit of the carbs will also cause popping and missing. Same goes for the CV slide diaphrams.

When I bought the bike the guy said he had just synched the carbs and they didn't need any adjustment. I know im just taking his word for it but when it runs good it runs really good so I don't think the carbs are out of synch. Plus I don't own the tool to do it yet.

I will check for intake leaks like you suggest. I know for a fact that the rubber intake boots look to be in bad shape. They look very weathered and have some cracks in them. Maybe I will try the old propane torch trick. With the engine running take a propane torch and leak propane around all the possible leak areas. If the eninge RPMs rise in a certain area then I have a leak there. Thanks for the ideas.

 

[naughtyG]

Maybe I will try the old propane torch trick. With the engine running take a propane torch and leak propane around all the possible leak areas. If the eninge RPMs rise in a certain area then I have a leak there. Thanks for the ideas.

Hey I've heard about this trick spraying water mist around vacuum leaks, and if the rpm drops you know you have a leak.

I'd be a little wary about using a propane torch for this around a hot engine?

 

[1stmax97]

Hey I've heard about this trick spraying water mist around vacuum leaks, and if the rpm drops you know you have a leak.

I'd be a little wary about using a propane torch for this around a hot engine?

That could work too, ive never had a problem with the propane though. Used it a couple of times on cars. Worst case senario the torch would light, then I would just put it out. Very unlikely though.