Carb problems?
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Joined: Jun 2009
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From: Cincy, OH
Carb problems?
Long time lurker, first time poster. I'm pulling my hair out over my bike and I'm hoping someone can help me.
Bike in question is an '06 1200, handmade air cleaner, 1 7/8"-2" step drag pipes, NGK DCPR7E plugs @ .040 gap.
Problem I've been having, it breaks up extremely bad in mid-upper RPM range if full throttle is applied. It'll run smoothly through the range (as far as you can) with 1/2 throttle or s. I assumed this was a lean condition, as the plugs are chalk white. As it sits, it has a 185 main jet drilled a few thousandths bigger, and a 45 slow jet. I've tried the 185, a 195, and this drilled jet, to no avail.
Anyone have any suggestions at this point?
Thanks in advance
Bike in question is an '06 1200, handmade air cleaner, 1 7/8"-2" step drag pipes, NGK DCPR7E plugs @ .040 gap.
Problem I've been having, it breaks up extremely bad in mid-upper RPM range if full throttle is applied. It'll run smoothly through the range (as far as you can) with 1/2 throttle or s. I assumed this was a lean condition, as the plugs are chalk white. As it sits, it has a 185 main jet drilled a few thousandths bigger, and a 45 slow jet. I've tried the 185, a 195, and this drilled jet, to no avail.
Anyone have any suggestions at this point?
Thanks in advance
Club Member
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From: Boynton Beach, FloriDuh
A vacuum (air) leak on the intake side can cause this problem. The more throttle you give it, the more it will tend to draw air through a leaky gasket. In particular, check the carb-manifold gasket and the manifold-head gaskets.
The additional air drawn through a leaky intake gasket will cause the lean mixture.
The additional air drawn through a leaky intake gasket will cause the lean mixture.
Cruiser
Joined: Jan 2008
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From: The Suncoast (FLA)
I agree with cHarley. I had similar problems with mine. When you let up on the throttle, do the RPMs hang-up and/or drop slower than normal? I replaced carb gasket and the intake manifold gaskets (don't cost much) and she has purred like a kitten ever since. Coughs-up a hairball once in a while though.
Last edited by Sundog; Jun 29, 2009 at 11:45 AM.
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From: fegfsg
what is the design of your ac? a straight tube sticking off to the side? you have to consider the airflow pattern passing over the intake as the bike is moving. I had a straight v stack for awhile and it did the same thing until i put a 90 degree tube pointing forward, besides fixing the stuttering problem i gained power at high speeds, feels like a turbocharger. it just shovels air into the engine.
also if the plugs are white then the spark is deteriorating replace your plugs and try slightly closer gaps, keeps spark strong at high rpms.
replace your rubber manifolds and coat them in grease so it makes a good seal and you can elimate leaking seals as a possible cause
also if the plugs are white then the spark is deteriorating replace your plugs and try slightly closer gaps, keeps spark strong at high rpms.
replace your rubber manifolds and coat them in grease so it makes a good seal and you can elimate leaking seals as a possible cause
Road Captain
Joined: Jul 2006
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Just a long shot here......are you sure your not hitting the rev limiter??? You didnt' give too much info relating to engine rpms or bike speed so I figured i'd mention it. I'm trying to remember here now....but I think the stock ignition is set around 5500 rpm rev limit, which at that point it will severely break up the spark. But other than that......like others said, check for air leaks, may consider trying a smaller main jet, make sure you not going too rich. Might also help to check and reset the ignition timing. One other thing I've seen a few poeple have a problem with is if you have chrome decorative spark plug covers, try to take them off and then run the bike, I've seen a few people that had issues with the spark arcing from the spark plug boot to the covers, and i've actually had the issue once myself with the covers, and it will cause a nearly identical problem at higher rpms.
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From: Cincy, OH
Thanks for the suggestions.
First things first, I searched for a vacuum leak, using the trusty propane torch method, and everything seems to be in line. Bike revs down perfectly normal like every other one I've ridden.
The bike is STONE STOCK otherwise. I can't give you any info on speed/RPM as I have no Speedo/Tach.
As for my aircleaner, here's a picture.
Rev limiter? No. If you pin the throttle, and keep it held, it will keep revving, even though it's breaking up BAD.
First things first, I searched for a vacuum leak, using the trusty propane torch method, and everything seems to be in line. Bike revs down perfectly normal like every other one I've ridden.
The bike is STONE STOCK otherwise. I can't give you any info on speed/RPM as I have no Speedo/Tach.
As for my aircleaner, here's a picture.
Rev limiter? No. If you pin the throttle, and keep it held, it will keep revving, even though it's breaking up BAD.
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From: SE Wisconsin
Just a long shot here......are you sure your not hitting the rev limiter??? You didnt' give too much info relating to engine rpms or bike speed so I figured i'd mention it. I'm trying to remember here now....but I think the stock ignition is set around 5500 rpm rev limit, which at that point it will severely break up the spark.
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From: Cincy, OH
If it was the rev limiter, it would stop revving period at a certain RPM, no matter how much throttle is applied. If you back the throttle off when it starts breaking up, it will continue to gain RPM. I know, the bike does not have a tach, but I'm 1000% certain it is NOT the rev limiter.
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From: fegfsg
If it was the rev limiter, it would stop revving period at a certain RPM, no matter how much throttle is applied. If you back the throttle off when it starts breaking up, it will continue to gain RPM. I know, the bike does not have a tach, but I'm 1000% certain it is NOT the rev limiter.
it actually might be, dont be so sure now, youll look like a fool later. find an aftermarket ignition to test out, its not a hard swap either. or otherwise change plugs with smaller gap like i told you.
oh and if the bike is still stock like you say then your not getting enough gas at those rpms, you need to shim or re taper the needle. especially with that ac and exhaust
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From: Boynton Beach, FloriDuh
I'd forget about it being a rev limiter issue or swapping out ignition modules. The posters above seem to be ignoring the fact that you said the plugs are "chalk white". The bike is (for whatever reason) running lean. IMO, you have either a carb mixture issue or a air leak on the the intake manifold side. Your propane torch test method I assume was done with the bike parked and not at speed where you experience the problem at WOT.
I recently had a similar problem that turned out to be a small tear in the carb-manifold gasket. Bike ran fine until I got on the road and grabbed a handful of throttle.
I recently had a similar problem that turned out to be a small tear in the carb-manifold gasket. Bike ran fine until I got on the road and grabbed a handful of throttle.
Last edited by cHarley; Jun 30, 2009 at 12:36 PM.