Twin Cam 88 Wont Idle
Thread Starter
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Novice
Joined: Mar 2020
Posts: 16
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From: Ft. Lauderdale FL
Twin Cam 88 Wont Idle
Hi All,
My 2002 FLSTC with a Twin Cam 88 won't idle and backfires when decelerating. I opened up the carb bowl and it was clean and the low speed jet looked OK. Any ideas? I assume maybe a vacuum leak on the intake but from where? The seal around the carb was very tight. I recently removed the front exhaust pipe to check the cam chain tensioners and put it back together with the same exhaust doughnut. It does not appear to be leaking exhaust and if it is it may cause a backfire, but I don't think it would have anything to do with not idling properly. Your thoughts?
Thanks
My 2002 FLSTC with a Twin Cam 88 won't idle and backfires when decelerating. I opened up the carb bowl and it was clean and the low speed jet looked OK. Any ideas? I assume maybe a vacuum leak on the intake but from where? The seal around the carb was very tight. I recently removed the front exhaust pipe to check the cam chain tensioners and put it back together with the same exhaust doughnut. It does not appear to be leaking exhaust and if it is it may cause a backfire, but I don't think it would have anything to do with not idling properly. Your thoughts?
Thanks
Thread Starter
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Novice
Joined: Mar 2020
Posts: 16
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From: Ft. Lauderdale FL
Thanks Max Headflow,
Yes, the idle air adjuster plug has been removed. I just recently replaced my petcock. Perhaps that is the culprit and there is a vacuum leak? The ends appear to be on the nipples pretty well. Is the best way to check for a leak to start the bike and spray some WD40 around the end connections and listen for change in RPM's? The bike won't really idle, but I can crack the throttle a little to keep it running or pull out the choke some. This is a carbureted bike, not injected..
Thanks
Yes, the idle air adjuster plug has been removed. I just recently replaced my petcock. Perhaps that is the culprit and there is a vacuum leak? The ends appear to be on the nipples pretty well. Is the best way to check for a leak to start the bike and spray some WD40 around the end connections and listen for change in RPM's? The bike won't really idle, but I can crack the throttle a little to keep it running or pull out the choke some. This is a carbureted bike, not injected..
Thanks
Seasoned HDF Member
Joined: Mar 2010
Posts: 38,592
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From: Honah Lee
What did the back chain tensioner look like? Were the tensioners orange in color?
Did this start with in one ride after any work you did? Maybe even a fill up at a gas station
I put a thin piece of paper held with needle nose pliers to inspect any exhaust replacement for leaks.
Check the plug for the vacuum outlet you took off the old vacuum petcock.
Replace sparkplugs. Ohm check wires and mist them in a dark garage and check for insulation leaks.
Propain check for air leaks.
Go here only after simple...
Did this start with in one ride after any work you did? Maybe even a fill up at a gas station
I put a thin piece of paper held with needle nose pliers to inspect any exhaust replacement for leaks.
Check the plug for the vacuum outlet you took off the old vacuum petcock.
Replace sparkplugs. Ohm check wires and mist them in a dark garage and check for insulation leaks.
Propain check for air leaks.
Go here only after simple...
Last edited by Jackie Paper; May 19, 2026 at 10:31 AM.
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Joined: Dec 2005
Posts: 19,925
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From: poway
Thanks Max Headflow,
Yes, the idle air adjuster plug has been removed. I just recently replaced my petcock. Perhaps that is the culprit and there is a vacuum leak? The ends appear to be on the nipples pretty well. Is the best way to check for a leak to start the bike and spray some WD40 around the end connections and listen for change in RPM's? The bike won't really idle, but I can crack the throttle a little to keep it running or pull out the choke some. This is a carbureted bike, not injected..
Thanks
Yes, the idle air adjuster plug has been removed. I just recently replaced my petcock. Perhaps that is the culprit and there is a vacuum leak? The ends appear to be on the nipples pretty well. Is the best way to check for a leak to start the bike and spray some WD40 around the end connections and listen for change in RPM's? The bike won't really idle, but I can crack the throttle a little to keep it running or pull out the choke some. This is a carbureted bike, not injected..
Thanks
Thread Starter
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Novice
Joined: Mar 2020
Posts: 16
Likes: 4
From: Ft. Lauderdale FL
Thanks Max Headflow,
Being that I just changed the fuel petcock and it did not have this problem prior to, I am suspect of a vacuum leak. I will try and check for that first before getting into the fuel pilot system. I did drop the bowl on the carb and check the low speed jet and it appeared to be clear...
Being that I just changed the fuel petcock and it did not have this problem prior to, I am suspect of a vacuum leak. I will try and check for that first before getting into the fuel pilot system. I did drop the bowl on the carb and check the low speed jet and it appeared to be clear...
Thread Starter
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Novice
Joined: Mar 2020
Posts: 16
Likes: 4
From: Ft. Lauderdale FL
Thanks Jackie Paper,
The chain tensioner pads were not to bad. A little bit of pitting but not grooved very deep. I do need to change them however. yes, they were orange. (I assume original) Yes , this problem started after changing the petcock. I assume it is probably a vacuum leak although the hose on the nipple at both ends (petcock and carb) appear to be secure. May need to pull the hose out and check for any cracking? Aside from propane, I guess I can spray WD40 around the ends of the vacuum hose and carb mounting seals to check for difference in RPMS while running..
The chain tensioner pads were not to bad. A little bit of pitting but not grooved very deep. I do need to change them however. yes, they were orange. (I assume original) Yes , this problem started after changing the petcock. I assume it is probably a vacuum leak although the hose on the nipple at both ends (petcock and carb) appear to be secure. May need to pull the hose out and check for any cracking? Aside from propane, I guess I can spray WD40 around the ends of the vacuum hose and carb mounting seals to check for difference in RPMS while running..
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From: Honah Lee
Go easy with the WD40. Like carburetor cleaner, it leaves the liquid, over spraying could catch fire.
And obviously, you need to be careful with propain.
And obviously, you need to be careful with propain.
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Seasoned HDF Member
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From: poway
Thanks Max Headflow,
Being that I just changed the fuel petcock and it did not have this problem prior to, I am suspect of a vacuum leak. I will try and check for that first before getting into the fuel pilot system. I did drop the bowl on the carb and check the low speed jet and it appeared to be clear...
Being that I just changed the fuel petcock and it did not have this problem prior to, I am suspect of a vacuum leak. I will try and check for that first before getting into the fuel pilot system. I did drop the bowl on the carb and check the low speed jet and it appeared to be clear...
Thread Starter
|
Novice
Joined: Mar 2020
Posts: 16
Likes: 4
From: Ft. Lauderdale FL
Thanks Max Headflow,
I did take out the air mixture screw and clean it. After installing it still has the same problem. After thinking about it, I recalled I removed the front exhaust pipe to inspect my cam chain tensioners and am now suspect of an exhaust leak. I installed the pipe with a new crush gasket but think it is still leaking. Some guys say torque them and others say just tighten to feel. Not sure what is the best method but I just tightened them equally to feel. It has been difficult up to now to leak check it as it has been very breezy where I live and I have no room in my garage. Have to wait for a calm day...
I did take out the air mixture screw and clean it. After installing it still has the same problem. After thinking about it, I recalled I removed the front exhaust pipe to inspect my cam chain tensioners and am now suspect of an exhaust leak. I installed the pipe with a new crush gasket but think it is still leaking. Some guys say torque them and others say just tighten to feel. Not sure what is the best method but I just tightened them equally to feel. It has been difficult up to now to leak check it as it has been very breezy where I live and I have no room in my garage. Have to wait for a calm day...