Bike backfiring and sputtering when cold - Harley Davidson Forums: Harley Davidson Motorcycle Forum
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Old 07-29-2012, 09:02 AM   #1 (permalink)
pas
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Bike backfiring and sputtering when cold

I have been searching the threads for a couple hours but cant seem to find my exact problem.
93 evo motor, straight pipes not sure about carb pretty much stock.

Bought the bike in 2000 the guy I bought it from was a perfectionist and the bike always ran flawlessly. Recently it started backfiring and sputtereing when cold, but 5-10min into the ride it runs fine with only slight hesitation when taking off. Plugs are white. Oil temp dipstick is at 180-200 riding in the city even though it's hot and humid in the 90's right now. Any help is greatly appreciated.
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Old 07-29-2012, 09:25 AM   #2 (permalink)
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Put a jet kit in the carb. You're running lean. Common problem with 90's Evo.

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Old 07-29-2012, 04:40 PM   #3 (permalink)
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Intake leaks....
Did you do any recent work?
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Old 07-29-2012, 06:21 PM   #4 (permalink)
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A slightly worn and leaking accel pump diaphram cause your symptoms. Try that first. 3 screws under the carb, right side (front) and replace it with an HD OEM one, not aftermarket.

If not, it sounds as if the Choke pintle passage and pintle itself is starting to get carboned up and needs to be cleaned. Choke cable beeds to be taken out of carb, and the pintle needs to be cleaned. In order to clean out the port, you need to take the carb off, unless you can speak a can of 2+2 with the little red hose thingy back there, and spray it in the hole well enough. It can be done of you just take the carb out of the intake and tilt it down.

Truthfully....if you're going to that trouble, I'd rebuild it while off and clean all the other passages as well. There's 12 years on that carb, and that's if it was rebuilt the day before you picked it up.

If that works....yer golden. If not, prepare to rebuild.
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Old 07-29-2012, 09:44 PM   #5 (permalink)
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Misinlink, no recent work. Dave will it damage my bike to ride it until I get the diaphragm to fix it?
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Old 07-30-2012, 01:08 AM   #6 (permalink)
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After checking what Dave said, if you still have the problem check your rubber fittings "compliance fittings" between the manifold and the heads for vacuum leaks. They can either get small cracks or the bolts or clamps can come loose. Had this happen a couple of times on my 87 Evo and it will make it run lean, causing the coughing on acceleration and white plugs. Been told these should be replaced as a maintenance item as often as every two years. That seems a bit excessive to me but if you end up taking the carb off to rebuild it anyway, I would replace them at the same time you have it all taken apart even if they aren't leaking yet. If they are leaking, the lean condition it causes will overheat your heads. Don't ride it this way very far!
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Old 07-30-2012, 06:18 AM   #7 (permalink)
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Quote:
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Misinlink, no recent work. Dave will it damage my bike to ride it until I get the diaphragm to fix it?
No....but it's annoying, and it's not going to get any better.

As well....if the rubber is delaminating off the diaphram, a piece can get stuck in the fuel passage, and you lose your accel pump all together.

$14 part, and about 20 minutes to repair.

If it's the beginings of leaking intake seals, that can cause a lean condition and that creates excess valve temps.
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Old 07-30-2012, 07:15 PM   #8 (permalink)
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I got to work on bike today. Pulled off air cleaner and the filter element was disintegrated from back fires. I tested accelerator pump with engine off and it seemed to spray well. I started bike and just let it idle it seemed to backfire less but also there was no load (didn't actually ride it) I did notice as I revved engine it would backfire when the accelerator pump didn't spray but that wasn't all the time. I sprayed WD40 around the intake seal, manifold and intake gaskets didn't notice any increase in rpms. I need to get parts but nearest dealer is 30 miles away so I want to make sure I have complete list when I go there.
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Old 07-30-2012, 07:17 PM   #9 (permalink)
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Quote:
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. I need to get parts but nearest dealer is 30 miles away so I want to make sure I have complete list when I go there.
Call ahead... make sure they have what ya need.
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Old 07-30-2012, 07:26 PM   #10 (permalink)
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I don't use WD40 to check intake seals. An intake can leak a little and WD40 won't be enough to trigger it. I use starting fluid. Be carefull not to spray back of aircleaner. That can produce false results.
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