backfire and condensation - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 5 (permalink) Old 08-12-2008, 04:16 PM Thread Starter
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backfire and condensation

Ok, here's a weird one that started yesterday. Went out to start the bike and it turned over one then a loud and I mean loud backfire. Sounded like the battery was dead after that. Got it to pop start and rode home. Today I noticed a ton of condensation on the carbs. Same thing when I went to start it. It's been exteremly rainy and humid in Maine for the past week or so. Last Saturday was nice and went on a 100 mile ride with no issues. I put a bit of dry gas in the tank just in case I had some water. Any ideas?
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post #2 of 5 (permalink) Old 08-12-2008, 10:54 PM
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Was the condensation on the carbs before or after your ride? I ask because in the carbs, the air/fuel mix gets compressed in the main body of the carb and then is allowed to expand as it goes into the main intake. This expansion causes the air/fuel mix to cool which could in turn cool the carb body and generate the condensation. I had a '68 Dodge Dart with a 318 that used to stall out in the winter for no apparent reason. Let it sit for about 5 mins and she started up again like nothing was wrong. I happened to take the air filter off once and saw frost on iintake below the carbs, just before the intake manifold. It turned out that there were heat risers in the intake that had been clogged with carbon. After I cleaned those out, the problem went away.
Piston engined aircraft also have carb heat levers in the cockpit to prevent carb icing. This reroutes some of the hot exhaust gas into the air intake.

Jim W
93 VN 750 "Ursula"
Moved R/R 08Sep06
R/R rewire 17Feb07
New R/R, Installed 14Jun08
New Stator installed 10 Jun08
Maintenance Free Battery 12Jan08
21480 Miles
VROC #8542
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post #3 of 5 (permalink) Old 08-13-2008, 06:10 AM Thread Starter
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It was before the ride. I went out this morning and I'm leaking gas from the carbs somewhere. I suspect maybe my petcock is failing or failed. My son..Mr. Outdoor power suggested that the cylinders are full of gas which is causing the pistons to act like they are locked up. I guess that would also explain the backfire.
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post #4 of 5 (permalink) Old 08-13-2008, 07:19 AM
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Does the petcock have the PRI-ON-OFF, or RES-ON-OFF? (<EDIT: I had that wrong previously)
If the first, are you sure it's not on PRI? That would allow fuel to continue to run into the carbs even if the bike isn't running.
If the latter of the two, a float might be stuck.

AKA: Tim & 'The Adventure Cycle' VROC #24567, NEVROC, SteelCity VROC

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Last edited by hyperbuzzin; 08-15-2008 at 10:09 AM.
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post #5 of 5 (permalink) Old 08-15-2008, 09:41 AM Thread Starter
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I've been shutting the petcock off after riding and have not had the problem since. I believe it's time for a petcock rebuild...Yes?
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