Air compression through carbs - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 5 (permalink) Old 02-08-2018, 09:46 AM Thread Starter
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Air compression through carbs

I bought a 97 Vulcan that sat in a garage for a few years, after a week of riding it started to sound like air compression going back through the carbs, replaced carb boots, flushed engine and changed oil and air filters just like mechanic said to do but still make sound, bike only has 6,624 miles on it, any help would be great
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post #2 of 5 (permalink) Old 02-08-2018, 01:49 PM
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Will it run? If so, how well?

It depends on the amount of air ... Could be simple reversion, which happens on a lot of bike carbs. If more than that, I would look for a stuck/sticky intake valve, And if not that, possibly the valve timing is off.

For a sticky intake valve, I'd run the correct amount of Seafoam in the oil for a while to see if it will free up. Sitting a long time, varnish on the valve stems can lead to being sticky, slow to close. This engine has two intake valves per cylinder, so it could still run with one valve being sticky, but it would be down on compression/power. An intake valve stuck open would mean that cylinder can't make any power, and should cause popping back through the carb.

Seafoam in the gas would also clean the lower portion of the intake valve stem.

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post #3 of 5 (permalink) Old 02-09-2018, 12:25 AM
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Sounds like a carb fart to me. Could be a valve problem, but it could be a lot of other things too. The fact that it started after a relatively short time after sitting for a relatively long time makes me think of a plugged carb passage or jet first.

+1 on Seafoam.
Make sure the battery is well charged and passes a load test (free at auto part stores). These bikes need really good voltage or they will not run worth a crap. Don't even think about push starting one, lol. The first sign of a failing battery, R/R or stator is often bogging, sputtering, backfires or carb farts.
Check the ACCTs, loosen a titch bit and let them snap tight, then manually force them in a hair, ride again and see if it helps.

hard to say more without riding it myself to hear and feel it. You know how it is.

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post #4 of 5 (permalink) Old 02-09-2018, 01:42 AM Thread Starter
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Iíve been putting lucas gas treatment the last 2 fill ups and has a cycle shop change the oil and us and engine flush, he said he could try a few different things but wasnít sure what it was and another mechanic said sounds like stuck valve because it didnít do it when I first got it, when first started up it has a few hiccups and have to use idle set screw to idle it up, Iíll try taking a video this weekend, bought new deep cycle battery with 220 cca
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post #5 of 5 (permalink) Old 02-10-2018, 01:01 AM
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What are your compression readings?

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