Air through carbs when cranking, very odd issue - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 4 (permalink) Old 01-13-2020, 09:29 PM Thread Starter
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Air through carbs when cranking, very odd issue

Hey everyone, I have a very strange issue with the front cylinder of my 1990 Vulcan. When I try and start the bike, after a few cranks, there will be a loud noise followed by a faint bit of smoke/air forcefully shooting out the intake on the carbs. The engine will also kick back and temporarily stop cranking.

Other information:

This does not occur with front spark plugs disconnected. When they are disconnected, the rear cylinder will start on its own perfectly fine.

One of the front plugs was fouled/had no spark/was very oily.

Valves are not sticking, and hold a seal. I put gas over the closed intake valves and it did not drain into the cylinder. It also has good compression.

With carbs off, cranking the engine over and placing my hand over the port results in me feeling a very strong suction, and no pushback from just the valves.

With the use of starter fluid, I can get the engine to fun for a moment or two on BOTH cylinders.

A slight blowback is felt at the intake of both the front and rear carbs when cranking over.

At this point, I think it's either a carb issue or timing. But could it be ignition timing or even an incorrect firing order? Valves don't hit, and this issue only happens when the front cylinder tries to fire. Any help would be greatly appreciated.
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post #2 of 4 (permalink) Old 01-13-2020, 10:12 PM
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What happens when you swop coils?

'99 Vulcan "Victoria"
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post #3 of 4 (permalink) Old 01-13-2020, 11:01 PM Thread Starter
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Originally Posted by TonyO View Post
What happens when you swop coils?
What do you mean by swap coils? Like change the plug wires?
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post #4 of 4 (permalink) Old 01-15-2020, 02:10 AM
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Is this a new to you bike, or was it running properly before? PLEASE don't use starting fluid. Use gasoline in a spray bottle. I have seen engines totally destroyed by starter fluid, including a nearly new $15,000 Yamaha outboard marine engine. 2 pistons were completely melted and the cylinders were damaged.

I am a motorcyclist, NOT a biker.


1997 Vulcan 750, purchased about a week ago
2006 Sportster 1200 Low
2013 Royal Enfield Bullet 500, converted to carb
2001 Yamaha XT225, heavily modified
2004 Honda Rebel 250
1979 Vespa P200E
2002 Vulcan 750 parts bike
1994 Yamaha XT225 parts bike
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