Startup problems, Merry f***in Christmas - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 4 (permalink) Old 12-24-2019, 02:20 PM Thread Starter
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Startup problems, Merry f***in Christmas

Hey guys, just tried to crank it up on this unseasonably warm Christmas Eve, and it was immediately acting funny. I never winterized it because I live in Georgia, and even during the cold months you can go for a ride maybe once every 3 weeks. Went for a short ride 2 weeks ago I think and it was fine.

I had a previous problem before with an oil leak, white smoke coming out of the manifold/exhaust, etc, after some diagnosing I figured out I had too much oil in the engine. So I drained out about a quart and it has run fine for about 6 months.

Usually upon start-up I turn the choke on (sometimes only halfway or two-thirds), I start it and the engine jumps up to about 1000-1500RPM. By the time I put on my jacket and helmet it's usually done warming up and jumps up to 2500-3000RPM, so I turn off the choke and it settles around 1200RPM. But this time I put the choke on, start it, and it jumps to about 1500, then 1000, then down to 500 and dies. I start it again and accelerate this time a little bit, only this time there's some smoke like last time. It goes to about 1500, then down to under 1000.

No one has messed with the idle screw, so it shouldn't be running low like this, but I turned it up, just so it would run around 1300 like it should. I noticed some oil leaking out of the rear cylinder manifold, not like gushing but pretty substantial puddle right onto the engine causing the white smoke. And I turned off the engine to check the oil level and it's normal.

So my instinct is that I need to replace some sort of manifold gasket? But that doesn't explain the low RPM's.... Any thoughts?


Also, maybe related, I recently had to replace a bunch of coolant. Noticed the levels were low so I filled it up. I think that's from a leak out of the radiator though. The plug up there is a little stripped... but holding. So I don't think the coolant is getting into the oil, I think occasionally it's just leaking out of the drain plug a little.
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post #2 of 4 (permalink) Old 12-24-2019, 02:27 PM Thread Starter
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Also forgot to mention, when I turned up the idle screw and was listening to it, I couldn't completely tell, but it sounded like there may have been a knocking sound. I should go turn it on in a minute and double check if I was imagining that or not.
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post #3 of 4 (permalink) Old 12-24-2019, 05:32 PM
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Start simple, are the carb boots snug? That’ll give you crazy idling as well as sputtering out.
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post #4 of 4 (permalink) Old 12-27-2019, 09:27 PM
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Check your air cut valve diaphragms. There is one on each carb, on the outside, behind a cover held on by 3 screws. There is also a spring behind the covers. I found mine completely melted once. I believe it was caused by ethanol gas. Anyway, a problem with those valves can cause all sorts of seemingly unrelated carb problems. It took me a while to figure it out. I actually found it by accident.

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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