Always something with this old girl. - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
Engine / Exhaust / Cooling
\ From the radiator, through the case and out
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post #1 of 6 (permalink) Old 04-24-2019, 09:47 PM Thread Starter
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Always something with this old girl.

So at startup I have white/blueish smoke from various points in the exhaust pipes and coming out of the exhaust pipes. Occasionally there will be a gas smell, and my MPG is sitting at a cool 20. I recently had to replace a fuel line because of a massive leak the old one started (guess what, the shop I took the Vulcan to broke the carb's fuel nipple so they replaced it with some weird straight brass piece, that is a pain to get to and keep the hose on.). There's also a decel pop, and occasionally when the bike is hot and I shut it off for a second, and go to start it back up, it'll try to not start and let out a nasty pop before it starts again. My coolant reservoir is also almost empty it seems, but I haven't been able to go refill it yet. I feel like I have a plethora of problems here, but I need some guidance. Sometimes the issues I get make me think I should sell my bikes and get a brand new one, but a 1987 Rebel and 1997 Vulcan don't go for very much... Anyway, help me out please? You guys have done amazing jobs before, so I'm eager to hear from you all again.

I have a love/hate relationship with this bike I swear to God.
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post #2 of 6 (permalink) Old 04-24-2019, 11:02 PM
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After it's warmed up, check the vacuum hose that runs to the petcock to see if there's gas in it. The hose should be dry, if it's wet, the petcock is leaking fuel into the vacuum hose. That will flood the front cylinder, even when it's not running. It will also put gas into the oil, to the point of being over full. You may notice the shifter feeling sticky after the engine is hot. Remove the oil fill cap and you may see gas vapor coming out of the hole.

Unburned fuel vapor will appear white to light blue, and is highly explosive.

The bad backfire on startup is usually low cranking voltage, I would bet there's a wet cell battery on there.

My bike will backfire every time if I open the throttle at all (hot). Leave the throttle closed (hot), and it starts right up.
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Last edited by Spockster; 04-24-2019 at 11:05 PM.
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post #3 of 6 (permalink) Old 05-01-2019, 03:19 PM Thread Starter
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I haven't had the chance to look at the vacuum hose yet, but the smoke definitely smells like it could unburned fuel vapor so that may be my culprit. Also the smoking on startup tends to come out of the exhaust pipes at various points from under the shielding. I'll also check the oil when I get a chance to see if that could be a problem, as she may need an oil change soon anyway. Will update later on.

I have a love/hate relationship with this bike I swear to God.
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post #4 of 6 (permalink) Old 05-02-2019, 02:58 PM Thread Starter
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So I checked the vacuum hoses, no leaks at all. There is a slight gas smell to the oil, and the sight glass is looking full entirely. I can only wager the float needles are stuck or something as the floats themselves are brand new. I have also not had any running issues aside from the backfiring and restarting when hot. I'll have to check the spark plugs soon.

I have a love/hate relationship with this bike I swear to God.
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post #5 of 6 (permalink) Old 05-03-2019, 05:44 PM
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Just as an aside backfiring on starting. Did you by any chance do the RLU bypass mod? When I did that I then had backfiring on starting on an 18 month old AGM battery fully charged (13.8 volts after the surface charge bled off). I cured my problem by removing the jumped direct connect and placing a waterproof 30 amp rocker switch in line. Switch off the headlight, start and switch on. No backfiring.

If you didn't do the RLU mod, ignore me. Do what Spockster suggests anyway. Seems I've got to also! :~)

My coolant bottle need filling now and then. No external leaks unless I over fill the bottle. Don't see it in the oil. Another VN750 mystery. :~)

2003 VN750
Velorex 562 sidecar w/trunk
2-wire mod
Headlight power switch
Manual fan switch
Shingigen SH775
Blue wire mod
Yellow wire mod
RLU removed
RR moved
Voltmeter relay wired
Coils direct wired w/relay
TOC MCCTs
handicap mods:
extended foot shift
heel shifter
extended brake pedal
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post #6 of 6 (permalink) Old 05-08-2019, 09:09 PM Thread Starter
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So I checked the reservoir, it was actually way over full, so that's why it overheated and boiled over most likely. The oil doesn't smell like gas at all, just oil. Then, I've not had a chance to check the spark plugs, but the smoke only happens at the very beginning when I start her up and goes away, which makes me wonder what's going on.

I have a love/hate relationship with this bike I swear to God.
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