Not a 750/but I trust the guru's on this forum.
96 Vulcan 1500 Classic - Carb CVK40.
Been a week and 5 days of problem free riding since I put the carb back on the bike and the same ole' problem I had last month resurfaced this morning. Felt her stumble at 20mph going through town and she smoothed out on the back road at speed. Pulled into the lot, shut her down and pulled the right side aircover. Fuel bubbling from the air intake jets and in front of the butterfly flooding.
What I've done in the last three weeks since this problem started.
Brokedown carb, fully cleaned three times
Fuel level set at 1mm below mating surface/using service fuel level tube
All diaphrams inspected/no holes or cracks/good seals
New fuel filter
Petcock inspected and screens cleaned
Every vent/vacuum/fuel line replaced
Tank vents inspected and operational/no pressure build in the tank (hissing/whistling or pressure when I pop the cap)
Its like some pressure is pushing the fuel level up/it seeps out the air intake and venturi vents past the butterfly into the cylinder. It will do this for about 15 minutes after the bike shuts off then stops (when engine cools down).
I'm considering a fuel pump bypass just to see if that may be the issue.
Also noticed some oily junk in the air switch where the crank vent hoses run. When I manually acticated the diaphram, oily gunk spit out of the tube where the carb plugs in. If that switch is bad, is it possible that it could create vacuum where it t's into the top of the carb which is "pulling" fuel up????
Grabbing for straws here.....I'm determined to track and fix this problem.