Yamaha FZR Vapor Lock in a Cylinder #1 or #4?

  • Thread starter Thread starter Rick Garrison
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Rick Garrison

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I'm getting vapor lock in my FZR. It looks like gas is being leaked or drained into one of my cylinders. This is giving me vapor lock when trying to start the bike. It sounds like a hammer hitting the side of the motor. If I do get the bike started it will smoke a lot out of the head down by the exhaust, gas burn off?? I’ve had 2 different sets of cards on the bike and 37mm Keihins. What causes this? I’ve have the bike for 17 years. One other bit of info, it is a 1990 FZR750RR a.k.a. OW01.
 
Because the bike is so old i'd recommend you replace your float needles and needle seats (if not pressed in), replace all the o-rings in the carb body and clean the carb very well. Vapor lock is most often caused by float needles not sealing or choke circuit not sealing.

Do not try to force a vapor locked motor to start! Liquid gasoline doesn't compress and can destroy the motor.
 
Sounds like you have two problems, the float needles are leaking but the bigger problem is (a) you're not shutting the fuel petcock off between rides or (b) the petcock is leaking even when turned off and needs a new seal kit. Fix the petcock problem and unless the float needles are leaking terribly, you won't have to fool with the carbs.
 
Because of the angle that the carbs are mounted to the cylinder head, when the carbs overflow, gas spills into the head and past the intake valves - filling up the cylinder with gasoline.
If there are no signs of the float needles leaking, lower the fuel level in the float bowls.

Fix this problem immediately before doing any damage to your engine.
I've seen engines bend connecting rods due to hydraulic lock.
 
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