What would cause a bike to shoot fuel back out the carb???

 

Anything that creates a vacuum signature on the float bowl will draw fuel up and it will send the fuel the direction the air is moving.

What is the motor doing when it happens?

 

Honestly I do not know. I overheard a conversation at a bike shop I am putting in an application with and they are stumpped. I was thinking that maybe it was the intake valves not getting a good seal and the compression pressurizing the carb and doing it that way..... I wanted to see if anyone else was on the same page....

 

I see where you are going and that is the only thing I can think of unless the carb is level and the floats are stuck. That would cause just as much fuel to run out the intake as runs down into the motor.


If the intake valves leaked, the worse the leak, the weaker the charge back through the carb. If there was a big enough leak in the intake valves to cause a negative vacuum signature at the carb, there is no way in hell the motor would have enough compression to fire.

Either the fuel is.............


Wait a minute.....Been down this road before. You are just messing with me again to see if i will bite, huh? [img]i/expressions/face-icon-small-happy.gif[/img]

 

Nope, being completly serious this time. I was thinking about calling back up there and giving them my thoughts to see if they had checked them. I was thinking maybe stuck floats also if it is filling faster then it is buring the fuel then the extra has to go somewhere....

 

LOL, K, just checking! [img]i/expressions/face-icon-small-happy.gif[/img] You kicked my **** last time!!! [img]i/expressions/face-icon-small-happy.gif[/img]



I would check the cam timing if it turns over, doesn't start and spits compression back through the carb. The compression forcing back through the carb will draw fuel up. It can't be too bad though or it would blow the carb off the intake when the blast hit the slide.

 

<div class="FTQUOTE"><begin quote>Originally posted by: DSNUT

I would check the cam timing if it turns over, doesn't start and spits compression back through the carb. The compression forcing back through the carb will draw fuel up. It can't be too bad though or it would blow the carb off the intake when the blast hit the slide.</end quote></div>

Yep that's what I think also.........

 

Sounds like I am thinking the right way at any rate. I will call up there and offer up our thoughts. May just help get me on there. That would be nice....

 

Depends on how much fuel is getting thrown back. At slow RPM's, there will be some fuel shot back through if the piston starts its travel back up and the intakes are not open. Some is normal on a single. Alot, the timing is off. It can also happen if you are reving it and chop the throttle.

Does it not run, or just some fuel in the snorkel?

 

I would check the cam timing. Is this a fresh rebuild you are starting for the first time or is this a motor you have been running for some time and this just started.