I’ve run nearly 10 hours on my carb and never had this issue, but the other day I was testing and the engine would start just fine for about 10 seconds, then fuel would spray from the cut in the black vent tube on the carb and the engine would die. I fixed this by slightly bending the prongs on the float arm in the carb so the valve stopping fuel from entering would engage sooner, and this has worked.
My question is: The arm has never been messed with before, so I’m not sure what changed to cause this problem. Was my arm-bending the only solution or is there something else going on? Can floats malfunction? Maybe something else?
dellorto floats can crack and fill up with gas, test by removing them and holding them under water, it they fill up, they’re no good. ALso look at the floats closely — you’ll notice they have “alto” cast into one end, alto means “high” in italian, so that is the top of the float…and they’ll rattle if they’re installed correctly. Round ends always go into the bottom of the bowl.
You should have not bent the float arms. This may have made your carb illegal. Check your associations rules. Your should have bent the tab that is in contact with needle valve. Remove the pin that holds the float arm and check the needle valve. The plunger in the needle valve is spring loaded. The spring may have broken or the valve may no longer be making a good seal against the seat. There also could be a possibility that the seat is not tight.
I will like to add to Tony’s post with regards to the needle valve, if you have used “carb cleaner” without removing the needle valve, there is a very good chance the rubber seal on the needle is ruined.
I ultrasonically clean my carb, so no worries about the cleaner. I’ll bend the arms back and bend the tab instead. What solvent is present in carb cleaner that would eat the seal that isn’t present in gasoline? An alcohol or acetate perhaps?
I’m not sure if carb cleaner is a culprit. Brake cleaner is a definite no-no. I’ve always removed the needle valve before spraying the inside of a carb. If you’re stripping the carb completely down before putting it in the ultrasonic tank, you should be good.
Have you gone back out and do you have the same problem?