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Curtis B.
Curtis B., Technician
Category: Small Engine
Satisfied Customers: 26049
Experience:  have worked on and around most engine models for 35 yrs./Polaris ATV expert
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I have a 79 yamaha, the cart was running fine up untill a

Customer Question

i have a 79 yamaha, the cart was running fine up untill a month ago. now the cart start occasionally but only runs for about 30 seconds. i have a new carb, coil and fresh fuel. engine has 100 psi compression max and has spark, cart seems to start after it sets for a while
Submitted: 1 year ago.
Category: Small Engine
Expert:  Curtis B. replied 1 year ago.

Is exhaust open? If exhaust is plugged, engine can't get fuel.

Customer: replied 1 year ago.
exhaust is clear, i even heated it to get excess oil out. has good exhaust pressure from tip of muffler, cart will run a little every once in a while with muffler unhooked but as soon as you let off throttle it will not start back up
Expert:  Curtis B. replied 1 year ago.

Have you ran a spark check as soon as it quits?

Expert:  Curtis B. replied 1 year ago.

With two cycle engine, your crankshaft seals may be leaking!

Customer: replied 1 year ago.
i have considered that possibility but figured with the amount of compression i could rule that out, it always has spark and fuel, maybe just not quite enough compression
Expert:  Curtis B. replied 1 year ago.
The crankshaft seals do not affect the compression. They only affect the air being drawn into the crankcase, if seals leak, the air is drawn into the crankcase and throws the fuel mix off! Only the rings and cylinder condition affects the compression. .If this is something you can do yourself, pull the engine, replace both crankshaft seals and install new rings at same time. That basically renews the inner parts of engine, other than bearings.
Customer: replied 1 year ago.
Ok sir I finally got all my parts and replaced seals and piston rings got the cart back together and engine fired up! So I decided to put the rest of it back together and rolled her out of the shop. Got 5 feet stalled and won't start. Right back to square one!
Expert:  Curtis B. replied 1 year ago.

Not quite! You know those parts are good. Do you still have spark> Is there fuel to the cylinder?

Expert:  Curtis B. replied 1 year ago.

Gas in the tank?

Customer: replied 1 year ago.
Full of fresh non ethanol fuel good spark carb is full of has fuel evident in cylinder/plug.
Expert:  Curtis B. replied 1 year ago.

Have you checked the needle valve passage? It takes very small amount of debris to plug it or restrict it!

Customer: replied 1 year ago.
In the carb brand new pulled apart three times to check it
Expert:  Curtis B. replied 1 year ago.

What kind of fuel pump? Pulse or electric?

Customer: replied 1 year ago.
Pulse, has plenty of fuel pull line off carb and it will pump when engine turns over
Expert:  Curtis B. replied 1 year ago.

Runs same with old carb?