Cranks but won't start.

[Docboy209]

Our 1990 Marathon has been driving me nuts for a long time now. It cranks, has 150psi compression, excellent spark, and it is getting fuel. I installed new crank seals already. I've tried putting gas right in the spark plug hole, but it still won't start! It's a 3PG engine. What am I missing?

Seriously considering a Predator engine conversion, but can't figure out how to keep reverse. Any ideas about doing that? In upstate NY there aren't many places to get used cart parts.

[cart around]

Has somebody replaced the piston? 150 psi is too high for that engine. I suspect that the piston is in backwards.

Remove the exhaust pipe so you can see up inside the cylinder. Move the piston up and down. If you see a pair of square holes in the side of the piston staring back at you, it's in backwards.

[slonomo]

If you switch to a Predator engine you will not have reverse since that cart requires the engine to run backwards for reverse. To have reverse you'll need an ME29 transaxle from a newer 4 stroke cart.

On the starting issue, try putting some gas/oil (128:1 ratio) in a spray bottle and spray the fuel directly into the carb when it's cranking. Putting fuel into the spark plug hole is just saturating the cylinder with fuel. Gasoline needs to "atomize" and mix with air (oxygen) in order to burn. Spraying the fuel mist will be ideal to test if it will run. If it runs on the spray, you might have a carb issue.

[Docboy209]

Originally Posted by cart around

Has somebody replaced the piston? 150 psi is too high for that engine. I suspect that the piston is in backwards.

Remove the exhaust pipe so you can see up inside the cylinder. Move the piston up and down. If you see a pair of square holes in the side of the piston staring back at you, it's in backwards.

I have not touched the piston. I was told by another member here that 150 was perfect.

[Docboy209]

Originally Posted by slonomo

If you switch to a Predator engine you will not have reverse since that cart requires the engine to run backwards for reverse. To have reverse you'll need an ME29 transaxle from a newer 4 stroke cart.

On the starting issue, try putting some gas/oil (128:1 ratio) in a spray bottle and spray the fuel directly into the carb when it's cranking. Putting fuel into the spark plug hole is just saturating the cylinder with fuel. Gasoline needs to "atomize" and mix with air (oxygen) in order to burn. Spraying the fuel mist will be ideal to test if it will run. If it runs on the spray, you might have a carb issue.

I know that I will lose reverse if I switch engines. I didn't know if there was a replacement axle that would be reversible.

I have tried spraying gas right into the carb inlet.

[Docboy209]

I'm an automotive technician with 22 years experience and I can't figure out why this won't run!!!

When the shop I work at bought it, it ran poorly. I changed the crank seals, and switched it to premix because the oil injection was running full blast and causing lots of smoke (the rod from the throttle was missing). It ran beautifully for a while! Then one day it just wouldn't start. The more I research this the more I've come to the conclusion that we need to sell this as non-running and save for another cart all together.

[cart around]

150 psi is for the four strokes. 120 is the best the 2 strokes ever did from the factory.
A high compression like that is an indicator of the piston being in backwards.
Since it ran, and nobody messed with it, we will move on.

The next thing is blown crankshaft seals. I know you replaced them, but they blow out. All it takes is one good backfire. Especially since it was such a sudden failure. They should be loctited in, and staked in three places.

It could also be an air leak on the case halves, cylinder mount, or head.

You could try checking the fuel pump lower diaphragm for for a tear, but it definitely sounds like the crankcase is not air tight.