88 marathon burnt piston

[jimboagogo]

I recently purchased a 1988 ezgo marathon, was cheap didn't run. It had no spark, fixed that. Still wouldn't run. Went through fuel pump and carb, got it to run. Purchased some new cables for throttle and oil pump. Installed cables and put new cab on (old carb had tons of wear on throttle plate bushings). Ran decent, onto the brakes. Replaced brake shoes, all good there. Drove it hard around the shop cause if it's going to break that's where I'd rather it broke. All good, load it on trailer and stop at the gas station, fill it up with premium fuel, off to the park I go. Got to the park, it started and ran fine for about 20 mins, then started making a noise then quit. I removed the spark plug and it had a bunch of small aluminum balls all over it. Burnt piston. Ok new cylinder and piston, I have the parts but want to prevent it from reoccurring. Do you think the cause would be premium fuel? Spark plug to high heat range? Carburator lean? HEI ignition spark too hot? The oil injection works, there's no verticle scoring in the old cylinder as if it was getting tight from lack of oil. I'm at a bit of a loss. there is an adjustment on the top of the new carburator which the old one doesn't have, is that fuel/air mixture screw? Do I need to fatten it up? Any thoughts or ideas would be greatly appreciated. I'm a diesel guy, have some two stroke knowledge but it ain't no Detroit!

[cart around]

Premium fuel is not better fuel. It has less energy, and is harder to ignite than cheap gas. That's why it's used in high compression engines to prevent preignition. They increase the octane rating by adding more ethanol. We do not have high compression engines.

I would think that the piston melted because it's running lean. Maybe sucking air.

There is no real adjustment on the carburetor. Did you buy a BV-24 replacement? Strange that it has different screws on top.

My suggestions would be find the air leak. Maybe around the intake plenum.

Get rid of the oiler. IT IS GOING TO FAIL.
Plug the banjo hole where the oil hose is with a 6mm screw.

Your first tank of gas with a new piston should be mixed at 40:1. After that mix at 128:1

[Spicyunicorn]

Check crank seals!!!!! Better yet just replace them!!!

[jimboagogo]

I don't know the model # of the carburetor. I purchased it online from golf cart king. The carb in the pic on the site for a 1988 is what I purchased, if you look at the pic it has an adjustment screw toward the top just behind the throttle lever shaft. I will definitely check for leaks. Maybe I'll compare the main jet size compared to the old one. I think most of these replacement parts are made off shore an I'm not certain quality is top priority over cost.

[cart around]

This manual is titled 1970 to 1990, but it's not. It is really up to 1980.

I'm posting it because it has information on the BV-24 carburetor in section J.

88 is the only year from the 80s that used the bv-24. It has a vertical choke. That screw you are looking at is the pilot screw. The manual says it is for low speeds.

[cart around]

I also agree with spicyunicorn. Since you have it apart, change the crankshaft seals.

EDIT Wile I have access to my files, this 85 manual will cover evrything except your carburetor, exhaust, front cowl, and wiring. Your cart has an extra micro switch in the FnR switch.

The 3-pg HEI thread up top will have the correct wiring diagram in the first post.

[jimboagogo]

Thanks guys that's great info. I'll let you know how I make out

[cart around]

When putting it together, the two most important things to remember are rings go bevel side up, and the hole in the side of the piston goes towards the intake side.

[jimboagogo]

Well I'm glad I used the advice given. A piece of the bearing cage had broken off and ruined the seal. So new bearings too. Found the one half of the case had been repaired previously for the starter/generator bracket and is cracked beside the old weld, off to the welding shop. Found good info in previous threads that helped remove the clutch, going through it also, it's pretty good except the lube seal needs replacing. I'm going to remove the driven clutch to clean and inspect/repair. I was off on my diagnosis the piston was starting to grab and broke the skirt off, I only looked through the spark plug hole and didn't see any scoring only some pitting in the top of the piston. I figured out with the help of the service manual it was likely caused by me not adjusting the oil injection cable correctly so it's going to be a gas/oil mixed engine from now on. It had some wear in the cylinder so t was time. I'm learning as I go, the manuals have been a tremendous help. I really appreciate the info. Thanks to all that helped. I will post more when completed.