1989 Marathon Hard Start

[slonomo]

Hey guys. I'm working on a friends Marathon 2 stroke. It had a $20 Amazon carb on it and she complained of rough running and hard start.

I checked the compression 135# cold. Fuel was 40:1 . Changed the oily plug to an NGK BPR5EH. Spark is strong and consistent.

I aquired the original Mikuni and trashed the china carb. The Mikuni was clean as a whistle and tight, but I soaked it and cleaned every jet etc. Reinstalled with fresh 128:1 fuel and it starts and runs, but smokes like a chimney. I'm sure the muffler is full of oil residue.

When cold, it takes 60-90 seconds of cranking to start.

When warm, it takes 15-20 seconds of cranking to start.

Seems to start faster in reverse?

When it runs it feels normal, about 10 mph and will climb small hills. Governor is set really low.

My question: Could a weak battery and/or weak starter gen cause this thing to be hard to start?

[cart around]

I think it's probably crankshaft seals wearing out. Spinning that long finally gets them to seal.

You could try loosening the exhaust to see if the muffler is restricted. A healthy dose of Seafoam wouldn't hurt.

I don't think it's an electrical problem.

[slonomo]

Originally Posted by cart around

I think it's probably crankshaft seals wearing out. Spinning that long finally gets them to seal.

You could try loosening the exhaust to see if the muffler is restricted. A healthy dose of Seafoam wouldn't hurt.

I don't think it's an electrical problem.

Thank you and ditto on the ignition/electrical.

New info:

I put the cart up on jackstands and let it run wot for a good 15 minutes. Smokes like crazy so I'm betting the muffler is full of gunk. With the engine warm/hot I checked compression and it's only 70 psi. Looks like it needs overhauled.

Yesterday morning I saw a nice 10" puddle under the cart, it was gas. Fuel is leaking from the crankcase at the bottom. This crankcase has fuel in it. It was hydrolocked when I got it, bad carb. I fixed the carb and it's not flooding anymore.

Question: Could there be residual fuel left in the crankcase? Could that be causing a hard start issue? Would that not burn off once it's running and hot? I've never seen this much fuel in a 2 stroke.

[cart around]

You could have a ripped lower diaphragm in the fuel pump.

https://buggiesgonewild.com/showthread.php?t=98839

[slonomo]

Originally Posted by cart around

You could have a ripped lower diaphragm in the fuel pump.

https://buggiesgonewild.com/showthread.php?t=98839

This is good stuff! I didn't realize that pump mounts directly to the engine. It's kinda hard to see in there.

So basically the fuel pump diaphragm is allowing fuel to bypass into the pulse line and then into the engine, correct? This explains a lot. That will solve the fuel leak and hydrolock issue.

I wonder if the extra fuel could be causing the low compression when it's warmed up. All that extra fuel could be cleaning the glazing off the cylinder walls and rings causing it to read low compression at 70 psi vs. cold 140 psi.

[cart around]

The best you should get is 120 psi, and be happy with 100.