88'runs strong in reverse struggles in forward

[1980EasyE]

I just put a new top end into my 88' Marathon 2 stroke. Now it wont run very well forward but when i took the muffler off it seamed to take right off so i got a new muffler. Still runs terriable. I've changed the plug a couple times, cleaned the carb, dosn't make any difference. After messing with it i found it runs very strong in reverse. It also has new belts, fuel filter, air filter and fuel pump. I've heard it may be the timing but it ran "OK" before I did the top end it was just starting to get low compression. So im not sure how the timing could have gotten screwed up. Any ideas?

[redcloud]

Did you put the piston in correctly? Ports to intake side?
Did you pull the engine for the rebuild? If so, you may have crossed a wire some place. Hard to know more without some more info of what was done.
Check that all electrical connections are tight to starter and reg.
If it ran well before then look very carefully at what was touched that could have been changed.

[ScooterMcTavish]

When you rebuilt the top end, did you redo the crank seals?

Usually bad in forward, good in reverse = crank seals.

[Dave Box]

It can be that the seals get worn in the forward direction which is 99% of the time and in reverse it scuff up the rubber enough to make a better seal. The good news is that the hardware is ~$7 the bad news is that (if it is the seals) the engine is coming out again.

Dave

[1980EasyE]

Thanks for the input. I'll pull it back out and put a crank seal in it. I'm sure I paid attention to the piston marks but I'll check it while I have it out. The only elctrical wires I unhooked was from the pulser and with the connector it cant be hooked up wrong.