77 140hp starts, exhaust backfire, dies

[manonfire296]

just replaced lower starboard piston, have 80psi, wall was scored a bit, total rebuild will came later, need it running now. Have 100, 90 on port side. 120 and 80 on starboard. Was extremely careful not to disturb carb, and throttle linkage during tear down and rebuild. Also replaced fuel line hoses and put in an in line fuel filter. Plugs were replaced with CORRECT Champion plugs, previous owner used $1.50 Auto Zone crap. Also used carb cleaner to clean throttle and carb linkage. Motor ran well in tank after rebuild. Next day put in water and now I have trouble getting it to run. When it does run, it runs for only about 45 seconds, dies and backfires through the prop. I drained fuel, replaced with premium, and Mercury 2 stroke oil 50 to 1. bulb is hard, and fuel is entering the carbs, although it seems like it floods a bit. Compression in starboard side dropped to 30psi in both cyls. I think that might be the gasket. Any sugguestions?

 

[tashasdaddy]

Re: 77 140hp starts, exhaust backfire, dies

Did you torque the flywheel? sure sounds like the woodruff key has sheared, and that throws the timing off. compression could be gasket, only way to tell is pull it and replace. read these > http://forums.iboats.com/showthread.php?t=244013

PULLING FLYWHEEL

you need a harmonic balancer puller, you need 3 - #8 harden bolts, that fit the 3 holes in your flywheel. standard hardware store bolts will strip out, causing more problems. loosen the flywheel nut, leaving it on so it protects the thread. thread the bolts in 7/16 of an inch. then tighten the puller, adjust so it has a straight pull. now tighten the puller, rap the center bolt with a hammer, then tighten some more. you may have to let it sit over nite, and repeat in the morning. this is a compression fitting, it will eventually POP!!. do not loose the woodruff key that goes in the groove of the flywheel and the crank shaft. then installing the flywheel, it has to be totally clean, no oil, woodruff key in place. then torque the nut to the specifications for your particular motor. if you do not do this, the woodruff key with shear, and you will be repeating these steps.

 

[crxess]

Re: 77 140hp starts, exhaust backfire, dies

Timing won't effect Compression test on a 2 stroke. Are you using the same test gauge? Head gasket may not have held. Head may need to be decked.

 

[tashasdaddy]

Re: 77 140hp starts, exhaust backfire, dies

agree^^, but it would sure make it backfire. also plug wire on wrong cylinder could do that also.

 

[kenmyfam]

Re: 77 140hp starts, exhaust backfire, dies

For such a small item the woodruff key can cause a lot of issues !!!

 

[manonfire296]

Re: 77 140hp starts, exhaust backfire, dies

When I pulled the flywheel the first time the woodruff key was stuck, I couldn't remove it, therefore it stayed where it was. It didn't appear damaged, how far is it supposed to stick out from the shaft? Using same comp. guage on all four cyls. Plug wires are correct, no mistake about that. Brand new cyl head was put on when piston was replaced. Will check the head gasket tomorrow, and check the woodruff key again.

 

[manonfire296]

Re: 77 140hp starts, exhaust backfire, dies

head gasket was wasted. new one on order.