76 johnson 35 horse backfiring and 1/4 power

While on the lake i was full throttle when the motor went to less than 1/4 power on it own and started to backfire. Changed gas tank same thing. Got it home put the muffs on and started motor. Same problem at idle. Checked fuel filter that looked good. Changed both sparkplugs,same problem. Took both plugs out,both plugs looked the same,they looked burnt meaning black and were dry. I think this is normal. I did a spark check on both coils and i got a good spark arc on both. Checked the compression on both cylinders,one was 130 the other 125. that seems good. The one thing i forgot to do is squeeze the gas bulb while its running,i'll do this in the morning. I'm running 50:1. All in all its still backfiring with white smoke and stalling and running at less than 1/4 power while the throttle is wide open. Im thinking theres some dirt in the carb jets. I've never rebuilt a carb before,any advice on this would be helpful. also any other advice on something else it could be would help. Maybe timing not sure how to do that either.

Thanks

Re: 76 johnson 35 horse backfiring and 1/4 power

classic case of the flywheel key breaking. there is a slot in the crank shaft and the flywheel that a woodruff key goes into. you need a harnonic balancer puller, and three 14x20 #8 harden bolts (auto parts store), to pull the flywheel. only use the manufacturer key to replace. other will break. the shaft and flywheel have to be clean and free of oil when reassemble, an nut retorqued. the part number for the key is 319456.

Re: 76 johnson 35 horse backfiring and 1/4 power

Not quite sure how to do this but will look into it. Any advice on how to take apart and put back together would be nice.

Thanks again

Jaydee4854

Re: 76 johnson 35 horse backfiring and 1/4 power

here's a picture of one in progress. you insert the bolts into the flywheel 7/16 of an inch. keeping them level so when you tighten the center bolt, you have a straight up pull. tighten the center bolt, then tighten somemore. do not hit the flywheel with a hammer or any thing else. once tighten. take a hammer, and rap the center bolt. then tighten again. it is not going to pop right off. i leave the puller on and periodically tighten. and usually amazingly the like to pop of during the night. picture courtesy of Paul Moir.

Re: 76 johnson 35 horse backfiring and 1/4 power

Ok, I've got the nut off and i have the puller in but the flywheel is not moving at all. I've tried tighting it as much as i can but im afraid to go any further. I don't want to break the flywheel. I've raped the center stud of the puller lots of times now. At this point i have wd40 soaking and the puller very tight in hopes it will break free at some point. Any advice would help. Thanks again you have been a lot of help. Nice site and you seem to know your stuff.

Jaydee4854

Re: 76 johnson 35 horse backfiring and 1/4 power

With pressure on the puller, tap the underside of the flywheel with a piece of wood and a hammer and it should come loose. Just give it a firm shot, dont kill it.