78 johnson wont go

[billy_goat]

ok heres what i have i believe its a 1978 18hp johnson (friend is letting me borrow it so im not posative on the year) anyway was out hunting yesterday and about half way to the duck blind the motor started vibrating really bad and jumping allmost like a hickup and no power at all.i checked to make sure the shear pin on the prop and everything was good since i just replaced it 2 weeks ago when i hit a log but all looks good.another friend was saying maby the shearpin on the flywheel?i have no idea so im hoping to get some suggestions on where to start to see if maby this is something i can fix before i have to pay a shop.

 

[jasper60103]

Re: 78 johnson wont go

Since it's a friends motor, not sure how far you want to go with fixing it? You really need to troubleshoot the engine. I would start with a compression and spark test. That hiccup could be a lean condition, but just a guess at this point.

 

[DJ]

Re: 78 johnson wont go

1. The "flywheel pin" is a good guess. You maybe right.

2. Good spark on both cylinders?

 

[billy_goat]

Re: 78 johnson wont go

the motor has power so i wouldnt think it was spark or compression or anything like that.what its doing is like the motor is reving but the shaft and prop arent.every second or so it will grab and start to spin causing the motor to jump and like hicup.loli dont know how to explain it sombody else suggested the flywheel pin to me allso so i will start there and see what i can come up with.