68 Johnson 85HP?

[ceeyahd1]

I just picked up my first boat a 17' startcraft with a 68 Johnson 85HP motor, I wanted to get everything checked out so I do not have any problems and when I took it out the first time it seems to have a miss at maybe 15% and 40% throttle, he said it could be carbs so he rebuilt the carbs last week and took compression test the #'s were 100,100,100 and 90. I took the boat out last weekend and it still seems to have a miss, it does not idle good at about 10% throttle it seems like it wants to stahl, checked speed it goes about 29mph.

If compression is too low what is the fix? Am I wasting money on this motor?

Thanks

 

[jimmbo]

Re: 68 Johnson 85HP?

I would be checking all the wiring pertaining to the ignition system, looking for any indications of wires shorting out as throttle is advanced. Distributor is under flywheel on this model. Carbs don't open very much untill timing is fully advanced. Sync between timing and carbs should be checked. Gap on spark plugs? Do a decarb on it. Are the idle mixture needles both adjusted properly? Air leaks in incuction system. The compression numbers don't look too bad, these aren't exactly Hi Compression engines, and they are within 10% of each other.

 

[ceeyahd1]

Re: 68 Johnson 85HP?

Great Thnaks for the response. Can a decarb be done at home with hose hooked up to motor? also what would cause it to make something like a coughing sound at medium idle, it is not a backfire. I am using L76V plugs that do not get gapped, is this a bad choice? these were the type of plugs that were in the motor when I bought it.

Thanks.

 

[ceeyahd1]

Re: 68 Johnson 85HP?

Also mechanic never checked timing or points, he rebuilt carbs. adjusted them and that was it. Should he have checked the timing and points?

 

[jimmbo]

Re: 68 Johnson 85HP?

I can't comment on the plugs, but what does champion recommend? This engine does use two sets of points, located under the flywheel. Probably wouldn't be a bad idea to change them. I would reccommend a good service manual to explain how to do it.