Motor problems, need help.

History, brief.
'57 Johson 18hp, top speed on a 14' v bottom is 7.3-7.5mpg via gps.

Compression is 95 top piston, 110 bottom piston.
Sprak is great, I syncronized the timing to the carb per the repair manual.

I rebuilt the carb, no difference.
Bought a used carb, rebuilt it, now she starts and idles great. I can get it started now on the first couple of pulls. However top speed is still 7.3-7.5mph.

I beleive the prop to be the original. From what I understand it has a rubber bushing. I have broken a couple shear pins, could I have broken that rubber bushing? Could my problem be the prop? How do I tell. Woudl it still work even if broken?

What else could it be?

Do you have the trim pin all the way in, next to the boat hull? Also sounds like you are running on a single cylinder to me. If you have no other method of checking cylinders while running (neon testers) then pull spark plug wires one at a time. If you pull one and it makes no difference that cylinder is not firing.

Yes, teh trim pin has been all the way in.

I'll the spark while running and see what happens. Water barrel OK for this test?

IF I am running on one piston how do I fix?

Hanr3 said:

Yes, teh trim pin has been all the way in.

I'll the spark while running and see what happens. Water barrel OK for this test?

IF I am running on one piston how do I fix?

Click to expand...

Water barrel will be fine for this test...... If its missing on one cylinder its probably a bad coil or plug wire.

Sorry to hear that the carb wasn't the only problem Sometimes I have to remind myself its all for fun and my hobby, and not to get too frustrated.

Thanks perchin!

I swung by to pick up some parts today, and that was a bust, they didnt have the spark plug wire. At least the kid behind the counter couldn't find it.

Hopefully by this weekend I get her running again. I don't mind doing the repairs, I've been wrenching on my junk since I turned 16. I also want to make sure eerything is correct and in top mechanical condition. I get a sense of pride from knowing I did that.

the more I think aobut it the more I believe it to be an electrical problem. I managed to cut a groove in teh one spark plug wire that has been functining properly. I haven't tested it yet, however I'd be willing to bet if I pull the other plug wire it wont make a bit of difference. I have some major things going on at work tomorrow and wont be able to mess with it until Thursday or Friday ta the earliest, and I still have to pick up some parts. Spark plug wire, more shear pins, and I think I'll get new plug wire connectors too.

Any luck?..... Mine gave me fits today, and didn't want to idle.... Think ill get some sea foam.

Yea, I swung by or called just about every marina, marine supply store and auto parts store in teh area looking for spark plug wire. NAPA had some, I stopped by, he had 39' left on a 100' roll & .43 per foot I bought all 39'. My other option was to order it on-line and that was 33' for $40 plus shipping. Needless to say 39' ought to last me a long, long time. :mrgreen:

I rebuilt the ignition from scratch again. This time paying more attention to details, and used a repair manual Jim was kind enough to provide links too. I know both pistons are firing. Pulled the plug wire off one at a time, and you could hear the engine difference.

I got her to fire and run in neutral pretty well, better than before I do belive. Maybe wishful thinking? I did notice the cam follower roller is worn, its made of rubber and has some grooves and flat spots. Im going to see if I can get a new one machined from brass at work tomorrow. It did fire up on the first pull twice tonight, once when I got home from work, and 2 hours later.

Next test is on the lake where I can set high speed.

Good luck with yours. Thanks for reminding me, I too want to add some seafoam to the gas tank.