1962 Johnson 75 hp engine troubles

[daveydb]

I took out our 75 hp Johnson today and it would idle ok but then when I tried to open it up, it sounded like it was misfiring or just wouldn't increase the RPMs. Any ideas on what this could be. I think it has a idle adjustment on the carb but I didn't see any high speed adjustment on it. We just changed the spark plugs. Anyone have any ideas on what to try. I don't go to the lake too often so a progression of what to check would be nice. Thanks

Dave

 

[Chris1956]

Re: 1962 Johnson 75 hp engine troubles

Check to make sure the carb is opening, when you advance the throttle. You have a bit of linkage on that motor, sometimes things get loose. If that isn't it, you need to check for spark on all four and go from there.

 

[5150abf]

Re: 1962 Johnson 75 hp engine troubles

I would make turning screws on the carb the LAST thing I did unless you have been messing with them, more often than not that isn't the problem and once you get your mixture way off it makes it that much harder to fix, they don't just all of sudden go out of adjustment.

If you do mess with screws(don't!) before you start count and write down exact turns to seat before you start so you can put it back where it was when that doesn't do anything(which it won't).

I think you have one of more dirty carbs, that is probly the most likely cause of a sudden power loss and a good place to start.
Pay special attention to the high speed jets- pull float bowl drain screw insert a small skinny screw driver into the drain hole and pull the jets, clean with a stripped copper wire, reinstall and see if that helps.
Always do the free stuff first

 

[Evinrude Boater]

Re: 1962 Johnson 75 hp engine troubles

Bad seal on gas lines? Kinked gas line? Tanks vent open? Take some mixed fuel in a spray bottle and spray into the carbs when it happens again and see if the engine responds better.
The two low speed screws can be turned out one and a half turns from a seated position and it should run OK. Fine tuning can be done after you get the engine running properly.
With no air filters on these down draft carbs you never know what gets sucked down them.

 

[F_R]

Re: 1962 Johnson 75 hp engine troubles

Check out the ignition system. Points dirty / out of adjustment? Distributor rotor pin-holed through to the shaft? If it is a mag system, coil arcing out?