1972 50HP Johnson--I'm stumped!!!

[bhwarchitect]

My trusty 72 50HP Johnson is giving me trouble. Only running on lower cyl. when you give it gas. Will START and IDLE on upper only or lower only cylinder (or both) but when you gas it only the lower cylinder goes. Switched coils--no difference. Took apart the upper carb--no difference. New spark plugs--no difference. Any ideas?? Help!<br /><br />Brian

 

[JB]

Re: 1972 50HP Johnson--I'm stumped!!!

Howdy, Architect. I would like to know if there is spark in that upper cylinder when it is not making power. If so, continue with fuel system. If not, look at ignition.<br /><br />Is it possible that you missed clearing the high speed jet in that upper carb? Did it have a bowl of fuel in it when you tore it down? Have you tried swapping carbs?<br /><br />My Clymer starts with '73 engines, so I don't know if you have the CD2 breakerless ignition or a magneto. There must be additional ignition parts you can switch between cylinders for troubleshooting purposes. There may be an electrical breakdown somewhere in the hi-voltage circuit.<br /><br />Good luck, and let us know what you find.<br /><br />Red sky at night. . . <br />JB

 

[clanton]

Re: 1972 50HP Johnson--I'm stumped!!!

Has pack with termials,

 

[bhwarchitect]

Re: 1972 50HP Johnson--I'm stumped!!!

Thanks Clanton and J.B. Answers: yes, I have a power pack so I'm not sure what other ignition parts there are. As to the other question, the upper cylinder plug is cool while the lower plug is hot after trying to give it gas so I'm quite sure there is no spark at the higher speed. There was a full bowl of fuel in the upper carb when I took it apart. However I shamefully admit I only checked the float and needle. Where is the high speed jet? Switching the carbs is a great idea and I'll try it if you think its worthwhile. However with the lack of spark (coolness) in the upper cylinder, am I not probably looking for an ignition problem?<br /><br />Brian

 

[clanton]

Re: 1972 50HP Johnson--I'm stumped!!!

You need somekind of spark tester to check both cylinders, find cylinder that is not firing. Then look for black/white and black/orange wires at termial 6 and 7 on pack. switch the 2 wires and check spark again, if the spark change from non firing to firing the timer sensor is bad. Only turn engine enough to get spark, donot try to start engine with wires switched.

 

[bhwarchitect]

Re: 1972 50HP Johnson--I'm stumped!!!

Thanks Clanton! I have a spark tester and I will try your instructions. I'm not with it until this weekend however. I'll let you know!<br /><br />Brian

 

[bhwarchitect]

Re: 1972 50HP Johnson--I'm stumped!!!

I know its been awhile but I just got back to my motor last weekend. I again took apart the upper carb. and lo and behold at the bottom of the carb. bowl is the FIXED high speed orfice (no adjustable high speed jet on this model) which hides behind the bowl drain plug. The orfice was totally clogged with crud (30 years of residue). I cleaned out the whole area (and did the same on the lower carb. which was pretty clean) and it runs like new again!! That's why it was starting and idling on either cylinder but wouldn't run with power--no gas through the high speed orfice on the upper carb!! Thanks for your interest!<br /><br />Brian