1973 Johnson 50 running on only one cylinder

[Panhead Jim]

I have a kinda weird issue with a 1973 electric start Johnson 50, model 50ESL73R. I runs on only one cylinder. Compression is good: 140 top, 135 bottom. New plugs, ignition tests fine with the old school tester, the Johnson tester with the 1/2" spark jump. Timing is good. New reed valves top and bottom. No obstructions in fuel lines. I have NOT tested the fuel pump. Of course I can't tell what's it's doing on the hose muff, but condition becomes obvious when you put it in the water. EVERY ONCE in a while, the other cylinder will hit, but certainly not under load. The throttle shafts, both of them, are sloppy shot. I mean wore-out shot. I can get 1/32 to 1/16 side play when I grab the levers and move the shafts around, worse on the top. The high-speed jets are fixed, low-speed jets are adjustable but have little effect unless you shut them all the way down. If you spray just a shot of starting fluid around the throttle shafts you get the expected jump in rpm. I'm leaning toward replacing the carbs, but the tough part is finding a set that is any better than the ones I've already got. Several questions: Is there a way to rebuild or refurbish the throttle shaft to throttle body fit? Is it likely that this is the problem? Will newer carbs, say late 80's with fixed low-speed jets, work on this motor? Other likely culprits? I'm really pretty stumped and don't want to just throw money at it. I've already done a good deal of that...
Thank you for any insights.
Jim

 

[gm280]

Re: 1973 Johnson 50 running on only one cylinder

I have a kinda weird issue with a 1973 electric start Johnson 50, model 50ESL73R. I runs on only one cylinder. Compression is good: 140 top, 135 bottom. New plugs, ignition tests fine with the old school tester, the Johnson tester with the 1/2" spark jump. Timing is good. New reed valves top and bottom. No obstructions in fuel lines. I have NOT tested the fuel pump. Of course I can't tell what's it's doing on the hose muff, but condition becomes obvious when you put it in the water. EVERY ONCE in a while, the other cylinder will hit, but certainly not under load. The throttle shafts, both of them, are sloppy shot. I mean wore-out shot. I can get 1/32 to 1/16 side play when I grab the levers and move the shafts around, worse on the top. The high-speed jets are fixed, low-speed jets are adjustable but have little effect unless you shut them all the way down. If you spray just a shot of starting fluid around the throttle shafts you get the expected jump in rpm. I'm leaning toward replacing the carbs, but the tough part is finding a set that is any better than the ones I've already got. Several questions: Is there a way to rebuild or refurbish the throttle shaft to throttle body fit? Is it likely that this is the problem? Will newer carbs, say late 80's with fixed low-speed jets, work on this motor? Other likely culprits? I'm really pretty stumped and don't want to just throw money at it. I've already done a good deal of that...
Thank you for any insights.
Jim

Yes there is a way to solve your carb problem(s). First, is he sloppy fit between the shaft(s) and the carb body more of a worn out shaft or worn out opening, or is it some of both? Reason I ask is because they do sell the shafts as replacement parts for your carb. But if it is a worn out carb body opening, then you will need to have some bushings installed as well as new shafts to fix those sloppy openings. But it isn't a major issue either way and old carbs can be easily refurbished with some bushings and new shafts... And a lot cheaper then new carbs or older carbs as well... They actually do that to many old carbs for vehicles. Maybe check with a machine shop for some help.

 

[Panhead Jim]

Re: 1973 Johnson 50 running on only one cylinder

Update on this old Johnny and a question. I found two used good condition carbs from a '73, cleaned them thoroughly and rebuilt them with OMC kits, installed and VIOLA, both cylinders now running. My hypothesis is that the fuel feed to the bottom carb from the top was completely stopped up or the float assembly on the bottom carb was stuck. Either way, it's running now. Here's the question: Do any of you have experience adjusting the low speed side of these carbs? Could you describe the procedure you use? I've installed new bearings and keepers in the low speed circuits, needles were fine in the replacement carbs and the circuits are clean. I've initially set them to 5/8 turn out as the manual prescribes. Now I need to fine tune a little rough idle. The manual suggests about 800 rpm in gear, adjust to highest and smoothest running, then adjust idle to max 700 rpm in reverse. I know I can't do this on the flush muff, have to take it to the river. Just making sure with you experienced ones that this sounds like the right procedure or asking if you have a better way. I do not have a test tank at home. Any help or comments appreciated.
Jim