1973 Johnson 25 HP // Idling and throttle issues

[creece09]

1973 Johnson 25 HP

25E73A

Pull crank



Replaced spark plugs and ignition coils. Replaced impeller. Lower fluid oil. Cleaned carburetor. Cleaned and set points. Had it idling good in a trash can. Took it to the river, running well, died while idling. Broke the crankshaft key. Got it replaced. Take it back to the river and it cranks on second pull, idles fine, drives great, hits top speed for a while and then starts shaking/sputtering. Never can get it to full speed again but it runs along at lower speed (but full throttle). Get to a spot and fish, go to crank it up and can’t get it to stay going. Turn the start handle a little more towards the fast setting and that does the trick. It will run but doesn’t get to full speed and it still shakes/rattles/sputters. Fish again, this time it won’t crank. It will start to try but never get to idle, a couple sputters and kaput. My mechanical novice mind says fuel pump issue, my wallet says hopefully it’s not that $150 issue. Looking at the “Top Secret Files” forum I’m suspecting a carb needle adjustment issue may also be at fault. I used a 50:1 gas oil ratio. Y’all helped me tremendously get it to where it’s at now, so hopefully y’all can help me here as well.




Thanks

 

[Roberthill]

Check crank key . Jmo

 

[PDean]

I ran a 25 for years and had similar problems. Always a fuel issue.. dirty carb and or fuel line. . And or bad fuel... water from the tank. Ethanol gas is ok if it’s fresh. Let that stuff set up for just a little while and it’s starts to break down and the by products will drive you nuts.

My suggestion is to start with your fuel tank. Pour it out. Purge you bulb and fuel line with fresh gas. Non ethanol if possible.
Remove the screw on the carb bowl .. stick a rag in front and pump fresh gas all the way through. Put bowl screw back in.
disconnect your fuel line at fuel pump carb side. Spray gumout into line until it fills up. Let that sit overnite.

Next day remove carb bowl screw and drain. Used compressed air and stick it in fuel line and blow it out.
Replace carb screw. Give the throttle body a good shot of carb cleaner.

Worked for for me several times. Purred like a kitten

 

[creece09]

Got it back home and checked it out. Crankshaft key was still good. What had happened was the screw controlling the front flap of the choke (idk the technical term) had come loose so it wasn’t choking correctly to crank. I think I’ll see an improvement now. The idling will still be an issue though. I tried to set the adjustment needle but was struggling to get it to idle long enough to back it down to the slow setting and keep going. I also noticed the idle adjustment screw had the top broken off. (Not the needle in the carburetor but the screw at the bad of the throttle handle that connects to the motor.

Thanks