75 50hp johnson

riverbronzeback · Jul 2, 2009

Ok guys, my buddy has a mid 70's johnson 50hp. First time we took it out it ran great. We got about 30mph(mid 70's 16ft basstracker, decked out.) Sounds like it runs pretty well, he just did both carbs in the fall. Next time we went out all he could get is 7mph although it still sounds like it is running good. He thinks it is something to do with the current as first time we were on a lake and when it started running bad we were going up river in a pretty good current. I told him to check spark cause it seems to me it might be running on one cylinder. I dont think it has to do with the river current. If he had bad compression it would run bad all the time right? It just seems weird if it was spark that it would do intermittently. Unless he has a coil/condenser wire rubbing on something sometimes. Primer ball was still firm and pumping it had no effect. I think he has a cylinder not firing sometimes. What do you think? When running well should he get more than 30mph?

CarlF · Jul 2, 2009

With a 50hp on a 16' tracker you should easily run 30, probably 40.

If it is running rough, then it could be a wide range of problems, from fuel to spark.
If it is running fine, & the RPM come up but you are only going 7 mph, you may have spun the hub on the prop.
Either way, get it running correctly before you over-rev it (prop slipping) or damage a piston (running rough). Running a 2 stroke rough, especially if it is fuel related, can do some damage.

riverbronzeback · Jul 3, 2009

And also he said it did it before and the next time he tried it it was ok. Then did it again when we went out. Will the prop slip only sometimes. Or when it happens it always happens?

CarlF · Jul 3, 2009

Usually, once the hub spins on a prop, it does it everytime you apply power to the prop. But you never know. Sounds to me like there is some other kind of problem.

riverbronzeback · Jul 15, 2009

Ok Got a call from my buddy and he finally checked spark and compression. Good strong spark on both and 120 compression on both cylinders. So fuel problem right? Also he said he took apart both carbs and they both look good but i know he may not have cleaned them out well enough. What do you guys think. Carb problem?

ben2go · Jul 15, 2009

riverbronzeback said:
Ok Got a call from my buddy and he finally checked spark and compression. Good strong spark on both and 120 compression on both cylinders. So fuel problem right? Also he said he took apart both carbs and they both look good but i know he may not have cleaned them out well enough. What do you guys think. Carb problem?

Possible.It could also be the fuel pump,miss matched fuel connectors,bad fuel line,I'd check the entire fuel system.Also check for water in the fuel.It sneaks in when you least expect it.

bassboy1 · Jul 15, 2009

That motor has 2 single barrel carbs - one feeds each cyl. If you think it is running on one cyl, my guess is he has a little crud in one of the carbs he hasn't cleaned well. Either a blocked passageway (high speed jet likely), or a stuck float.

riverbronzeback · Jul 16, 2009

Thanks for the responses. Would love to get my hands on it myself. Friend is going out of town for a week so he wont mess with for a couple of weeks. Would love to get this back on the water cause I cant take my boat for lack of a hitch on my vehicle right now. And it figures, i have all my days open this summer to fish and cant. IT SUCKS.