Johnson 50 HP 1981 WOT problem

[bryan65]

I have a 1981 J50belcic. Engine runs smooth at idle and no load. then bogs down at WOT especially under load.

The engine sat for 7 years, Had a mechanic give it a once over before i put it in the water.

things done - New fuel pump and hoses. New spark plugs and new wiring harness rebuilt carbs

Since then have Replaced power pack and both coils (due to spark issue) I am now getting good spark.

I replaced a damaged prop. which caused problems to get worst

With old prop (15 pitch) I get 4700 RPM, and 20 - 22 mph. the throttle goes about 3/4. then bogs down, Have to pull back a little to get sweet spot;.

with new prop. I got only 4000 rpm, with same throttle issue.

This weekend, I went with 5 adults and 2 kids. Could only get 4000 RPM with old prop, and about 11 MPH. (same throttle issue) when was done, dropped all but 2 of us off, And took it out, Got the same 4500 - 4700 RPM and 21 MPH, with same throttle issue. Did not even try new prop, as it was already bogging down with just 3 of us.

I have a 1981 starcraft SS 161 I redid over the winter.

I was reading in another thread about putting a pin through high speed orafice (can't find this in book) and was wondering where this was. Also, book says to check for bent reed valve, Which I will do once the rain stops (been raining for like 2 weeks here)

any way, Was looking for help here, and possibly other ideas. Would really like to get this fixed. i understand a 50 is small. and will not do everything I want with alot of people. But I would like to at least know it is running good so I do not tear engine up,and get out of it all I can until I can afford and FIND a bigger motor.

 

[fireman57]

Re: Johnson 50 HP 1981 WOT problem

take the carbs off and run the wire from a bread twist tie through all the jets/orafices and then spray them out good with carb cleaner. That should do it. Anytime an engine sits for a while this should be the first thing done as they varnish up pretty quickly with the cheap gas we have now.

 

[bryan65]

Re: Johnson 50 HP 1981 WOT problem

take the carbs off and run the wire from a bread twist tie through all the jets/orafices and then spray them out good with carb cleaner. That should do it. Anytime an engine sits for a while this should be the first thing done as they varnish up pretty quickly with the cheap gas we have now.

Thanks. I assume the mechanic would have done this, but it never did run right. I did try carb cleaner, But heard this was not enough! Yeah this stinking gas. costs alot more. but so crappy!!

 

[fireman57]

Re: Johnson 50 HP 1981 WOT problem

If he just gave it the once over I am betting that he just put it in a tank and ran it, it started and pumped water so he figured it was good enough. If something else was wrong then you would bring it back to him and he would look a little deeper.

 

[bryan65]

Re: Johnson 50 HP 1981 WOT problem

If he just gave it the once over I am betting that he just put it in a tank and ran it, it started and pumped water so he figured it was good enough. If something else was wrong then you would bring it back to him and he would look a little deeper.

well he did take it to a dock and put it in the water. But yeah, he did not put the boat in the water, but it took him 3 weeks before. I do not want to wait that long again, Summer is short..lol

 

[fireman57]

Re: Johnson 50 HP 1981 WOT problem

easy job to do yourself and save some $$$$

 

[bryan65]

Re: Johnson 50 HP 1981 WOT problem

update:

Took both carbs apart. Ended up getting rebuild kits for both of them. One of the carbs did not have a nozzle gasket, the other one had one but was messed up. Needle valves were worn. One of the bowls was missing the clip. so just rebuilt both carbs.

After rebuild. Put on new 15 pitch prop I had got a month ago but could only get 4000 rpm out of.

Took it to the water, When opened up, immediately went to 5500 rpm (according to specs I have found WOT is 4500 - 5500 in my engine) and held at 28-30 MPH (per GPS) with three adults on board.

Curious now to see how it runs when I put a few more people on board (had 6 a few weeks ago and could only get 11 mph out of it)

Either way, I am happy now. and SAVED LOTS OF MONEY!! Thanks!!

 

[fireman57]

Re: Johnson 50 HP 1981 WOT problem

Glad to hear it. Now you know there is definitely a difference between giving something the once over and actually solving the problem. Happy boating for what is left of the season.