Johnson GT 150 issues

[sutor623]

Got a 1987 GT150. Motor ran perfectly the first time we had it out. This was after I had put in a waterpump, rebuilt the carbs, new plugs etc.

Well next time I had it out, at around 3000 rpms the motor would pick up to 3250rpms for a split second and then go back down to 3000. Like it’s gaining power. Boat actually surges forward.

Primer ball stays tight.

I checked the plugs and the ones on the left looked too dark so I checked thermostat and poppet, pulled carbs again, checked timing at all cylinders after indexing flywheel and they’re perfect. So I popped a powerpack a d three ignition coils onto the left side. Didn’t help at all. I took the powerpack that came off that side and swapped it to the other and no change. Stator was a bit out of spec on port coil so I put a brand new one on and no change.

I also disconnected the primer lines from the enrichment and that didn’t change anything.

Kinda out of ideas here fellas. Compression was great when I replaced the exhaust manifold gasket but there was some carbon on exhaust side starboard ring seats.

any ideas on where to go from here?

 

[flyingscott]

Is the VRO still connected? Which primer ball? the fuel ball should not stay tight after it starts.

 

[sutor623]

Scott!! Whats up man I hadnt been on here in a while.

VRO has been disabled, but the factory pump is still in place. I should have said the primer ball stays full, not tight.

There are all new hoses on the engine. The tank is brand new with all new fittings. I restored the boat and put this old girl on there.

If I run the motor up higher rpms it does the same thing. Its almost like a dead cylinder and then cuts on for a split second.

Oh and one other thing. If the motor is idling on the muffs or in the water it idles perfectly. When you give it revs on the muffs (to 2500 or so) the rpms will pick up on their own to about 3000/3250. I pulled every spark plug wire one at a time and grounded it to a spark tester and the motor still picks up the rpms on its own.

I have been working on these motors a long time. This one is foolin me!!

 

[racerone]

Well , post those ---" great compression numbers "

 

[sutor623]

They were all 92-95 psi.

 

[flyingscott]

Hows it going Sutor? What about the carb linkages themselves? Are they all in good shape no slop? Throttle cable in good condition?

 

[JerEazy]

You seemed to have eliminated any electrical issue - so that basically just leaves air and fuel. When you did the carbs you did a link/sync?

 

[Faztbullet]

These motors are bad about plug wires burning out where spring enters wire, even a TSB on it. Check em…..

 

[sutor623]

Thanks everyone!! Fazt good info bro.

So I figured it out. It was a combo of two things. One was the stator because my left bank plugs were burning much cleaner after that was replaced.

next thing I figured out was my fuel primer valve was slowly dying because it started flooding out my motor and when I removed it and plugged the hoses the motor now runs perfectly!! I think it was just soaking the plugs and they would catch every once in a while.