Johnson 28SPL dies under load!

Hey guys, just picked up a 1987 Johnson 28spl that seemed to be in great condition, isn't that the way most of these threads start?

Anyway, the motor starts up instantly, but ran a little rough. Did a carb clean and rebuild, got a new fuel line, replaced the spark plugs, threw some seafoam in the tank and took it out to the lake.

On the lake, the motor starts up like a champ and purrs at idle. With the warming lever it revs freely up to the upper ranges with little hesitation. Throwing it into gear however, it bogs, acts like it's not getting enough gas and dies. We trolled around with it for a bit pushing the throttle to the point where it would start to stutter and took it back a bit.

After a while the motor started to lunge so we gave it more gas. this time it didn't die, but kept going at low rpm and lunging into higher RPMs intermittently. Those lunges came closer and closer together until it seemed something was breaking loose and we planed out a bit, not quite up to full revs though. We ran with it for a while and then stopped to check the spark plugs. It never got up on plane again, still choking out when we took it past idle.

Any ideas?

Re: Johnson 28SPL dies under load!

The high speed jet is clogged somewhat... a common problem. It is located way in back of the float chamber drain screw plug, horizontal in the center bottom portion of that float chamber. Clean it carefully with a piece of single strand steel wire.

Re: Johnson 28SPL dies under load!

I had similar issues. I went through coils, condensers, spark plugs, fuel tank, fuel lines, and more until I realized the fuel pump was bad. Take the fuel pump off the motor (leaving the hoses connected). Pump the bulb. If any gas comes out of the back then it's a ruptured diaphragm. Quick and easy way to eliminate one issue.

Re: Johnson 28SPL dies under load!

When you take the pump off of the motor, you will need to reinsert the mounting screws and place nuts on the back to keep the two halves of the pump togetner for the test jonbellamy is suggesting, otherwise you'll get lots of gas leaking around the case.

Re: Johnson 28SPL dies under load!

Thank you very much for the reply guys, I'll give it a try and get back to you!

Re: Johnson 28SPL dies under load!

Been fighting this motor for a while now, Rebuilt the carbs, rebuilt the water pump, motor still starts perfectly and won't rev in gear and under load, but it will rev with the warming lever! Also, the motor leaves more oil in the water than it should, plus once I leave it sitting in my garage lots of oil drains out of the exhaust over the next day.

Any Ideas?

Re: Johnson 28SPL dies under load!

Have you checked spark on all cylinders?
Does the fuel bulb hold firm with engine off?
hows compression?

Re: Johnson 28SPL dies under load!

If they a ok, check timing

Re: Johnson 28SPL dies under load!

replaced the spark plugs but have not checked spark on both cylinders, I'll do that this evening.

Fuel bulb is NOT maintaining a lot of pressure in it, but I was able to run it for a half hour at idle and part 1/2 rev in neutral with out issue.

Have not checked the compression.

How do you check timing?

Thanks for the help by the way!

Re: Johnson 28SPL dies under load!

Check it holds pressure with engine off, it may seem ok at idle but might overload it at higher rpm
Check you have spark from every sparkplug then we can move on to timing.
Check compression too, even if you use your thumb to check they are approx even.