91 Johnson 50 Hesitates w Reduced WOT RPMs

[Shinyboat]

I have a 91 Johnson 50 with a jet on a 14’ boat. It used to run about 4900 RPM at WOT and was smooth the whole way from idle.

A few days ago we were running and on one launch it capped out at 4600 RPM. It would run smooth to 4500 RPM and as soon as pushed the throttle just a tad further to WOT it started hesitating real bad and would only get to 4600 RPM.

I pulled the plugs and they looked fine. I replaced with new plugs and the same thing happened.

I noticed oil dripping from the backside of the cowling now. I’ve only run this engine a handful of times and I don’t remember the dripping but maybe I don’t remember?

How would I go about troubleshooting this? Does it sound like a fuel, carb, electrical, or compression issue?

 

[racerone]

Step #1 is a compression test.----Post your numbers.

 

[Crosbyman]

good old carb with simple HS jet behind the lower carb bolt. how about opening it up and at minimum blasting it with carb cleaner... if you do not have a compression meter for step #1

 

[Shinyboat]

I’ll try both of those. Hopefully I can do it tomorrow with my daughters while I’m on dad duty!

 

[Shinyboat]

Step #1 is a compression test.----Post your numbers.

105psi both cylinders after 2 tests after running the river.

Plugs looked really good when I pulled them.

Several times the rpm’s jumped from 4600 to 4800. Once it almost died and came back as the boat slowed down.

 

[saltchuckmatt]

105psi both cylinders after 2 tests after running the river.

Plugs looked really good when I pulled them.

Several times the rpm’s jumped from 4600 to 4800. Once it almost died and came back as the boat slowed down.

Sounds like a fuel supply issue.