1996 Johnson 88 spl low rpm

[Zpaulk20]

Hey guys I’m new to the forum. I have just recently bought a 2000 17’ polar center console with a 1996 Johnson 88 special on it and when I take it out it is maxing out at full throttle at about 3500 rpm and only reaching around 23 mph. Is this a common problem with these motors? It currently has a 19 pitch prop on it I believe

 

[jbuote]

Hey there! :welcome:

It may be something as "simple" as the wrong prop for your application.
The guru's will know better, but to start with..
No idea how mechanically inclined you are or are not..

Sounds like you should first get a baseline health of the engine as it is now...

Any chance you can run a compression test on it?
Might be able to rent a compression tester from local auto parts store if you don't have one.

Also, spark test with an adjustable open air spark gap tester.. Also available at local auto parts store..
Will spark jump a 7/16" gap on each cylinder?

Post those results and these guru's will be better able to help you..
At least they'll be able to say if there are unexpected results, or if you're looking at a prop change or not, etc...

No better group of knowledgeable minds I've found than right here...

Going to follow along and see how you make out!
Hope it helps!

 

[interalian]

Agree with checks in post 2. That's a fair bit fo boat and prop for 88HP though - any idea if it ever ran faster?

 

[Lightwin 3]

Hey there! :welcome:

It may be something as "simple" as the wrong prop for your application.
The guru's will know better, but to start with..
No idea how mechanically inclined you are or are not..

Sounds like you should first get a baseline health of the engine as it is now...

Any chance you can run a compression test on it?
Might be able to rent a compression tester from local auto parts store if you don't have one.

Also, spark test with an adjustable open air spark gap tester.. Also available at local auto parts store..
Will spark jump a 7/16" gap on each cylinder?

Post those results and these guru's will be better able to help you..
At least they'll be able to say if there are unexpected results, or if you're looking at a prop change or not, etc...

No better group of knowledgeable minds I've found than right here...

Going to follow along and see how you make out!
Hope it helps!

Excellent advice. I don't think you're hitting on all four cylinders, unless that boat is REALLY heavy.

 

[Zpaulk20]

So I tested the sparkplugs and one cylinder is not firing good. Haven’t checked compression yet but am gonna try to do that also today

 

[Zpaulk20]

My compression was 120,118,112,110

 

[Zpaulk20]

Also one side of the motor is hotter than the other side

 

[Lightwin 3]

Compression is a little low but consistant, which is good.

Wear are you seeing the temp difference?

If on the heads, you may have lost the deflectors in one head. They are under the head covers and look like solid vacuum tube.

 

[Zpaulk20]

Yes it is the heads. I will have to take them off and have a look.

 

[Zpaulk20]

Is there a water cooler below the heads where the hose from the heads runs to?