Lost 1,000 RPM this season.

[levittownnick]

Johnson '97 150 HP, J150EXEUE. Starts easily but acceleration at higher rpm suffering and does not get above 4300 rpm. Checked compression and found same readings as in 2007 (10 years ago). Re-did timing and no change in settings or performance. Last season it ran normal. When It was winterized, I noticed a leak caused by a crack in the electric choke, so that part was replaced, also, failure of the fuel filter cartridge over the winter (the Bowl FELL OFF!) caused me to change to a different spin-on filter. The linkage all looks OK.
Do you have any suggestions?

 

[ondarvr]

Have you checked for spark on all cylinders?

 

[levittownnick]

No, not directly, but all the plugs looked normal and I replaced them anyway. Other than the lost power, the engine appears to run normal without an apparent miss.

Thank you,
Nick

 

[boobie]

Do a cylinder drop test on it.

 

[Roberthill]

Decarboning ?

 

[gm280]

I would certainly test for spark on all cylinders like "ondarvr" suggested in post #2

With the engine running, remove one at a time spark plug wire. If the engine changes RPMs that cylinder is firing. If there is no change in RPM that cylinder is not firing. Then replace that spark plug wire and go to the next one. Once you finish, you will know if you have a dead cylinder or not and that will help to eliminate that issue up front. It would be even better if you could somehow load the engine while testing the spark plug wires. But that may be harder to do. JMHO

 

[interalian]

Hang a timing light on each lead in turn and try running the engine at WOT. Look for any dark spots in the 'stream' of light that may indicate dropout.

 

[levittownnick]

Thanks folks, there is definitely some good advice on here. I will run the engine and remove the wires one at a time.
Thank you,
Nick

 

[levittownnick]

8/6/17 checked all 6 cylinders at idle and each one contributes to the idle. No problem here. I am planning to do a full power check out on the water later this week, the date is not firm, depends on schedule & weather.

Thanks,
Nick

 

[jakedaawg]

Compression test 1st