1990 Johnson 60 hp no at power full throttle, no cough or sputter

[utfisherman]

I have a 2 stroke 1990 Johnson on my 18 foot bass buggy pontoon. I am running at a high elevation lake about 8000 feet. the motor runs great idles fine sounds like it revs to about 4000 rpm tachometer works is sporadically. When the tachometer is working and I'm on the water it reads about 3000 RPM. The problem is the boat will only go about 5 mph with the fish finder gps.
Could I have a prop slipping? or is there anything else I need to look at. or maybe wrong size of prop. this is the first year I have ran this boat?
TIA Doug

 

[racerone]

Post the facts to get help.----Does spark jump a gap of at least 3/8" on all leads, yes or no ?----Post compression test numbers.-----

 

[utfisherman]

I have not tested the spark yet. the compression is 110 on all 3 cyl I have this boat in a slip for about a month when I first put in the lake it would do about 15 mph now only 5. there is no miss or cough when it is running. WTO or at idle.

 

[tphoyt]

Is there a lot of growth on the hull? You can mark your prop with a marked to check and see if it is slipping. Mark the prop and the hub and after a run check to see if the mark no longer line up. With your rpm’s running high it could possibly be a spun hub.
Best.

 

[utfisherman]

The bottom is clean I am going to mark the hub this week. this is the first year I have had this boat. It came from about 3000 ft elevation. I wonder if a different pitch prop would help. If I remember the prop that is on it is a 17 pitch. I dont know what to change it too for the higher altitude to help the problem.

 

[Chris1956]

If the motor is truly going 3000 RPM and you are going 5 MPH, it is not the elevation or growth. Either the tach is wrong or more likely, the prop or gears are slipping.

 

[racerone]

Some trouble shooting is required.-----Sounds like it is running on 2 of 3 cylinders.-----compression., post the numbers.-----Spark.-----Carburetor linkages.----Timer base moving.-----And does the tell tale hose come off the side of the block or was it moved per a service bulletin.----Should come off the top of the block.----Impeller replaced.-----Water pump kit has details for this.

 

[utfisherman]

Thanks I am going to try changing plugs and then go from there. I have ran it about 30 hours with out changing plugs. I am not sure about the tell tale hose I did put a new pump in this spring and I am getting a good stream from the tell tale hose.