Losing RPMs but consistently 1000

[Randy40a]

I have a 60hp Johnson engine, 3 cylinder, 2 cycle, adding oil to gas. The engine runs wide open at 5100 rpms, then drops to 4100 with no warning and at full throttle you cannot get over 4100 Does it cold or warm. So far I feel I have eliminated I think most fuel issues, new pump, hoses, filter, squeeze ball. I have also replaced the 3 coils and spark plug wires and plugs. The issue is sporadic, goes for days with no problem, then will give me trouble all day. When the rpms drop it runs rougher like a cylinder is not firing but not rough enough to think that it is only running on 2. HELP!!!! Driving me crazy. Any one have this issue?

 

[jimmbo]

A model number would be sort of handy

 

[boobie]

Do a cylinder drop test on it when it acts up.

 

[jakedaawg]

Clean and tighten ALL the grounds for the electrical components (coils, power pack, etc) first. Then do as boobie mentioned. Intermittent issues can be a bear...you have to wait for the issue to diagnose.

 

[Randy40a]

thanks for your tips, Model number is J60PLSID and year is 06/2000. I am not sure what you mean by "cylinder drop test" can you expand on this. The boat is on a lift year round, when the water level goes down, I winterize it and cover it where it sits. Is the cylinder drop test something you can do in the water? Had the boat out Saturday, ran like a charm, took it out Sunday and it ran like crap. Very frustrating.

 

[racerone]

Test run with cowling off.-----Do another test run with different tank and hose.----Possible water in fuel ?

 

[Randy40a]

On the fuel, I have a 25 gallon tank on the boat and a 2 gallon red metal tank. I have switched out, with engine off, and with engine running, no change. I add fuel additive every 5 gallons. I usually only put 10 gallons at a time in the big tank. Yesterday I ran the 2 gallon tank, fresh gas and 50-1 mix. Same issue. It really acts like water in the fuel but fresh gas and oil yesterday in the small tank did not change anything.

 

[jakedaawg]

Cylinder drop test...while you are experiencing the issue use a pair of nylon plug wire pliers and pull off each wire one at a time to see if there is a change. No change on one plug indicates the problem cylinder...

 

[Faztbullet]

A 1000rpm drop is a cylinder.....test ignition system as posted above...

 

[Joe Reeves]

A similar problem I encountered many years ago.... a bug floating in a carburetor float chamber. With the engine tilted, sometimes that bug would be near the edge of the fuel that is now much higher than normal within the carburetor due to the tilt angle, and when the engine dropped to it's normal running position, the bug would stick to the top interior portion of the carburetor... out of the way, no problem!

At other times, tilted, that bug was simply floating on the gasoline... and as the engine dropped to its running position, that bug, floating, was free to be drawn into the high speed jet area as soon as the throttle was fully opened... creating a fuel shutdown of that individual carburetor. Something to keep in mind.

Boobies mention of a cylinder drop test would reveal which carburetor might be involved.

 

[Randy40a]

Thank you Joe, the boating season is pretty much over up north, I plan on taking the boat out one more time, do the drop cylinder test and then take apart the carb(s) to see if something like that is in play.

 

[jakedaawg]

If its intermittent it's most likely electrical. Not trying to discount Joe's story, just most likely.

 

[Randy40a]

I may have found the issue, based on your input, I tested the cylinders firing and found that it appeared that I had 2 cylinders not firing based on the cylinder drop test, boat would not get over 2,000 rpms I have replaced the power pack (pricey $215 after market) and have started the engine and it seems to be running smoothly Only problem I have is I can't get it off the boat lift anymore to test under full throttle, lake level have been lowered. In neutral it seems to crank up and it keeps running. Hoping a little rain in New Hampshire this week will raise the lake enough so i can test under way. Keeping fingers crossed. Thank you all for your input, if this does not solve the problem then others have indicated it might be the stator. Another pricey item. Thanks again. Randy