NO HIGH SPEED RPMS IN FORWARD

[LA.RICH]

I have a 1992 40 hp Johnson its on a pontoon the problem is only 1800 rpm's in forward gear when boat is tied to dock, about 2200 rpms wide open throttle moving. The motor operates fine on the trailer with flush attachment. This motor works fine in reverse. What i have eliminated so far is linkage,spark,fuel,plugs, and rectifier. Someone told me the prop hub might be spun. Any help or ideas will be helpful. thanks RICH

 

[F_R]

You can bet the farm it is running on one cylinder. Now, that can be caused by spark, one clogged carburetor, or compression. You have to do some troubleshooting.

It is NOT a spun prop hub or rectifier. You will just waste money replacing stuff on a guess. #1 first thing you should be doing is check the compression, and while you are doing that, check for spark on both cylinders. If both check out ok, check for gas in both carburetors (remove drain plugs). Check for gum or varnish on the ends of those drain plugs which would indicate clogged high speed jets.

Another possibility is stuck timer plate advance. Or throttle not opening for some unknown reason..