Reduced RPM under load

[oldgrumman]

I have a 1981 35hp Evinrude that runs great. In a static test on land and at idle in the water I can run it up to 4200 rpm. In gear on land I can get the same rpm. However, in the water in gear I can't get it above 2000 rpm. This problem just started and would like advice for correcting it.

 

[SpinnerBait_Nut]

Re: Reduced RPM under load

Welcome to iboats.
Wrong forum.
Belongs in the Johnson/Evinrude questions and repair forum.
I will move it there now.

 

[jtexas]

Re: Reduced RPM under load

welcome to iboats!

first, reving your engine on land any more than it needs to keep from dying puts you at risk for thermal runaway, in which it races uncontrollably and won't respond to throttle or keyswitch, with potentially disastrous consequences.

In the water, back-pressure on the exhaust puts a load on it even in neutral, that isn't there when you run it with a flusher. How it runs on land is no indication of how it will run in the water.

You're describing a classic symptom of clogged hi-speed jets which can be cured by a carb rebuild.

Might want to do a compression test & spark test to rule those out first.

 

[Silvertip]

Re: Reduced RPM under load

Or you have an engine that is running on one cylinder although you "think" it's running on both. An engine will rev freely on one cylinder as long as there is no load. Spark and compression checks are in order. Pull one plug wire at a time with the engine running. If the engine has a functioning cylinder, a noticable drop in RPM or even stalling should occur when the wire is removed. If you pull a wire and there is no change, you found the dead cylinder.

 

[oldgrumman]

Re: Reduced RPM under load

Thanks for getting back to me.
When I tested the engine on land, I had it hooked up to my flusher and then ran it for just brief seconds.
To perform your suggested tests, could I run the engine with the flusher or should it be in the water; i.e., tank or lake?
Thanks again!

 

[tashasdaddy]

Re: Reduced RPM under load

do a compression, spark check. you can pull the plug wire while running on muffs. keep reving it and you are going to get a face full of connecting rod. never over 1500 on muffs.