RPM's fluctuating

[shane1]

I have a 91 21' party barge with a 40 horse Johnson. I've only had it about a month. Last weekend while out on the lake under WOT the RPM's would fluctuate. Not to bad but enough to where I noticed it. <br />Anybody have any experience with this problem. I haven't had time to look into yet but I'm hoping it's a bad plug or something simple like that.<br /><br />PS Does anyone know what the WOT RPM should be on the 91 40 horse Johnson?<br /><br />Thanks<br />Shane

 

[DJ]

Re: RPM's fluctuating

shane,<br /><br />Operating range is 4500 to 5500. Are you pumping water OK?<br /><br />Could be fuel related, is there a filter on the engine in line with the fuel hose?

 

[shane1]

Re: RPM's fluctuating

Yeah water water is coming out fine.<br />There is no inline filter not sure about on the motor. I would think it would have one somewhere?<br />I'm only getting about 3800RPM's out of it.....if the Tach is accurate? <br />What type of plugs does this Johnson take. I'll be putting an inline filter in tommorrow.<br />The first time I took it out it was turning a solid 4000RPM.<br /><br />Thanks<br />Shane

 

[Bob_VT]

Re: RPM's fluctuating

That's allot of barge for that motor! Is it trimmed properly (not cavitating)? Your plug type should be listed on the wires if not most parts stores will be able to look up what Champion plug is recommended. Djohns is right could be fuel related. Is the prop in good shape? <br /><br />Bob

 

[shane1]

Re: RPM's fluctuating

Well I changed the plugs and it stopped the fluctuation! I still have yet to change the fuel filter. I took it out Sat. and it performed pretty well turning right at 4000RPM.<br />The prop is in fair shape. Should probably get a new one.<br />The tilt on the motor is set all the way down...it's not electric. Next outing I'll mess with the tilt a bit and see if that helps.<br /><br />Thanks <br />Shane

 

[almost retired again]

Re: RPM's fluctuating

Hi Shane,<br />If your tach is right you should drop down in pitch until you get it running in the proper RPM range. With what this motor is pushing you are probly lugging the engine,which is hard on the engine. When you get it up to the proper RPM you might even gain some speed.