1990 175 XP Raising and Lowering RPMs

My 1990 Evinrude 175 XP ( model E175STLESE )engine both raises its RPMs and also lowers them - seems to have a mind of its own. I will be at a fast idle ( +/- 1500 rpms ) and suddenly the engine will rev up to about 2000+ rpms and run that way for about a minute before settling back to my original speed. On other occassions, I will be running at about 3500 - 4000 rpms and the engine will drop down about 500 rpms or so for a short time and then raise back up to my original speed. Sometimes I have to manually lower the throttle when it is overreving and raise the throttle when underreving. Both problems are not constant - thank goodness - but both problems will occur at least one time each time I take the boat out. I need your feedback to see if this is something I may be able to repair myself or take it to the professional. Thanks all!!

Re: 1990 175 XP Raising and Lowering RPMs

Welcome baffled - That is a bit of a puzzler. I would look for your motor to be dropping one or more cylinders and picking them up again. Check the appearence of the plugs & see if they tell you anything.<br /><br />If you plan on doing your own work a manual is a must. Look here:<br /><br /> http://www.theoutboardwizard.bizhosting.com/parts_service_and_owners_manuals.html

Re: 1990 175 XP Raising and Lowering RPMs

Thanks SoLittle. I will pull the plugs, but since I am not overly mechanically inclined, what exactly should I look for? I replaced them about a month ago and also had regulator replaced after that when I discovered my cranking battery was not being charged. Had a shop replace the regulator after they diagnosed the problem. Ran fine for 1 trip out and then this latest problem developed. Also, my tach "over reads" the actual RPMs - reads about a 1000 RPM ( +/-) what it is really is turning... Maybe this is all caused by same thing?<br />( raising/lowering RPMs and tach problem ).

Re: 1990 175 XP Raising and Lowering RPMs

Hi Baffeled. Don't feel alone on the rpm problem. I have a 97 90 horse Evinrude SPL and it does the same increasing and decreasing rpm thing. But, mine ONLY does it with the muffs on.As far as the tach, I assume it is correct. I don't have a way to check it against a calibrated tach.

Re: 1990 175 XP Raising and Lowering RPMs

I hope that one of the more experienced guys will jump in on this.<br /><br />To me your symptoms describe an intermittant interruption of the juice that fires one or more of the plugs resulting in the rpm changes. This could be caused by a weak connection (loose/crud) or component failure. Often these are heat related - the component gets hot/warm - it fails or has reduced performance - when it cools it works again. One way to observe this is by looking at the plugs soon after the problem shows up. What you are looking for is one or more plugs looking different than the others. This tells you that the firing of that cylinder(s) is different.<br /><br />Tha may seem quite logical but the same type symptoms could occur if you have an intermittant flow of good fuel due to water, crud in a carb etc.<br /><br />Ain't this fun!!??

Re: 1990 175 XP Raising and Lowering RPMs

Thanks Jcrain and SoLittle. I was afraid that the problems with the ol' Rude wouldn't be easy to diagnose! Like you said, maybe someone with a similar problem has found the solution and will help out!<br /><br />baffled - again..

Re: 1990 175 XP Raising and Lowering RPMs

Since mine runs excellent in the water, I haven't really worried about it. The fluxuating rpm thingy has been there since new. At first I was concerned but, like I said, in the water ...no problems ( so far, knock on wood)