115 HP Evinrude Abnormal RPM's

[czroger]

I have a 1977 115 Horse Evinrude that has been recently be starting to act up on acceleration above 3200rpms. Anything below that it runs fine. When the throttle is at 3200rpms and up to max there is a fluxutation in rpm every few seconds. Speed up, speed down, speed up, speed down. Like its not getting enough of something. I can tell its not reaching top RPM. It has new plugs, clean flowing fuel, starts up right away, performs great under 3500rpms. The only thing I found out of normal was the top right plug had minor wet fouling. The rest of the plugs were the normal tan light gray color. Any help would be greatly appreciated.

 

[OBJ]

Re: 115 HP Evinrude Abnormal RPM's

Hi ya' CZ...welcome to iboats.<br /><br />Sounds like what it ain't gettin' enough of is fuel. That's just off the top of my head.<br /><br />But...Don't know the last time you did a tune up, so if it were me, I'd first do a compression test and make sure the cylinders is OK. Compression readings should be with in 10 to 15%.<br /><br />Make sure the individual sparks will jump AT LEAST a 7/16" gap with a hot lighting like spark.<br />And make sure all the sparks are there.<br /><br />Check your fuel system for leaks. Look at where the fuel lines connect to nipples and such. If they are cracked at the ends or the fuel line has lost it's flex, replace it. And do make sure the fuel line to the engine is good and the tank is venting.<br /><br />Is the cooling system OK? Ain't getting hot?<br /><br />When was the last time you over hauled the carbs or do you know if they ever have been? Look at the float bowl gaskets. If they are black, chances are the carbs are way over do for over haul.<br /><br />This should get ya' starte and I'm sure some of the other guys will jump in and add comments.<br /><br />Keep us posted. Thanks.<br /><br />PS...if ya' don't have a service manual, get one. Will make life a lot easier for ya'.

 

[Melvin Hatcher]

Re: 115 HP Evinrude Abnormal RPM's

What does the color of the float bowl indicate and what is the needed frequency rate for cleaning the carbs? <br />My gaskets are black, the ones in the recently purchased kits are brown...I plan to over haul this winter in my spare time.

 

[OBJ]

Re: 115 HP Evinrude Abnormal RPM's

Hi Dofer....Depending on the age of the engine, the floats will either be made of cork coated with a type of varnish or the newer poly material that won't get harmed by the new fuels we use today. If you have a cork float, time to rebuild.<br /><br />The kits from Bomby (was OMC) use Viton gasket material that holds up better to the new fuels than the old black stuff that was once used. The new fuels will dry out the old material and cause it to become hard and brittle. Same with fuel lines. The Viton material is more resistant to the fuels used today and last longer.<br /><br />Carb overhaul is really a factor of how much you use the engine. An engine that is used hard over a season could go two to three years. But personnally I wouldn't go over two....just me. I like to know everything is Kosher in there. On the other hand, an engine that is used just on weekends once in a while can go several years with proper PM.