Evinrude 140 won't go over 4000 rpm, planes slowly

[clint]

I tested my 1979 140 Evinrude today and it slowly planned out to 4000 rpm's under load. I had similar problem 2 weeks ago but rpm's only went up to 2500 and that was it. Now when put at full throttle it eventually goes up to 4000 rpm's and thats it. Top rpms was always 5500 rpm's max. 2 weeks ago I checked the spark and plugs and in the#4 cylinder had a clean plug. I changed wire and coil today and tested engine in test tank and it ran like a champ. Checked plugs and all plugs were firing and were brown. I then went to the bay to see if there would be better performance. After test run when I got home and checked spark again and sparkplugs to find #4 clean like it was brand new again?:| Could my head gasket be bringing water into that cylinder or is it a bigger problem? Please help,,,

 

[kenmyfam]

Re: Evinrude 140 won't go over 4000 rpm, planes slowly

Clean plug usually means water getting in from somewhere. Have you done a compression check ??

 

[AlanR]

Re: Evinrude 140 won't go over 4000 rpm, planes slowly

Do a compression check.. If it shows low scores pull ur heads cause you prob got a blowen head gasket.

 

[Walker]

Re: Evinrude 140 won't go over 4000 rpm, planes slowly

If compression checks okay then I suspect dirty carb/carbs

 

[AlanR]

Re: Evinrude 140 won't go over 4000 rpm, planes slowly

I also agree with you commander

 

[clint]

Evinrude 140 won't go over 4000 rpm, planes slowly

I will do a compression check tomorrow and see if cylinders are ok. Why would the spark plug be so clean after running engine? At idle it was a normal brown color? After run in water it was crystal clean? Engine was rebuilt with new power head in 1998.