evinrude 4 HP low power

[dave1000]

1985 Evinrude 4HP model 4BRHCOB
ran fine last year, but this year seems to have much less power under load - won't build RPM beyond about 1/3 to 1/2 throttle.

have fresh gas in tank.
other than speed/power problem, seems to run OK. starts on 1st pull. idles smoothly and when in neutral can run RPM through normal range - no problem. under load, sounds smooth, water flow seems good and feels cool when placing hand on top of cover, but can't get RPM to increase after about 1/3 to 1/2 throttle.

any ideas?

 

[tashasdaddy]

Re: evinrude 4 HP low power

contaminated carb, clean and rebuild.

 

[Rick.]

Re: evinrude 4 HP low power

I would also say you should check to make certain your getting good spark to both cylinders. They do run fine on one but won't have the normal amount of power you expect. Let us know what you find. Best of luck. Rick.

 

[film495]

Re: evinrude 4 HP low power

Run for a while and check to see if one plug gets hot and the other is cool; careful not to get burned fingers. If one is hot and the other not, you know you are not firing on one cylinder. If this is the case pull the spark plugs out for 1/2 hour and leave the cylinders open, but put the cowl cover on so a bird doesn't fly in there or anything. If it is flooded this will let the extra gas evaporate, when you put the plugs back swap them, and if the problem moves from one cylinder to the other, you got the one bad plug in a million, but I would guess you just have flooded out one cylinder.

 

[dave1000]

Re: evinrude 4 HP low power

good ideas!
will report back once I've had a chance to clean the carb, check the spark and check for firing on both cylinders.
thanks for your help,
Dave

 

[dave1000]

Re: evinrude 4 HP low power


great advice!
started by pulling the plugs to check spark for each. plug from upper cylinder had strong spark, plug from lower was totally fouled. cleaned them both and regapped at 30. standing knee deep in the creek, it started on the first pull and had enough power to try to push the motor stand out of my hands.

as Rick said, even on only one cylinder it seemed to run smoothly, just didn't have any power.

thanks guys, I appreciate the help.
Dave

 

[Rick.]

Re: evinrude 4 HP low power

Hey that's great. They are fantastic little engines. Do yourself a favor and get a new set of plugs for it. Rick.