evinrude 25 rev problem??

[ribdrummer]

Hi, i have an 80's era evinrude 25 hp outboard that i got with a rib. Engine starts fine on the first/second pull and engages the forward gear well but will not get up to high revs and just pushes the rib along at about 10 mph. Taking the top cover off and pushing on the carb arm manually produces high revs in neutral so the engine is capable of high revving just not from the twist throttle. Looking at the movement from the twist throttle it seems to moves the carb arm all the way to still not enough revs? seems like a mechanical arm/stop problem but no amount of tinkering has produced results.. any suggestions?

thanks
Brian

 

[Cofe]

Re: evinrude 25 rev problem??

Welcome to IBoats ribdrummer!

With the motor off, shift into forward gear. Twist the throttle grip and observe the movement of the cable, linkage, spark advance plate and carb butterfly position. The butterfly should be in the horizontal position at full wot.
Another thing to look at is the neutral detent rod. When the motor is in neutral, the plastic rod stops the spark advance plate from turning, thus limiting the rpm's in neutral. When the motor is shifted to forward, the detent rod should not engage the spark advance plate.

Also, do not rev an outboard in neutral by bypassing the linkage connections. The motor can over rev and runaway.....possible RUD
Rapid Undetermined Destruction.

 

[ribdrummer]

Re: evinrude 25 rev problem??

Welcome to IBoats ribdrummer!

With the motor off, shift into forward gear. Twist the throttle grip and observe the movement of the cable, linkage, spark advance plate and carb butterfly position. The butterfly should be in the horizontal position at full wot.
Another thing to look at is the neutral detent rod. When the motor is in neutral, the plastic rod stops the spark advance plate from turning, thus limiting the rpm's in neutral. When the motor is shifted to forward, the detent rod should not engage the spark advance plate.

Also, do not rev an outboard in neutral by bypassing the linkage connections. The motor can over rev and runaway.....possible RUD
Rapid Undetermined Destruction.

Hello Cofe and thanks for the quick reply.

I take note of not bypassing the throttle linkage and will not do it again.
It was the only way to get the engine revs up and compare with the revs given by the throttle grip. i take your warning though.

I looked at the engine and followed your advice and the carb butterfly is horizontal and the detent rod works as described.

i took the plugs out and one is tan coloured and the other shiny and looks as though it has never fired. Could it be I am only firing on one cylinder, either electronically or physically?

regards
ribdrummer

 

[outlaw241]

Re: evinrude 25 rev problem??

yes it could be running on one cylinder,i would do a compression test and a spark test

 

[Cofe]

Re: evinrude 25 rev problem??

Yes you need to check that cylinder for a good spark. It needs to be a strong blue spark. Compare it to the other cylinder spark.

Could be that plug, plug wire, or coil.

Let us know what you find.

 

[ribdrummer]

Re: evinrude 25 rev problem??

thanks guys, I have a friend who is more engine savvy than me so will call him over tomorrow to try your spark suggestions and compression.

thanks
ribdrummer

 

[ribdrummer]

Re: evinrude 25 rev problem??

hi again,
guys..an update.

My engine savvy mate has had a look and reports the following: Both cylinders firing,spark plugs sparking and the right colour and engine sounding as it should. water cooling working. Engine a bit smoky on start but cleared as it warmed up. He thinks although the gear select detent does slides down when in forward it is capable of just fouling the throttle, so the gear lever need holding forward as it selected to ensure it clears. Next step is to put in in the water and test his theory.

any other suggestions or advice gratefully received.. but thanks for your help so far!

cheers
ribdrummer

 

[F_R]

Re: evinrude 25 rev problem??

Nuts and phooey. You said yourself the plugs were one tan colored and one shiny like it has never fired. How much more clue do you need? It obviously was running on one cylinder. If it isn't a spark problem, it is a compression problem, or a water getting in the cylinder problem.

Either that, or Mr Savvy fixed it.

 

[ribdrummer]

Re: evinrude 25 rev problem??

Nuts and phooey. You said yourself the plugs were one tan colored and one shiny like it has never fired. How much more clue do you need? It obviously was running on one cylinder. If it isn't a spark problem, it is a compression problem, or a water getting in the cylinder problem.

Either that, or Mr Savvy fixed it.

Well that is an interesting way of putting it but i can only tell you what he said. The two plugs are different colours but he assures me both cylinders are firing and it sounds as it should. Will report back when it see water again if the problem if the physical gear mechanism..