Originally Posted by Xk59D
4000rpm under load? i.e in the water in use?
you shouldn't be revving the nuts out it on land hence the question.
first thing i would do is check compression, 4600rpm is too low for most outboards, should be circa 5800-6k for most motors.
if you have only ever got 4600rpm then you may have ruined the engine by running it while over propped for long periods.
need more info really to point you in a direction, but i would start with a compression check, then spark, fuel etc.
Hi, thanks for taking the time to look. I may have been a bit deliberately vague too see if I was missing anything really simple!
The engine is an aged Honda BF90 (carbs) the manual says it should max out at 5000rpm (presume off load) When I bought it I think it was somewhat over propped and a change down moved me from 3800 max to 4600 which I reckoned was about right.
Ran like that for a couple of years but as I said, spring this year, serviced the raw water pump and dropped a load of revs.
Not bogging down just not making revs......
So have done compression test and serviced carbs, running smoother now but still lacking RPM. (when say done, I do mean have had done. I am not a spanner spinner)
Make any more sense with more info? I am at a a loss!