Mercury 90hp low max rpm

[redhatsuxx]

hi

I have a mercury 1990 90hp 2 stroke the engine its my first outboard i believe the max rpm is 5500 mine will only reach 4200 it seems to idle fine
and ive had the compression check which is fine i was told the problem maybe electrical

if it is electrical what could be the problem?

otherwise what else could cause the problem?

for a start could some one give me info on the reasons my engine will not reach max rpm only.

many thanks
glenn

 

[Laddies]

Re: Mercury 90hp low max rpm

You are dropping a cyl. as you have already figured out, check it for spark if you have it, must be low compression or a dirty carb. You will have to check the engine out, don't just through parts at it.

 

[marty53]

Re: Mercury 90hp low max rpm

just a suggestion here- but you may be way overpropped. I'd need more details about your rig (what type of boat, normal loaded weight, current top speed at 4200 rpm).

I had a similar situation with my 1990 75HP (almost same motor). I could only get it to 4500 tweaking the trim with my 21P merc prop (i think that is factory setup). I changed it out with a 19P x 13 Amita i got on ebay for $50 and i am now spinning about 5100 RPMS at WOT. It made a huge difference overall to top end, and my hole shot is sweet now.

 

[redhatsuxx]

Re: Mercury 90hp low max rpm

ill have to check the prop type it was factory fitted and the engine has previously run correctly. the compression test im told were ok could there be an electrical problem.