90hp Weird idle

Hello!!

Mercury 90hp
1988
s/n 0b312461

Recently had our boat on holiday for a couple of weeks and part way through this time a problem started with the motor. Wouldn't idle very well...

Symptoms: Motor stalls at random times (2 - 3 times per min) when at idle (in or out of gear), and needs plenty of throttle to restart again.

When it is running at idle every few seconds or so it does a funny thing thats hard to describe... kind of sounds like on cylinder gets an extra bit of "oomph" and revs jump every so slightly (maybe 50 - 100 rpm) for a second or two then settle back at 900rpm. Then it'll do it again after a few seconds (maybe 7 - 10 secs between), and thats if it doesn't stall!

At revs, this motor runs perfectly.
Idles at 900rpm in water
Has fresh fuel.
Used a can of Power Tune in it less that 12 months ago
Motor was fogged for winter
Battery is less than 12 months old
Motor is producing over 13v for charge

So I'm not sure what to do about this. I haven't touched anything so far.....

Any advice??

Donald.

Re: 90hp Weird idle

Anyone? Do you think the carbs could do with a rebuild?? As far as I know, this has not been done since the motor was new.... (23 years!)

Re: 90hp Weird idle

Well, it is a tune problem, probably lean at idle. Could be fuel pump, or dirt in the carbs.

Re: 90hp Weird idle

OK, so I should take it to the shop and ask them to clean/rebuild the carbs and put a fuel pump "kit" in her?

Re: 90hp Weird idle

Have booked her into the local Merc dealer who has a mechanic I trust. He is going to do a compression test for me as well. I should have asked him at the time, but if a cylinder comes back with low compression, what is likely to be wrong, and what am I in for (repair wise and $ wise?) - I'm hoping she comes back with good compression on all 3 cyl, as we cant really afford any expensive repairs!

Thanks,

Donald.

Re: 90hp Weird idle

You are putting cart in front of the horse. Relax dude. Get the results first.

Re: 90hp Weird idle

Hello - I have a 1987 90 HP three-cylinder Mercury that just started idling poorly, and the symptoms sound very much like yours. Did you ever get yours fixed? If so, what was the problem?