Logo

Mercury 90hp 4 stroke 2004 with carbs

burkstar

Contributing Member
Hi all, hope you can help
All the time I have had this engine it's fine at tick over but as you rev up just as it get up on the plain it coughs and splutters a bit but once it up it fine. Revs round to 5.5k no problem.
End of last year all of a sudden the tick over got bad and it died, started Miss firing and wouldn't run.
since then I have.
replaced spark plugs, had the carbs sonic cleaned twice. Still running bad so then replaced all the fuel lines and filters still running bad but I noticed that if I pumped the bulb it run ok for a while but there was obviously an air leak somewhere so replaced the diaphragm in the fuel pumps and now it runs well on tick over but as I rev up it coughs and splutters and won't allow full revs. I would guess only revs to about 4K maximum after a fight.
All this is on the trailer, not under load. Has fresh fuel, new oil.

Not sure what to try next but run out of ideas, please help !!!!

regards.
 
Hi all, hope you can help
All the time I have had this engine it's fine at tick over but as you rev up just as it get up on the plain it coughs and splutters a bit but once it up it fine. Revs round to 5.5k no problem.
End of last year all of a sudden the tick over got bad and it died, started Miss firing and wouldn't run.
since then I have.
replaced spark plugs, had the carbs sonic cleaned twice. Still running bad so then replaced all the fuel lines and filters still running bad but I noticed that if I pumped the bulb it run ok for a while but there was obviously an air leak somewhere so replaced the diaphragm in the fuel pumps and now it runs well on tick over but as I rev up it coughs and splutters and won't allow full revs. I would guess only revs to about 4K maximum after a fight.
All this is on the trailer, not under load. Has fresh fuel, new oil.

Not sure what to try next but run out of ideas, please help !!!!

regards.
I have also compression tested the engine and that seems fine.
 
Just had a thought, its acts like the choke is stuck on, with my small outboard when the choke is on and when it has warmed up a little as you rev it it chokes. As soon as you turn the choke off it will rev freely.
is there a way I can check this ?
 
Check the vent hoses on the carbs. Sometimes small insects build nests inside the main vent hose that goes down to the cowling. This will starve your carbs.
 
I seem to have it running fine now, adjusted the mixture screw on the bottom carb.

just wondered has my outboard got a rev limiter fitted ?
 
Back
Top