Mercury 90-HP FOURSTROKE Stalls at Idle - Moderated Discussion Areas

  ContinuousWave
  Whaler
  Moderated Discussion Areas
  ContinuousWave: Whaler Repairs/Mods
  Mercury 90-HP FOURSTROKE Stalls at Idle

search | FAQ | profile | register | author help

Author Topic:   Mercury 90-HP FOURSTROKE Stalls at Idle

Caribe posted 07-20-2011 02:33 PM ET (US)
I have a 2002 Dauntless 16 with a Mercury 90-HP FOURSTROKE. When I shift from Forward to Neutral, or when at idle, the Mercury 90-HP FOURSTOKE outboard engine dies. It makes it very hard to dock, especially when the wind is blowing. [Give] any advice.
george170 posted 07-20-2011 05:14 PM ET (US)
Did you check the spark plugs? When I bought my 170 Montauk it did the same thing. If you gave it throttle when going into gear it would be fine, otherwise it would stall out. Changed the plugs and everything ran great after that. Mine is a 90 2 stroke not a 4 stroke, but it wouldn't hurt to check the plugs.
Buckda posted 07-21-2011 03:14 AM ET (US)
Sounds like a carburetor adjustment is needed. Unless that motor is EFI.
jimh posted 07-21-2011 08:38 AM ET (US)
Your Mercury 90-HP FOURSTROKE outboard engine needs a tune-up. You may need to have the carburetors repaired. Problems with carburetors on this Mercury motor are very common.
A2J15Sport posted 07-21-2011 01:58 PM ET (US)
Call your Mercury. dealer. There was a [manufacturing defect] with a fuel supply tube (under cowl). It was a recall. The tube would delaminate, within.
In essence, it would, intermittantly, choke off fuel supply to the engine.
We had the same issue with a 'toon', with a 75 (same engine).
captbone posted 07-21-2011 11:54 PM ET (US)
This is not an EFI engine correct?
swist posted 07-24-2011 09:05 AM ET (US)
Same problem here, same engine.
While these carbs seem to be a common source of trouble, could someone be more specific as to the solution to the problem - rough idle/stalling at idle but performance perfectly satisfactory at all other speeds?
I am not a expert on these complex carbs but this does not sound like a general rebuild or disassembly/complete cleaning situation. I would think the most stress on the fuel delivery system is getting on plane or full throttle -and the engine runs fine in those situtations.
There isn't much you can simply adjust other than the idle speed (raise it?). The mixture screws are sealed.
pcrussell50 posted 07-24-2011 01:16 PM ET (US)
I'm afraid that since this motor became EFI not much later, that the body of knowledge out there, or the numbers of good mechanics who know the intricacies of these things has already peaked, and is in decline. Not that there were that many to begin with. I have one of these motors, too. I live with it nervously, with my fingers crossed, though I have not had any problems.
-Peter
jimh posted 07-24-2011 04:49 PM ET (US)
Peter makes a good point regarding expert knowledge among Mercury mechanics. Mercury sells so many different outboard motor products, including engines like this 90-HP four-cycle carburetor motor which was mainly manufactured by Yamaha, that it is a challenge--perhaps impossible--for a mechanic to be an expert on all the motors. There are old classic Mercury motors with carburetors, classic motors with simple fuel injection, repainted Yamaha and Tohatsu motors of all kinds, Orbital Combustion System motors ( or OptiMax as Mercury calls it), supercharged motors like the VERADO, VERADO-derivative motors without the supercharging (VERADITO) motors, and who knows what else.
Just keeping parts in stock for all those different motors, made all over the globe, must be a tremendous challenge for Mercury Marine, and for the dealers.
I think Peter's speculation may be acute: the local Mercury mechanic may not be an expert on the carburetors used in the 90-HP FOURSTROKE model that is actually mainly a Yamaha motor. He may not be versed on the complicated fuel enrichment system used. He may not be familiar with all the adjustments.
samwhaler posted 07-24-2011 07:44 PM ET (US)
Take it to a Yamaha mechanic. I had a terrible time with the same engine last year. The boat sat at a Mercury dealer for almost 3 months. The Yamaha mechanic fixed it in a couple of hours, added a fuel filter, and advised me to never use gas containing Ethanol. Have not had a single problem since.
Sam
swist posted 07-24-2011 10:09 PM ET (US)
I added a fuel filter two years ago.
If you tell me how to put non-E10 gas in, I would be thrilled. It just isn't around in the Northeast.
haskell posted 07-25-2011 08:50 PM ET (US)
Had the same problem last year. Caused by fuel line being damaged by ethanol and then clogging carburetors. I replaced the fuel line, cleaned carburetors, replaced fuel filter and only use non-ethanol gas; have had no additional problems.
Antonioimp posted 08-01-2011 09:32 PM ET (US)
The bottom carburator is not sealed turn the screw 1/8 of turn clock wise and see if the idlle speed increase.
swist posted 08-04-2011 03:39 PM ET (US)
I did increase the idle speed as directed, maybe by a 100 rpm (can't go up too much - that wonderful clunky Merc shifter has enough trouble going smoothly in gear at factory idle - 850).
But obviously this is a stopgap. It should be able to idle at the factory spec. Things do seem better however.
The crud in the fuel line theory makes sense - it would explain why the problem is intermittent as opposed to some permanent fault in a carb.
So someone explain to me how crud can cause a bad idle but the engine runs perfectly above 1700 rpm, WOT or planing out under full throttle with a max load are no problem. I would think these conditions would expose any blockage (or any other fuel delivery problem) more than idle.
tedious posted 08-04-2011 05:49 PM ET (US)
Your carbs have two different orifices, called "jets" which let the fuel flow into the airstream passing through. One jet, which tends to be smaller and thus more easily plugged, is used at idle, and the other at speed.
Tim

Hop to:

Contact Us | RETURN to ContinuousWave Top Page

Powered by: Ultimate Bulletin Board, Freeware Version 2000
Purchase our Licensed Version- which adds many more features!
© Infopop Corporation (formerly Madrona Park, Inc.), 1998 - 2000.

Author	Topic: Mercury 90-HP FOURSTROKE Stalls at Idle
Caribe	posted 07-20-2011 02:33 PM ET (US) I have a 2002 Dauntless 16 with a Mercury 90-HP FOURSTROKE. When I shift from Forward to Neutral, or when at idle, the Mercury 90-HP FOURSTOKE outboard engine dies. It makes it very hard to dock, especially when the wind is blowing. [Give] any advice.
george170	posted 07-20-2011 05:14 PM ET (US) Did you check the spark plugs? When I bought my 170 Montauk it did the same thing. If you gave it throttle when going into gear it would be fine, otherwise it would stall out. Changed the plugs and everything ran great after that. Mine is a 90 2 stroke not a 4 stroke, but it wouldn't hurt to check the plugs.
Buckda	posted 07-21-2011 03:14 AM ET (US) Sounds like a carburetor adjustment is needed. Unless that motor is EFI.
jimh	posted 07-21-2011 08:38 AM ET (US) Your Mercury 90-HP FOURSTROKE outboard engine needs a tune-up. You may need to have the carburetors repaired. Problems with carburetors on this Mercury motor are very common.
A2J15Sport	posted 07-21-2011 01:58 PM ET (US) Call your Mercury. dealer. There was a [manufacturing defect] with a fuel supply tube (under cowl). It was a recall. The tube would delaminate, within. In essence, it would, intermittantly, choke off fuel supply to the engine. We had the same issue with a 'toon', with a 75 (same engine).
captbone	posted 07-21-2011 11:54 PM ET (US) This is not an EFI engine correct?
swist	posted 07-24-2011 09:05 AM ET (US) Same problem here, same engine. While these carbs seem to be a common source of trouble, could someone be more specific as to the solution to the problem - rough idle/stalling at idle but performance perfectly satisfactory at all other speeds? I am not a expert on these complex carbs but this does not sound like a general rebuild or disassembly/complete cleaning situation. I would think the most stress on the fuel delivery system is getting on plane or full throttle -and the engine runs fine in those situtations. There isn't much you can simply adjust other than the idle speed (raise it?). The mixture screws are sealed.
pcrussell50	posted 07-24-2011 01:16 PM ET (US) I'm afraid that since this motor became EFI not much later, that the body of knowledge out there, or the numbers of good mechanics who know the intricacies of these things has already peaked, and is in decline. Not that there were that many to begin with. I have one of these motors, too. I live with it nervously, with my fingers crossed, though I have not had any problems. -Peter
jimh	posted 07-24-2011 04:49 PM ET (US) Peter makes a good point regarding expert knowledge among Mercury mechanics. Mercury sells so many different outboard motor products, including engines like this 90-HP four-cycle carburetor motor which was mainly manufactured by Yamaha, that it is a challenge--perhaps impossible--for a mechanic to be an expert on all the motors. There are old classic Mercury motors with carburetors, classic motors with simple fuel injection, repainted Yamaha and Tohatsu motors of all kinds, Orbital Combustion System motors ( or OptiMax as Mercury calls it), supercharged motors like the VERADO, VERADO-derivative motors without the supercharging (VERADITO) motors, and who knows what else. Just keeping parts in stock for all those different motors, made all over the globe, must be a tremendous challenge for Mercury Marine, and for the dealers. I think Peter's speculation may be acute: the local Mercury mechanic may not be an expert on the carburetors used in the 90-HP FOURSTROKE model that is actually mainly a Yamaha motor. He may not be versed on the complicated fuel enrichment system used. He may not be familiar with all the adjustments.
samwhaler	posted 07-24-2011 07:44 PM ET (US) Take it to a Yamaha mechanic. I had a terrible time with the same engine last year. The boat sat at a Mercury dealer for almost 3 months. The Yamaha mechanic fixed it in a couple of hours, added a fuel filter, and advised me to never use gas containing Ethanol. Have not had a single problem since. Sam
swist	posted 07-24-2011 10:09 PM ET (US) I added a fuel filter two years ago. If you tell me how to put non-E10 gas in, I would be thrilled. It just isn't around in the Northeast.
haskell	posted 07-25-2011 08:50 PM ET (US) Had the same problem last year. Caused by fuel line being damaged by ethanol and then clogging carburetors. I replaced the fuel line, cleaned carburetors, replaced fuel filter and only use non-ethanol gas; have had no additional problems.
Antonioimp	posted 08-01-2011 09:32 PM ET (US) The bottom carburator is not sealed turn the screw 1/8 of turn clock wise and see if the idlle speed increase.
swist	posted 08-04-2011 03:39 PM ET (US) I did increase the idle speed as directed, maybe by a 100 rpm (can't go up too much - that wonderful clunky Merc shifter has enough trouble going smoothly in gear at factory idle - 850). But obviously this is a stopgap. It should be able to idle at the factory spec. Things do seem better however. The crud in the fuel line theory makes sense - it would explain why the problem is intermittent as opposed to some permanent fault in a carb. So someone explain to me how crud can cause a bad idle but the engine runs perfectly above 1700 rpm, WOT or planing out under full throttle with a max load are no problem. I would think these conditions would expose any blockage (or any other fuel delivery problem) more than idle.
tedious	posted 08-04-2011 05:49 PM ET (US) Your carbs have two different orifices, called "jets" which let the fuel flow into the airstream passing through. One jet, which tends to be smaller and thus more easily plugged, is used at idle, and the other at speed. Tim