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1999 60 HP idling and runs rough problems

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Bigdaddy65

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Ok so here goes. She's a 99 60 HP outboard. Definitely had bad gas so I drained the tank 18 gallons. Changed the old water/gas separator filter with a new one. Changed the gas filter under the cover blew out the gas lines and filled the tank which is a plastic Plano with high octane gas. Installed three new NGK spark plugs. The motor ran on the old gas but horribly. Spit and stuttered but ran !! Now with the new gas she won't hold a idle. And now has a noticeable and backfire. Smoke comes out of the cowling. The only way I can keep her running is in high idle. Or in a low idle when she is just about to die I push the key in to activate the choke and she purrs right a long for a bit them I need to hit the key again before she dies. I'm assuming something's gunked up in one of the three carbs or even all of them. But I think there's more what's up with the backfire. ?? Is the timing off. Oh and yea I drained all the old gas out of the three carbs by opening the three screws on bottom of the carbs. So all the bad gas is surely gone.
 
The carbs need to be removed and cleaned. Too much air and not enough gas in the "mix" to the cylinder will also cause a backfire or a "lean sneeze".
 
Ok Thanks so much for the reply. Is it recommended to rebuild the carbs at this time as well. Or just a good cleaning. I don't have access to a parts washer any recommendations ?
 
Clean and rebuild the carbs as Graham said. You don't need a parts washer. A gallon bucket of carb cleaner from an autoparts store will do. Soak the hard parts overnight as a minimum...blow out all passages w/compressed air. Lacquer thinner is another good cleaner for dissolving hardened fuel varnish...keep a lid on the it though.
 
Yes - and "rebuild" means different things to different people.

At minimum if I "tear down" a carb to clean it I usually replace any gaskets that I disturb (bowl gasket etc). If the float looks fine, I leave it alone (just check for proper adjustment). Pull out the float needle valve - if it's distorted replace it and the seat (if applicable) - if it's nice and pointy like a sharp pencil I leave it alone - etc

Gaskets and o-rings are cheap enough that I figure it's worth replacing them if disturbed, but leave "hard parts" alone unless they look worn...

It's mostly the "cooties and gunk" that you are after - make sure you soak and then blow out any "channels" in the carb body - it's those little things that cause the motor to run like crap if they are clogged up.

Carb cleaner can "eat" plastic parts - so metal only if you go that route. A good plastic safe solution (I use it extensively with OMC's Marelon (a type of plastic) carb bodies) is plain old automotive gas line anti-freeze. You can pick up a couple ounce bottle for a buck at the parts store.

It takes longer to work (soak for at least 24 hours) and then I blow out everything with compressed air (maybe 15'ish pounds from the compressor with a blow gun), but it won't eat plastic or seals (like some needle valve seats).
 
Ok so the carbs came off and I cleaned them overnight. During the disassembly process I was really hoping to see a lot of gunk but to my amazement it was pretty nominal. The soak continued for 24 hrs and I blew out all the carbs with my air compressor. So now ther are clean.
During reassembly procedure I replaced the gaskets one for each bowl and the ones for the cylinder heads. When I reinstalled the needle valves one for each carb for a total of three before removing them I screwed them all the way in and counted the number of turns for each needle valve. I wrote that number down for each carb and each needle valve. When I screwed them back in I screwed them all the way in and then backed them out the number of turns I wrote down. Each screw head was in the same position and facing the same way.
So with that all done I put the cards back on hooked everything up primed the gas bulb and fired her off !!
She fired right up!! First turn of the key !! No more Coughing or sneezing as she was doing before.

So here's the question ------- now when she runs and I let her run on the hose for a good hour at a idle I can hear the revs go up and down a little. So what's that ?? It's not much I don't have a tach on her but I can hear the pitch change. She hasn't hit the water yet and I haven't even hit W.O.T yet. My assumption is to just rum her hard for a while on the water get her good and hot. Them see how she works. But trying to avoid Sea Tow. !!
 
Big Daddy..went thru the same deal on a 60 merc..the difference is mine is a 2010 efi 4 cycle....no carbs...i still have a slight change in rpm at about 1100 or 1200 rpm when idling out of my camp area...a slight surge...if i tap it up 100 rpm its gone..its getting better with time and seems to be gone with one of my two tanks...i think if i run the yellow cleaner from merc in every tank it would be gone by now..i am not worried about it as the motor performs perfectly at all other rpms and idles fine.. i have not tried to fill the fuel system with sea foam and ler her sit overnight...i would do that if it was a 2 cycle carb engine just in case i was not aware of a lean condition at higher rpm..
 
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Big Daddy..went thru the same deal on a 60 merc..the difference is mine is a 2010 efi 4 cycle....no carbs...i still have a slight change in rpm at about 1100 or 1200 rpm when idling out of my camp area...a slight surge...if i tap it up 100 rpm its gone..its getting better with time and seems to be gone with one of my two tanks...i think if i run the yellow cleaner from merc in every tank it would be gone by now..i am not worried about it as the motor performs perfectly at all other rpms and idles fine.. i have not tried to fill the fuel system with sea foam and ler her sit overnight...i would do that if it was a 2 cycle carb engine just in case i was not aware of a lean condition at higher rpm..Carl..had a good summer on catfish on some fancy noodles i built...one 40 pounder last trip...
 
When I screwed them back in I screwed them all the way in and then backed them out the number of turns I wrote down.
Click to expand...
The carbs are cleaner than before. You need to adjust the idle mixture screws to find the perfect idle point ...sweet spot...the add 1/4 turn CCW to richen the idle. The oscillating RPM should stop. The adjustment is best done in the water in gear. Tie the boat to a dock or back it into the water to make the adjustment. You can also adjust the idle speed at that time.
 
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