Backfire from exhaust

[Wood2002]

I’ve got a 50 hp Yamaha 2 stroke that has a popping/ miss fire sound coming from the exhaust. I’ve cleaned all three carbs payed to have them cleaned again, changed water separator, plugs, new fuel line, bulb and even sea foamed the outboard and it’s still runs like crap. Before I did all that it wouldn’t hardly idle and would go dead when put in gear. I’m at my wits end trying to figure this outboard out.

 

[racerone]

First check flywheel key.----Check to make sure wires are going to correct coil and cylinder.

 

[99yam40]

did you follow the link and sync procedure when putting the carbs back on?
It includes setting and checking the timing to be sure it is in spec and advancing as it should with a timing light.
check you fuel pump to make sure it is not dumping fuel into the #3 crankcase.
backfiring in the exhaust means there is unburned fuel getting into the muffler/tuner and igniting there

 

[racerone]

Likely the timing is off , wires wrong or sheared flywheel key

 

[Wood2002]

Sorry I’m new to this how exactly do I check flywheel key and I’ve checked all three coil wires and there right. I took the boat to a mechanic who took me for $500 dollars to change the water separator and clean my carbs , he said he adjusted the carbs too but before I took the boat it wasn’t backfiring. I took the boat because I could crank the boat up cold and it would run great down the river and get on plane no problem but after I would shut it down to fish in a spot and tried to start it back up it would Sputter and go dead when I put it in gear. I filled up a 3 1/2 gallon gas tank with sea foam and ran it through it with muffs in the driveway with no change.

 

[Wood2002]

Ok I’ll check the flywheel and timing too and check the thread.

 

[Wood2002]

Ok I’ll check the flywheel and timing too and check the thread.

Flywheel is good. I’m going to get a timing light and check that. Outboard cold it runs pretty good but when I run it awhile and warm it up then turn it off and let it sit it wants to die and kills our if I put it in gear until it I play with the throttle.

 

[LundAngler1650]

Make sure that fuel lines are not running close to anything that gets hot, if so, replace with new hose and wrap in reflective tape before installing. If its a hot only issue, could be too running too rich, but could also be hot fuel going to the carbs. Also did you replace the intake gaskets when reinstalling the carbs? Carbs synched properly? A shop will be able to synch them for you if not sure how, and don't have access to a carb balancer.

 

[Wood2002]

Ok I’ll check the hoses and wrap them. The carbs are all connected on a rod that has plastic fittings so not sure how I could adjust those. Quick back story ran the boat great for several years with no problems decided to change water separator and grease prop shaft shortly after I did those two things the problems started. At first I could crank boat stop fish and it would kinda bog down when I would start it back up and try to take off and get on plane. Now it goes dead multiple times if I stop and try to restart and put in gear but if I start outboard let it sit a few minutes and play with throttle it’s like all of a sudden it will pick up and throttle up and take off.

 

[Wood2002]

Ok it’s also making a noise at idle every couple seconds that sounds like a bottle rocket kind of a chirp. Can’t tell if it’s coming from carbs.

 

[racerone]

What oil are you using ?----Oil injection working ?-----Post the compression numbers.---Then again the low speed mixture screws might need to be adjusted to richen the mixture a bit.

 

[Wood2002]

I’m using quick silver oil and my compression is good on #1 and #3. #2 is low around 65. How much should I enrich ?

 

[99yam40]

motor is toast if #2 is only 65.
need to find out why.

 

[Wood2002]

Yea the thing about it is cold start runs great but once it sets a bit then it acts up. Cold I can get up on plane a get down the lake.

 

[LundAngler1650]

65 psi compression on #2 is a huge problem.
Rings?
Scored cylinder?

Does this motor use a reeds? If so have you replaced them?

Does it have a power valve system?
Is it working properly if it does?
They get gummed up and stuck.
Is spark still strong when hot?
Engines have good spark cold, and bad, or none when hot.


But I would begin with looking to fix that low compression Issue.

 

[racerone]

Pull cylinder head and inspect.----65 PSI indicates a problem.----Not going to get any better by itself.

 

[Wood2002]

The low 65 was after I had #2 carb float got stuck and flooded that cylinder. I sprayed a little oil in that cylinder and went up 110. Has good spark on all three plugs. Seems like for whatever reason when I put my boat first in it will crank up and get up on plane but after I get to a spot and stop for awhile then try to crank up it wants to kill out as soon as I try to throttle up. If I wait a bit and let it idle then move the throttle it will out of nowhere pep up and throttle up and get on plane and does great till I stop and turn the boat off then if I crank up again starts over.

 

[99yam40]

so why not post up what all 3 cylinder compression readings are now.
there is a good possibility, that washed out cylinder was harmed from the extra fuel if this was not a premix.
you are throwing bits of info out there and then come back and say that was not really true.
not much can be determined from that

 

[racerone]

Time to take it to a shop to get it fixed I think.

 

[Wood2002]

Sorry for lack of info I’m new to this working on outboards. I’ve taken it to a mechanic (which there are not here) and he said he fixed it by adjusting and cleaning the carbs and putting a water separator on it. I took the boat out still was killing out after it got warmed up. Took it back and he said I should just go buy another outboard and to just run it. I took it back home and ran it with muffs to see if it was any better and that’s when I noticed a miss or sneeze sound which is a new thing. Thanks for any help