Merc 50 Help...One cylinder down!

[jbman45]

Well I'm obviously not a great mechanic or I wouldn't admit to being stumped! But I've put lots of sweat and dollars into this 1985 50 hp merc with not too many hours to get it up to speed. Have found many issues that are now fixed but have one that just came up and I'm stumped.

First...engine has new stator, plugs, water pump, fuel pump, new carb rebuilds...and ran great for about an hour; then started missing. I've determined #2 cylinder is not firing but it gets fuel This engine is a 3 cyl with 2 carbs! So cyl. 1 and 3 get fuel and run. I get spark on all 3 cyls; though maybe 2 isn't as strong as others; but it nails you if you get close! With a test light spark looks pretty close on all 3.

It could be fuel? since the plugs have been swapped number of times and always work; but 2 looks dry.

SO...how can 2 be dry, if there are only two carbs supplying 3 cyls. Is there a reed valve issue maybe? Compression 120 in all 3 cyls. pleanty of fuel in carbs I think.

Any suggestions??????

 

[zorak]

Re: Merc 50 Help...One cylinder down!

You say it nails you if you get close? If you can just touch a plug wire and get zapped then you might have an issue with a plug wire.Start it up in the dark and look for any corona discharge as electricity will take the path of least resistance ( bare metal or your hand).

 

[jbman45]

Re: Merc 50 Help...One cylinder down!

Thanks Zorak, good idea and since it's finally a bit warmer down here in FL night won't be so bad! Kinda think it might be fuel? but doesn't make sense unless there's just not enough to get to the middle cylinder, coils go down as well so I might swap those too.

thanks..

 

[jbman45]

Re: Merc 50 Help...One cylinder down!

Well I'm ready for any ideas! Got lots of spark, both at plug and with plug out....but no fuel! Absolutely no gas is getting to cyl 2 and I can 't figure it out since there's 3 cyls and 2 carbs; and cyl 1 and 3 are running with fuel ok. I don't know if a bad reed valve would do this?? Anyone know.

 

[Faztbullet]

Re: Merc 50 Help...One cylinder down!

A bad reed will cause cylinder not to pull fuel and but it also could be a bad plug. Try swapping plugs first to see if problem follows it..

 

[jbman45]

Re: Merc 50 Help...One cylinder down!

Thanks Faztbullet...I was afraid that comment might come back. I've swapped plugs, put in different plugs and checked spark thoroughly; even ran the engine without cyl 2 plug, pleanty of spart at the plug hanging grounded, dry air coming out of the cylinker.

So your comment a bad reed sounds on the money but I've never got that far into the engine so a new game for me I guess. suppose they are right behind the carbs so I'll try and looksee....

 

[dckchsr]

Re: Merc 50 Help...One cylinder down!

cracked/broken reeds will definately stop fuel from coming into the cylinder. if they break off and lodge sideways it stops all fuel/air from coming in. you should be able to see if they are broken if you take your carbs off and look into the intake with a flashlight.

 

[Faztbullet]

Re: Merc 50 Help...One cylinder down!

Easy test.. my compression guage unsnaps and lets me attach air hose to it.. apply about 20-30psi of air to cylinder and rotate flywheel till exhaust port closes...if reed/s is broken you will hear air coming from the carbs.

 

[Lone Duck]

Re: Merc 50 Help...One cylinder down!

get a spray bottle filled with proper fuel and squirt in the other carb throat while cranking If #2 fires and keeps firing as long as you squirt fuel, I would look into that carb again before getting into reeds & stuff.

 

[divinginn]

Re: Merc 50 Help...One cylinder down!

I had a plugged up elbow fitting that screwed into the carb. that drove me crazy,it leaked through just enough gas to fire intermittently. Easy fix,took it off and sprayed and poked it clean.