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1982 Mercury 25hp WONT IDLE FOR ANYTHING.

U

USSMUDHEN

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Hello Fellow Outboard Church Members.

Long time lurker, but I finally needed to ask some questions. I have a new to me 1982 25hp Mercury on my 16 foot Jon boat. This Motor came to me not running but with 115 psi on both cylinders and being told it needed a carb cleaning.... LOL oooh boy.

I have had the carb apart 4 times, I have rodded, soaked, and used compressed air to blow out all the passages. I know that all the passages are cleaned and I even bought a Mercury shop manual to be thorough.

But here is my problem.

Motor will fire up first or second pull of the cord and will idle for about 5 seconds with the choke on. then there will be a cough and the motor will sputter and die....

If you fire up the motor on the choke and then play with the butterfly roller on the throttle cam the motor will run at approximately 1500 rpms for as long as you wish... it will Rev, it will return to 1500 rpms... but don't ask it to idle... as soon as it goes towards idling, there is a PUFF out of the carburetor and then death...

I have fresh plugs, I have a rebuilt carb, I have visually looked at the reeds and they appear to be closed but the "puff" makes me think they may be bent or broken...

So I have bought new reeds, bought new reed cage gaskets and I purchased the reed cage rubber seal that separates the two cylinders.

Does anyone have any pointers? For the life of me I cannot find a pilot jet like a normal carburetor and the Shop manual does not mention one, So I have blown out every passage I can Find.

I have no doubt this motor could be a fun little motor if I could ever get the darn thing off the dock. My duck season and Deer season are being hammered by this little motor!
 
Serial # of your motor ?----Is there not a screw with a spring on it ?----Surely you would have had that out when doing the cleaning ?
 
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That screw with the spring is the low speed mixture screw.----Sometimes called a " pilot jet " I believe.-----Does spark jump a gap of 3/8" or more on a testing device , yes or no ?----Checked the flywheel key ?
 
Flywheel is tight, spark is strong. I really don’t think it’s a spark/timing issue. The motor will fire up consistently on choke, run briefly and die out like it’s lean.
 
I agree it's a gas flow problem: it's too lean at idle. You might have to run a fine drill through the passage where the tip of the needle goes. It might be corroded enough to be too small in diameter, even with the needle way out (ad it doesn't take much!)

Jeff

PS: I had both of my Edlebrock 1409 four-barrel carbs do this to me--and they were brand new. Had to drill the little holes where the needle goes larger to get more gas to flow. Before then, the motor would not idle right at 4 plus turns out, but it was fine after drilling (1 turn out as I recall).

Another case: Two modern lawn mowers I "inherited" from their owner (he couldn't get them started) needed the treatment as well. The Federal emissions crap required them to be jetted so damn lean I had to use starting fluid every time. Enlarging the main jet (not idle circuit) cured the problem. Ran perfect warmed up as well.
 
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Jeff, what do you have with 2 Edelbrocks? Yes, this newer stuff is set to be tamperproof and run lean.
Perhaps the needle tip is neatly broken off and plugging the low speed metering seat there at the back of the chamber.
 
I was thinking about that needle tip… the needle is pretty dull. I have tried to find a new one on oldmercs.com but i am having trouble finding one and it doesnt come in the carb repair kits…
 
Does that have the fuel pump built into the carb? What happens if you pump the bulb?If so check the base gasket make sure it is not covering any holes. Those needles are generally dull not real pointy.
 
flyingscott said:
Does that have the fuel pump built into the carb? What happens if you pump the bulb?If so check the base gasket make sure it is not covering any holes. Those needles are generally dull not real pointy.
Click to expand...


I used a merc gasket, no obstruction. Squeezing bulb while running doesnt change anything.

Random question, there are 4 holes at the back of the lower cowl. When the motor is running I now have water spraying out of these holes and only dribbles coming out of the tattletell
 
Took the reed cage off to verify any additional problems

Bottom end looks good and tight with no sign of water intrusion. I have faith the top end is also in good shape from what I could see. I found 2 broken pedals (one on each side) cracked at about a 45 degree angle which left a noticeable gap open on each side of the cage. (could see through no problem...obviously bad.)

I also found the rubber seal that separates the two cages had morphed into some sort of gel-i-fied powerbait from hell. very soft, goopy and LONG past sealing anything.

Replaced the reeds, thoroughly cleaned all the mating surfaces and reinstalled everything. Replaced the sealing gasket, reed cage gasket and adaptor plate gasket.

Carb dipped the Carb for 4 days in the gunk pale. Carb came out super clean and I found 2 holes that I know where not as clean as before. Used compressed air and blew the carb out and replaced everything with a new Quicksilver carb repair kit.

Tomorrow is the day if this thing starts. Wish me luck.
 
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