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help w/ 1993 Mercury 25ELH 25HP 2 stroke stalling / won't start. Video & pics included.

T

the ill postino

New member
Hi all,

I'm having some trouble with my 1993 Mercury 25ELH 2 stroke outboard and hoping you can help.

I bought it two years ago and it worked pretty well for most of the time I've had it. It had a tendency to stall at idle after first start but if I got into gear pretty quickly it was fine all day.

Recently it stalled on the way back in to my dock and wouldn't re-start. So I took the carb out and cleaned it with gum-out. No obvious issues or gasket tears etc. Put it back together and it started right up but stalled after a minute or so. Couldn't get it started again. Took carb *back* out and tried to be even more thorough in inspecting and cleaning. Re-installed and it started right up. Then died.

This time I left it alone for a day and when I went back to it I figured out that I could start it by slightly advancing this arm (in red in picture 1) manually to give it more gas. After I let it run for a minute I turned it off and was able to start it by just pushing the starter (see video linked below.) Did some donuts around my dock, put it into reverse, forward, more donuts, but then it died and would not restart. The advance-the-arm trick no longer worked including after taking the plugs out and wiping them down.

I've replaced the gas tank and fuel line and fuel filter. Spark plugs are pretty new. A picture of one of the plugs after the latest stall is attached. Carb mixture screw is set to 1.5 turns out. I tried a half turn more closed and a half more open and it didn't seem to help. When it was running at 1.5 turns the idle sounded pretty good:

Thanks in advance for any suggestions!
 

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If my research is correct, when you choke your motor it actually primes the motor by squirting a little fuel into the carburetors to help with cold starts. That keeps you running for 10 seconds. Your carburetor is clogged. I've attached a blown up diagram of your carburetor. Spraying crap all over it to make it look pretty, isn't going to do the trick. Every single passage needs to be cleaned out thoroughly. #14 on the picture is your pilot jet. It supplies fuel until you reach about 1500 RPMs. Take that jet out and make sure you can hold it up to the light and see a perfectly round hole. I'd try running a single strand of speaker type wire through it, then gradually work up to 2 strands, 3 and so on until you're confident that it's perfectly round and clean.

 
flyingscott said:
Do a compression and spark test.
Click to expand...
Thank you – I don’t have the tool for testing compression, but can borrow or find one. Googling how to do a spark test mostly comes up with a lot of guys joking about how to electrocute their wives or buddies. Any further info on how you recommend going about that here would be much appreciated. Thanks!
 
Oldsaltydog said:
14 on the picture is your pilot jet.
Click to expand...
Thank you. I was using the spray tip on the gum out to shoot through all holes and passageways, but this is really helpful to have a specific opening to pay special attention to, and I did not use any physical objects to make sure I was clearing any debris out. looks like this carb is coming out for a third time – will definitely be even more thorough.
 
flyingscott said:
Do a compression and spark test.
Click to expand...
flyingscott said:
Buy one of these to check spark set gap to 7/16"
www.lislecorp.com

50850 Ignition Spark Tester

Quickly Checks Spark at Plug Wire.
www.lislecorp.com www.lislecorp.com
Click to expand...
Ok I did a compression and spark test. A spark jumped the 7/16" gap on both plugs. I got 100psi for the top cylinder and ~97 or 98 for the bottom. This was with the engine cold. I don't really know what I'm looking for here but gather that this is on the low end, but good that the pressure is roughly equal in both?
 
Oldsaltydog said:
If my research is correct, when you choke your motor it actually primes the motor by squirting a little fuel into the carburetors to help with cold starts. That keeps you running for 10 seconds. Your carburetor is clogged. I've attached a blown up diagram of your carburetor. Spraying crap all over it to make it look pretty, isn't going to do the trick. Every single passage needs to be cleaned out thoroughly. #14 on the picture is your pilot jet. It supplies fuel until you reach about 1500 RPMs. Take that jet out and make sure you can hold it up to the light and see a perfectly round hole. I'd try running a single strand of speaker type wire through it, then gradually work up to 2 strands, 3 and so on until you're confident that it's perfectly round and clean.

Click to expand...
Thanks again for the suggestion, @Oldsaltydog . I took the carb out and apart and am having trouble identifying the jet from the diagram. Is it this little thing with the hole on the bottom and two sides? They look pretty open and round.
jet overview.jpgjet side opening.jpgjet top down.jpg

Or I also wondered about this (non-removable?) brass jet (?) in the middle of the picture of the float chamber or bowl. I've sprayed gumout down in there but should I also try to get a wire in? Thanks in advance to you or anyone else for further thoughts! Since the compression and spark seemed ok (maybe? - see other reply below) I am still focusing on carb issues for now...

carb front shot.jpg
 
Yes, that's it. Gas flows in from both sides and is sucked up into the carb. There should be an opening on the top, and while you're there, clean out that tube that goes up into the carb. The Emulsion tube. The attached diagram calls it the "main nozzle". If that doesn't come out, look in the throat of the carb and it should have small holes in the sides of it that might be clogged too. When air flows into the carburetor, the suction causes negative pressure which sucks gas up that tube to feed the motor. Making that jet nice and clean including the small opening at the top and those air holes in the main nozzle, should get you going with good fuel delivery. Let us know how that goes. If that does't do the trick, you may have a bad fuel pump. The diaphram sometimes deteriorates and gets holes or tears in it. The fuel pump uses the up-down movement of the piston and the compression/suction that it causes to make the diaphram "pulse" to pump gas. All pretty simple stuff that all works together to make these motors "purr"!
 
Oldsaltydog said:
Yes, that's it. Gas flows in from both sides and is sucked up into the carb. There should be an opening on the top, and while you're there, clean out that tube that goes up into the carb. The Emulsion tube. The attached diagram calls it the "main nozzle". If that doesn't come out, look in the throat of the carb and it should have small holes in the sides of it that might be clogged too. When air flows into the carburetor, the suction causes negative pressure which sucks gas up that tube to feed the motor. Making that jet nice and clean including the small opening at the top and those air holes in the main nozzle, should get you going with good fuel delivery. Let us know how that goes. If that does't do the trick, you may have a bad fuel pump. The diaphram sometimes deteriorates and gets holes or tears in it. The fuel pump uses the up-down movement of the piston and the compression/suction that it causes to make the diaphram "pulse" to pump gas. All pretty simple stuff that all works together to make these motors "purr"!
Click to expand...
Many thanks again for your help! Googling around it does seem (from discussion of a similar though not identical merc carb) that the emulsion tube is not removable without risking damage since it's pressed in. But I should be able to get a thin wire in there. And it sounds like it may be worth just going ahead and getting a carb repair kit since I believe it would include the diaphragm for the fuel pump. I'm looking at this one.

Will update after I get a chance to work on it again!
 
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