Yet another Merc 40 2 Stroke 4 Cylinder won't idle.

[RickM46]

I have a 1992 Merc 40 2 stroke 4 cylinder I have owned since new with WMA carbs that ran great 4 years ago; now, it won't idle. Has been in the garage for 4 years and not used. When I last winterized it, Stabil in gas tank, fogged it, drained the carb float bowls, filled the float bowls with Stabil, squirted fogging oil into the cylinders. This June, hauled the pontoon out into the driveway, added 10 gallons of fresh gas, added new plugs, dunked lower unit into a tub of water. Got it started but it really did not want to idle - figured it needed run on the water.

Launched it and found that it would run great at 1500rpms, 2000, 3000, 4000, and 5000 and ran like new; smooth up and down the throttle range; I normally run at 3500 rpms; however, it would die at idle in gear (800 rpms) or out of gear (1100 rpms) after about 10 seconds and sometimes would die immediately.

I have read the accounts of other posts about this problem and it seems the consensus is the carbs need cleaned.
I would like to verify that the problem is not electrical and not fuel pump and truely is the carbs before I get into the carbs and its idle circuit - whatever that is. I have the shop manual.

So, is it electrical or fuel pump or fuel filter or carbs?
What is the idle circuit?
Any help would be appreciated.

 

[WesNewell]

Try keeping the squeeze bulb pumped at idle. Does it still die? if not, then I's suspect a fuel system problem. Maybe filter. maybe pump. More likely a filter if it runs ok otherwise.

 

[RickM46]

Thanks Wes, will try squeezing the primer bulb to see if that helps. Can you recommend a carb cleaner that won't damage plastic and rubber carb parts? Do you know what the idle circuit is? Is that a separate jet other than the main jet?

 

[RickM46]

Per the help above,went ahead and attempted to start the 40 and squeeze the primer bulb to keep it firm with pressure on the carbs.. Took about 50 2 second hits on the starter with the electric enrichener activated (pushing in on the key) and the fast idle arm at full up to get it to start.

After that, it would only stay running at about 1700 rpms with the fast idle arm up about halfway; as I lowered the fast idle arm to drop the rpms, I would squeeze the primer bulb to keep it hard but as soon as it got to 1300rpms it would die even with the primer bulb hard.

Also noticed that the black Quickksilver rubber primer bulb though pliable and no cracks made my hands black while squeezing it.

Folks, any suggestions?

 

[mgjtkt]

Since your motor runs at all RPMs "except" idle, it's time to clean the carbs. That motor ( I have one) should idle smoothly and start with just a bump of the key when warm. Even though it was running fine when put away you may want to go back to the basics by checking compression, spark that will jump a 3/8" gap, etc.

 

[joshua04]

I just got a motor like yours that would be difficult to start. (It’s had a bunch of problems besides that) and it wouldn’t start easily. My problem with the idling turned out to be the crabs needed a really good cleaning and tune up with the floats being set wrong and the idle screws being incorrectly set as well. Then the throttle linkage needed to be adjusted. It now starts up on the first cranking (even with 2 crappy coils in it). With that being done you may have to re-time it too depending on how much your throttle linkage changes. If you are mechanically inclined I suggest getting a service manual for it and doing it all your self. It’s pretty straight forward as long as you take your time and you'll probably only need a couple new gaskets for it. And a few bucks in gaskets is pretty cheap if it fixes your problem before jumping into the expensive electrical side.
I’m having a problem that the advance cuts out around 25-30 degrees which I assume is electrical and since your motor runs fine all the way through the RPM range I suspect your fuel system needs a good cleaning and tune up.