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

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RickM46

Regular Contributor
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.
 
Here is a chart on how different parts of a carburetor effect the motor operation.
attachment.php

It sound like your "mixture inlet needle" circuit is clogged.

You might want to try probing the very small holes in the venturi with a very thin brass wire before taking the carbs off and cleaning them.

It is a shot in the dark, but it might work.
 
Thanks FishinLine, I will give that a try; as part of winterizing it since new, I have been pouring pure Stabil into the empty bowls by pouring it into the fuel line just above the carbs; is using Stabil for this a bad idea?

Can you recommend an aerosol carb cleaner or any carb cleaner?? I think Gumout is highly corrosive to plastic and rubber.

Thanks for the help!!
 
Rick,

I am not a fan of Stabil, If you go to their website they talk about using it in ethanol blended fuel.

I personally never run ethanol blended fuel in any of my small engines or outboards.

I typically add Seafoam (snake oil) to my gas cans at a rate of 1 oz./gal. for 4 strokes and 2 oz./gal for two strokes.

I really don't know if it does any good or helps keep them running but it doesn't hurt.

I live in Minnesota, at the end of my boating season I do not run my outboards dry. I disconnect the fuel line, take the fuel tanks out and dump the unused fuel into my pickup truck. then top my truck tank off with fresh ethanol blended gas. Fog my cylinders, check the lower end lube for moisture, and put them away. In the spring/early summer they fire right up on a fresh tank of gas.

I never use any spray carb cleaner, I don't believe it does any good.

But, I do have a heated ultrasonic small part cleaner that I fill with a solution of Simple Green "Purple". An old tooth brush, some soft brass wire, some care, a new set of gaskets, 20 minutes through the parts cleaner, a good rinse in hot water, and drying with compressed air and my carbs look and work like new.

20170221_105100.jpg

These are the carbs on my 1985 - 60hp Merc 2 stroke after cleaning.

This is probably more than you needed. Fish on....
 
Thanks a million FishinLite for the tips.
Took a look at Seafoam on Youtube at https://www.youtube.com/watch?v=agAWXnT4-EQ and it did well for a 4 stroke truck engine; another video https://www.youtube.com/watch?v=a6pHSn8lLAQ said it was originally made for fuel treatment of 2 stroke engines.
I get the idea that it is good for our 2 strokes - thanks for the info!!
Quite encouraging to hear that your 1985 Merc 2 stroke is still running well!
When you refer to the carb gaskets, are you referring to the gaskets where the carb mounts to the head?
Do you remove and clean your carbs from time to time??
 
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I generally don't have to clean carburetors on a time to time basis. An once of prevention is better than a pound of cure (ie...seafoam/snake oil).

When I take carbs apart I always replace all the gaskets I find. Gasket kits are relatively cheep and if I have gone through the effort to thoroughly clean things and remove all the old gasket material which may have failed when I take them apart; I don't have to worry about damaging the old gasket.

The 85 Merc came on a project boat I bought. The wiring off the stator and the stator was shot. The rectifier/charge circuit was shot. The insulation on the wires from the switch box to the coils was crumbling. The trigger wires were in similar condition. The plug wires were the originals. There were a few miscellaneous pieces missing. The carb were in a sad state and the general condition was a gooey dirty mess. BUT the compression was GOOD and it was worth the effort.

I spent about a year of my spare time working on the project.....Tin_boat_Avitar.JPG

From a $800 bargain to a sweet fishing rig.

Fish on......
 
FishinLite, thanks a bunch for the info; I saw that Seafoam fuel treatment is offered by many stores including Walmart, NAPA, Advance Auto, Autozone; will give them a visit to get some and add it to the tank at 2oz per gallon.

My plan is to add Seafoam to my gas; start the engine and keep it at a fast idle - about 1300rpms to warm it up. Gradually bring it down to the stall idle and squeeze the primer bulb to test the fuel pump and fuel filter - if it stabilizes then could be the fuel pump or fuel filter; if not, then on to the carbs. However, since the engine runs great from 1500 up to 5000rpms, I don't think it is the fuel pump and filter.

Your boat looks great; to tackle such an engine, you have more guts than I Gunga Din!

I take it you bought your gasket kit from a local Merc dealer?? Your info is much appreciated!
 
Any time the boat goes on the trailer you should run the carburetors DRY.-----That keeps them clean and ready for next launch.-----No need to fill with stabill at all.
 
Thanks racerone! My boat is a pontoon which spends a season at my dock. Since my boat gets stored for a few years at a time, at the end of a season at storage time, I have always drained the carbs by loosening the nuts that hold the float bowls on and letting the gas drain out; then, filled the bowls with pure Stabil thru their fuel lines. That has worked since the engine was new - 1992; Maybe the pure Stabil in the bowls is not a good idea.
 
Went ahead and attempted to start the 40 and squeeze the primer bulb to keep it firm with pressure on the carbs this AM. 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?
 
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Those carbs have a tiny hole in the base where gas comes up to the body of the carb. If that hole gets plugged up....

You got to pull. soak, blow out with compressed air, and reassemble them.

Jeff

PS: If the hoses to the carbs are old and breaking down, tiny rubber particles will get inn the carb and...
 
I took a shot in the dark before I schedule the pontoon to be pulled out of the water and put in my driveway to work on the carbs. Dumped a quart of Seafoam into 12 gallons of gas in the tank and cruised the pontoon for 2 hours varying rpms from 1700 to 3500 rpms - smooth. After 2 hours, it seemed to idle in neutral more smoothly and hold steady at 1100 rpms but eventually died after 5 minutes; still wouldn't idle in gear. BUT, this is a significant change. The Seafoam must have done some good; definitely points to the carbs and not the fuel pump. Now, to rent a pontoon trailer to get it pulled out. Hoses are now on my radar too.
 
FishniLite - finally took a good look at the graph you supplied above. Don't know where you got it, but good stuff. Glazed over when I first saw it.
Have figured out (as is obvious from the graph) that the mixture inlet needle controls idle speed beginning with 1/8 throttle (.125 X 5500rpms) or 687.5 rpms till throttle valve holes take over at 1/4 throttle (.25 X 5500rpms) or 1375 rpms. So from my tach, 1500 rpms is around where my engine runs great up to 5000rpms - only tested it once at 5000.

Now, I am assuming the mixture inlet needle is the flat head screw #19 in the diagram http://www.marineengine.com/parts/mercury_marine_parts/sn/0D096308/1040412MD/543_80

Anyone know if that is right??
 
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What not to do:
Engine will not start.
Four second bursts with/without enrichener for 15-20 minutes.
Finally, battery depleted, starter motor so hot cannot be touched.
Risked burning out starter motor but after I recharged the battery, luckily for me the starter worked again.
Decided to quit torturing the engine hoping to drive it to a haul out landing.
Now, I will have the boat towed to a landing and hauled out and delivered to my driveway to begin the carb cleanings.
Oy vey!!
 
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Have finally located pontoon trailers for rent in my area: one private owner - 1 available and the local John Deer Dealer/Rental place - 3 available.
These rental trailers are ballbats with no frills, no tie down fittings, no crank to pull the boat onto the trailer.

Will have to tow the pontoon from my dock to a haul out ramp 2 miles away with my 14' outboard powered fishing boat.
Any pointers on how to do this besides don't?
 
Decided to do a compression test on the '92 Merc 4 cylinder 2 stroke at my dock.
Bear in mind, the boat sat in storage for 4 years.
Cold engine - won't start anyway.
In prep for that, I engaged the emergency kill switch to stop spark at the plugs.
Lifted the fast idle lever all the way up.
Disconnected the main fuel line from the engine.
Drained the engine fuel line by pressing in the pin at the connector at the engine.
Drained the float bowls (what came out of them seemed nasty).
Removed all spark plugs.
Results:
1995 - #1 140, #2 138, #3 140, #4 138 (Long ago).
2019 - #1 140, #2 138, #3 140, #4 127 (Today).
The plug for #4 was not even wet as the others were wet a bit.
Ethanol gas and 4 years in storage - I think the carbs are definitely due for cleaning.
Any comments on #4??

Have a spare tank I just filled with fresh non-ethanol gas; will connect that, fill the carbs and try to start it tomorrow.
 
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Thanks Jeff!
One last shot at getting the engine to run so I could motor it to haul out - nope, won't start.
Yesterday, I drained both float bowls and internal fuel lines as much as possible - what came out onto white paper towel was dark yellow gas remaining from the main tank - 4yr old ethanol gas with new ethanol gas added at the beginning of the season - yes, now I know.
Attached a spare tank with 50:1 and fresh non-ethanol gas; primer bulb'd to fill float bowls; drained them out again onto white paper towel - dark yellow - what was left in the fuel pump and internal lines.
Primer bulb'd the bowls full and let them drain 2 more times to wash out the old gas; got nice white gas on white paper towel.
Did no good; engine would not even kick over; will have to tow to haul out; then, pull the carbs.
Two good videos on cleaning carbs:
https://www.youtube.com/watch?v=8rgZwnH51aE
https://www.youtube.com/watch?v=dsHndfDy2k8
 
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One last test before haul out - have a Lisle 20610 spark tester arriving tomorrow - will test to see if I even have spark.
 
Hi Whitey22.
Weather finally cleared here today - sunshine and no wind so I was able to position the pontoon in the water to get at the motor. Checked the spark with the Lisle 20610 spark tester. Spark is hard to see in bright sunlight. While fumbling around, got a slight electric tickle on cyl #1. Finally figured out that wrapping the glass spark bulb in a black ball hat made the spark visible. The spark only shows up on one end of the tester. Looks like spark is getting to all the cylinders.

As a bonus, discovered that the plug wire for cyl #3 had a bad clip and doesn't click onto the plug; will have to order a new one; that plug was always dirty, now I know why.

Leaving ethanol gas in the main tank for 4 years did the fuel system in; at haul out time 4 years ago I put Stabil in the tank and into the carb bowls. Stabil is only good for 2 years. Will be running non-ethanol gas from now on.

This Saturday, I will tow the boat to a haul out and transport it to my driveway. Then I will take the carbs off and clean them. Will remove the main tank and clean it. Neighbor commented that algae will grow in the tank and carbs due to the moisture. There is a repair place here that sells a chemical to eliminate the algae. Have a gasket kit, jet cleaning wire kit, Berryman carb cleaner AND last but not least, the good fellas on this forum.

Will give a status when I am done.
 
Lastly, many thanks to the fellas on the forum for the above advice; learned a lot about the carb and fuel idle circuit and when each component comes into play!! Priceless!!
 
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