Idle Trouble Merc

[CTsalt12]

Hi Everyone,

My Merc keeps stalling out at idle speed.  115 ELPTO 4 cylinder, the type that runs on 4 cylinders at WOT and drops down to 2 below about 2000 RPMs.  Idle speed is less than 500 RPMs, noticeably  less than before I had my carbs cleaned.  It also shudders and vibrates quite a bit which didn't happen before.  Plugs are just changed, like I said, carbs cleaned professionally.  Gas is good, although it has Ethanol I've been going through a tank a week so at least it's fresh.  

My gut tells me I need to adjust idle speed to get the RPMs up.  Is this done with the idle screw?  Any thoughts from the experts out there?

[fitz73222]

Oh boy,

My favorite Merc! I have twins on my 22-2. The idle quality is controlled by mixture and timing. Mixture screw static setting for the top two carbs is 1 1/2-1 3/4 out from lightly seated. The idle speed is adjusted by altering the timing using the idle speed screw. Your base idle timing should be between 2 degrees BTDC to 4 degrees ATDC at 300 rpm cranking speed (with the spark plugs removed and grounded). The process to set this engine up for timing and throttle syncronization gets involved. Your idle speed should be 650 rpm's +/-25 in gear, in the water. You cannot correctly adjust this engine without back pressure, in forward gear and in the water. I can go through the details of setting up this engine tonight, after work. My advice is, take it back to the "professional" that repaired the carbs and tell him to fix it...

[CTsalt12]

Thanks Fitz.  Man, the quality of info on here is so much better than THT.  I agree I need to take it back to professional.  Could I harm anything by adjusting idle screw myself?  Assuming I make note of how many turns I've taken in either direction so I can always change back.  

I don't really blame my guy because it idles fine at first after starting the engine.  It's after going up on plane and coming back down that the problems start to occur.  Fitz- is this telling of other symptoms?

[fitz73222]

Thanks Fitz.  Man, the quality of info on here is so much better than THT.  I agree I need to take it back to professional.  Could I harm anything by adjusting idle screw myself?  Assuming I make note of how many turns I've taken in either direction so I can always change back.  

I don't really blame my guy because it idles fine at first after starting the engine.  It's after going up on plane and coming back down that the problems start to occur.  Fitz- is this telling of other symptoms?

You're really not going to hurt anything assuming the base timing is correct. Turning the idle screw inward will retard the timing, unscrewing the idle screw will advance the timing and normally will increase idle speed. It doesnt take much adjustment to change the idle speed considerably. I found that 950-1000 rpm on a flush will get you close to 650 rpm in the water, in gear. What exactly is the engine doing when coming up or slowing down from plane as you describe?

[CTsalt12]

I didn't explain that well.  The trouble is always when idling, it's just that I've noticed my first idle of the trip, after starting up, is fine, maybe a little excess vibration but never stalls.  As my trip goes on, I've gone at cruising speed and come back down., the idle gets problematic, stalls out, takes multiple times to get started and in gear etc., stalls when docking and I'm idling or changing gears or whatever.  I was just making the point that my mechanic wouldn't have noticed the bad idle when he tested boat at dock, because the problems only occur after opening up the throttle at least once.

[fitz73222]

This only started after the carbs were rebuilt or has it been a symptom for sometime?

[CTsalt12]

After carb rebuild, which was brought on by water in fuel I should add.

[fitz73222]

What I'm having difficulty grasping is why the engine starts up cold and idles and runs fine and then runs poorly after it has warmed up. If he had the carbs set up rich ( the needles more than 1 3/4 out) it might explain the engine running OK when it is cold and then loading up and running rich after it has warmed up. This might explain why the engine idle speed is low because of an overly rich mixture. Your engine has an accelerator pump to help boost the fuel at the 2000 rpm transition between running from 2 to 4 cylinders. He may have hooked up the accelerator pump lines backwards when he had the carbs off or has the enrichner purge hose crossed with the accelerator pump discharge hose. I'm grasping at straws here. Look to see if there is any fuel leaking around the accelerator pump stem that contacts the throttle cam. There is a diaphragm in there that could be leaking and it will leak around that stem if it is bad.

Other things this could be-
Incorrect float height causing it to start flooding when warmed up.
Leaking float needles or a piece of trash stuck in the float valve seat not letting it shut fuel off when the float rises back up in the float bowls. Did he replace the float needles and reset the float height?
Old style (pre '96) two stage stator that looses fire or weak fire at idle when warmed up. I cant imagine it still has the original stator.
Bad switchbox also causing a weak or no fire condition after the engine has been running and when you pull back to idle the engine quits running. (It took me a couple of months to figure it out on mine because when the engine cooled down after 20 minutes or so, it would fire up and run fine!)
When the engine stalls after running at higher speeds, how do you get it restarted? Do you have to push the key in to get to light off or do  you have to run the throttle up in neutral to clear it has if it is flooded?

I wish I was there, I know your engine pretty well and I hate guessing at things without a complete understanding of what she is doing.

[CTsalt12]

I get it restarted by just letting it rev up in neutral for a bit longer than normal, and having a real quick transition from neutral into gear.  It sounds like it's almost gonna die then it gets going.

Was told by my mechanic over the phone that the carbs probably need to be adjusted a little richer to give the engine more fuel on the 2 cylinders.  He also said it probably works better when I'm just getting it started up because I'm using the choke and flooding the engine with gas.  Which made sense then, but now I'm realizing every time I start it up I'm using the choke so that doesn't make sense.  I also let it warm up for a bit when just getting it started as opposed to restarting when I'm fishing and anxious to get another drift in.

[fitz73222]

I get it restarted by just letting it rev up in neutral for a bit longer than normal, and having a real quick transition from neutral into gear.  It sounds like it's almost gonna die then it gets going.

Was told by my mechanic over the phone that the carbs probably need to be adjusted a little richer to give the engine more fuel on the 2 cylinders.  He also said it probably works better when I'm just getting it started up because I'm using the choke and flooding the engine with gas.  Which made sense then, but now I'm realizing every time I start it up I'm using the choke so that doesn't make sense.  I also let it warm up for a bit when just getting it started as opposed to restarting when I'm fishing and anxious to get another drift in.

Hey Salt,
Where did we wind up with this Merc? Did bumping the idle up cure the problem? One other thing to check that I didn't mention earlier I want you to look at and it seems to be critical to most Mercs is the throttle pick up roller for the carbs. In the idle position, you should have between .005-.040 clearance between the idle cam and the throttle roller. I usually set them at .025-.030 with a feeler gage. If you need to adjust it, loosen the screw that connects the throttle roller to the carb linkage, insert the feeler gage, hold the throttle cam and roller together with the feeler gage in between and retighten the throttle roller. Idle speed is controlled strictly by timing with no influence from the throttle butterflies being open.

[CTsalt12]

Fitz,
This one turned out to be a total curveball.  My mechanic and I checked it out and he noticed something did not look right in the oil line.  Not sure the proper technical term but it's the small plastic tube oil goes through on the lower port side of the engine.  

Upon further inspection, we determined the stopper valve for this oil line was shot.  Again, I don't know the proper term, but it's a valve used to keep the flow of oil going one way, so oil enters the engine and  fuel does not mix with the oil directly.  We pumped the primer ball and the valve was leaking gas.  What was happening was this valve wasn't working properly and fuel was mixing with the oil.  Took an oil sample and it wasn't thick and green like it should be, but liquid and somewhat clear.  Replaced the valve, took out the old oil and replaced it with fresh oil.  Pumped bad oil gas mixture through the tube till it was pure oil, and ran the engine for a while until we started seeing some smoke.  So I was running my engine on a oil gas mixture for a while, great.  Luckily it's not prime fishing season and I was away for 2 weeks so I haven't put a ton of hours on it.

[fitz73222]

Fitz,
This one turned out to be a total curveball.  My mechanic and I checked it out and he noticed something did not look right in the oil line.  Not sure the proper technical term but it's the small plastic tube oil goes through on the lower port side of the engine.  

Upon further inspection, we determined the stopper valve for this oil line was shot.  Again, I don't know the proper term, but it's a valve used to keep the flow of oil going one way, so oil enters the engine and  fuel does not mix with the oil directly.  We pumped the primer ball and the valve was leaking gas.  What was happening was this valve wasn't working properly and fuel was mixing with the oil.  Took an oil sample and it wasn't thick and green like it should be, but liquid and somewhat clear.  Replaced the valve, took out the old oil and replaced it with fresh oil.  Pumped bad oil gas mixture through the tube till it was pure oil, and ran the engine for a while until we started seeing some smoke.  So I was running my engine on a oil gas mixture for a while, great.  Luckily it's not prime fishing season and I was away for 2 weeks so I haven't put a ton of hours on it.

I know exactly which valve it is. It's brass check valve that meters the oil flow from the oil pump and oil tank into the main fuel line leading to the carbs. I found out mine was bad because one of my water separator sight bowls turned blue with oil like it had pre-mix in it when it should have been straight fuel. It was back feeding through gravity back into the fuel hose. When I would crank the engine up it smoke like crazy on the super concentration of oil and gas in the filter.

[CTsalt12]

Fitz,
This one turned out to be a total curveball.  My mechanic and I checked it out and he noticed something did not look right in the oil line.  Not sure the proper technical term but it's the small plastic tube oil goes through on the lower port side of the engine.  

Upon further inspection, we determined the stopper valve for this oil line was shot.  Again, I don't know the proper term, but it's a valve used to keep the flow of oil going one way, so oil enters the engine and  fuel does not mix with the oil directly.  We pumped the primer ball and the valve was leaking gas.  What was happening was this valve wasn't working properly and fuel was mixing with the oil.  Took an oil sample and it wasn't thick and green like it should be, but liquid and somewhat clear.  Replaced the valve, took out the old oil and replaced it with fresh oil.  Pumped bad oil gas mixture through the tube till it was pure oil, and ran the engine for a while until we started seeing some smoke.  So I was running my engine on a oil gas mixture for a while, great.  Luckily it's not prime fishing season and I was away for 2 weeks so I haven't put a ton of hours on it.

I know exactly which valve it is. It's brass check valve that meters the oil flow from the oil pump and oil tank into the main fuel line leading to the carbs. I found out mine was bad because one of my water separator sight bowls turned blue with oil like it had pre-mix in it when it should have been straight fuel. It was back feeding through gravity back into the fuel hose. When I would crank the engine up it smoke like crazy on the super concentration of oil and gas in the filter.

Yep you got it.  One more reason to use the filters with a clear bowl on the bottom and to check it.  Since these things go bad it should be a routine check every season...

[fitz73222]

Well I'm glad it all worked out. This was a good one...I had forgotten about that check valve as a potential issue. Let us know how she runs..