Farthest lean setting for idle mixture

[gatorfan6908]

Quick question... Can't find this specific answer anywhere and I'm looking for an answer in a pinch. I know it's Saturday afternoon, so of course the experts are out on the water... Lol. Anyways, I have a '82 merc 90hp L6. Idles best with the mixture screws about 3/4 turns out from lightly seated. I'm wondering if this is too far in... I don't have it running well enough to take out on the water to check the plugs to see if its too lean, so a piece of mind till then will suffice.
If I turn them any further out, the engine starts sneezing and kicking viciously. I know the plugs run a really dark brown, and the 3 plug runs wet black and covered w soot. That's why I leaned them out so much. I just want to make sure this isn't an excessive fix to a deeper problem such as an air leak... Any info is appreciated. Thanks!

 

[GA_Boater]

Re: Farthest lean setting for idle mixture

Setting it too lean can lead to holy pistons, and I don't mean blessed. Are you setting the screws on muffs or in a barrel of water. Final adjustment has to be with back pressure from water.

 

[gatorfan6908]

Re: Farthest lean setting for idle mixture

I just can't figure this out. I was in the water, trying to make it as accurate of a troubleshoot as possible. It all started when the number 3 plug was black and covered w wet soot. The spark is strong all over and the compression is great. Damn thing just will not idle with the screws over 1 turn out. I've toyed w the timing, but kept it as it was during my link and sync. I notice that the primer bulb won't stay super hard, and when I pump it sometimes it will even out the idle. I have noticed some fuel dripping in the bottom of the fuel pump, but I can nearly guarantee it is correctly replaced and tightened down snug.
I've removed the inline filter, just trying to remove anything that could cause a problem. I'm running 3/8 from tank thru primer up until tank side disconnect. Motor side disconnect is 5/16 up to pump and all lines on the motor are new 1/4. I've read about anti siphon bulbs, and the one on my tank is brand new.
Main problem I'm getting is the plug fouling on 3 and the sneezing and kicking during idle.

 

[oldman570]

Re: Farthest lean setting for idle mixture

It could be a bad set of reeds for that piston causing the trouble you are having. If the idle jet needle is not damaged and it only is on that one piston then a chipped or cracked reed will cause the cylinder to run rich. JMO
Oldman570

 

[gatorfan6908]

Re: Farthest lean setting for idle mixture

Ouch. Not the answer I was looking for... Either way, have any other troubleshooting steps before I go ripping the block apart? Thanks for the info, as I know this motor is old and the reeds probably won't let it idle right...

 

[GA_Boater]

Re: Farthest lean setting for idle mixture

Aren't the reeds for a pair of cylinders? Three sets in total for an L6 so the #4 plug should look about the same as #3. Is the spark good on #3? Also you said that fuel is dripping around the fuel pump and new hoses. Are the fuel hose connections good and tight? Have the carbs been rebuilt?

You still have some things to check before tearing to to the motor. It may still happen, but don't rush.

 

[Dave1027]

Re: Farthest lean setting for idle mixture

Main problem I'm getting is the plug fouling on 3 and the sneezing and kicking during idle.

Sneezing usually indicates a lean condition. Check the simple things first like fuel pump, carbs and possible vacuum leaks.

If I turn the mixture screws too lean on my motor it will cough and die eventually.

 

[Chris1956]

Re: Farthest lean setting for idle mixture

The idle mixture screws on that motor are usually 1-3/4 tun open or thereabouts, when set properly. You have some other issue, I would think. If the link and synch is correct, clean and rebuild the carbs with new gaskets, inlet needles and floats. Adjust the floats properly