Idle mixture screw stuck
 

I'm trying to adjust the idle mixture, the screw won't budge, I suspect it's a dissimilar metal corrosion issue. The engine stalls at times when going to idle, recently installed indigo PCV kit. Ran well before. Is there another solution other than a new carb?
Thanks Chris

I'd try a combination of penetrant (PB Blaster is good), time, and heat. As for the heat, I'd avoid direct flame - it's not too controlled. Rather, I'd use an oven. Heat will cause the housing to expand more than the screw and might just loosen the screw. You've got nothing to lose.
Alternate to a new carb is a used one. Keep an eye open on eBay - they show up now and then at reasonable prices.

Just looking around in my area at things and look what I found.

https://yuma.craigslist.org/bpo/d/yu...792043030.html

air leak
 

For sure fix the idle screw, but if it ran well before installing the PCV kit maybe there is a tiny air leak to find.

My advice would be to customize a high quality screwdriver with the thickest tip that will fit into the slot. That will be a fairly large screwdriver, so you'll need to cut down the edges with a Dremel. This will become your dedicated carb jet screwdriver. Insert it carefully, press hard, twist forcefully, and accept whatever happens.

I had a problem like that with one of the jets a couple of years ago and stripped the head with my screwdriver. Just could not get it out. C'est la vie, I scrapped the carb. Maybe I could have dug it out with a series of holes drilled into the center, and a tiny EZ-out...but maybe not, and I'd blame every bad thing that ever happened to the engine on that repair.

Not sure if a best practice to head this off would be to apply a dab of anti-seize compound to the threads, but I've been tempted to do that the next time the carb comes off.

Interestingly, we don't talk about rejetting the A4 carburetor like people do who have motorcycle carburetors. Jets cost less than $10. Are we comfortable that the stock jets are the best jets, aside from the possibility of the adjustable main jet that Don sells?

Interestingly, we don't talk about rejetting the A4 carburetor like people do who have motorcycle carburetors. Jets cost less than $10. Are we comfortable that the stock jets are the best jets, aside from the possibility of the adjustable main jet that Don sells?[/QUOTE]

We rejet bike carbs when we modify them to change the air flow but with the Atomic Four we just want them to run stock. I dont see much need to rejet.

I could be wrong, been wrong before but this suggests to me a carburetor that has not enjoyed regular cleaning/rebuilding/maintenance.

have not touched the carb in the 5 years I've owned the boat. Typically we motor in and out of the slip, however this year we have been cruising left Maine mid October in Titusville Florida now.
The question I should have asked is that if the idle mixture is lean, is it as bad as if the main jet is lean?
Thanks
Chris

"The question I should have asked is that if the idle mixture is lean, is it as bad as if the main jet is lean?"

In my mind, yes. Because of the stall issue at low RPM. Doing the bridge dance on the ICW with several other boats is exciting enough without adding the potential stall.
Have you tried PB blaster or some other product to free up the idle mixture adjustment?
Not a fix but you can use the choke to help control air flow. Partially blocked fuel ports, unregulated air from PCV or a air leak all lead to a lean mixture.
I see a carb cleaning in the future.

Dan
S/V Marian Claire

The idle mixture screw should be oiled enough to turn by hand. If you can't move it with a screwdriver, it is in dire need of lubrication. Regular removal, disassembly and cleaning of the carburetor is important. Probably no need for a new one except as a spare. While you have it apart, check the jets for obstructions. Get new gaskets.

After living with the engine for the last month or so i have figure out the trouble, when i installed the pvc kit i bent the throttle cable bracket to provide room for the kit. I suspect i can now turn thee rpms down to below where the engine will run. I am more carefull when throttleing down to make sure i dont push the trottle forward ad far. I will adjust the idle speed soon. I dont have a tach so i really dont know how fast its turning kind just keep an eye on the amp meter to know when she is producing amps.

Before you adjust the idle be sure the ignition system is correct. As necessary adjust the advance, timing, and if you have points the dwell all to spec.
Then go to the carb and adjust the idle mixture and the idle speed in small increments until you get a satisfactory idle.
If you can't get a satisfactory idle by this procedure there is most likely a problem with the carburetor. Or maybe the PCV system is interfering somehow.

TRUE GRIT

Sounds to me like you found another problem which has nothing to do with the original problem of a stuck mixture screw.