Air/fuel mixture screw

Hi,
Screwing in or out the air/fuel mixture screw on my #4 carb (81 seca 750) seems to have no noticable effect on the engines running/idle. Engine responds as it should to adjusment on other 3 carbs.
ideas?
John

 

Most likely that port is clogged so no more fuel can get in when you open it. It is probably pulling fuel from the starter circuit to run at idle. Easy way is to try a seafoam treatment and hard way is to pull and clean the carbs.
I would also check for spark on that cylinder since in trouble shooting it must be kept in mind that fuel mimics fire.

 

Also, someone might have screwed it in too hard and broke off the tip of the screw inside the hole.

 

Thanks
will check screw end.
and go from there.
John

 

I was thinking at lunch, (something which usually leds to headaches for me) that we had a turbo at the first NTCC with a cylinder missing due to a clogged pilot jet. We removed the mixture screw and poured seafoam directly into the port. Let it sit for about 4 hours and on the ride at the end of the day it started hitting. Of course a can of seafoam to two gallons of fuel in the tank will work also. Run it unti you get that white smoke that tells you the seafoam is in the carbs, shut it off and let it sit overnight.

 

You should also check that your vacuum is in sync. I had the same problem when I got my Seca. The butterfly on #4 was still open quite a bit with the throttle closed. I used Rick's "Old School" method to set the initial sync and the mixture screw started affecting the idle.

 

will do.
thanks.