What is the correct positioning for the fuel mixture screw on these carbs? I got the rebuilt kit from Atkins rotary and the directions just say "loosely seated and back out twice" but... how loose is to loose and how loose is too tight... this is my first time rebuilding one of these... help please

 

Someone just asked this in another thread. Turn it in until it just stops but don't "torque it down" because the screw is brass and you can damage the tapered tip. Then back it out 2 full turns. Watch the slot on the screw head - doesn't matter if it's starting at 9&3 o-clock, or 10&4 or wherever - turn it out 2 full turns. I don't know if 2 turns is correct but if that's what they said, that's what they mean.

 

i just turn it in by hand, and then i use a screw drive to turn it out, and just count half turns. start at about 3, and then when its warmed up, it should probably want to be turned in.

so the mixture screw has a tapered head, and when you screw it in, it is literally just going into the passage that the mixture goes through between the idle jet and the engine. it needs the taper because that way it acts more linear, it has to do with the relative areas of the screw and passage, vs the thread pitch, if that makes any sense.

 

Yes and no.. so you turn it by hand until it gets hard to turn, and then back out 3 half rotations with a screw driver?

 

Essentially yes. If you pull out the spring (only temporarily) and then screw the mas all the way in, the point where it stops spinning is where it is 'seated'. Lightly seated just means don't crank on it past that point. When you put the spring back in it should now be fairly obvious where that point is. You should be able to get it all the way in by hand, although I use a screwdriver since it's easier.

And I always thought it was 3.5 full turns out (so 7 half turns) for baseline, but maybe I'm crazy. Am I crazy?

Once it's up to temp just give it whatever it likes best - it might take some fiddling though, as the mixture screw has some effect on deceleration and milage. You'll really have to drive around to get it dialed in.

 

There will be some sudden mechanical resistance when it's seated. Go slowly you'll feel it.