Needle valves/Homebuilt carburetors

[jpeter]

Don't get me wrong, I vote for the long taper because of the broad adjustments it gives me. Never-the-less what you say about the 1/4 turn is close to what I find with my engines, even with the long taper. I can't turn 1/4 turn away from the sweet spot and have any of them running right or maybe at all.

 

[jpeter]

Another thing to try is to choke it off a little. Try putting a short choke tube in the intake with about a #45 hole for the air. You'll get better draw at slow rpm. Fooling with the intake size has been a big factor in getting my small hit & miss engines running well at slow speeds.

 

[compspecial]

Brian
Do you think the sensitivity could be due to the very course thread? I think the 2-56 and so on series are based on national coarse threads something finer wouldn't advance the needle so much per turn. Beautiful engine!

 

[mu38&Bg#]

Have a look at a needle on a Walrbo carb. The needle taper and the thread pitch both influence the change in orifice area for a given angle of adjustment. If you can get it adjusted to where you're happy with how it runs, I say you're done. If it's tough to get set, a finer taper can improve this. Having run RC model engines where one "click" on the needle is rich or lean, I like to get as much adjustment as practical. I had one unique setup that gave over two full turns of the needle in adjustment from missing rich to missing lean, it was wonderful.

 

[jpeter]

Brian, I think thats just the way there are. In the model airplane motor biz we speak of clicks in or out. A click in or out makes the difference in haveing it right or too lean. A full turn might be 12 clicks.

 

[tel]

I went with the spring arrangement, mainly because that how just about every 'real' mixture screw is, the needle may need a bit more work, but it is just done with a file.