Slide Carb Question

I have another slide carb question...

I think I know the answer, but I want to see if you guys think I'm on the right track.

If you are cruising at 35mph in 4th gear, RPM's are probably in the 2k range, is the majority of your fuel coming from the needle jet and jet needle?

Pilot is only off of idle, and main is only 4/3-full throttle. So it seams that while cruising the needle jet and jet needs are providing most, if not all of your fuel. Is this correct?

The carburetor circuit isn't based on rpm, it is based on throttle position. What position is your throttle in to achieve 35 mph in 4th gear?

slayer61 wrote: The carburetor circuit isn't based on rpm, it is based on throttle position. What position is your throttle in to achieve 35 mph in 4th gear?

I would guess somewhere around 1/4 throttle at the most?

At 1/4 throttle your needle jet circuit is in operation.

You can pretty much mark your throttle lever in 4 positions from idle to WFO and tell what circuit its on. My guess would be a little of the pilot & a little of the needle

Sudco Tuning Manual, 4th Edition





Good Fortune!

I'd be surprised if you were at 1/4 throttle cruising at 35 MPH.

On the 550's, you can cruise 55 to 60 MPH at 1/16th to 1/8th throttle.

Either way, 1/8 or 1/4 throttle, changing the needle position will have the most affect. The main will affect it slightly at 1/8, and a little more at 1/4.

Thanks for the input. And I think you're right, it probably is closer to 1/8 to 1/4 throttle.

So I bumped my needle up a notch and it appeared to help a bit. I also realized I was running a colder plug rather than a hotter plug like I thought I was. So I went from a b9es to the stock b7es and it appears to have helped a bit also.