Tech question.. new car running a stumble valve, when I got it the barrel valve was st 22%, I put it back to 14% as per engine sheet and it ran like a pig of the line. Do you need to run the barrel valve a lot richer when using these? Are they worth it or keep it simple and take it out? Sorry, hawk midget engine if that makes a difference. All other settings checked and set as per builders dyno sheet.

Yes most time you will set barrel a touch richer. The stumble will generally be its most effective between 2500 and 4500 rpm. When used I do like to include a shut off valve for the stumble. It can help keep the motor a little cooler during yellows etc. to shutoff the valve. Also the driver can easily test restart response both using the valve and having it shut off.

Seems like everything comes and goes, what you never had trouble with before, suddenly becomes an issue. This may only work for me, but I removed the low speed bypass, idle bypass I call it, and eliminated it, I did set the barrel valve a tad richer, but also found that to make it perfect, I had to lead with the throttle a bit, just ride the brake a bit, and get a little throttle in it, before the green, worked for me, may not for you, I was also told that FI didn't work well on short tracks, especially indoors, mine worked great! Bob

Thanks for that. I'm going to do away with it, if it stumbles, I'll put it back on and fatten up the BV a bit. The way it is set up with the main pill I would have to do some serious re-plumbing to put a shut off on it.
Thanks again for the responses, cleared up my line of thought on the issue. People here seem to be using but not understanding them!

I ended up re-installing the stumble valve and put the BV back to 21%, the thing was a jet, thanks again for the advice. Then the brakes broke ....