All NEW Parts, 1 annoying miss HELP

[dluna11w]

Does it make sense to consider a high float to be causing this issue?

[rubbinsracin]

possible. one thing i have learned over the years working with carbs is that you can never rule anything out. having a good bit of carb knowledge or a good carb guy goes a long ways. i have had a motor stumble just because it didnt like the carb. took one off a good strong running motor and put it on a different motor, same specs on the motor, and it didnt like it. bolted it back onto the old motor and it ran like a champ with no changes.

[dluna11w]

Carb builder also suggested I turn out the mixture screws another 1/4 turn or just under. Timing is about 30 at 3500 rpms or so, so he wants me to make sure it is at 32 before I touch the screws. I can't imagine 2 degrees of timing would cause a stumble, but I've been wrong many times before

[rubbinsracin]

2 degrees can make a significant difference. we start with are screws a 1.5 if i remember correctly. but like i said having a good carb guy goes a long ways!

[odb93]

Is the timing still advancing 8 degrees?

[dluna11w]

I set the timing to 32 degrees at 4,000 rpms. The timing moves around 3 to 4 degrees from idle to 4,000 rpms. My idle screws are 1.75 out. I've tried 1.25 and 1.50. There is still a stumble at 2500 rpms. It happens at idle and under load. The carb builder suggests 7.5 for the pressure. I tried lowering it to 6.75 and reset the float levels to have a small bubble at the top of the glass. There is still a stumble. I cleaned every hole possible in the carb before putting it back together. If we get rained out this weekend I may send the carb back to the builder to look it over.

[odb93]

Does it consitantly advance or retard 3-4 degrees? Or does it jump?

[dluna11w]

As I give it more throttle it barley moves a total of 3 to 4 degrees from idle to 4,000. I am getting this number by turning my dial light to 32 and the TDC mark on the balancer is hitting really close to the 4 degree mark on the timing pointer. As I increase rpm, TDC eventually lines up with 0 on the pointer.

[50j]

Why not bolt on a known good carb and see what happens?

[dluna11w]

Did it. Borrowed a 2 barrel carb and there was no miss. I don't have a 4 barrel available to borrow. I've basically thrown out any possible electrical issues now.

[rubbinsracin]

has to be your 4barrel. id take it to a good carb guy and have it rebuilt to the needs of your motor. ie appropriate cams, jetting, etc

[dluna11w]

That is what I tried with this piece. $1,100 later I have a nice looking new carb that produces this stumble. These guys sell these carbs all over the country, maybe I just happened to get a bad one. I think it will run just fine at higher rpm. I'm mainly concerned about a restart at this point.

[dluna11w]

wanted to give an update:

I had an oldtimer come by and look at the carb at the track before the first race. He didn't like the glass sight plates and thought I had the floats too high. I lowered them and have yet to have a stumble on the track. I will check the timing tomorrow before heading to the track and see if I can still hear the miss without a load. Very strange deal I must say, but it seems to be working. Won on Saturday night.

[sj valley dave]

A bubble at the top of the clear glass sights is too high of a float setting...The old tryed and true way works for us...while the car is idling we rock the car some and gas sloshes out of the hole...