All NEW Parts, 1 annoying miss HELP

[powerslide]

im guessing you checked fuel pressure at 3k if not and its dropping maybe the fuel filter is installed incorrect? said it was a new motor not sure if it was changed or if a whole new car. just an idea.

[dluna11w]

Thanks for the reply. New car to me. I did check the fuel filter before hooking up all the fuel lines.

[grayarea58]

if this wasnt a racecar id say you have a clogged cat or restricted exhaust.have you put a vac gauge on it .check vac at stumble.low or no vac, check for valves to tight,or restricted exhaust. after sitting all winter we found a nest in a muffler drove use nuts.just a thought..

[dluna11w]

Tried the 2 barrel. No miss anywhere through the RPM.

Took new carb completely apart, cleaned every hole I could see. Put it back together and I would call it raceable now. There is a pretty big stumble around 2500 to 3000, then it clears up and runs pretty clean the rest of the way on up to hitting the 6200 chip. The carb builder recommends 7.5 for the fuel pressure. I did a test at that and at 6.75. I want to say it was a little cleaner, but don't really know. Can anyone clarify where I should be running the float levels. I've ALWAYS ran mine to where it just trickles out or comes out with a slight nudge on the frame. With these glass sight bowls, I have them all the way up the glass until the very top I've left a bubble. I don't know why I didn't test it with both bowls lowered a bunch. oooops

[rubbinsracin]

we run our 2 barrel so it just trickles out and our 4 barrels so when you bump the chassis they "spill"

[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.