Hello,

Holley list 80498-1 950 alcohol carb on my kid's car. We tested for the first time with this carb yesterday and the engine was breaking up just before the 1/8th mile stripe. It's 144 jetted all around, which seems smallish to me. I did look up this list and 144s are what came from Holley. I noticed that the carb that superseded this one has 172 jets all around.

Was planning to go up a bit on the jet but there's a big difference between a 144 and a 172.

Wondering what anyone is running on a 370-400ci engine with this much carb. The car picked up 2 tenths this carb from the 750 that we pulled off but want to get it to run clean all the way down the track.

check everthing could be an ignition issue

I have one and it has 152's all 4 corners start there. This was on a 355" so you may need about a 155-160?

This message has been edited. Last edited by: HR3377,

My APD 750s have 150 jets and my 950 has 152 jets. The 750s have been run on 347-434 with no jetting changes. The 950 has only been run on my 434 so far.

Is the carb Brand New? More specifically Needle and Seats and floats New?
What fuel pump? Electric or Mechanical?
What was fuel pressure at finish line when it was breaking up?
Did you put new plugs or plug in there and make a pass to see what it looked like? Fat or Lean? Sounds like you are assuming it is lean and it may be but if so that is a fuel supply problem. If you have a mechanical pump and or old needle and seat you could be way too fat at RPM.

Usually jets are perfect from factory or good carb builder and if you have to change them it is a band -aid to some other issue such as fuel pressure or Needle and Seat or Floats. And for most part it does not matter cubic inches for jetting.

So first thing I would do if the needles and seats or floats are not new is replace them. Then put at least one new plug in and make a pass and look at plug. Then verify actual fuel pressure at finish line. Data logger or even Go Pro camera on fuel gauge.

If all that is good, when was last time you changed Cap, Rotor, plugs and wires? Also 7AL-2 boxes have been known to go bad and they just do not want to turn much RPM.

I would add blow out all the air bleeds with air or carb cleaner until you hear and see fuel coming out. If one of those are clogged the carb acts stupid.

If it is "breaking up", also check the ignition box power and grounds, and the cap/rotor...

This is an LS-based engine so it has the coil near plug igntion and appropriate MSD box that is about a year old. With the coil near plug system plus crank and cam triggers I don't think it's ignition related. Plugs look fine but I haven't put a fresh set in and made a run yet.

I'll go up on main jets and see if it helps/hurts.

quote:

Originally posted by HR3377:
I have one and it has 152's all 4 corners start there. This was on a 355" so you may need about a 155-160?

Yep! Have a 950 on my sons 355 in his S10 and we're jetted at 164s.
Jetted it down and it slowed down