1989 AC Cobra

[Blake999]

Hi all. Not my car, but a very good friend. The car was bought as an investment some 20+ years ago with 500 accredited miles on the clock. Now I've done 936 miles and the problem is it never runs right especially at low speeds. To cut a very long story short, it was found that the wrong carburetor was fitted, reasons for this can only be speculated as it's a show car and rarely used. Would it matter as long as it runs is the popular guess, however he would very much like to have it running as it should so the decision was taken to purchase a brand new out of the box 600 CFM Holley from a reputable Holley dealer. Fitted the carburetor and to our amazement it won't start. It fires up, but just on the fuel that is pumped in from the accelerator pump jets. Once that burns off it dies. It won't run now, but I think I have double checked all and can see nothing wrong refit the old carburetor. She starts instantly and idles perfectly, refit the new one and she won'tt run which is baffling me.
Things I've checked:
Sealing to manifold
Vacuum Plugs
Fuel pressure 6 psi
Float level
Throttle blade adjustment
Timing 10°
Idle adjustment adjustment screws
Can there be an internal fault with the new carburetor? I know this would be a million to one chance, but really what else can it be? Put simply, it's not pulling fuel from the fuel bowl. Any sensible input would be greatly appreciated.

[BITE_ME]

Send in the carburetor for warranty repair.

[Gaz64]

What is the slowest speed the engine will run at, 3000, 2000, 1500? In other words, when does start to die? I find it hard to believe it could have all idle circuits blocked. Gary

[Blake999]

That's the problem, it does NOT run with his carb fitted; just a single burst when it uses up the fuel from the pump jets. I know it's extremely unlikely that both primary ports be blocked on a new carb, but honestly what else can it be?

[Gaz64]

Send it back for a replacement. I've never had a Holley, or any carb not fire up, like you've described. You have no idle circuits or primary main circuit, if it won't run at all. It should at least run at some point in the fuel curve. Gary

[Blake999]

I agree, I've been in this trade for 50 years and never seen anything like it. As you say, it should run at some point and just to make absolutely sure stick the old one on and fires up instantly. Also slightly annoying when the dealer asked had I put it on the wrong way even if had some catastrophic brain fade she would've still run. Although the throttle linkage would have been interesting to fit. LOL. Would love to have a look at that metering block, but as it's new, better not.

[Gaz64]

Sounds like no doubt the fault is within the metering block, as if both main wells are dry and not being supplied from the bowl. I.E.: Blank main jets, (not drilled), or machining rubbish after the mains.
A friend of mine a few years back changed a carb in the backyard, and about 20 miles later it developed a huge driveability issue. I asked him where he did it, he said under that tree. I found blades of grass in the main jets. Fell in via the bowl vent tube. Chances were near zero, but still happened. We still laugh about it. I personally never fit out-of-box carburetors. Even if I void warranty. Even if I need to replace some gaskets, etc. I still like to know what's in there. Hope Holley sorts your issue for you. Gary

[Blake999]

Spoke to the dealer today and they reluctantly agreed to have it back and send to Holley for inspection, but I'd rather have a look myself simply to save face. They could tell me anything or worse nothing at all, it's not that it's sealed, I could have a wee sneaky peek at the metering block?