Holley 750: When first starting the engine ( 454)the choke is closed and its starts fine. The electric choke seems to run open pretty quickly and as soon as I hit the gas just a little the ilde kicks down and the engine stalls because it is still cold but the choke is open. Anyone seen this before?

Absolutely. I've never seen an aftermarket Holley that had the choke adjusted properly from the factory.

There are several things that "could" cause the problem you describe. And since there's no way for me to know which it is, you need to start from the beginning. And that means ignition timing properly set; idle mixture screws properly adjusted, curb and fast idle speeds properly adjusted.

The choke coil could be adjusted too lean. The choke coil is adjusted based on HOW FAST it needs to OPEN. It is NOT NOT NOT adjusted based on how you think it should CLOSE. A properly-adjusted choke coil will snap shut like an alligator munching chicken at ~60 degrees F, and that scares the crap out of some folks. Having the choke coil too lean would account for the choke opening too soon. I'd start with the coil set to the index mark, no leaner. IF (big IF) the engine then gargles on gasoline when FIRST STARTED...

...You need to verify that the choke blade is being popped open by the pulloff piston the CORRECT amount for YOUR engine. NO lean stalling; NO gargling. It should just plain run good when FIRST STARTED. And then...

...with the engine off, you need to verify that when the choke blade is in EXACTLY the same position it would be in when the pulloff first opens it (SOMETHING like 1/4" gap between the wall of the air horn and the top of the choke blade, but that can vary some) that the fast idle screw is aligned with the SECOND highest step of the fast idle cam; and then re-confirm that the fast idle is set for a reasonable speed.

ANY one of these--or some combination--could be the problem.

In general, folks have the choke coil set too lean; the pulloff is often too rich; and the fast idle cam rod is at whatever random adjustment it happened to get at the factory. They try to compensate for the rich pulloff with a lean choke coil--and it DOES NOT WORK RIGHT. Eventually, they get frustrated and pull it off and install a manual choke, or just wire the thing open.

Which is pretty much crazy; an automatic choke is not new technology; and they work SEAMLESSLY if adjusted properly and when used on an engine in good operating condition and with a stock, mild, or moderate camshaft. Wild-ass camshafts will probably require additional carb tuning to get decent cold idle quality--and most folks won't drive such a car in cold weather anyway.

This is great information, thanks. Can you tell me what the pull off piston is and where it is located? Also, the high idle cam is the plastic piece( in my case)behind and under the choke cap, correct?

Thanks!

it's inside the choke housing. there's a link you bend to adjust it. yes on the fast idle cam.

Schurkey is speaking out of many years of experience about the common maladjustments. My 25+ years of Holley experience says about the same thing. The fast idle is just a trial and error thing *after" you get the pull-off and rich-lean in the ballpark.

I have extensive experience with Holleys going back over 25 years now. I have no idea why the out of box adjustment is so far off. You'd think they'd have learned something by now. I will say that several of the SAs I've worked with were much better. They were 670 and 770, haven't had an 870 SA yet.

Can you tell me what the pull off piston is and where it is located?
Brass piston about 1/2 inch diameter--maybe less. Sits in the bore inside the choke housing. Two possible sources of vacuum, depending on the carb. "Internal" vacuum is supplied through drilled passages in some carbs; then sealed to the choke housing with the silliest, tiniest square cork gasket you can imagine. EASILY lost or mis-positioned meaning that the vacuum can't get to the pulloff piston. Second method is "External" vacuum; there's a vacuum hose from a nipple on the front of the carb to a smaller nipple on the front of the choke housing. Requires a vacuum hose that's bigger on one end than the other end--or--you take a small diameter vacuum hose and fight it over the larger nipple; and replace it in about two years when it splits open.

Long discussion with photos on another post-- http://www.chevelles.com/forums/showthread.php?t=254549&highlight=pulloff+piston.


Also, the high idle cam is the plastic piece( in my case)behind and under the choke cap, correct?

Well, it's kinda between the choke housing and the carb body. There are a few different styles, but yeah, generally plastic.

Awesome information gents. Many thanks!!