[Forrest]

hey Dan, I own a 72 h/o and have been looking for a carb for mine, and saw your mess. about the carbs, I remembered seeing this in the 72 service man.; the 72 carb also has the second boost venturi removed, and the small boost venturu skirt lengthened to increase air flow, so which carb do you think flows the best? thanx Forrest

[Forrest]

hey Dan, I own a 72 h/o and have been looking for a carb for mine, and saw your mess. about the carbs, I remembered seeing this in the 72 service man.; the 72 carb also has the second boost venturi removed, and the small boost venturu skirt lengthened to increase air flow, so which carb do you think flows the best? thanx Forrest

[Rocky Rotella]

1972 455HO Q-jets are of the normal 750cfm casting. The 1971 455HO Q-jets (7041267, 7041268, 7041270, 7041273) were the only carbs to have the primary booster ring not cast in. The booster ring delete help curb nozzle drip and increased air flow to 800cfm. That is what makes them so desirable for performance.

[Dan Jensen]

Forrest, I agree with what Rocky has said above. All '72 Q-Jets, even 455 H.O.s, were of the normal 750 cfm casting. Only the '71s had the modifications for increased flow capabilities.

The '71 400 manual transmission Q-Jet, #7041263, is like the H.O.s, where it lacks the booster ring for added flow.

[Rocky Rotella]

Dan, I was unaware that the 7041263 was also a non-booster ring carb. Have you personally seen one of these carbs or is that just what you've heard? I don't doubt you, I just want to know for my own records. Thanks for the help Dan. Rocky

[Forrest]

hey guys, according to the 72 factory service man. the 72 ho carb.(#7042273,man.&7042270 auto) only, also has the venturi boost removed, if this is so , then would`nt it flow the same as the 71 ho carb? being that the standard 455 carb for the 72 flows 750, then with the booster venturi removed for the 72 ho only carbs ( according to the factory books for more flow!!??) it must flow more than the standard 750 455 carb, right ! thanx , I here what you guys are saying about the 71 ho. carb but according to the books the 72 is the same??!! well whatta ya think , Im confused Forrest

[Rocky Rotella]

Forrest, with the outer booster ring removed, the carb will flow 800cfm. What manual are you referencing to? Is it the 1972 Pontiac Service Manual? If so, what page? I have the 71 and 72 Pontiac Service manuals so we'll look at this together. Rocky

[Rocky Rotella]

Ok, I just read the 1972 Pontiac service manual. Page 6B-59 states that the outer ring is removed on 455 HO carbs. I compared the text of most of the chapter and it is a direct carry-over(reprint) of the 1971 Pontiac service manual. I believe, and hopefully Dan will agree, that NO 1972 455HO Q-jets were of the 800cfm variety. I have seen quite a few 72 455HO cars and I know that none had the 800cfm carb. I was under the impression by experience (and from the factory service manual) that the non-booster ring 71 Q-jet was available on the 1971 455HO. I didn't think that the non-booster ring 800cfm carb came on any other Pontiac that year.

[Forrest]

thanx Rocky, well you would think that the 72 ho carb having its own part #( different than the standard 455) and being for a "ho" motor would flow more!( especially w/ ram air) according to the book it does. Soo, does anybody have a 72 ho carb that can look at the venturis , and tell us if in fact the booster ring is in fact removed for more flow according to the books!! ( hopefully someone can tell us if pontiac scimped a little on their 72 ho carbs!!??) weelll seee thanx all, Forrest

[Dan Jensen]

The '72 service manual was never updated to incorporate the changes made to the '72 455 H.O. carbs, i.e., they had the booster rings like the rest of the '72 lineup. The '72 service manual is doing a disservice to those with '72 H.O.s. I've seen a number of '72 H.O. carbs (7042270 and 7042273) with correct date codes, and they all had booster rings. No doubt they were re-installed to help the H.O. meet tighter emission requirements.

The '71 7041263 400 manual trans carb has been a hot commodity the past few years as more and more people (like '71 H.O. owners) have discovered that it was a cheaper alternative to buying the "real" thing. Because of its sudden popularity, its prices have risen as well, but not to the extent of the H.O. carbs. I have several of these 400 carbs that I bought from the local speed shop, all without the booster rings. Most were plumbed for a transmission vacuum modulator during remanufacturing! (Sorry, these carbs have been sold out for a few years now.)

I hope this clears up some of the confusion!

[Leonard Welch]

Goodness! I have a '71 WK code 400 4 speed convertible...242671P111920...with a 7041263 carb. I've always heard that it 'could' be an 800 cfm. Nice to hear that it is definitively! I was going to trash it because it runs terribly when the secondaries open up. It's a hesitation, skipping, kinda what I call a 'flutter'. Any ideas?

[Dan Jensen]

Hi Leonard,

There could be a number of causes for your carb to hesitate when the secondaries open up. My first instict would be to check to see how loose the secondary air valve is adjusted. Its adjustment is more critical on manual trans cars. (Automatics can mask a lot of troubles due to their slipping convertors.) If it feels too loose, try tightening it up with a quarter-turn on the spring-adjustment screw. Hopefully, the hesitation will go away. If not, my next suggestion would be to try richer secondary metering rods, or try a lower-lettered (closer to "A") hanger to raise the rods a little for a faster transition to the power mixture.

Let me know what you find out.

[Chiefpontiac]

Your symptom could also indicate a faulty choke pulloff. The choke pulloff on a Q-Jet is responsible for more than one function. One of them is sensing the load on the engine. When vacuum is high, as at idle, the pulloff holds the secondary air valves (flaps) closed until the engine revs up and vacuum drops. When you floor it from a stop, vacuum drops and the pulloff holds the secondaries closed momentary until the rpms come up to match the load. If the pulloff is faulty, the spring Dan discussed is the only thing holding the secondary air flaps closed and you will get a bog or flutter upon acceleration.

[mike nixon]

Another item to look at is the sec. air valve[flaps]. Make sure they aren't sticking closed. If the car runs bad and loads up when cold check the pull off first. You also may want to check for vac. leaks that may be affecting the pulloff's operation. Hope this helps. If you're still thinking about throwing your carb out than throw it my way! mike nixon