Author Topic: Buick Q-Jet 7043240  (Read 6200 times)

Offline oldsman70

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Buick Q-Jet 7043240
« on: February 09, 2009, 01:55:32 PM »
Cliff
 Have been reading your book , am confused on the subject , Air Bleeds . This carb has idle bleeds in the air horn also has air bleeds in the main body, upper and lower. I am using page 96 for the lower Idle bleed and page 27for the upper Idle bleed , the air bleed in the air horn looks like page 126 and is called main air bleed,
In your Third Recipe, page 113 , Is the bleeds in the air horn called upper idle air bleeds or main air bleeds. I notice If they are different settings by what they are called.
Am I off in left field and don't understand what i'm reading ?? Help me out.
Thanks Tom

Offline Cliff Ruggles

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Re: Buick Q-Jet 7043240
« Reply #1 on: February 10, 2009, 06:05:25 AM »
Your carburetor (1973 Buick) should NOT have any upper idle airbleeds in the airhorn, they should be just above the idle down channel restrictions in the main casting.

Basic rules for idle airbleeds.  All q-jets have lower idle airbleeds in the main casting.

There will be one pair of upper idle airbleeds, in one of two locations, not both. 

After 1975, they will be in the main casting for all models, just above the idle downchannel restrictions, haven't seen an exception to this aside for Marine units or Service Replacment carbs for older units.

Until apprx 1970, most models will have the upper idle airbleeds in the airhorn, with a few exceptions. 

Between 1970 and 1975, it we saw both styles, Chevy's using main casting upper idle airbleeds, and Pontiac having them in the airhorn, for example.

Here's the bottom line on the upper idle airbleeds, if you see 4 holes in your airhorn inside the choke housing, two of those holes are going to be upper idle airbleeds.  They will be the pair closest to the front of the housing.

If you look in and only see two holes, those will be main airbleeds, and will directly above the main fuel supply passages to the boosters, when the airhorn is placed on the main casting.

We see some mixing a matching of airhorns, and a high percentage of commercially "remanufactured" carburetors may have blocked of one pair of the upper idle airbleeds, in attempts to produce a "generic" carburetor.

Some well meaning carb builders also mix and match parts, which can also produce a carb with two pairs of upper idle airbleeds, although that particular carburetor is NOT going to work well.

Offline oldsman70

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Re: Buick Q-Jet 7043240
« Reply #2 on: February 10, 2009, 07:43:27 AM »
Hummmmmmmmmm , I just checked the other Buick carb and one of the oldsmobile Q-Jets 7042251 , they have the same thing ????? the area I am speaking of is the brass holes in the air horn right next to the screws choke housing. Is this called main air bleeds ? What does it bleed ? On page 96 it shows the air bleeds that are in the housing I have , Plus the brass holes in the air horn. Hope I'm not being to much of a pain , Tom

Offline oldsman70

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Re: Buick Q-Jet 7043240
« Reply #3 on: February 11, 2009, 12:25:20 PM »
OK Cliff , I am a Dummie , after reading and studying and a little shop inspecting The Buick and the oldsmobile Q-Jet Do not have idle air bleeds in the air horn . The Bleeds in the air horn are Main Air Bleeds.Thanks for such a great book . I should have done some closer inspection in the first place. I am sure I will have some more dumb questions in the future.
                                                                                      Tom

Offline Cliff Ruggles

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Re: Buick Q-Jet 7043240
« Reply #4 on: February 11, 2009, 03:32:26 PM »
No problem.  Just keep in mind that regardless of model, there are always at least one pair of main airbleeds in the airhorn, even if they are angled brass tubes.

Any time you see two pairs of airbleeds inside the choke housing, one pair will be idle airbleeds, they are the pair closest to the front of the housing.

It always pays to check both the main casting and airhorn on any carburetor you are working with,  to make sure the wrong top hasn't been swapped in and we have upper idle airbleeds in both places, which will not work well......Cliff

Offline oldsman70

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Re: Buick Q-Jet 7043240
« Reply #5 on: February 26, 2009, 11:14:23 AM »
After I get the the base plate back from you , I am going to convert this carb to the race version ( remove the power piston , spring and pri. rods ) I have been runing 74/75 main jets , the smallest main jet I have is a 68 . Do you stock smaller ? Just for info what # main jet do you run in your Pontiac ? I also resized the lower idle air bleed as it was right at .080 , the upper was  .070 Now they are 70/70 , the main air bleed is .052 I think that should be ok for a main jet of 66/69 , Think ?
                                                                                                             tom

Offline Cliff Ruggles

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Re: Buick Q-Jet 7043240
« Reply #6 on: February 27, 2009, 06:54:09 AM »
Yes, we stock jets from 65 to 77.  I'd start out around 65-66 and see how it acts, should be pretty close.  I use 65 main jets in my own carburetor....Cliff