I posted this over in the Regal Modified area.. http://v8buick.com/showthread.php?t=208132 After reading several pages of responses over here in the Q-jet section, I'd like to hear your take on it. I posted that as a quote i have from that thread, to make a correction, I replaced the primary throttle shaft with one from that of the 80's 454 Chevy truck, to get my TV Cable for 2004R to work. Another thing too, is that my choke plate in the primaries is wired open all the time,( never did the choke coil installed, because I do't drive it in the winter, didn't know if that being that was a cause or contributing cause, never did replace the choke pull-off vacum valve when I rebuilt the carb. I also staked the plunger that always kept coming out when hammered. Now with that said I will check my hard lines to the tank when I replace the fuel sending unit. I want to get this sorted out so I can a full throttle complete pass at the BPG Nats. Thanks Guys
Carb#7041540 Definitly need to replace the secondary air valve vacum piece, I removed it pushed the plunger in and put my finger on the end of the tube, and it popped right back out. I read somewhere its Standard Part #CPA38? Now not being carb smart, there is a second vacum pot of sorts at the rear lower passenger side of the carb, removed the rubber line, did the same test, didn't hold....... what part is that and a replacement part #? and does/should it be replaced? Those Secondary flaps flip down very easy even if you breath on them, so adjusting them is in order, (adjusting the tension spring) . Can tightening up the secondariers be done without the engine running, the carb still on the intake and with no secondary air valve vacum piece in place? thanks guys
You need a primary choke pull off part# Q3801 (Plastic vacumm diampham on front pass side of carb) and you also need to adjust or replace sec. air valve/flap spring part # Q2702. These 2 fixes should eliminate your bog. Also pick up a good Q-jet book to learn about the Q-jets, I carry 2 books on Q-jets. Rear or Secondary pull off (towards rear passenger side) is not manditory for racing but can be replaced with part # Q3851. Give me a call if you need more info.
Greg Thank you for the response . That part# Q3801 , whos brand is that? Standard, Hygrade or GP Sorensen? Is that something I can pick up locally like at a Auto Zone, Carquest or NAPA... or something like that? Other than the quirk of the bogging and stumble I really enjoy my car.. low budget built. and FUN!! BTW Your SLEEPER 72 GS is awesome!! Like the write up that HodRod did. never knew one could that much from a cast iron heads,manifold,and exhaust manifolds.. amazing. Thanks for letting out "some" of your secrets.:TU:
I don't know if those brands use the same pulloff that I use and rebox them or not. I can't amagine that there is more than one company making this increasinly hard to find parts. If you need one, I keep them in stock.
A throttle shaft from a 1980 Chevy truck carburetor does not fit a 7041540 carburetor. It is too long, and none of the choke hardware will work. I would also replace the secondary plastic cam, and the spring. The cams wear down, cracks, and get loose on the shaft. They are seldom replaced during rebuilds, and a big contributor to stumbling off the line, bog, hesitation, etc. I would also upgrade the accellerator pump to a later style pump with Viton seal. The later pumps use a garter spring to keep the seal in contact with the pump bore for improved fuel delivery from the pump. Early pumps have weaker springs, and are another contributor to poor full throttle performance......Cliff
Several things follow Cliff's observations on this. First, if the choke does not operate correctly, there will be a bog, hesitation, stumble off idle during warm up. If the choke pull offs do not work, the choke will require non-standard adjustments for them to work. With respect to the accelerator pump "skirt," bear in mind that these were borderline at best in the '70's, with the crap we called fuel back then. With the fruit salad we now call fuel, these may not work immediately after installation, never mind after a year. These chemicals attack these compounds immediately, which will destroy the interface in a very short time. Also, with respect to fuels, it may be necessary to tune for the fuel you are using, especially for off-brand fuels. There are various parameters affecting their chemistry that directly affects their performance in a carb, most of which is tuned out using the fuel injection computers. Also, with respect to Cliff's recommendations, the secondary metering rod cam frequently wears out, cracks, etc, making tuning the secondaries impossible. The way to do this is to first, go back to factory stock. This gives to a place to start. Check the advances, both centrifugal and vacuum, and get both the choke and the heated air cleaner working. Both of these directly affected the carb metering. Make ONE change at a time after that, carefully evaluating the results. Let us know... Ray
Cliff R & RAbarrett Thanks for the responses. Cliff R I still have the orginal throttle shaft I can switch back to, but how do I get my TV cable for my 2004r to adapt or work correctly? I pick up the secondary vacum piece tonight and I will get it installed, i will order the primary choke pull off too. I will go back to factory as much as I can......( still missing the rod to to the primary choke plate, and all the fixxings need to to run the choke from the manifold.. I have the Eldelbrock Performer intake. Now with that said I do have a "76" carb #17056540 , untouched , after reading as much as I could in this Q-jet forum, I ran accross a thread stating that the 76 Carbs were better. http://v8buick.com/showthread.php?t=205707&highlight=76 Should I work with that one? still 800 cfm right? Will I have to change the jets and the needles and seats? to get the performance of what Im used too? RAbarrett I will replace that, the cam and springs on the secondariers no matter wich carb I use. Again thanks Guys
The hardware from the later shaft can be installed on an early/shorter shaft in minutes. Grind off the staked portion and gently drive the shaft down thru the parts on the end of it. You really only need to change the outer linkage in most cases, but all of it will fit the early shaft. Once in place, we MIG weld them here. I've seen others drill/tap and hold the parts in place with a screw. Aftermarket replacment shafts also use a screw to retain the parts, but I'm not at all comfortable with that set-up, MIG welding them in place helps me sleep better at night. The 71-74 Buick 455 carburetors are among the very best of the Q-jets, and the only large CFM divorced choke units. 1975 and later units have a few nice features, but not any better anyplace than the large cfm early Buick carb, unless you need an electric choke on the carb. We actually use the 71-74 Buick main castings to replace Pontiac center castings for high HP applications, some classes of racing, etc......Cliff
