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 Post Posted: Sun Dec 25, 2011 9:12 am 
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I did a similar swap when I was a kid on a 283. ;-) Went from 2 to 4 with that kind of an adapter. I don't remember if it helped but it sounded cool when you put it to the floor. \:D/ \:D/ \:D/

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 Post Posted: Sun Dec 25, 2011 9:40 am 
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Sergey Quadrajet carbs are a little more complicated than your typical Holley but I guess you've already found that out. The primary metering rod carrier on some of these have an adjustable stop that hits against a pin mounted inside that carrier. There is also a spring inside there that is overcome by engine vacuum until WFO throttle allows that to decrease enough to pull the metering rods out of the main jets. Only thing I've ever done with those is change jets and if memory serves, most have a main jet numbered around upper 60s to lower 70s.

These carbs have a nitrofil float that sometimes gets saturated with fuel and then will no longer work correctly. Ethanol blends are usually harder on them than standard gasoline. Years ago I use to replace those floats with a brass one that was available at the local parts house. Not sure if they are still around though.

The single needle seats are what I would consider to be relatively small for these carbs in some instances, ie, performance applications. I use to modify the ones I raced by carefully drilling out that brass seat to a larger diameter but you must be careful not to go too large because of the needle's viton tip. Unless you're going to use this for a performance application I'd probably skip that part. Oh, and if you decide to do that I'd suggest that you use a lathe so you make sure that the hole will remain concentric with the body and screw threads that hold it in.

On the secondary side, fuel adjustment is done by two different things. The secondary metering rods do fit into a fixed jet. To change the amount of fuel delivered, you can use a metering rod with a smaller tip on it. The smallest I've ever seen were "AX" metering rods that came in carbs that were on 67/68/69 396 cu in BBC engines found in Chevelles and other passenger cars. There are also different metering rod hangers and the difference in those is their height. They have a letter stamped on top that identifies them but I can't remember which is which any more. If you have two different ones, then you should be able to determine this by looking at the two side by side.

The secondary air valve can be adjusted to make it open faster but there is a point you cross where it opens too fast and will create a "bog" when the throttle is snapped open. I think that screw that controls the spring usually has 3.5 turns on it from when the flap closes. That air valve also has a vacuum brake connected to the linkage. The vacuum inlet on the diaphragm has a brass insert in it with a tiny hole in it. The bleed off rate on that can be shortened up by enlarging that hole but again, too large and it will also add to the “bog” problem.

The secondary main wells on the bottom of that main body have what appears to be a lead type plug in them. Early on these plugs would begin to leak and when you fist started the engine you would get a puff of black smoke. Some rebuild kits came with a foam pad that fit into the base and when the carb was assembled that foam would help seal off that mainwell plug leak. This latest carb kit that I got for the over haul I recently did DID NOT have that foam plug but the gasket appears to be made of a different material than what I'm use to seeing. So maybe that gasket will help seal off any potential leaks from the secondary mainwell plugs.

More info to come when my old feeble mind can remember it.

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 Post Posted: Sun Dec 25, 2011 10:00 am 
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On the manifold thingie, IMHO you would have probably been better off trying to find a 500 CFM Holley two barrel carb. That carb would probably be much easier to adapt to that manifold and probably would perform better overall as well. And, there's plenty of Holley tuning knowledge here that you could tap if needed.

FYI, I've got an 83 Chevy 1/2 ton truck that has a 350 SBC engine with a Qjet carb on it. A few years back I swapped out the intake for an Edelbrock dual pattern one and drove it with that Qjet for a while. Then I ordered one of the Holley replacement 600 CFM "smog" certified carb and put it on that same engine and the truck not only ran better, but it got better fuel mileage as well. If memory serves the Holley was like 2 MPG better than the Qjet had been.

Ennywho, since you seem to like to tinker with stuff I guess it's all good in the end though.

Oh, on the secondary main jet thingie? All those things I've ever seen had what appeared to be a stainless steel fixed jet pressed into them and I have seen some evidence of wear on the metering rods (which are chrome plated brass) from them rubbing those fixed jets.

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 Post Posted: Sun Dec 25, 2011 10:29 am 
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You can also change the secondary metering rod hanger
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 Post Posted: Sun Dec 25, 2011 10:32 am 
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You can also remove the stainless steel ring that the secondary rods reside in and tap for regular jets.
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 Post Posted: Sun Dec 25, 2011 12:57 pm 
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Ken0069 wrote:
The secondary main wells on the bottom of that main body have what appears to be a lead type plug in them. Early on these plugs would begin to leak and when you fist started the engine you would get a puff of black smoke. Some rebuild kits came with a foam pad that fit into the base and when the carb was assembled that foam would help seal off that mainwell plug leak.


Those plugs were aluminum I think. It seems to me those plugs leaking would empty the bowl making a cold start with a mechanical fuel pump difficult. There were also repair plugs available that had o-rings on them. You would have to file off the peened over part of the casting and drill a hole in the plug so you could use a self tapping screw to pull it out. You had to use one of those foam pads to keep them from falling out.

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 Post Posted: Sun Dec 25, 2011 1:17 pm 
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On the well plugs u can use a apoxy on them
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 Post Posted: Sun Dec 25, 2011 6:55 pm 
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gearhead1011 wrote:
Ken0069 wrote:
The secondary main wells on the bottom of that main body have what appears to be a lead type plug in them. Early on these plugs would begin to leak and when you fist started the engine you would get a puff of black smoke. Some rebuild kits came with a foam pad that fit into the base and when the carb was assembled that foam would help seal off that mainwell plug leak.


Those plugs were aluminum I think. It seems to me those plugs leaking would empty the bowl making a cold start with a mechanical fuel pump difficult. There were also repair plugs available that had o-rings on them. You would have to file off the peened over part of the casting and drill a hole in the plug so you could use a self tapping screw to pull it out. You had to use one of those foam pads to keep them from falling out.


Yeah, I used more than a few sets of those "O" ringed aluminum plugs over the years but I've not seen any of them for years now. At some point along the way the foam pad appeared which was "suppose" to stop the leaks if there were any even in the bradded in factory plugs. The main body gasket I used on the one I rebuilt last week looked to be made out of a different kind of material, which leads me to believe that even if those mainwell plugs were to leak now, that fuel couldn't get out of that recess in the throttle body. That and there was NO foam pad in this new kit?? That kit I used was made by HyGrade and years ago they called them Jiffy Kits and they were made by HyGrade then also. So new gasket material and no foam pad must = no leaks even without the foam.

Ennywho, looks like Sergey is getting some good info for his rebuild. ;-)

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 Post Posted: Sun Oct 21, 2012 4:31 pm 
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Mixture screws in the later carbs were set at the factory and sealed, but you can knock the plugs out and adjust them. A chisel from the bottom of the base will cut through and usually take them out.


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