General Category > Quadrajet Carb Talk and Tips
1970 350 quadrajet questions. 7040208
Chris_Oz:
The fuel inlet fitting I have only has 0.280
Cliff Ruggles:
The specs from the 1969 carb do NOT apply to your 1970 carb.
Even with the smaller metering rods it is too lean on the primary side.
Your 1970 model uses large MAB's near 1/8" and the 1969 and older units use very small MAB's. They are calibrated in a completely different way.
Not sure why you are using manifold vacuum to the advance, most of those used ported vacuum. Those tiny cammed truck engines don't need a lot of timing at idle and it can make the exhaust stinky (simulates a rich condition) if you put too much timing in them.
If the carb has a distributor port on the main casting in the front on the drivers side use it for the distributor VA.
If you would have called the shop I could have explained all this and set you up with a good kit and tuning parts for what you are doing.
If you were running "rich" with the stock set-up there is a fundamental issue someplace.
I stock the correct power piston spring as well. Trying to get the PP up really quickly is a crutch fix for trying to overcome a lean condition as the jets are too small and primary metering rods too large for that carb number.
That carb also has an APT system in the baseplate. I would try to use it. We make an external APT screw if you can get the factory one out. It usually takes a little work with a propane torch and penetrating oil, but once you get it out fine tuning becomes much easier without taking the top off the car IF you have the correct parts inside.
Anyhow, we've been having some issues with the website far as getting logged on and posting, sorry for the issues but if you want help with the carb call the shop and I'll get you set up with what you need......Cliff
Kenth:
I
Chris_Oz:
--- Quote from: Cliff Ruggles on December 04, 2019, 05:05:48 AM ---The specs from the 1969 carb do NOT apply to your 1970 carb.
Even with the smaller metering rods it is too lean on the primary side.
Your 1970 model uses large MAB's near 1/8" and the 1969 and older units use very small MAB's. They are calibrated in a completely different way.
Not sure why you are using manifold vacuum to the advance, most of those used ported vacuum. Those tiny cammed truck engines don't need a lot of timing at idle and it can make the exhaust stinky (simulates a rich condition) if you put too much timing in them.
If the carb has a distributor port on the main casting in the front on the drivers side use it for the distributor VA.
If you would have called the shop I could have explained all this and set you up with a good kit and tuning parts for what you are doing.
If you were running "rich" with the stock set-up there is a fundamental issue someplace.
I stock the correct power piston spring as well. Trying to get the PP up really quickly is a crutch fix for trying to overcome a lean condition as the jets are too small and primary metering rods too large for that carb number.
That carb also has an APT system in the baseplate. I would try to use it. We make an external APT screw if you can get the factory one out. It usually takes a little work with a propane torch and penetrating oil, but once you get it out fine tuning becomes much easier without taking the top off the car IF you have the correct parts inside.
Anyhow, we've been having some issues with the website far as getting logged on and posting, sorry for the issues but if you want help with the carb call the shop and I'll get you set up with what you need......Cliff
--- End quote ---
Thanks for the reply,
I live on the east coast of Australia, I have only just found your page and site, I appreciate your time to reply.
I don't know where to go with this carb now, The fuel inlet is stripped and I think its not really worth fixing. Shipping to and from the US is out of control, we pay import tax and duty on every item we buy or import, even if it was ours and we sent away for repairs, we are taxed when it comes back in.
I have a 1976 carb off a Pontiac Lemans, 400ci auto. 17056264, i got it off the original car owner and its dirty but all there.
I understand these are higher CFM, but given the way a Qjet works, should it be ok?
I have a milling machine and lathe and would love to repair my 704 carb if I could buy a tap/insert and helicoil kit at a reasonable cost.
Again, thanks for the advice, if this carb ever goes back on, I will use ported vacuum.
I have a 625cfm street demon on it at the moment (had spare on the shelf)and to be honest, it is running pretty well, it was rich out of the box, like they all are, but 2 sizes smaller on the primary jets and its getting 15mpg and goes fine.
I just want my Qjet back, so it is factory again.
Chris_Oz:
Hi again,
I also was able to get the Power Piston adjustment screw to move. I let it soak for a couple days in penetrating oil and it moved fine, I counted out the turns and reset it to the same when I re assembled it. It still had the factory plug/cover over it, so I would hope it was in its factory position.
It has a spring steel U shaped item it pushes on and moves the power piston up in its bore.
seems to work but limited with the movement as far as I can tell.
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