marshal135

Hello,
I have a carb question for the forum.
I looked today at my carb to see what# is on it.
I recently purchased a 68 427/390 hp 4spd car.
I was told the carb was wrong when I purchased the car.
The car runs great.
I do need to pump the accelerator briskly till it fires up.
What is on the car now is a 209202 DH 0169.
Other sites report this as a 69 350/300 hp auto application.
Am I cheating myself out of more performance with this carb?
It gets decent mpg and runs great.
Other than application/year am I cheating myself on the performance side?
Thanks in advance for all responses.
I'd like to have the right 7028209 FG if I can find one and if its a big improvement.
Marshal

7T1vette

Basically, all Q-jets made prior to 1975 can be made to work on any engine requiring 750 cfm airflow or less. All that needs to be changed (for reasonably good function and performance) are the rods, jets and maybe some throttle/choke linkage connections.

If your carb performs well, is reasonably economical on the highway, and the spark plugs look good when you inspect them, that's all you need to know. The excessive 'pumping of the throttle' to get the car started could be an accelerator pump seal issue or loss of fuel in the carb's fuel well due to syphoning back to the tank after the engine is shut down. And, if performance is not a problem, then your accelerator pump is likely fine.

You may want to change the fuel filter and replace it with one that has a check valve flap so that fuel cannot back-flow out of the carb.

marshal135

Thank you for the education on the Q-Jet.
It is good to know what's on there is usable.
I see the cast# for my year and engine can be quite expensive.
The check valve in the fuel filter is a great idea like in my sump pump.
I wasn't aware fuel would drain back towards the tank.
Acceleration is good.
I'm new to the car so I'll drive awhile as such and monitor performance.
I'll check with the auto parts store for fuel filter with anti back drain feature.
Marshal

Ganey

If you are into perf., Holley makes a Q-J replacement DP. Also avail. as a VS.
Q-J are normally 750 & have very small primary. There is an 800 Q-J that has larger primary that would be good on 383+ even if more cfm was not needed. Any Q-J prior to the 80s electronic can be set up to work well.

You can check the accel. pump for a strong shot & there is normally an accel. pump adj.

Mike Ward

Contrary to myth, a carb different from a QJ won't get you more HP. There's been thousands of people who switched to a Holley or Edelbrock or brand X only to see no change.

Keep what you've got and tune it as required.

TWINRAY

Thanks for the tip - keeping the original Q jet for my replacement ZZ4 motor

cardo0

If u want the skinny on Qjets u need to read the book by Cliff Ruggles. The better Qjets came out in late '70s with electric chokes too. An original '69 Qjet won't make the power a later '70s series will.


Good luck,
cardo0

7T1vette

Actually, there are some changes to parts in a late 70's Q-Jet that need to be made so that it will perform as well as those from earlier years. I think you need to re-read Cliff's book.

rcread

I think his point was that Cliff said if you are going rebuild a carb, the later ones are a better choice than the earlier ones. Either way, you are going to have to build it for the engine that is in the car.

cardo0

U need to speciy what u think your talking about. What changes would a late 70's carb need that a 69 Qjet didn't??

But i do know an 800cfm qjet with APT will be an improvement over a stock '69 750cfm Qjet without APT. And the stock body plugs sealed much better than early year carbs too. Like Rochester was'nt improving their carb's? Its a no brainer they made big improvements to remain competetive. Maybe u need a tutor to help u read Ruggle book.

cardo0

SmokinBBC

In my experience, a BB with a properly tuned qjet will accelerate like a raped ape. If you are looking for satisfactory performance, sounds like you have it.

Ganey

Marshal
The 350 Q-J is probably lean & accel. pump weak. You can pull the sec. rods & check the 2 letter code.
Since you asked about performance I mentioned the Holley Double Pumper. Do you know what that is?

PS Regardless of a 350 Q-J that probably needs tuning, the stock guys basically say leave it stock & forget performance in which case a stock Q-J works good for economy.


Some might find this interesting.
CARBS Tests TQ/HP
http://www.corvettefaq.com/c3/carbcomparo.htm

Tim H

If you switch to a Holley and your car doesn't run better you better haul your old horse to the glue factory and cash it in now.

noonie

If you want to modify a qjet then a 76 or later is better.
The later carbs were improved for emissions are are extremely lean. At minimum the air bleeds have to be changed to be able to go back down in jet sizes so the available jets and rods can be used. The later carbs are already maxed out in jet and rod sizes in stock form.
Without getting too detailed, that is basically why a stock old qjet will outperform a stock later carb.

7T1vette

Correct. Later Q-Jets were made to be lean for emissions, not tuned/constructed for performance. The APT can be an asset to tuning, but having it is not a requirement for improving the carb's performance or function.

marshal135

Well Gentleman,
After a bit of jousting and a very informative thread, I've been comforted to know that what I have is working satisfactorily.
I do not want to smoke the tires off just enjoy it and if I step in it have it respond as designed.
I will eventually pull the secondary rods and report back what's in there now and see if any improvement can be made for wide open throttle.
Thank you again and much more informed.
Marshal

73, Dark Blue 454

Chevy Q-Jets to 1974 are basically the same. As stated above, rods and jets would be different depending on the engine and as stated above, 1974 and prior carbs are preferable for performance. They have a broader tuning range.

One thing I always do, since the Q-Jet's achilles heal is it's small fuel bowl, is swap to the larger needle and seat (.135" vs. the stock .125") which will allow the fuel bowl to keep up with demand if yo're running more HP. If you need, I can forward the GM part number.

Here's a great source for q-jet parts to help with tuning, rods, jets, etc.

http://www.carburetion.com/quadrajet.asp

But learn about the Q-Jet. The more you learn, the more you'll like it!

kf4cln

Can you give a name and possible location that I can find a backflow fuel filter ?
Thanks Rob

78anniversary

Go to NAPA and ask for part # 3052

marshal135

Thanks everyone,
I'm going to tune what I have and appreciate the responses.
Filter # was a bonus too
Marshal