newly rebuilt rochester quadrajet woes - Team Camaro Tech
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post #1 of 10 (permalink) Old Aug 26th, 09, 02:45 PM Thread Starter
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newly rebuilt rochester quadrajet woes

after problems with vacum leaks at the base bushings and a stuck accel pump I had the carb rebuilt by a reputable carb shop.
every carb he built for me worked flawlessly.
except this one.
ok mixture screws set at 4 turns out
19" of vacum
no external vacum leaks.
primaries work great but once I get into secondaries it sputters and breaks up a bit.
doesnt seem to open secondaries at all?
but in park and operating without a load they open?
any ideas?
Im a holley man and this quadrasuck is a pita!


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post #2 of 10 (permalink) Old Aug 26th, 09, 04:04 PM
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Re: newly rebuilt rochester quadrajet woes

I wonder if you need to tighten up the sec. spring on the pass side just below the choke arm connection. You need an alan head and a small flat screw driver. Hold the screw steady before you losen the set screw(alan) then add just a tiny tiny more preasure to the spring tension. That will hold out sec till you need them. Your primarys could be too small and it goes lean if the sec open too early. The q-jet needs overlap between idle, primary, sec. It can be set up to be seamless thoughout the ranges well.
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post #3 of 10 (permalink) Old Aug 26th, 09, 04:39 PM Thread Starter
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Re: newly rebuilt rochester quadrajet woes

ill try that thanks


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post #4 of 10 (permalink) Old Aug 27th, 09, 03:44 AM Thread Starter
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Re: newly rebuilt rochester quadrajet woes

took car out this morning and secondaries open?
I hate intermittent problems.


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post #5 of 10 (permalink) Old Aug 27th, 09, 06:24 AM
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Re: newly rebuilt rochester quadrajet woes

You'll hear the secondaries open on a Q-jet, just like Krass & Bernie comics, WA-AA-AA!

This is also a choke lockout on top of the air horn pass side. If choke plate is partially close, this lockout will prevent the air valve from opening up. Check to make sure the exhaust crossover is open under the carb so the divorced choke heats up enough to open the choke, or shorten the choke linkage to adjust the stroke.

Once the choke potential problem is fixed or found to be working correctly, snap carb from idle to WOT and transition to WOT throttle should be smooth. If air valve opens too fast, the engine stumbles; if too slow, engine is lazy. You will not be able to get the secondaries to go completely open sitting in neutral, but you will be able to see/witness the action of the opening secondaries.

As said. you can adjust the the spring controlling the opening point of the airvalve witha 3/32" Allen wrench and a 1/8 inch flat blade screwdriver. Books/papers suggest 1/2-3/4 turn of the spring is correct, but I have found more than full turn is needed. After adjustment, its trial & error on tension; 1 turn almost, another 1/4 turn is better, but still there, etc., etc.

Also, another factor in engine acceleration is timing. You may need to advance initial timing to help.

Good job on acquiring 19" of vacuum - leakfree intake system.

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post #6 of 10 (permalink) Old Aug 27th, 09, 06:33 AM
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Re: newly rebuilt rochester quadrajet woes

If adjusting the secondary air valve doesn't fix the problem or doesn't make much of a difference take a look at the secondary rod hanger.

"Incorrectly Adjusted Secondary Rod Hanger Height Results in: Lean secondary performance, flat spot going into the secondaries, poor WOT power.

Comments: It is common for the secondary rod hanger to not pull the rods up out of the metering holes adequately. This produces a lean condition with associated poor power. The distance from the top of the choke rear airhorn wall to the center of the rod holes with the secondary airvalve in the wide open position should be 41/64.

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post #7 of 10 (permalink) Old Aug 27th, 09, 06:54 AM Thread Starter
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Re: newly rebuilt rochester quadrajet woes

Quote:
Originally Posted by Everett#2390 View Post
Also, another factor in engine acceleration is timing. You may need to advance initial timing to help.

Good job on acquiring 19" of vacuum - leakfree intake system.
yes i advanced to a point of engine running rough. (too far advanced)
then backed off.


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post #8 of 10 (permalink) Old Aug 27th, 09, 08:54 AM
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Re: newly rebuilt rochester quadrajet woes

Have you checked to see that the secondary accelerator circuit is working? The tubes are in place and at the proper height? The wells are filling properly? If you open the secondary butterflies while the engine is idling then push the air valve open slightly you should be able to see fuel emanating from the accelerator ports.

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post #9 of 10 (permalink) Old Aug 27th, 09, 02:57 PM Thread Starter
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Re: newly rebuilt rochester quadrajet woes

ok all is well
found the carb just needed a tweak here and there.
but the secondaries problem was that they didnt open up all the way.
throttle linkage was way out of adjustment.


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post #10 of 10 (permalink) Old Aug 27th, 09, 04:52 PM
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Re: newly rebuilt rochester quadrajet woes

Cool!

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