QJet Secondaries Only Open 60 Degrees - Hot Rod Forum : Hotrodders Bulletin Board
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Old 11-27-2005, 11:24 AM
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QJet Secondaries Only Open 60 Degrees

Engine is a mild Olds 350, 8.5:1 compression, Performer Plus cam and Performer intake. HEI ignition with 18* initial advance as is typical for Olds/HEI cars -- plus 16* mechanical at 3500 rpm.

Acceleration isn't real strong and trans upshifts from first at 4000 rpm and second at 3000 rpm. So, wondering if secondaries are opening all the way. Have checked air valve spring and loosened it from 3/4 turn to about 1/2 turn with no change.

Anyway, when opening the throttle by hand at the carb, it looks like the throttle blade shaft only opens about 60 degrees -- doesn't go to 90 degree verticle.

Does this matter on a mild engine?

Also, I don't see the air valve open when I blip the throttle. Is this because the vacuum pull off doesn't have time to release the air valve lockout with a momentary blip?

Thanks,

John

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Old 11-27-2005, 12:52 PM
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if the car is shifting that soon at wide open throttle, then the kickdown cable needs adjusted. adjusting the secondarys on the carb won`t change the shift points.
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Old 11-27-2005, 01:00 PM
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engine off , hold open with hand, take finger and see if you can push blade open to 90 degree, a bile of engine will not open carb blades
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Old 11-27-2005, 01:25 PM
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Quote:
Originally Posted by JohnTN
Acceleration isn't real strong and trans upshifts from first at 4000 rpm and second at 3000 rpm.

Anyway, when opening the throttle by hand at the carb, it looks like the throttle blade shaft only opens about 60 degrees -- doesn't go to 90 degree verticle.

Also, I don't see the air valve open when I blip the throttle. Is this because the vacuum pull off doesn't have time to release the air valve lockout with a momentary blip?
Thanks,John


May be a bad vacuum modulator or governor problem on the TH 350 transmission (you didn't say what trans you have). Modulators articulate the governor operation... Modulators are adjustable also.

The smaller GM engines with Quadrajets the secondaries do NOT open all the way. Period. They are mechanically restricted to prevent overcarburetion. I have a factory (Pontiac) car that only opens about 1/2 WAY. (you don't need 800 cfm kicking in)

The air valve will only open with sufficient air suction. You are probably not going to see it move (much) just revving it up.


check out www.readershotrods.com drag cars/georges drag strip
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Old 11-28-2005, 01:34 PM
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xntrik,

Trans is a Th200 4R so no vacuum modulator.

The shift cable is set for delayed shifting, so I was thinking that the engine just isn't putting enough load on the trans to keep it from upshifting. But, it sounds like the partial opening of the secondary throttle blades is not what is holding it back.

Thanks,

John
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Old 11-28-2005, 02:30 PM
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Hi John... For the trans question, i'd suggest asking either Crosley or Airworld on the "transmission board" on this forum. The TV cable must be set correctly or you will suffer some really bad trans problems.

For the qjet questions, the secondaries won't open when "bliping" the throttle. The choke pulloff has to unload before the secondary top butterfly will open.

Like others have said, the secondary butterfly is preset according to the stock factory setup that its used on. Some open to 45 degrees, some to 85 and all the ways inbetween. If you think you need more opening, you can file the limiting tab on the pass side of the secondary butterfly. Personally, I set mine to 85 degrees. Anything past that is supposed be a hinderence to the performance. You can do it on the car with some patience or pull the lid and get better access to the limiting tab.

Mark

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Old 11-28-2005, 04:21 PM
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The secondary throttle shaft and plates (NOT the air valve) are not designed to open to 90 degrees. If they do, the airflow aroung the metal plate in the secondary bores in the center section is disturbed, decreasing airflow. This can be corrected by altering the opening linkage on the throttle cable side of the carb.

tom
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