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Discussion Starter #1
This is on a mild Olds 350 engine of 8.5:1 compression with a remanufactured QJet.

I finally discovered the throttle stop on the QJet and can see that the primary butterflies only open about 85 degress and the secondaries only open 50-60 degrees. Would this affect performance on an engine that requires much less than 750 cfm?

From reading a couple of books on QJets (with the new Ruggles book the best), it looks like I need to remove the carb, take off the base plate, and bend the stout looking throttle stop to allow more rotation of the primary throttle shaft.

Any guidance?

John
 

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Hates: Liver. Loves: Diesel
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NOOOOOO.....


Sorry, that was my dramatic panic mode :) Just kidding.

The throttles aren't supposed to open the whole way. The flow is kept turbulent by that little angle and opening it the whole way will cause terrible mixture inconsistencies and in general be a bad move.

You won't get any more flow by opening it the whole way, and you'll make a heap of problems, not the least of which is a worthless carb when you're done.
 

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Plus... even if it did restrict flow by 30%, that Qjet is still capable of supplying way more than your 350 can take.
 

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Discussion Starter #5
Well, okay.

Then any recommendations to make sure the throttle opens all the way only applies to engines that need the whole 750 cfm?

John
 

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Discussion Starter #6
I checked two other carbs I have, one is a 1988 electronic QJet off of a 307 and its primary and secondary throttle blades open fully 90 degrees before the throttle stop contacts the carb base. The other carb is a 1973 off of a 454 Chevy and it opens fully, also.

I don't understand why a 307 carb would open fully but a 350 doesn't need to.

I am looking at the opening of the throttle butterflies, not the air valve. The air valve will open fully but not the butterfies.

Are you sure the butterflies don't need to open fully? Sorry for asking the question a second time, but my other carb open fully.

John
 

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Discussion Starter #7
Mark,

When you don't do your own work on a streetrod, you can make a career out of first finding the mistakes and then figuring out how to correct them.

The new book by Cliff Ruggles answered some questions that the Roe book didn't. I have changed my primary jet/rod combination based on the Ruggle book and the car's off throttle response is better.

I have always thought the secondary opening was limited, and finally in the Ruggles book, on page 89, there is a picture of the throttle stop on the primary shaft that controls its opening, and then by linkage the secondary opening. But it is a really stout tab that looks hard to bend.

The pages you referenced in the Roe book (139-140) are ones I have read over and over with very little enlightenment. I think the procedure in the pictures are for quickening the pickup point for the secondary opening, not for allowing full rotation of the primary shaft. I could never find understandable information in the Roe book on how to adjust the primary shaft for full opening.

Thanks for your reply. I enjoy figuring out how these old cars can be made perform better, and there is no end to new adjustments I find.

Just last night I measured the driveline angles because the car has a little vibration or exhaust drone (not sure which) at 55-60 mph. Turns out the engine down angle is 2 degrees and the pinion up angle is 6.5 degrees. Not in the acceptable range. So there is a new problem to work on -- how am I going to rotate the differential down 4 degrees.

Talk to you later,

John
 

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I would have to agree that the PRIMARY blades need to open fully. Make sure it's not hitting the intake or adaptor, gasket ect...



I should read post better. :mad:
 

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Discussion Starter #9
Umm, didn't think about that. But, it looks like it would only take a little bending to get the primaries to 90 degrees. Or maybe I could grind the stop pad down.
 
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