Rochester Q-jet Float Setting - Team Camaro Tech
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post #1 of 5 (permalink) Old Feb 19th, 07, 06:55 PM Thread Starter
Join Date: May 2002
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Rochester Q-jet Float Setting

My '69 Camaro SS 350 has me confused concerning the carburetor. Last Summer of '06 I freshened up the original #7029202 Q-jet with a carb rebuild kit which also included a complete new accelerator pump and AC Delco #A46R float. After reassembling and installing the carb I test ran the engine and found that the fuel was leaking out of the front of the carburetor. Immediately I figured the float may have been mis-adjusted or stuck, etc.. during the re-assembly. To my amazement after pulling it apart again the float wasn't stuck, binding or mis-adjusted. With trial and error the end result was setting the float at 13/32" instead of the carb manuals instructions of a float setting of 7/32". From that time forward I have never experienced any fuel leaks or poor operation of the carb. All has been flawless.
Just recently I had the opportunity to purchase a #7029202 Q-jet core which I rebuilt and experimented by setting the float at the book spec of 7/32". Just today I pulled the original carb and installed the rebuilt core and did a test run. I received the same results with this carb with the fuel leaking from around the top section air horn gasket. The reason I tried the book spec float setting was to rule out a possible flaw with the original carb not accepting the 7/32" float setting.
Has any one else experienced this huge discrepancy in the float setting from the original book/service manual specs. I just can't believe that the service manual and all the related spec sheets in the rebuild kits are so severely off in this float setting.
One other bit of info. I installed a new AC Delco #40987 Fuel Pump about two years ago which is the correct pump for the SB 350. This to me rules out the fuel pressure being too high.
Can anyone shed some light on this problem. Thanks, Ray.......
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post #2 of 5 (permalink) Old Feb 19th, 07, 07:32 PM
Join Date: Aug 1998
Location: Waldorf Md. USA
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Re: Rochester Q-jet Float Setting

Stupid question, but where are you measuring the float ? Every Q-jet I have seen is measured at the end away from the pivot point. Most of the GM floats actually have a small "line" molded into the float at the correct spot to measure. I have probably done a hundred of them over the years and have always used the stock setting.

Also, how are you checking them ? I always hold down on the bail wire and then push the float down against the needle with another finger.

A lower float setting will usually work fine on a normal street car. It could run out of fuel if you made enough power and made a long full throttle run, but its doubtful.

Bill Koustenis
Advanced Automotive Machine
Waldorf Md
1971 Chevelle "Heavy Chevy" original owner

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post #3 of 5 (permalink) Old Feb 19th, 07, 07:50 PM
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Re: Rochester Q-jet Float Setting

I'm with you, Bill, when I was in the repair field, I rebuilt a LOT of Q-jets and always set the float to spec. I held the top cover upside down so the float seated the needle and measured to the molding line at the front of the float. If I remember right you need the bowl to cover gasket in the measurement too. That would drop the float down the thickness of the gasket, if he isn't measuring with it on the cover.

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Last edited by Lost in the 60's; Feb 19th, 07 at 08:05 PM.
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post #4 of 5 (permalink) Old Feb 19th, 07, 07:54 PM Thread Starter
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Re: Rochester Q-jet Float Setting

Bill. Thanks for the reply.

I'm measuring or gauging from the top of the casting down to the top of the float at the toe end. This is exactly how the Rochester 4MV manual shows to do it and yes there is a line molded in the float at the toe end. I've checked the setting just as you described by holding the retainer in place and gently seating the needle while measuring. I've also double checked this setting by holding the float bowl assembly up-side down while keeping the float retainer in place. Both measurements came out the same.
It's really got me boggled. I'm usally not heavy on the accelerator but I've been known to punch it before and have never experienced any hesitation or sluggish acceleration. She goes like a bat out of hell!! I'm surprised no one else has ever experienced this problem since I believe this #7029202 is a fairly well known carb from the 60's.

Thanks again for your input.
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post #5 of 5 (permalink) Old Feb 20th, 07, 12:36 PM
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Re: Rochester Q-jet Float Setting

I have yet to see a Q-jet that wouldn't run with the float set at 1/4 in but I think the float seting is not your problem. The carb top is warped because of overtighting of the front two mounting bolts. The only way to fix it is with a hammer, a block of wood and when you get it close a big file. The front two bolts do not need to be very tight. I stick a nylon washer under them and tighten very lightly they won't come loose.
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