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Old 09-02-2011, 09:44 PM   #1
49trucknut
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Rochester Carb Troubles???

I just installed my professionally rebuilt Rochester single barrel carb from 1949 Chevy 1/2 ton truck with 216 engine. Tune-up went well - timing, dwell angle, idle speed, vacuum, fuel mix.... The engine sounds great.

Unfortunately, I'm having one problem. When accelerating or under light load, the engine stumbles, sort of like its not getting enough gas.

Is there an adjustment on the carb - perhaps with the accelerator pump, that can be checked or adjusted? Prior to having the carb rebuilt there was no hesitation when under load.

With the engine tuned so well, I'm sort of at a loss. Having only rebuilt the carb, it seems like this must be a carb issue. Any ideas what I might look for?
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Old 09-03-2011, 10:32 AM   #2
DeadZoneTruckin
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Go get a cup of coffee & read this.....

http://chevy.oldcarmanualproject.com.../5020mts00.htm
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Old 09-03-2011, 11:33 AM   #3
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Thumbs up "Rottenchester " carb

You could check if the floatation level is right , check your nozzles to. There *re not so many adjustment possebillety only air/petrol adj. screws.
I went the same road and finally changed the "Rottenchester" carb out with a remanufactured Carter YF with aut. choke and Stovepipe. Man that made a big difference. This carb is great for your 216/235 engines.

Good luck Martinius.

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Originally Posted by 49trucknut View Post
I just installed my professionally rebuilt Rochester single barrel carb from 1949 Chevy 1/2 ton truck with 216 engine. Tune-up went well - timing, dwell angle, idle speed, vacuum, fuel mix.... The engine sounds great.

Unfortunately, I'm having one problem. When accelerating or under light load, the engine stumbles, sort of like its not getting enough gas.

Is there an adjustment on the carb - perhaps with the accelerator pump, that can be checked or adjusted? Prior to having the carb rebuilt there was no hesitation when under load.

With the engine tuned so well, I'm sort of at a loss. Having only rebuilt the carb, it seems like this must be a carb issue. Any ideas what I might look for?
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Old 09-03-2011, 12:13 PM   #4
vwnate1
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Post Flat Spots

These engines have had this problem since new , make 100 % sure the vacuum advance unit on the dizzy isn't leaking (holds vacuum when you suck on it) and that there's ZERO vacuum to it when the engine is idling , vacuum tube connected .

Timing *must* be dead nuts ball on pointer @ 600 RPM's or less .

Then print out the Carby Service Notes book Joe posted & take it out to the truck with you......

Report back here if no go .

The Carter YF carby is simply hands down better but I use the Rochester leaks - a - lot Series 'B' because , well I dunno why I just do and it works fine even though it's damp at the joint , _always_ .

Learning to raise the engine off idle before letting the clutch out helps lots too .
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Old 09-05-2011, 07:43 PM   #5
49trucknut
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OK, I checked closer. I have a steady squirt or stream of fuel into the throat when I stomp on the gas pedal. I can also report that the vac advance is working and the carb piston moves freely.

Measuring the float per the GM Model B carb service manual, (float hanging down), I measure 1 15/16". The manual says I should measure 1 3/4". By my thinking, at 1 15/16" I would have less gas in the bowl. With no real experience in this area, I wonder is this 3/16" delta enough to be significant?

One new development - the air horn screw that also mounts the choke cable bracket was snug but not as tight as the other three screws. When I tried to tighten this screw to be consistent with the others, the screw stripped - well, not the screw but the carb bowl casting threads for this screw. This might potentially explain the sluggish behavior I suppose - if there was an air leak there.

Perhaps my shop friends can repair this - maybe with an insert or maybe just a larger tap/screw. So far, the only "real" issue seems to be with the float adjustment. I'm just not ready to believe it could be that simple... stay tuned, I'll report back after getting the screw fixed. Your feedback is welcome and much appreciated.
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Old 09-05-2011, 09:42 PM   #6
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Post Consider :

Sending it back as they didn't do a good job if they sent you a " rebuilt " on a bad core......

Once you begin screwing with it , they'll refuse to make it right .

Oddly , CARTER Carby Co. sells very good rebuilt Rochester 'B' series carbys , the host here carries this line .

Under $100 last time I used one .
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