Carb adjustment help

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Wageslave

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Jan 25, 2017
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I've got an '83 El Camino with a freshened up 350 and an Edelbrock 1406 carb. When I give it full throttle from a dead stop, it bogs pretty badly for 2-3 seconds and before finally taking off. If I only go 2/3 throttle it will do fine, and if I give full throttle from 10 mph or more it takes off like it is being shot at.

What might I need to do to get rid of this issue?

Here are my drivetrain specs:

1990 350 Chevrolet Truck Block
Comp Cams XE262 Cam
062 Vortec Heads
GM HEI Distributor
Factory exhaust manifolds with 2" true dual exhaust
TH 200 Metric Transmission (yup, it sucks)
2.73 Rear End (also sucks)


Thanks
 

pontiacgp

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Mar 31, 2006
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did you check the vacuum to make sure you have the right spring? Do you have an air/fuel mixture gauge?
 

airboatgreg

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Oct 2, 2016
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Sounds like the secondary's on the carb are opening to soon and/or too much
 
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Bonnewagon

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X2!! Greg is correct. Everyone loosens the secondary flap when it actually needs to be tightened. You want the primaries maxed out before the secondaries open. I'm not sure how you do that on an Edelbrock but on a Q-jet it is simple.
 
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TURNA

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How to Adjust the Secondary Air Flap on an Edelbrock Carburetor

 
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Wageslave

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Jan 25, 2017
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I don't have an A/F gauge right now as I have no O2 bungs in my factory manifolds. I am pretty sure that it is running a little rich on the primary's, but I haven't had a good chance to retune this carb from the old smog headed 350.

My initial timing is advanced as far as it will go before it starts running badly. I do have the advance hooked to manifold vacuum instead of ported, but it had some issues with dieseling before it was switched.

I will give the secondary flaps a check after I get the mower out of the garage.

Thanks for the advice so far.
 

Bonnewagon

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Turna- great vid. The procedure is the same as a Q-jet. The location of the adjustment screws is in a much better place. Thanks! Wageslave- does that cam number stand for 262° advertised duration? If so that would be a very streetable cam, perhaps ported vacuum would be more appropriate. I would also use the stock initial crankshaft timing specs. What kind of manifold vacuum numbers are you getting?
 

Wageslave

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Jan 25, 2017
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Sorry I have not been more responsive today but I have had the rear end off my tractor today fixing leaks and that was a nasty mess, but that is a story for another forum.

I am pulling about 14 in/Hg at 650 rpm. Here are the specs on the cam:

IMG_20170312_223821.jpg
 

Bonnewagon

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Hmmmm. I ran a Crane HMV-260-2 cam in several Pontiac V-8's and I always pulled 21" or better vacuum at idle. It is virtually identicle to your cam with 260/272 duration and .427"/ .454" lift. (Pontiacs prefer less lift than Chevies) It was a bit lopier in a 350 than a 400 but I wonder if something else is affecting your vacuum. Did you try using stock crank timing and ported vacuum to the distributor? I know some motors experience low vacuum and a crummy idle unless the vacuum advance is hooked to manifold vacuum. But what that does is give full vacuum advance at idle- covering up other problems. Are you using a stock intake manifold or something else?
 
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