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Discussion Starter · #1 ·
Hi guys just want seek some of the knowledge that is out here, A fellow hotrodder requested some of my help on his 67 chevelle, among some wiring issues that I believe I have fixed he has a performance problem I havent dug into that yet but maybe I can get some suggestions, this car was restored nicely but I have been told it was a body guy and he did not know much about the mechanical end...I have been told its a 68 396 from what I seen its pretty well stock and that is what he was told, the car idles really rich and falls flat on its face when trying to take off, the carb was just rebuilt and still if you turn the mixture screws in the idle does not change. I was told the following vaccum steady around 10 inches base time 12 BTC running HEI, carbs power valve is 6.5... from what I seen today it fires right up and idles nice, but it burns your eyes its so rich, under no load it took gas without much of a problem,,,The guy also told me he checked intake and carb base for vaccum leaks and found none , going back weds to finish up the wiring and start on the performance any suggestions would be appricated sorry this is so long and jumpy...

Thanks in advanced
 

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Lot's of possible causes. The first thing I'd check is the carb adjustment. If the idle mixture screws don't do anything, it's probably not idling on the idle circuit. That's likely due to the throttle being open too far. If it won't idle with the carb properly adjusted then there's likely a problem elsewhere. Elsewhere could mean a lot of things. Crossed wires, bad coil, fubar carb, slipped timing chain, fouled plug, mis-adjusted valve, etc., etc..
 

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x2 on getting the timing set right to start. I had a similar problem with my fathers when I got it running last year. Some sputtering, backfiring, etc upon acceleration. Got the timing set and it ran like a top.
 

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Discussion Starter · #6 ·
18 degrees with or with vaccum advance my thought would be with out and hopefully total would be about 36 correct ??
 

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18 degrees with or with vaccum advance my thought would be with out and hopefully total would be about 36 correct ??
Yes, 18º initial without vacuum advance but that figure only applies if your distributor adds around 18º. Unless the car won't be driven, total is much more important than initial. Set total to 36º and check where initial winds up. If it's not where you want it you'll need to recurve the distributor to get the proper amount of centrifugal.
 

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When you do everything else, start it up at night in the dark, and look for jumping sparks. If you don't see any, look at the cap and rotor for moisture and carbon tracking.

If it has the original Q-jet, it may be leaking from the welsh plugs on the bottom of the carb, making it rich. All you have to do to fix that is epoxy the plugs in so they don't leak. They used to make a kit for that. Was very common. If the car has been sitting for a while, the float valve may be leaking, making it run rich. If you can look down the carb while it is idling, and gas is dribbling from the venturi clusters, the float may be leaking. If it has a plastic float, it may be gas soaked and no longer floating, causing it to run rich. Get a new float.

If it has original exhaust manifolds, make sure the heat riser valve is working. Make sure the heat passages in the intake manifold are open. Make sure the carb has the right gaskets that do not block off the heat passages.

If it has an aftermarket manifold, like a Torker or Victor, if one plug is even slightly bad, it will affect all the other cylinders, and make a bog. They are not as forgiving as 180 degree manifolds. If it is running rich, I would look for a fouled plug first.

Make sure the centrifugal advance is working properly in the distributor. Make sure the rotor returns to to unadvanced position.

Put in some AC 45 type plugs. Find why it is running rich. That would be a good starting place. It probably has plugs in it that are too cold.

Do a compression check and tell us how it comes out. Take the coil primary wire to the distributor off while doing the compression test so you don't have any sparks flying around.

You should have more that 10" of Vacuum.
 

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Discussion Starter · #9 ·
Thanks guys you gave me alot to check and start with I should be heading back to the guys car Weds, I will start with the plugs, before I run it and get it hot, then go from there, thanks again for the feedback,,,, I will post my findings :)
 

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put a vacuum guage on the distibutor's advance port , ten bucks says thats your problem,, your timing is set to low. if you had a vacuum leaks around the carb then you would be running lean not rich, your problem is in the timing. and when you figure this out hold on to your hat , there's no replacement for displacement
 

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x3 (or x4, wherever we are) on 18* initial timing.
x2 on vac advance. Connect it to manifold vacuum.

These will let you get it to idle on the idle circuit, lean out you idle and improve response.
 

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Discussion Starter · #12 ·
Ok update time.... timing full advance 60 degrees yuck.... base is now at 15 with a total of 37 degress carb is adjusted idles around 800 at ilde mixture screws set with vaccum gauge, vaccum average 12 to 13 inches and fairly steady ..good squirt in carb . steady good flow. Plugs carbon fouled autolite 402 ?? replaced with ac rj44 no 45's in stock, now runs alot better but still stumbles from a hard accelleration and when goosing the throttle with no load ot still backfires through carb once in a while.. no back fire on roadtest..I moved the accel pump cam no real change.. so close but still not 100 percent and suggestions ??? BTW thanks for all the good info to get me where I am now :)
 

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Discussion Starter · #14 ·
Now it's time to increase the size of the shooters. See what # is stamped on there now, then increase it 3 number sizes at a time until the hesitation goes away.
What about the occasional back fire through the carb ? wouldnt increasing fuel increase the possibility of more pops ?
 

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A pop through the carb usually means it's lean.
 

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Discussion Starter · #16 ·
just the oppisite of what I thought.......Pens just scored 3 to 2 LETS GO PENS !!!!!!!!

Oh thanks for the lean info

:)
 
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