Rebuild the carb or not?

[ChevyGuyNC]

I've got a 72 Cheyenne Super, 350/350... 47k original miles, and she runs good, not great...

Recent plugs, wires, coil, points, condenser, rotor, cap, etc...

Adjusted everything with vacuum gauge and timing light. 8* timing, 15" vacuum.... idles nice at 650 or so when warm...

Truck runs really good, but she stumbles when cold, and even when warm there's a hesitation if you goose her.

I poured some Berryman down the carb, and dumped a can in the tank, and that made a difference, but the hesitation is still there.

So, thinking carb needs a rebuild.

Thoughts?

[kwmech]

Possible small vac leak somewhere. take a 1/2 wrench and see if the bolts holding the carb down will take a little twist....don't over tighten. Accelerator pump could be bad if it is original from '72. New gaskets and a float may help things out. Did you check the vac advance?

[Wrenchbender Ret]

Sounds like a carb cleanout is in order. Like KW says, the accel. pump is probably bad. The metering rods may be stuck. If you think you are qualified to do it yourself go after it. Don't let just anyone do it though. You don't want it butchered. Of all things don't exchange it for a "reman".
George

[kwmech]

Originally Posted by Wrenchbender Ret

Of all things don't exchange it for a "reman".


George

Absolutely---keep the original carb with the engine

[Caddylackn]

If you have the factory Quadrajet, get the Cliff Ruggles Quadrajet book. He sells quality rebuilt kits specific for your carb https://cliffshighperformance.com/.

He also has a forum to post up questions (which he will reply to) and view other rebuilds in progress.

[68Gold/white]

Posts 3 and 5 are the gospel about carbs!!!!

Is it a Quadrajet carb???

[geezer#99]

A slight stumble can be caused by retarded timing.
A 47000 mile timing chain can stretch enough to reduce your initial timing 4 degrees.
Instead of setting your timing at 8 degrees just bump it up to 12 degrees. After you bump it up adjust your mix screws on the carb and turn the idle back down. You’ll likely gain 2hg of vacuum too.

If you want to check timing chain stretch just pop the distributor cap off and rotate the crank forward and back and watch the rotor movement.

[LT7A]

Good info being shared here. Makes me think of people who had vehicles that they liked, but just got tired of them never quite running right.

[ChevyGuyNC]

Originally Posted by 68Gold/white

Posts 3 and 5 are the gospel about carbs!!!!

Is it a Quadrajet carb???

Yes, Rochester Quadrajet 7042210

Thanks for all the replies. Sent a quote request to Cliff's and been reading through the forum there.

[MikeB]

Originally Posted by geezer#99

Instead of setting your timing at 8 degrees just bump it up to 12 degrees. After you bump it up adjust your mix screws on the carb and turn the idle back down. You’ll likely gain 2hg of vacuum too.

Good idea on 12 degrees initial advance. Yes, vacuum on a stock engine should be more. I'd say at least 18", even for an engine with more miles than yours. You may have a leak somewhere.

[dmjlambert]

Did you replaced the fuel filter? There is a holder for the filter in the carburetor front inlet and there should be a spring behind the filter. Be careful not to cross thread or over tighten the inlet.

[MikeB]

Originally Posted by Caddylackn

If you have the factory Quadrajet, get the Cliff Ruggles Quadrajet book. He sells quality rebuilt kits specific for your carb.

He also has a forum to post up questions (which he will reply to) and view other rebuilds in progress.

Excellent advice!

[ChevyGuyNC]

Originally Posted by MikeB

Good idea on 12 degrees initial advance. Yes, vacuum on a stock engine should be more. I'd say at least 18", even for an engine with more miles than yours. You may have a leak somewhere.

I'll give the timing a shot. I could be wrong on the vacuum; my memory isn't what it used to be. I'll check it again tomorrow.

[ChevyGuyNC]

Originally Posted by dmjlambert

Did you replaced the fuel filter? There is a holder for the filter in the carburetor front inlet and there should be a spring behind the filter. Be careful not to cross thread or over tighten the inlet.

Yes, new filter.

Interesting anecdote about the filter. A friend I met who has lots of experience with carbs mentioned that he always takes the paper filter out and uses an inline filter. He said the paper ones aren't made for today's gas and they get clogged easily.

[Steeveedee]

I think that the reason the paper filters fail is because the new fuel has alcohol, which loves water, and the paper filters don't.

[chevmn]

No one has mentioned, but one of the biggest issues with Quadrajets is the float. I learned this the hard way years ago when I tore one down several times, and finally took it to a guy and asked him to rebuild it. The next day he had it done, and told me the float was saturated (he weighed them), so he replaced with a brass float. I always buy kits with brass floats now, and no more issues with floats. If your has the "fiber" type float, and it has been in there a while, my bet is it is heavy and or sunk. Also check primary throttle shaft for play.

[ChevyGuyNC]

Talked to Cliff, and ordered a kit plus a choke pull off.

What a great knowledgeable guy.

Thanks for all the tips!