Projects 1946 Chevy COE 216 wont come off idle

It idles great and did before this engine but doesnt like to come off of idle and will slow and die no matter how much you play with the pedal. All the tune up parts are new and set as correctly as i can set them to standard specs and the carburetor has been rebuilt. The shop that rebuilt the carburetor tests them on a good engine before shipping them back. I put inline filter and good gas in a clean tank. New hoses for vacuum wipers that work and new hoses for 2speed rearend. The engine is on standard pistons and was rebuilt before me. Had the head worked on and has 120lbs in each cylinder. The intake and exhaust has been checked for cracks and welded and machined flat. All new gaskets.
When the original engine did this it was exactly the same. So the only part that they share is the rebuilt carb. I think its the carb. New plugs that idled for 5 minutes came out dark black. Not wet. So i think the carb is running really rich. Just not sure why it idles so good but wont rev up.
Valve lash set. New advance that works good. New coil. New everything.
Motor doesnt smoke at all.
New fuel pump and i am running clear gas with a lead additive.
Alot of work put into this truck only to have the same problem.
Its got the updraft carb and its not easy to get at. But i will say that this time around the carb doesnt dribble gas out of the bottom little hole. It did before the engine swap.
Any ideas on what this problem could be?

 

plugged exhaust? i had one that was packed with a mouse nest so tightly it wouldn't even start.

 

This reminds me of the Rochester carbs with power valve springs, that will make the engine sputter or die when coming off idle if the wrong springs are used.

I looked up the carb used for 1946 and your truck and it looks like if you have the original Carter BB1 - 517S it uses two power valve springs .... (scroll down)
http://www.carburetor-parts.com/Carter-BB-1-Updraft-Carburetor-Kit_p_940.html

Don't know these carbs, but you can contact @carbking who can probably help if it's carb related.

 

Does it sputter or back fire?
From what your saying it slowly dies out as your accelerating?

Plugged exhaust , air filter on or off? ( plugged oil bath filter)

Points coil plugs etc good and right?
Have the distributor set correctly?
Base engine timing, ignition timing, then octane selector ?


Fuel pump new? ( think so but eh, I forget easily)

Had it happen to me once on a Chevy V6
Had 2 plug wires crossed idled great on accel it would stumble fart and die.

 

no exhaust hooked up right now.

 

Cool. I think i will check on what spring was used! Thanks. Its warrantied so i can send it back to get tested.

 

No sputter. No backfire. Just goes to a duller lower power noise and gets lower idle and dies kinda quietly. If i hit the peddle super quick it sometimes sounds dead and then roars to life at a little bit higher idle but then does it again and dies.
Tune it is good and new.
Dizzy set correctly but i may play with it a bit by turning it ccw. Did last time with no help.
Engine timing seems good and ignition timing seems good and also did with original engine. But same problem with new engine.
Yup. fuel pump new and spits strong.

 

Idles really nicely and smooth for awhile. Minutes. Going to test how long it will do that. Did get it from very low good idle to about 500-600 rpm for about a minute smoothly with the lightest touch of the pedal but then boom. Low idle dull sound and dead.

 

Yeah just looked. They make ALOT of different rebuild kits for the bb1 i heard and you do have to be carefull picking the correct kit. The place that rebuilt and tested it said they had the correct kit. But when i first got it it did want to go to a higher idle the very first couple of times... May have gotten clogged? Or float bad? Just need to take it off and inspect it. But dont want to void the warranty after paying 350.

 

If exhaust is not restricted, with it idling have a can of carb cleaner or starting fluid ready, open throttle while spraying into carb. It should rev up as you open throttle.

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Have you put a vacuum gauge on it? If not I would put one on and tell us what the reading is

 

Maybe they just got the rebuild kit but kept the springs that came with the carb.
Springs are available separately and are matched to the engine (vacuum).

Call them and check if they remember replacing the springs as well.

Also make sure to use the matching base gasket with the slots that line up with the hole on the carb base surface.

 

will try that but its gonna be kinda difficult with the carb being so far down.

 

So idled great again last night but noticed vacuum advance quit working now. Put vacuum guage on it showing 17 lbs at idle. Switched advance unit for another i have and it is working and shows same vacuum 17 lbs. When it has its issue it drops to 15 lbs. Blocked both vacuum hoses and same vacuum with same problem. I set the timing with a light with no difference. Doesnt like distributor moved ccw or cw very much. No improvement.

 

Yeah i have to call them and try to find out. Thanks.

 

Are you 100% sure exhaust isn't restricted?
Distributor advance (weights, springs) ok and working? If this is ok and throttle butterfly opens fully and spraying carb cleaner or starting fluid into carb make it rev up...carb is problem. You could fabricate a longer hose...I've even used propane. Of course...you have to be careful!!!!!
Stupid question...is choke ok? Fully open?

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w.o.t. the vacuum should be super low, if not zero.

 

Well i called Ace Auto that did the carb and they are the BB1 experts. He said that it is the Accelerator pump itself that has gotten swollen. Some fuel additives can do this to this type of pump. I told him everything including that i used ethanol gas i had to check the old motor and hear it fire up for the first time and that i used drano down in the gas tank line that drops into the gas tank leading to the very bottom of tha tank. It was clogged with varnish. I guess i didnt clean it out good enough or whatever.
He is going to put a new accelerator pump in ti to fix it and said it should run like a dream. This type has a spring on the bottom of the pump as a return spring and that should be ok but it got too big for its hole and is stuck. Sees this all the time. Thanks for all your help and i will post the running truck video here when it gets back.

 

Accelerator pump has a leather wrap on the bottom of it. Didnt know leather and gasoline mixed.

 

Is fuel tank original? If it is or just old you'll probably need a new one. I wouldn't run ethanol in it.

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So they didn't replace the leather on the piston with the high $ rebuilt ?

Ethanol laced gas doesn't affect the leather, even if the gas evaporates inside the carb.
I got leather pistons in my 1BBL Carters on my truck, sucking ethanol gasoline for over a decade.
I just add Marvel Mystery Oil to the gas, so the floats don't get stuck if it sits for a few weeks.

 

Fuel tank is the original one. But aside from the tube that was blocked it is really clean inside.

 

They did replace it but an additive in the fuel or some thing other than fuel in the gas tank went through the carburetor and possibly made the leather swell up. He said this happens all the time. So we will be running clear gas and lead helper.
It may not have been the ethanol gas that harmed it but an additive of some kind in that fuel. possibly.