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GMC V6 and V12 Engines Engine repair and rebuilding

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  #1  
Old July 8th, 2017, 02:14 AM
Mark Mark is offline
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Default Truck deing when choke is pushed all the way in

Hi Everyone -
Looking for advise. I have 62 with a 305D and a Bendix Stromberg WW 2 bbl.
Truck starts fine with the choke OUT, but when I push the choke IN, the truck dies. I've done some tinkering with trying to get the pattern, and it looks like it seems like its not the choke per say, but when the idle slows down.. When the choke is OUT, its at a fast idle, but when the Choke is IN, it slows down the idle (If I push the choke in, and don't flap the gas peddle to slow down the idle, it still runs).

The truck has been stored over winter and then wouldn't start. Turns out the carb float was stuck, so I took it off and cleaned it out without taking it apart.

(of note) To re-start it, I need to pull the choke way out, floor the peddle, and it start, then I need to push the choke in to almost closed and it runs..

I'm planning on checking timing, dwel to make sure this is a carb issue. If those seem fine, i'll see if I can find a vacuum leak with a propane torch.

Any other ideas on what could be going on?

thanks!
Mark
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  #2  
Old July 8th, 2017, 03:14 AM
AZKen AZKen is online now
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Default Re: Truck deing when choke is pushed all the way in

Lean condition. Like you said, vacuum hose broken or off or a gasket. It's either too much air or not enough gas.
1. Vac leak detection, broken hoses hard to see, also check for loose carb and manifold bolts and gaskets.
2. See if you have a squirt of gas in carb throat
3. Replace all fuel filters.
4. Do a fuel pump flow test.
5. Try with air cleaner OFF
6. Be sure gas tank/gas cap is venting
7. Crappy batch of gas?
8. May need to renew carb guts (esp needle valve) and reset float level and drop. Could be gummy inside carb.
9. Possible accelerator pump leak, not sure about that one yet.
report finding

Last edited by AZKen; July 8th, 2017 at 03:20 AM.
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Old July 8th, 2017, 03:48 AM
Mark Mark is offline
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Default Re: Truck deing when choke is pushed all the way in

thanks for all the idea's, i'l give them a try.
What do you mean by: See if you have a squirt of gas in carb throat
Is this the accelerator pump squirting or something else?
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Old July 8th, 2017, 06:01 AM
AZKen AZKen is online now
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Default Re: Truck deing when choke is pushed all the way in

The accelerator pump is squirting. Try to get motor running a little first, then shut down. Air cleaner off, choke held open, look down throat with a flash light and push throttle fast open. Should see a good shot of gas come out of the inside wall of throat. It's always good to see that. Tells a lot about the situation if you don't see it or it dribbles. May see two streams with a two barrel.
The way you describe how it won't take a hard accelerator but will take a soft pedal to keep running could mean there will be weak or no squirt when tested. If so, that is your problem. That problem has several causes.
Motor warmed up but not running during test. You are just running enough to fill fuel bowl not getting it "warm" per se.
Let's use the words open (full air passage) and closed (blocked air passage) instead of in and out regarding choke. BE SURE TO CHECK THAT THE CHOKE BUTTERFLY IS DOING WHAT YOU THINK IT'S DOING. (closing when knob pulled out and openinng when knob pushed in and all positions in between). Check that first. Then the squirt. If the choke cable, linkage, clamps or butterfly is not operating properly, that's a problem. Need to do these simple baseline tests/inspections before we get deeper....and of course you said you are looking at all vac hoses etc.

What does this mean exactly? "so I took it off and cleaned it out without taking it apart." How do you know float was stuck? and how did you unstick it without taking apart? and how do you know it's not still sticking? It this (July) the first start up after winter or was it running good recently? Are you able to actually drive it and get it going and accelerating under load?

Last edited by AZKen; July 8th, 2017 at 06:34 AM.
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  #5  
Old July 8th, 2017, 11:15 PM
Mark Mark is offline
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Default Re: Truck deing when choke is pushed all the way in

Definitely not getting anything from the accelerator pump. I took the carb off, hooked up a handpump, and pumped, I was seeing squirts just fine. I put it all back on since I knew it was working and not clogged. Still didn't work.
I then decided to check the fuel pump pressure, i'm getting about 4 psi on a pressure gauge. manual says 5-6. Would the accelerator pump not work at those pressure values?

See inline below:
1. Vac leak detection, broken hoses hard to see, also check for loose carb and manifold bolts and gaskets. -None
2. See if you have a squirt of gas in carb throat -No
3. Replace all fuel filters. - done
4. Do a fuel pump flow test. -getting 4 psi
5. Try with air cleaner OFF - most of the tests have been
6. Be sure gas tank/gas cap is venting - need to test
7. Crappy batch of gas? - maybe, 6-8 months old.
8. May need to renew carb guts (esp needle valve) and reset float level and drop. Could be gummy inside carb.
9. Possible accelerator pump leak, not sure about that one yet.
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  #6  
Old July 9th, 2017, 02:31 AM
Mark Mark is offline
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Default Re: Truck deing when choke is pushed all the way in

figured it out. the float in the carb was set to low. Kind of odd, its been running for a year and was rebuilt at a carb shop...

Running great now.

thanks for the help.
Mark
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