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Old 01-10-2018, 08:32 PM   #1
71rehab
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Black Exhaust after long rest

My 71 C20 with the original engine and QJet sat for a few months while I did some metal and paint work.

When I went to restart it I had to prime the fuel pump by dumping fuel down the carb. That worked fine but now my issue is that there is a large amount of black exhaust when it fires and it runs too rich before dying. If I manually open the clutch it will stay running.

The truck was running well, was timed and fuel mixture screws were set before resting it for a few months so i'm not sure what happened. I'm certainly no expert in dealing with carbs so I'm sure I'm missing something simple.

would appreciate any help
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Old 01-10-2018, 08:47 PM   #2
demian5
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Re: Black Exhaust after long rest

Smack the front of the carb with the plastic handle of a screwdriver a few times.
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Old 01-10-2018, 08:48 PM   #3
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Re: Black Exhaust after long rest

You probably have some dried fuel making the float stick a little, if the choke is opening all the way. Two things to check; choke opening properly would be the first one. If you have a brass float, you could pour a little acetone down the bowl vent tube and let it dissolve some suspected crud. Don't do this if you don't know what your float is made of; I believe that acetone may dissolve the composition float.
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Old 01-11-2018, 09:58 AM   #4
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Re: Black Exhaust after long rest

Either it Dried fuel or Seperated Fuel. The 10% Ethanol fuel Seperates after about 30 days, and will gum up you "old style fuel delivery system". Put about a half tank of clean gas with a can of Sea Foam, and run it. It'll run like crap for a little bit but, it'll clean everything out. If that doesn't work, you're looking at a carb rebuild to fix your issue
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Old 01-13-2018, 10:31 PM   #5
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Re: Black Exhaust after long rest

Thanks guys. Carbs banged and sea foam in with fresh gas. We'll see.
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Old 01-23-2018, 11:31 AM   #6
71rehab
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Re: Black Exhaust after long rest

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Originally Posted by custom10nut View Post
Either it Dried fuel or Seperated Fuel. The 10% Ethanol fuel Seperates after about 30 days, and will gum up you "old style fuel delivery system". Put about a half tank of clean gas with a can of Sea Foam, and run it. It'll run like crap for a little bit but, it'll clean everything out. If that doesn't work, you're looking at a carb rebuild to fix your issue
Same issue. Will fire with a big puff of black exhaust and will not stay running unless I manually hold the choke open. When warm, idles nicely.

Carb rebuild time? I see QJet rebuild kits all over the place. Is one better than another? Brass or rubber float?
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Old 01-23-2018, 11:51 AM   #7
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Re: Black Exhaust after long rest

I get my rebuild kits here, https://cliffshighperformance.com/ and here, https://quadrajetparts.com/ As far as the floats go, the new Quadrajet Nitrophyl Carburetor Float Part # [1402] will withstand the riggers of moonshine. (alcohol)
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Old 01-23-2018, 11:56 AM   #8
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Re: Black Exhaust after long rest

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Originally Posted by 71rehab View Post
Same issue. Will fire with a big puff of black exhaust and will not stay running unless I manually hold the choke open. When warm, idles nicely.

Carb rebuild time? I see QJet rebuild kits all over the place. Is one better than another? Brass or rubber float?
Sounds like your choke pull off pot is kaput or the linkage is wacko.
Easier to replace the pot.
Easy to check the pot too. Draw a little vacuum on it, it should pull in the arm.
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Old 01-23-2018, 12:21 PM   #9
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Re: Black Exhaust after long rest

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Originally Posted by geezer#99 View Post
Draw a little vacuum on it, it should pull in the arm.
Thanks for this. I like the idea of easier. But could you explain how to test this like you were explaining it to a 4-year-old? My carb knowledge is very shallow.
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Old 01-23-2018, 12:54 PM   #10
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Re: Black Exhaust after long rest

This could be fun! LOL!!!

On the passenger side of your carb you’ll see a vacuum pot. It has a vacuum hose attached to it. Pull the hose off the pot, use a longer vacuum hose and draw some vacuum on it. Use your lungs for that. The plunger arm on the pot should move inward. If not it needs replaced.
That’s the fun part. You get to suck on a nasty tasting vac hose. JK!!
If you’re wondering what the vac pot’s use is, I’ll splain it.
If your choke is working correctly then thechoke plate closes completely when you open the throttle to start a cold engine. When the motor fires, it creates vacuum. The vacuum pulls on the vac pot and the linkage opens the choke plate about 1/4 inch. Just enough to let your motor run without being too rich. There are adjustments in the linkage to vary the amount of choke plate opening.

If you need a longer vac hose sometimes you can use one of the windshield washer hoses.
Easy stuff, eh!

Last edited by geezer#99; 01-23-2018 at 01:00 PM.
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Old 01-23-2018, 01:59 PM   #11
71rehab
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Re: Black Exhaust after long rest

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Originally Posted by geezer#99 View Post
This could be fun! LOL!!!

On the passenger side of your carb youíll see a vacuum pot. It has a vacuum hose attached to it. Pull the hose off the pot, use a longer vacuum hose and draw some vacuum on it. Use your lungs for that. The plunger arm on the pot should move inward. If not it needs replaced.
Thatís the fun part. You get to suck on a nasty tasting vac hose. JK!!
If youíre wondering what the vac potís use is, Iíll splain it.
If your choke is working correctly then thechoke plate closes completely when you open the throttle to start a cold engine. When the motor fires, it creates vacuum. The vacuum pulls on the vac pot and the linkage opens the choke plate about 1/4 inch. Just enough to let your motor run without being too rich. There are adjustments in the linkage to vary the amount of choke plate opening.

If you need a longer vac hose sometimes you can use one of the windshield washer hoses.
Easy stuff, eh!

This is what I needed! Well done!

I will try this but I'm pretty sure the plate is partially opened when cranked cold. Isn't this a sign that it is working? Or not necessarily?
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Old 01-23-2018, 03:43 PM   #12
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Re: Black Exhaust after long rest

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Originally Posted by 71rehab View Post
This is what I needed! Well done!

I will try this but I'm pretty sure the plate is partially opened when cranked cold. Isn't this a sign that it is working? Or not necessarily?
Not necessarily would be right.
Depends on how the linkage is set up.
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Old 01-23-2018, 07:22 PM   #13
71rehab
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Re: Black Exhaust after long rest

wow. So I didn't have the port on the vac pot hooked up to vacuum or plugged. Oops. Runs perfectly now. Thanks for the troubleshooting. I owe you a beer
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Old 01-23-2018, 07:34 PM   #14
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Re: Black Exhaust after long rest

Generally it’s always something simple!
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