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Old 06-18-2012, 05:14 PM
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1986 chevy 3500 5.7 issue

I bought a 1986 GMC 3500 Vandura (short bus) with the chevy 350 5.7 and Rochester Quadrajet. It was running pretty decent, needed a tune-up but it was reliable. I went ahead and changed plugs, plug wires, air filter, and fuel filter. At the same time I told my younger brother he could take the carb off and clean it up for me. I believe this is where I went wrong. after putting everything back together it fired right up and idled for 2 seconds before dying. Sounds like its flooding and i pulled a few plugs, all of which were covered in fuel. No adjustments were made to the carb so I am kind of at a loss. I did replace a bunch of vacuum lines but I'm almost positive I connected them properly but if anyone has a diagram for the vacuum lines I would appreciate that.

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Old 06-18-2012, 05:23 PM
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More than likely he flipped it over and when that's done it makes the needle stick in the open position. You'll have to pop the top to correct it.
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Old 06-18-2012, 07:04 PM
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If you can remove the fuel line and connect a hand vacuum pump to it, you can determine if the needle is stuck.
-- If you use the pump to pull vacuum on the fuel inlet (most hand vacuum pumps come with a variety of adapters) it should hold vacuum since you are pulling the needle down into the seat.
- If it does not hold vacuum then I would tap lightly on the front of the carb near the fuel inlet and see if you can get the needle to drop onto the seat.
- If it does hold vacuum, then you might have a stuck float. Tapping on the carb may also jar the float and let it drop into position.

If none of that works, you need to pop the top off the carb and take a look at the float, needle and seat. You will probably need to buy a new gasket for the carb body, since the old one may break apart as you separate it.

Bruce
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Old 06-19-2012, 12:14 PM
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Ok so I popped it apart last night and neither the needle or float were stuck and when I put it back on the issue was the same.
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Old 06-19-2012, 02:59 PM
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Float level would be the first thing I'd check.

Vacuum lines wouldn't make it flood. Are you sure it's fouling the plugs because it's flooding? Plugs will also be wet if the cylinder isn't firing from bad plugs, wires, incorrect firing order, bad components, etc.


A few possibilities:

Needle hung on float through the hole, not like it should be- from the cross piece nearest the power piston
Choke hanging shut
Fuel pressure too high
Float soaked w/fuel
Defective needle or seat, or fuel leaking past a defective or missing or doubled gasket/seal under the seat (was the seat unscrewed from the carb during the cleaning?)
Teflon tape (can be almost invisible) fouling the N&S

Have you tried tapping/rapping on the fuel inlet area w/the plastic handle of a screwdriver while running (briefly running- if the carb is really flooding this is wearing the cylinders and rings at a rate a thousand times more than normal), to see if the needle will seat?

Possible not probable- the check valve-equipped carb-mounted fuel filter (inside the fuel inlet) was removed or replaced w/a filter w/o a check valve.

Last edited by cobalt327; 06-19-2012 at 03:05 PM.
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