DESPERATELY NEED HELP...carb troubles!!

[slammd72]

i have a 77 longbed 3/4 ton pickup i got from an auction and i am now trying to get this thing runnin right. i need to know which needle is air and which is fuel. and also some suggestions or advise on how to get it tuned right. any help is very appreciated. thanx in advance

[slammd72]

heres a pic.....i think this is a 2bbl? am i correct?

[plumbcut]

Looks like a 2bbl. Both of those needles are for fuel. One's for each venturi (barrel)

Got anymore info about the truck? Your best bet would be to rebuild the carb on there and do a complete tuneup (including distributor)...

pc

[jimfulco]

Do you mean the idle mixture screws near the bottom of the picture? Both control fuel flow at idle, one for each barrel of the carb. Turning them clockwise will lean the idle mixture, CCW will richen it. Turn them all the way in GENTLY, counting the turns so you'll know where you started. Once they're lightly seated, turn them out ~2 turns for a starting point. Warm up the engine & set the ignition timing & idle speed. Then turn one of the mixture screws inwards (clockwise) until the engine slows down or begins to miss, then turn it back out 1/8 to 1/4 turn. Do the same with the other one. Reset the idle speed if necessary, & do the mixture screws one more time to fine-tune.

[slammd72]

Originally Posted by jimfulco

Do you mean the idle mixture screws near the bottom of the picture? Both control fuel flow at idle, one for each barrel of the carb. Turning them clockwise will lean the idle mixture, CCW will richen it. Turn them all the way in GENTLY, counting the turns so you'll know where you started. Once they're lightly seated, turn them out ~2 turns for a starting point. Warm up the engine & set the ignition timing & idle speed. Then turn one of the mixture screws inwards (clockwise) until the engine slows down or begins to miss, then turn it back out 1/8 to 1/4 turn. Do the same with the other one. Reset the idle speed if necessary, & do the mixture screws one more time to fine-tune.

oic.....that helps ALOT...well..i am in need of a starting point b/c i bought the truck from an auction in april and have some time now to work on it, but i let my father in law work on it last week and ever since he messed with those to mixture screws the truck will not run and drive without stalling. i used to be able to start it up (with a jump due to an electrical problem which i also fixing) and it would go into gear and i could drive it up and down the street just fine. but it would lag when i steped on the gas. i also replaced the fuel filter in the carb, the inline filter shown in the pics, the fuel pump, and treated the gas b/c there was no gas cap and it sat for 3 months. also bought a cap.

more info: it is a 350 auto

P.S. if i rebuild the carb (which i thought would be fitting) can i set those mixture screws at a point where the truck would run but need adjustment?

[1986Silverado]

Originally Posted by jimfulco

Turn them all the way in GENTLY, counting the turns so you'll know where you started. Once they're lightly seated, turn them out ~2 turns for a starting point. Warm up the engine & set the ignition timing & idle speed. Then turn one of the mixture screws inwards (clockwise) until the engine slows down or begins to miss, then turn it back out 1/8 to 1/4 turn. Do the same with the other one. Reset the idle speed if necessary, & do the mixture screws one more time to fine-tune.

As stated above in the quote that would be a good starting point after a rebuild and to fine tune it.

[1972C10]

I like to set mine with a vaccum gauge but isnt nessacary

If you have a vaccum gauge use the already posted directions and try to achive maximum vaccum at idle

I normally start them off at turn and half but anything will really work as a starting point.

[jimfulco]

Get some fresh gas running through it before you pronounce it dead. Old gas doesn't burn well, and can gum things up & plug small passages. Fresh gas will dissolve the gummy stuff away, although it may take a couple of days.

Might pull the distributor cap & look under the rotor at the advance weights & springs. Those old HEI's were prone to having trouble with the weights at the point where they pivot, & if they don't work right it can make it run bad. Make sure that they move outward smoothly & that the springs retract them smoothly when you let them go. Bad plug wires (high resistance) can cause the pivots to erode & have excess play. This can also make it run bad.

[raceman6135]

It looks like that carburetor is a rebuild anyway. If I'm not mistaken, that white and red sticker is from Autoline.

If you do decide that you need a rebuilt/remanufactured carburetor, find the carburetor number stamped on the carburetor. It's a much more accurate way for your parts person to get you the correct part, as opposed to just going by year, make and engine size.

DJS