I have a 1984 chevy silverado with a 1971 Corvette 350 4bbl carb. Lately it has been giving me troblues cutti

Question

ng off and i wonder if it is that i am not letting it warm up enough during this cold weather or of some problems with the carb. Maybe the cold because when i dont have the accelerater down it wants to lug and cut off?

It does not give me trouble when the truck has warmed up to operating temperature. Today I let the truck warm up for about 10 minutes and it didn't give me any trouble. Will pumping 98 ocatane gas help with anything besides the problem that I have now? I didnt know that the change of gas would help with anything???

Answer 1

there's a few things this could be, and i have a few questions?
one does this still happen after it has warmed up?
if your answer is no, then i would look at my choke, it maybe slow to open or hanging up.
take some carb cleaner and spray the carb down, also look at your plugs, if warn they could be the problem, and check the plug wires as moister could be built up on cold motors and spark bleeds throw.
if your answer is yes it still does this then i would look at my plug wires and plugs as they can do this warm or cold.

and this makes me want to ask another question

did you use the distributor as that one still used points?
if your answer is yes, then again moister can build up in and on a cold motor, have they been changed? even if you don't drive it much they should be change twice a year.

the other thing that comes to mind is the intake and base of the carb, if every thing else checks out ok then i would take some carb cleaner and spray the base of the carb and along the intake right next to the valve covers, you may have a small vacuum leak and goes away after warm up as metal expands with heat

Answer 2

I own a shop, and that thing ought to fly!!! I would think the choke needs cleaned and reset. You have to do this about twice a year, when it gets cold, and when it warms back up. Make sure the choke is working properly, not sticking, and opens & closes as it should. If it has an electric thermostat that opens it, then it may not be working, or burned out. If it runs good after it warms up, then fix the choke, and you should be good to go. The choke should be set to where its closed all the way when its cold, and the choke pull off should crack it about 1/4 of an inch when vacuum is applied to it. I'll bet you have to pump the gas to get it to start too. If not, then it probably just needs cleaned, and set for winter.
Part 2:
Octane of fuel wouldn't make it cut off when its cold!!! When the engine is cold it requires more fuel, and less air to run properly. This is why they have a choke. As the engine warms up, the choke opens up, thus the engine runs smooth during the whole process. The choke involves cutting the air flow down, thus giving it more fuel. If the choke is sticking (not closing enough, or closing too much) the engine will shut off. Since you don't see black smoke, and it starts back up, then the choke isn't closing enough. When the engine starts, the choke pull off will open the choke about 1/4 of an inch, and if the engine starts to stall, the vacuum falls off thus closing the choke more. In other words the pull off regulates the amount of choke the engine receives by the amount of vacuum produced by the engine. The choke thermostat is a spring that expands as the temperature of the engines rises, or if its an electric choke, it has a heating element that expands the spring, thus the choke opens fullly once the spring is hot enough to expand, and since its attached to the choke, the choke opens up. There is a black pot on the side of the carburetor, and this is the thermostat. It either has a wire going to it, or it has a heat tube that runs from the exhaust manifold to it to supply heat. If you will look at this thermostat, it has three screw around it to secure it in place. At the top you will notice some marks, and the black portion of it has a mark on it too. These are settings for the choke. You can loosen the three screws, and turn the choke thermostat to adjust it rich or lean. If the thermostat is working properly, and the pull off is working, then you should be able to adjust it to where it will run good when its cold. With the engine running pull the hose off the choke pull off, and see if it moves when you do, If not its bad. Always; before doing any work or adjustments to the choke, clean it real good with some choke/carburetor cleaner to get it free, and just crack the throttle about an inch, push the choke closed (with engine off and cold) and while you hold the choke closed, release the throttle, and the choke should work free then. Loosen the 3 screws, and close the choke by turning the thermostat. You should be about the center on the marks I talked about earlier. You want to go one maybe two lines past the center marks, and lock it back down. Apply vacuum to the pull off, and it should open the choke about a 1/4". Do all of this, and if it still stumbles when its cold, adjust it a line or two more. If after all of this you still aren't sure about how to do this, then you should find a mechanic that has experience with carburetors. I hope this resolves your problem.
Glad to help out, Good Luck!!!

Answer 3

Rochester Quadrajets also have a choke pull off which over rides the amount choke valve opening on cold starts. It's controlled by a small vacuum diaphragm on the riders side if the carb. Also you may want to check the velocity and strength of the fuel being discharged from the accelerator pump nozzles. It's relatively easy to un-screw the top of the carb, lift it off and replace the accelerator pump plunger. Buy it at your local Chevrolet dealer as aftermarket stuff is not as good. By shortening the aluminum plunger end .060 the plunger travels further in the pump bore giving you a longer acellerator pump shot into the throttle bores.

Answer 4

My best guess is that the cam has lost it's opportunity to lift the # 8 cyl's. valves as well as #1's!. The #8 cam lubrication schedule has been documented to be non-exhistent through many years of production. Chevy chose to drop the ball on this one contigent area of deflective concerne. Take the valve cover off this side to uncover the route of your evil. Replace the exhaust stud ,on #8,to recover some semblance , of a LT-1 song!

Answer 5

think it might be the fact that the motor is 31 years old and today's gas is junk? you motor was made for 98+ octane with lead, is the timing retard to deal with today's gas? and have the heads been rebuilt with "harden seats? for the valves?