Ok, the Vette’s been running great, got my tach working again, plugs 5 and 7 aren’t fouling, been a joy to drive. All of the sudden I go to take her out for a drive and it just turning over like it was out of gas or not getting spark. After a few tries I took off the air filter and gave it a couple sprays of autostart. Almost started with that but didn’t keep running. Now I know it’s getting good spark so I hit it a few more time with the autostart. Got a couple flaming back fire flames through the carburetor so I gave it another shot of autostart, put back on the air filter, and started cranking it over again. Started up and kept running no problem. The whole rest of the day no problem at all starring up. Next day same thing, turns over like a champ but no startup. Off goes the air filter, couple sprays of auto start and contact, starts up, runs the rest of the day no problem. I’m running the original Quadrajet carb on the stock 350 1971 motor. I’m thinking fuel pump maybe? Any other thoughts?

 

With engine OFF, see if the accelerator pump in the carb is allowing good 'squirts' of fuel into the primary throttle bores when you actuate the throttle manually (WOT with the carb linkage). If no 'juice', the seal on your accelerator pump rod has a problem. Not a difficult fix.

If you have good fuel squirts, your problem is likely an issue with ignition. Is your ignition circuit still wired as from factory with resistance wire going to coil AND 12 vdc line to coil from the starter solenoid (this last item sends full 12 volts to coil during starts).

 

Is there a fuel filter that you can change? If so it could be clogged.
Can you see inside the gas tank to see if the sock filter is clogged or torn/rotted?
BEFORE you start the car...take the air cleaner off and look in the throat of the carb to see if gas has puddled in the bottom of the intake manifold.
Work the throttle arm on the carb to full throttle several times...did fuel squirt into the throat of the carb?
After you drive the car for an hour...stop and turn the engine off...raise the hood and listen for hissing/boiling noise coming from the carb. The gas could be boiling out of the carb which would make it hard to start the next day.

Let us know what you discover.

 

Ok will have a look tomorrow or Saturday to see if any of the above suggestions are at falt…. Thanks guys…👍🏻

 

There are lots of threads about Q jet carbs and hot starting problems.
2 MAJOR problems are fuel boiling off on a hot engine or fuel siphoning back to the tank. Either problem results in no gas in the carb the next day.
The fuel boiling can be solved by opening the hood when parking for the day, using a phenolic spacer, heat sink spacer, etc. Lots of previous threads on this.
The siphoning of the gas back to the tank can be solved by using the in the carb filter with the anti siphon valve/flapper that is built in. Info in previous threads also.
This issue is exacerbated with the current gas/alcohol fuel.
The above issues can be checked by looking down the carb and working the linkage as others have noted above.

 

I'm sure you know unlike FI cars you need to pump the accelerator to get it to start? Sounds like its not a hot start issue because you say when you first try to start it, cold?

 

I have heard this said before, but can it get back thru the fuel pump, then either thru the main line or return line?
shouldn't the check valves in the pump stop any flow back?
does the small carb filter with flap/check valve fix the problem, or are they more of a restriction?

 

Yeah I always give it several good pumps before I start tu turn over the engine and several more as needed to get it running. Once again this is a new issue that I never had before and only happens on a cold start after sitting in the garage overnight or a couple days….

 

you know you have good spark? how do you know? points? they wear. i used to pop people's hoods and regap points when i heard a car cranking more than 5 seconds.

 

Yes.....several good suggestions here:
1) Check for squirt when cold
2) Check fuel filter for condition and to see if it has check valve
3) Check point dwell with a dwell tach...if in fact you do have points......

Jebby

 

before you start it take off the air cleaner and move the throttle to see if you are getting fuel out of the squirters (accelerator pump nozzles). I ould say you dont or you get a few squirts then they stop. I had this issue and either the fuel is draining back down the line and syphoning the fuel out, I doube it or its boiling off. THe third option is it is leaking though the base of the bowl and draining into your intake. You can put a one way valve filter in, or a valve in line. Or bypass the mechanincal fuel pump and put in an electric back near the tank. The third option is a very good choice because you can put a fuel shut off switch on a relay in the passenger compartment.

When you dont have any fuel in your bowl you have to continuously crank the motor to get the fuel pump to get fuel into the bowl and fill it up before you can get fuel to the squirters and get that baby to start. Its frustrating and can wear down the battery. An electric pump will fill the bowl until the float shuts it off and then it takes 1 to 3 pumps and she will start. IF you want to test whether there is fuel in the bowls you can try starting it and if it doesnt, get a 30cc syringe or turkey bastor, fill it with fuel and squirt it down the vent tube in the top of the carburetor. It doesnt take a lot, maybe an ounce and a half. then pump the accelerator until you get a steady squirt. THat should be enough to start it.

If you are opposed to an electric fuel pump, take the carb off, and elevate it on some makeshift stands above some clean whit paper. Fill the bowl with fuel down the vent and let it sit over night. If you have stains on the paper in the morning your bowl is leaking and you will need it repaired or a replacenment. I ended up with an NOS Edelbrock quadrajet that I went though with the Cliff Ruggles Quadrajet book. Worked like a champ and never had an issue again.

 

The filter with the check valve does help on my car. I've tried it with and without. I'm not sure if it goes back through the fp or the return line.
I doubt that it is too restrictive for a stock car. May be a problem for a hopped up, high hp engine. They are stock GM parts for later Qjets.

 

Also….the solid needle seat vs. the windowed one prevents drainback…..

Jebby

 

Had a look today, tried starting it up and had the same situation, turns over like crazy but doesn’t start. Took off the air filter and manually pumped the throttle cable and did see gas squirting into the primaries…. Noticed the choke was stuck wide open. Engine on or off wouldn’t budge. Played with an adjustment screw on the side of the carb and was able to free up the choke. Seems to be better, the Vette is running great once again, very responsive and good power. Gotta love a Quadrajet, they’re so quirky but when they are dialed in right it seems to know what you want and when you want it…. We’ll see what happens tomorrow when I go to get her up for a meet with a classic car group…

 

I always have atleast one fire extinguisher in the car and a can of starting fluid!!!! Even when I had EFI...

 

that is not dialed in right. you messed with the choke until it closed. now it needs to be figured out.

 

How long did it sit between runs? A Q-jet will evaporate dry in say 3 days. This will also lose the prime for the accelerator pump. If you pump to set the choke and crank for maybe 10 seconds it should fire off.

 

My Q-Jet can set for weeks and start right up.

 

depends on how pourous the casting is it may not go up , it might seep out the bottom