HEAT PROBLEMS; RUNNING DRY

[omaha]

Hello again
    Now I have a new problem with the carb on my daily driver. Its a num. 17057256 on a 350 Pontiac (stock '70 motor) in a 68 Chevelle. Lately it's been very hot outside in the evenings (mid to high 90's). When I drive home from work it starts and runs fine when moving (about a 15 min drive) unless I must stop for any length of time towards the end of the trip. Then it seems like it runs out of fuel (no visible stream from the accel pump). Let it cool down and it starts up again. Im using an electric fuel pump (small FACET made for carburetors and no regulator, around 5.5 psi  according to the mfg.) I rebuilt the carb last year before knowing about the book that Cliff has wrote or all the new parts he supplies. So all it has is a cheap rebuild kit from the local auto parts store and a new float.
   Is this a problem with the needle and seat? I've heard of needle and seat sticking open but not closed.

[Cliff Ruggles]

Yes, the needles can stick closed, we have been seeing a LOT of problems with them in recent years with this modern fuel.  Unless they are Viton, they may completely fail, or get "gummy", stick, cause flooding, etc.

The other problem we see is that the correct fuel inlet seats (diameter of the orifice) are NOT being supplied with any over the counter kits, and even today they put rubber parts in them, despite the fact that ethanol is in just about every gallon of gas sold no matter where you live.

At least once a month we'll buy kits from the local parts stores, just to check out the contents.  Just a few weeks back, we purchased a new kit from a leading parts supply store (National Chain).  It was for a 1971 Pontiac carburetor. 

The kit contained a soft white accellerator pump with a black rubber seal on it.  We submerged the pump in fresh gasoline, and in 30 minutes it has swelled up enough to easily fall of the pump.

I checked it today, and it was at least twice it's normal size!

Folks also believe because they find a "blue" seal in the kit that they are safe.  Not so.  There are at least 5 grades of the blue pump seals, and the light blue ones typically found in over the counter kits are "soft" and will swell up/rip/tear/fail in long term contact with ethanol. 

Our kits contains the best grade of Viton® fluoroelastomer, dark blue in color and ethanol compatable.......Cliff

[omaha]

  Thanks Cliff for the reply
    Will be ordering a kit for the carb soon.   Gotta go all through it though, shaft bushings, sec. rod cam,
maybe a pulloff etc. Just gotta find something to put on it temporarily. May be a 2 bbl. 
 

[Schurkey]

  it starts and runs fine when moving (about a 15 min drive) unless I must stop for any length of time towards the end of the trip. Then it seems like it runs out of fuel (no visible stream from the accel pump). Let it cool down and it starts up again. Im using an electric fuel pump (small FACET made for carburetors and no regulator, around 5.5 psi  according to the mfg.)

Is the fuel pump mounted in the engine compartment or back by the gas tank?  I'm guessing it's in the engine compartment.

This is CLASSIC signs of vapor-lock.

Has nothing to do with the carb; the fuel is boiling in the plumbing and the pump can't move vapor.

[omaha]

Hey Shurkey, thanks for the tip. Will try moving the fuel pump to maybe outside of the fenderwell.
When I first mounted it, I thought the inner fenderwell would be a good spot as long as I didnt put it too close to the exaust manifold. I never thought about the under hood heat {when its 103* outside}.
I still need to go through the carb though as the throttle shafts are leaking air {runaway idle} and the acceleratoer pump has a tendency to hang up a bit and the top casting is warped a little.

[rattlehedchris]

I have the same symptom, it's a pontiac 350 in a 66 gto, but the carb just rebuilt due to leaks, and it starts cold no problem, and runs fine, but after I shut it off and try to start again, it won't. If I try to start it the next day, starts instantly. I was told it was a backflow problem. I will do more research and get back to you.

[cobalt327]

Hey Shurkey, thanks for the tip. Will try moving the fuel pump to maybe outside of the fenderwell.

That's better, but an electric pump has a difficult time "pulling" fuel- it does a better job "pushing" fuel, so mounting it lower than the fuel level, back at the tank, is better.

Don't forget to filter the fuel, as well.