GT500 stalls at stop lights/signs

Brian, If your engine is idling at 1100 RPM, then that's too high, your engine shouldn't idle any higher than a normal car. 600 to 700 rpm would be closer to normal. 1100 rpm and your transmission is engaging. Set the idle down and if it wants to die then check closely for vacuum leak somewhere like what mentioned before. I would not use soap and water because if you have a V. leak it will try to suck the liquid in and not make much difference. It you use carb cleaner or perhaps WD40 the engine will actually smooth out when sucked in giving you an indication of where it's leaking. Do you have a vacuum guage, if so. take a reading and post the figure.
Mike

 

Brian, if you only getting 7 miles out of a gallon of gas (I'm assuming you meant 7mpg rather than 7mph) then it sounds like the engine is getting way too much fuel when idling. Even if you were actually moving down the road at 1100 rpm you would get better mileage than that, even out of a 428 c.i. You would have to be activating the other six barrels all the time. I've had both a 427 Galaxie with 2 fours and a 67 Shelby with the 428 2 fours as well and neither got that bad of mileage unless you ran wide open (which I did a few times, ahem).
Did anyone ask if this engine has a radical camshaft installed? If it does, it could really affect engine vacuum. Also, what altitude are you at, that also will affect engine vacuum.
Dumb question. Have you taken off the air cleaner after driving and the engine is warm and looked to make sure the chokes are fully open?
Mike

 

Those are excellent points. Wouldn't the fact that it idles in neutral and only has the problem when in gear eliminate the chokes being stuck shut, though?

Josh

 

The fact that it idles in neutral at 1100 rpm is already a problem..and there is no load on the engine. Once in gear, there is a some load on the engine and that's when the problem is compounded. I am suspicious of the carb area. Do your carbs have a bi-metalic controlled choke?
Also, an over rich mixture would show up on a spark plug. Take a look a couple of plugs, if there black and sooty, it's running to rich.

Uh oh, this is a big block, not so easy to get to the plugs.

 

Best way to check for a vacuum leak is a a propane bottle with a hose on it .
if the rpm goes up you have a leak.

 

'67 G.T.500s came with short 4160s (no rear metering plate), list numbers 2804 and 2805 (actually '63 1/2 427 LR carbs) as standard. This was the only year that this setup came stock. The carbs sat "backwards" on the intake and had progressive linkage. The secondaries were synchronized with a vacuum tube. I'd be curious as to the list numbers on your carbs.

The choke was bi-metallic with a long tube that ran from the left side where the choke was mounted to the front carb to the right side exhaust manifold. Hope this helps.

Do you have any pictures of your setup?

 

Brian,

Can you read the list numbers on the air horn?

 

When i was checking my recent brake flush and adjustment, i nailed the brakes hard and the car died and would not restart. i have a 66gt350 w/ 4 speed. any suggestions? i finally got the car to restart but only after holding the gas pedal floored and cranking. what could be the cause?
tia,
ed

 

based on what it took to restart it, sounds to me like a bunch of fuel sloshed out of the rear bowl as your nose was diving and flooded it.

 

I just discovered this thread as my '68 GT500KR was doing the same thing after I put a new, date-coded correct 4150 Holley on it from Pony Carbs. One call to Pony Carbs solved the problem. The cathedral float (the front big screw on top with a nut under it) was not set right. I lossened the screw, turned the nut 180 degrees (1/2 turn) counterclockwise and problem was solved immediately.

 

Assuming the air fuel mixture is okay (the engine isn't drowning in fuel).
If your car has the O.E. ignition system, replace the condenser in the distributor. Back in the 1970s my Boss 302 was doing what your car is described as doing. The master mechanic at the Ford dealer explained that in my case the electrcial insulation inside the shell of the condenser was failing. The stored charges for each plug firing cycle had time to breakdown through current leakage to ground through the shell. At higher engine speeds the next cylinder got the charge before the current could escape to ground through the shell. Cheap fix was a new condenser.


The other more recent problem has been very low quality replacement power valves. I test new valves for leak down before I install them. I was working on a friend's Boss 302 in 2008. I went to town four times to get new valves. The valve that came in the Holley brand kit was poorly machined and would not seal. (Not sealing means at idle and low speeds the engine will get way too much fuel.) I got tired of going to town to get a new Holley brand valve so on my last trip I bought every one they had of the calibration I was after. I tested a handful before I found one that worked as good as a 1960s one. I would guess I have to buy on average three or four new valves to get one that doesn't leak when it shouldn't. A 1965 GT350 owner had so much trouble finding a new Holley brand power valve that didn't leak he designed and made a test fixture for his own preuse testing.


Good luck.

 

by your description your float was set too low and the jets were uncovered when you came to a stop.

99% of the time the problem is the oppisite of what yours was. Holley secondary floats set to factory specs chronically overflow gas out the vent tubes, dumping gas down the venturies during a moderately fast stop.

Z.