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Hey all:
I recently replaced my carb to a 750 CFM ULTRA DOUBLE PUMPER from Holley. Yesterday, it was very hot (in the 90's) and I was driving the car to get aligned. On the way there, after about 8 miles of driving, the car just stalled as I pulled into the intersection. I had taken my foot off the gas and was preparing to down shift. The RPM's just drop and the car dies. Then...the car was difficult to start again but finally did. This happened twice on the way home. I had to keep my foot on the gas to keep the engine going while preparing to stop. However...if the car is started, it will idle all day long. What do you think is wrong?
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My car was giving me alotta' trouble. Every time I go get gas the car would not start at the station, it was flooding for some reason. I had to roll it over until it cleared and blew smoke everywhere. I insulated the carb, regulated the fuel pressure, reinstalled the internal filters, adjusted the floats and replaced the needle/seat... So far, so good...
On this holley, I have the nice glass sights into the fuel bowl and it is full. Again, the car ran for miles without issue. I am not sure if it was a heat issue or ???. Here is the list that I think might be wrong including your feedback:
1) Floats
2) Clogged Filter
3) The "tank sock" debris floats around but after constant suction from the pump, the debris clogs the fuel pick up in the tank
4) Fuel pump can't keep up
quote:
I have the nice glass sights into the fuel bowl and it is full

If the gas is over the sightglass the floats are set to high. Gas level in the bowls should just be visible in the sight glass. With the old style sight screws the gas should have been just at the bottom of the hole, so you could shake the car and a little gas would come out of the hole.
Jeff
Check routing of fuel lines to see if they can be moved away from heat sources. Insulate fuel lines. Install non metallic carb spacer.

Mechanical pump? It may have a hole in the pumping diaphragm. Replace?

Installing an electric pump will often cure things, too.

Not quite sure your symptoms are quite right for vapor lock, though. But it sure did come to mind when you said 90 degrees, and I was pretty sure this is your first summer with the car.

Larry
Is it a new carb? You may have to take it apart and clean it out including blowing out idle and other passages. When they started being manufactured outside the U.S.Demon carbs had a problem with metal shavings from manufacturing clogging up the new carbs. Poor quality control. If your fuel level is set correctly and the bowls show fuel when you stall, it's probably not a fuel supply problem. Does your intake slope at an angle?, could be fuel sloshing over when you slow or stop?
quote:
Originally posted by 4NFORD:
Is it a new carb? You may have to take it apart and clean it out including blowing out idle and other passages. When they started being manufactured outside the U.S.Demon carbs had a problem with metal shavings from manufacturing clogging up the new carbs. Poor quality control. If your fuel level is set correctly and the bowls show fuel when you stall, it's probably not a fuel supply problem. Does your intake slope at an angle?, could be fuel sloshing over when you slow or stop?

Brand new carb. The intake looks level to me but I'll put a level on it to see.
If the Carb is the only thing you changed and the symptoms are only apparent on braking then it sounds to me like fuel slosh out of the bowls and into the vent tubes causing the engine to go rich and stumble.

This is often reported as more of a problem on Pantera's with the mid engine design and under braking as fuel from the secondaries sloshes up the vent tubes and floods the engine. You can set the secondaries float just on the low side to help and/or you can get extension tubes that extend the vent tube to help prevent fuel sloshing.

You say your car is running on the rich side anyway, which may be adding to the problem. Did the carb coming appropriately jetted for your engine/conditions?

On the classic Holley carburetor, the accepted method for setting the float level is to run the engine until everything is warm, and with the engine at idle, unscrew the plugs in the sight windows for the float bowls. Raise the float just until fuel begins to escape from the window, then lower the float back down a bit and lock everything in place. So you really shouldn't see any fuel in the sight glass if properly adjusted.

Good luck,
Julian
Last edited by joules
I had similar issues, and it turned out to be a combination of a few things. One of which was a slightly too high, secondary float, which did flood (will not restart for a good few minutes). As well as a slightly too low primary float that starved... and lastly the most difficult thing to figure out, was that I suddenly got fuel starvation issues due to crud in the fuel tank, that would sometimes partially clog a fuel line, intermittently and cause all sorts of problems.
Just a hint, if and when a car overflows or whatever, push the accelerator to the floor and keep it there and keep turning the starter until it starts. When the throttle plates are fully open there's no vacuum to pull fuel through the carb, and as soon as the extra fuel from the accpumps clears (2-3 seconds), it'll start. I've started a few Panteras like that for people in Modena and also a vintage Thunderbird standing in the middle of an intersection, with a worried pensioner behind the wheel... Smiler

About your problem, if you look at the link below and take the time to do each step, it may help:
http://www.tuningmadeeasy.com/...a-carburetor-part-1/

How stock is your engine? A 750DP is too much carb for a stock'ish engine IMHO.
quote:
Originally posted by Pantera 1887:
I have a working Holley 600 you can use for testing.

Mike

Mike...you are the angel of the pantera world. I still have the old carb (650) if I need to switch. It was running a bit rich and my mechanic (possibly former mechanic) convinced me to go up to a 750. Anyway, I need to find me a mentor that can walk me through the carb tuning ritual. I like the tuning made easy site as it will educate me but there is nothing like having an experienced person to walk you through it.
Hello Khan,
It looks like your having some fun sorting out your car,
Don't get stuck on the fuel but defiantly eliminate it as a problem.

Also it may be a electrical problem,
Some of the one’s I have encountered are and act the same,

Coil for the plugs would heat up and cut out like no fuel, fix was a new coil and
a resistor wire or ballast resistor rated at approx 1.4 ohms.

Electrical short or break, recently I had a reverse lockout switch on a Hotrod give me problems would cut out when driving.

All easy fixes once you find it!

Mark
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