70 LT-1 stalling
I've finally got my 70 on the road and am having a stalling problem. When it starts cold it runs fine, fine on the expressway but after it is warmed up and I'm in normal traffic and have to stop for lights I have to keep the RPM's up to keep it from quitting. It's a real dance back and forth between the clutch, brake and accellerator. The coil is a new GM restoration, The amp box on the TI has the new chip in it. It only does it after it has warmed up good. Is the intake manifold getting too warm and vaporizing the gas at low RPM's before it gets sucked into the engine? Timing is set right at idle but it does jump pretty good when rev'd. Also seems to run a bit rougher after it gets warmed up, maybe missing some fires. Everything is new and rebuilt. What's the tweak?
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Re: 70 LT-1 stalling
Check for a vacuum leak.
Did you set the timing when the engine was at normal operating temperature? -
Re: 70 LT-1 stalling
Wayne,
If the car runs rough, quits and restarts right away I don't think it's the coil.
Take the car for a drive to get it hot then remove the air cleaner and readjust the A/F screws with the idle set at spec, engine good and hot. If they have no effect on RPM something is amiss in the idle circuit or gaskets not sealing inside carburetor causing rich idle condition.
First, make sure the inital timing is correct and no issues with ignition...THEN CARBURETOR..
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Re: 70 LT-1 stalling
Change the power valve - just had the same issue with a 6210.
Did the change and issue gone immediately.
I had no vacuum leaks and my ignition checked out too. I realized it was the power valve when cupped my hand over the air horn and it started to idle just fine. The newer Holley carbs are deigned to protect against PV blowout, but not sure about the older ones built back in the early 70's.
All it takes is one good backfire and it can mess up the thing.Comment
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Re: 70 LT-1 stalling
Wayne, I have a 72 Lt1 which had the same problem last fall. It would run great until it was good and warm then it wouldn't idle. In my case it got progressivley worse to the point I had to maintain about 3000 rpm just to keep it from stalling. I am having the carb rebuilt now so I can't tell you what the problem was yet but I bet it is some clog in the metering block.Comment
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Re: 70 LT-1 stalling
Checking the P/V is a good idea, I recall a post here where it's suggested to put your finger over the vent hole and if the motor stalls instantly the valve is bad.
On the other hand I have seen cars with blown power valves and they run really bad.
Many times the metering blocks or main body surfaces warp and the gaskets don't seal the passages in these modular carburetors. Idle vacuum can find gasoline in the idle well or the base plate to body gasket area.
Is there a heat shield under the carburetor and are the carburetor to manifold gaskets correct? Is the heat riser operating free?
If the idle adjustments don't seem to effect the idle then it's getting gasoling somewhere else.Comment
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Re: 70 LT-1 stalling
Why does everybody think it's running RICH? Like original post asked, is the fuel boiling or vaporizing before getting to cylinders?Comment
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Re: 70 LT-1 stalling
Not tryin to be a smart a or suggest he richen mixture. It's just that Holley carb service guide addresses this problem of high underhood/carb temperatures causing fuel PERCOLATION,further stating that a carb "is designed to meter fuel, not VAPORIZED fuel." To me sounds like need to get carb temp down with spacer/heat deflector,such as Mr. Gasket makes, possibly insulating fuel line and blocking heat crossover passages in manifold and tying off heat riser valve.Comment
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Re: 70 LT-1 stalling
Wayne a very quick and easy check to determine if your power valve is ruptured in your Holley is to remove the air cleaner lid. Start your LT-1 and put a large enough finger over the front vertical vent of the Holley. If your LT-1 engine dies upon putting your finger over the vent, your power valve is ruptured. Simple fix, replace the power valve. The power valves, metering block gaskets, and fuel bowl gaskets are sold individually.
Be ready with something to catch the fuel that will run out of the lower fuel bowl when the bowl retaining screws/bolts are being removed. I keep a retangular plastic motor oil container that I modified/cut to fit under the fuel bowl to catch the fuel. The bottom is cut to contain the fuel and the top is cut as the spillway.
If your LT-1 continues to run for several seconds with your finger on the fuel vent the power valve is OK. Holding your finger on the vent will eventually stop it from running.Comment
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Re: 70 LT-1 stalling
I'll get at it tomorrow. When I put the TI back on and cranked it the first time I did geta whopper of a backfire so it's possible the power valve is ruptured. When you say put my finger over the vertical valve are we talking about the brass tube about a quarter inch around sticking straight up out of the horn?Comment
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Re: 70 LT-1 stalling
A "whopper" backfire will rupture the power valve. It does not even take a whopper of a backfire to rupture a power valve though. When the power valve is ruptured the applied vacuum to the valve to close the valve when the engine is running is unable to keep it the power valve closed enriching the mixture. Yes, the vertical brass tube is the vent pipe for the fuel bowls and is what you put your finger on.
If you want to do more with the metering block off when replacing the powr valve, buy a can of GUMONT carb cleaner and use the stem applicator to apply the carb cleaner in the openings of the metering valve.Comment
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