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Hard Starting L72

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Old 01-17-2017, 09:09 AM   #1
Lotsacubes
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Default Hard Starting L72

If it hasn't been started for a week I have to crank and pump quite a while before she starts to sputter (maybe 30 seconds). The carb is an Eric Jackson restored/rebuilt 3247 Holley with new choke hardware. Choke seems to be setting fine with about 1/8" gap when set. I use 93 octane non-ethanol. The day after a drive it almost immediately fires. Is this a modern fuel phenomenon? I really don't mind the ritual too much if others experience the same thing. One old corvette guy said he solved this by adding an electric choke. I'm not going to do that but maybe my choke needs some adjusting. Am I alone or is this common?
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Old 01-17-2017, 11:04 AM   #2
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More than likely the gas is evaporating out of the front (and rear) fuel bowls. Mine does the same thing. The 3247 front bowl has two vents - one on the bowl and the vent in the throat area so it gets pretty good cross ventilation and the fuel evaporates out in a matter of days. I started mine after sitting 4 or 5 days last week without priming and had to pump and crank it for awhile. My carb was restored in Holleys shop but it has always been plagued with gas evaporation.

Usually, I prime mine before starting through the front vent in the throat area. I use a squeeze bottle like ketchup or mustard comes in. I think mine is actually from a hair saloon so chemicals (fuel) don't seem to affect it. I prime through the vent until I see fuel starting to drip on to the throttle plates, replace the air cleaner top, pump twice and hit the key. It will fire immediately and continue running on the choke.

I also have an electric fuel pump mounted in the rear that I can switch on to pump fuel through the mechanical pump up to the carb. This is an alternative - run the pump for awhile prior to the 2 pumps and ignition. For some reason I've never had as good of luck with this.

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Old 01-17-2017, 11:27 AM   #3
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Ok. Good news. I think I've read you mentioning your priming process before Dan. You'd think the worst of the evaporation would happen while the engine cools but apparently not since next day starting is normal. Just another aspect of her personality and modern fuel. Come Spring I'm going to run some Av gas just out of curiosity.

Thanks, I'll experiment with your priming process and relieved it's normal.
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Old 01-17-2017, 01:20 PM   #4
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I have 3 old carbureted cars (a Ford, a Mopar and the Vette) - one with an Edelbrock and two with Holleys. They are all the same after sitting for a week or so - either crank them for a long time to start (which I don't like to do) or prime them. The only difference is how quickly the fuel in the bowl evaporates before they need to be primed. The Ford fares the best - sometimes it will start on the first turn for up to 3 or 4 days after having been driven. If you don't see signs of gas leaking on your intake, or wetness down inside the manifold (before trying to start) it's most likely today's more volatile gas.
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Old 01-17-2017, 01:40 PM   #5
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Quote:
Originally Posted by Lotsacubes View Post
Choke seems to be setting fine with about 1/8" gap when set.
No it's not. Even at room temperature the choke valve should close all the way, then open slightly when the engine fires by the choke vacuum break. See your CSM.

Duke
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Old 01-17-2017, 06:49 PM   #6
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Quote:
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No it's not. Even at room temperature the choke valve should close all the way, then open slightly when the engine fires by the choke vacuum break. See your CSM.

Duke
Engine vacuum will pull a lot more fuel with the choke fully closed. If adjusted properly, the choke take-off will open slightly as soon as the engine starts.
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Old 01-18-2017, 07:40 AM   #7
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No it's not. Even at room temperature the choke valve should close all the way, then open slightly when the engine fires by the choke vacuum break. See your CSM.

Duke
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