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Old 04-15-2008, 02:02 PM
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Carburetor Leaking Into Cylinders

I fired my 383 project up and it was running great. I took it for a test drive and it seemed to be running rich. This was all last week. So i went down three jet sizes and it still seemed to be rich. So when i went to get some smaller jets, the guy at the speed shop suggested that the power valve might be broke since i did have it backfire.

So this morning i put the power valve and smaller jets in. I go to fire it up and it is running real rough and pouring black smoke and eventually stalled. So i figured i had flooded it somehow and let it sit for a hour or so and tried again and didnt get anything. So i pulled the #1 plug and it is soaked in gas. So then decided to pull the rest and they are all soaked. Then i get to #6 and 8 cylinders and gas starts pouring out of them. They were near the point of hydro-lock. The #6 stopped leaking, but the #8 intake must have been open so it kept on leaking.

I looked down the carburetor to see if anything was leaking, but cant see anything dripping.So now i got to pull the bowl off the carb and when i was draining it, less than a teaspoon of gas came out. Then i put the bowl in a container and turned the engine over a few times and all of the gas stopped coming out of the cylinders. Then i reassmebled the carb after some time to let things dry, but it started to leak into the cylinders again. What the hell is goin on?

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Old 04-15-2008, 02:06 PM
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What carb is this?
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Old 04-15-2008, 02:08 PM
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Holley 650 vacuum secondaries on a 383.
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Old 04-15-2008, 02:12 PM
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Are you running a fuel filter? If not then some debris might be keeping the needle from closing all the way into the seat. Or even if you used teflon tape after the filter there might be a little piece in there. I would pull the carb and check.
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Old 04-15-2008, 02:16 PM
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Quote:
Originally Posted by mightycarlo10
I fired my 383 project up and it was running great. I took it for a test drive and it seemed to be running rich. This was all last week. So i went down three jet sizes and it still seemed to be rich. So when i went to get some smaller jets, the guy at the speed shop suggested that the power valve might be broke since i did have it backfire.

So this morning i put the power valve and smaller jets in. I go to fire it up and it is running real rough and pouring black smoke and eventually stalled. So i figured i had flooded it somehow and let it sit for a hour or so and tried again and didnt get anything. So i pulled the #1 plug and it is soaked in gas. So then decided to pull the rest and they are all soaked. Then i get to #6 and 8 cylinders and gas starts pouring out of them. They were near the point of hydro-lock. The #6 stopped leaking, but the #8 intake must have been open so it kept on leaking.

I looked down the carburetor to see if anything was leaking, but cant see anything dripping.So now i got to pull the bowl off the carb and when i was draining it, less than a teaspoon of gas came out. Then i put the bowl in a container and turned the engine over a few times and all of the gas stopped coming out of the cylinders. Then i reassmebled the carb after some time to let things dry, but it started to leak into the cylinders again. What the hell is goin on?
Carb a 650 Holley, what is the fuel pump, and where is the gas tank higher or lower tham the carb?

Bogie
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Old 04-15-2008, 02:40 PM
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Is it an electric pump?
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Old 04-15-2008, 02:50 PM
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Quote:
Originally Posted by BBCMudbogger
Is it an electric pump?
OK, does it for sure shut off when the enigne is shut down? Cylinders full of fuel leaves me wondering if the pump shuts off when it should.

What kind of pump and do you know what pressure it delivers? High volume pumps for carbs or a pump intended fro EFI deliver from too much to way too much fuel for a carb. In any circumstance some pressure regulation may be in order, 3 to 6 psi at the carb is adequate. More than 6 psi will force the needle valve off its seat which will keep the bowls too full.

Another thing is too look at pressure bleed after shut down, the line pressure should gradually fade to zero without forcing fuel into the carb.

Bogie
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Old 04-15-2008, 02:55 PM
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Three things to consider. Needle and seat not sealing off. Float level set too high. Fuel pressure too high and over riding the needle and seat.
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Old 04-15-2008, 03:00 PM
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The only reason I ask is last fall I had a bad regulator and it filled my brand new engine...pulled the plugs and blew fuel everywhere. I squirted a little oil in the cylinders afterwords because the cylinder walls will be bone dry after all of that fuel. Change the oil too.
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Old 04-15-2008, 03:53 PM
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whats the fuel pressure? if there is no gauge get one or your in the dark. Was there a vapor vent going to a carbon canister you blocked off? if so this will make the fuel pressure shoot up to about 15 psi. My 86 cutlass did this same thing with a stock fuel pump and the pressure buildup in the tank was causing it to blow needle and seats apart. Fuel pressure regulator didnt stop it either, finally I had to leave the vent open, it was the only way to get the fuel pressure to stabilize. I ruined a new engine with fuel wash since it flooded so many times, and no, at the time I didnt have a fuel gauge, a lesson painfully and quickly learned when I got one and seen what the fuel pressure was doing.
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Old 04-15-2008, 04:07 PM
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I would double check that power valve, I had issues with flooding and that was the culprit.
Another thing to check is the accelerator pump arm to linkage setting.
They should just touch, the pump lever must be free to move sideways and not be under pressure.
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Old 04-15-2008, 05:09 PM
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I would be you knocked the float off kilter or got it stuck somehow.
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Old 04-15-2008, 07:41 PM
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Thanks for all the info. When i installed the power valve, the gasket wasnt seated right. I fixed it and it fired right up. But then i shut it down after like 30 seconds to change the oil which smelled somewhat like gas.

I have another question though, I went from a 69 jet to a 65 and it is still running rich. The guy at the speed shop said when you start moving a lot of sizes in jets, its an indication that something else is wrong. I just assume to go down some more sizes because four sizes doesnt seem to be a lot. I am seeing improvements on the plugs though so i think i'm gonna try like a 62 tomorrow. When i had the 69's in there the plugs were black as hell with deposits forming. Then with the 65's the plugs were black but you could kinda still see the ceramic.
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