Holley help needed
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Junior User
Joined: May 2009
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Holley help needed
I have a holley 390 cfm carb on a 78 F250, 300 I6 with headers and an offy dp intake. Somewhere i am getting way too much fuel to the engine and it is sputtering and smoking bad. I have checked the float level, needle and seat, and power valve. All seemed ok but i replaced the power valve and needle and seat on the primary side just to be sure. Even with the float level adjusted way low and the idle mixture screws turned way in the truck would still sputter and spew out black smoke at idle and all throttle positions. I can't figure out where the gas is coming from. I checked to make shure the butterflies were closed and they were. I looked down the throat of the carb when it was running and didn't see any gas rushing in. When i take the carb off the bottom is soaked and the gasket and spacer is all soaked and theres gas sitting in the bottom of my intake. Where is this gas coming from? I'm not expert on carbs but i can find my way around if someone could point me in the right direction.
Thanks.
Thanks.
Freshman User
Joined: Nov 2005
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I would first guess the power valve. I know you replaced it,but could still be bad. What power valve are you using? How much vacum does the engine have? If not that recheck the gaskets. If they are the correct ones and not out of place you may have a cracked metering block.
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Junior User
Joined: May 2009
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I would first guess the power valve. I know you replaced it,but could still be bad. What power valve are you using? How much vacum does the engine have? If not that recheck the gaskets. If they are the correct ones and not out of place you may have a cracked metering block.
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Junior User
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i have tried that also. It is not just at idle where my problem is. It is anywhere. Anytime the truck is running it is smoking and shuttering.
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Junior User
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I will check the baseplate gasket and maybe just replace it since I have one. If i'm going that far I might just put a rebuild kit in it.
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Postmaster
Joined: Jan 2003
Posts: 3,775
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From: Conway Arkansas
That checkball thing is garbage if you ask me. I installed one in an old vacume secondary carb I had and it still blew them when it would cough/backfire
I also knew a guy that bought a brand new one with the kit preinstalled and it blew powervalves as well.
I also knew a guy that bought a brand new one with the kit preinstalled and it blew powervalves as well.
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Cranky Old Guy
Joined: Mar 2008
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From: Raphine, Virginia
I'm still learning mine, but is there a chance the secondaries are opening. I put the quick change spring kit in mine and was unsure if I had lost a check ball. No help from instructions, just said "may" be a check ball. Check with "Abandoned Bronco" in the six cyl forum. Seems he was having a problem with fuel puddling.
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Junior User
Joined: May 2009
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There were a few things I noticed when I took the carb all apart and was cleaning it. First, the vacuume passage on the base that I had my vac advanced hooked up to was all plugged up. Not sure if that was part of my problem but i'm sure cleaning that out would help some. I also noticed a hairline crack on the metering block. It is on what I think is a passage for the accelerator pump. It is right above the power valve on the spring side. It is at a round part right before a diaganal passage goes to the bottom of the block. I would put a picture in here but i'm not sure how. Any of those findings sould like they could be the culpret?
Thanks
Thanks
Thread Starter
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Junior User
Joined: May 2009
Posts: 90
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I'm still learning mine, but is there a chance the secondaries are opening. I put the quick change spring kit in mine and was unsure if I had lost a check ball. No help from instructions, just said "may" be a check ball. Check with "Abandoned Bronco" in the six cyl forum. Seems he was having a problem with fuel puddling.
Post Fiend
Joined: Jan 2005
Posts: 26,337
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From: Paradise Found!
There were a few things I noticed when I took the carb all apart and was cleaning it. First, the vacuume passage on the base that I had my vac advanced hooked up to was all plugged up. Not sure if that was part of my problem but i'm sure cleaning that out would help some. I also noticed a hairline crack on the metering block. It is on what I think is a passage for the accelerator pump. It is right above the power valve on the spring side. It is at a round part right before a diaganal passage goes to the bottom of the block. I would put a picture in here but i'm not sure how. Any of those findings sould like they could be the culpret?
Thanks
Thanks
The cracked metering block is the most likely problem. Also, you do not want your vacuum advance hooked to the baseplate vacuum port. It should be hooked to the ported vacuum port on the choke side of the carb. Using the main engine vacuum port on the baseplate will give full advance at idle, and as you open the throttle you will get less advance.
The port on the choke side will have 0 vacuum at idle, and as you open the throttle it will deliver more vacuum to the vacuum advance.
Thread Starter
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Junior User
Joined: May 2009
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The cracked metering block is the most likely problem. Also, you do not want your vacuum advance hooked to the baseplate vacuum port. It should be hooked to the ported vacuum port on the choke side of the carb. Using the main engine vacuum port on the baseplate will give full advance at idle, and as you open the throttle you will get less advance.
The port on the choke side will have 0 vacuum at idle, and as you open the throttle it will deliver more vacuum to the vacuum advance.
The port on the choke side will have 0 vacuum at idle, and as you open the throttle it will deliver more vacuum to the vacuum advance.
