Carb Problem

Old 12-18-2012, 03:36 PM
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Join Date: May 2003
Posts: 35
Default Carb Problem

I have a Speed Demon, #1402010, which is suppose to be a 750 cfm. When I put it on my street 454 and it seemed to drown it with fuel. I then switched to a Holley 650 cfm and it runs better. But I thought I'd get more power with the 750. Any suggestions? Here is my engine run down:

454 block
forged pistons - 10.75:1 compression
new chromoly rings
cam - .544 lift
roller rockers
rebuilt open chambered heads
Weiand aluminum intake
Mallory distributor
Stock mechanical fuel pump
gullion454 is offline  
Old 12-18-2012, 06:02 PM
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There are a few things to look for. Since is seems to run ok with the 650 you fuel preesure should be alright. Check your float level. Then make sure your jetting is in the ball park for that carb. Do some research to find out the factory jetting should be. That will be a good starting point. Then check your power valve(s). They could be ruptured or wrong for your application.

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Old 12-21-2012, 04:48 AM
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id be lookin at that 750 float level for starters.that engine should be able to handle 750.
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Old 12-22-2012, 06:10 AM
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A larger carb doesn't always mean more power. Lots of things to consider. The biggest thing is calibration. It's got to be right for the motor it's on or it won't make a difference at all, and can even lose power. I'd take that carb completely apart and blow out all the passages, make sure there's no debris in it at all. Put it back together and set the floats with the level at the bottom of the sight glasses to start, and see how it does from there. What jetting, air bleeds, etc are in the carb? Did you get it used or new?
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Old 12-29-2012, 10:20 AM
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Default carb

That motor should like a 750 cfm carb.
All the above info /tips I agree with.
I have put 850 CFM DP holleys on 454's with similar parts, and it was fine.
You probably have a carb issue with the 750
Good Luck
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Old 01-01-2013, 09:15 AM
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thanks guys.
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Old 01-08-2013, 08:00 PM
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Default 750 carb

that holley 750 out of factory should have 75 front and 75 rear jets with a 6.5 power valve in both front and rear. no power valve in rear, then step rear jets up to around 82(and try 84s). you may have to step up the timing at idle to get the carb to idle properly(and remove some timing from the full advance position) art
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