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Carburetor experts only please

Old 08-06-2008, 08:21 PM
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Default Carburetor experts only please

Twin small blocks had big"1100 cfm holleys on them ran good but last 1/8 throttle boat nosed over and lost 3-4 mph unless you pumped the throttles hard and squirted the excelarator pumps? then it would pick right back up. Was told they were 2 big for the motors which i thought sounded right. Bought 2 brand new holley 750's double pumper and ran tonight and runs better does not fall of at all but if you pump the throttles at WOT it pick up about 1-2 mph then stop pumping it settles right back down? Is it possible that they are pulling vacuum and the power valves are closing?

Carburetor experts only please
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Old 08-06-2008, 09:00 PM
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First off check your vacum at idle
divided it in half add one, that is the size you need for your power valve .#2 sounds like you need to go to a larger jet size . Have you checked your spark plugs after w.o.t. sounds like its lean. #3 fuel pressure and volume. Hope this helps
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Old 08-06-2008, 09:04 PM
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Not an expert but I know one.

Call Nickerson. Everything they've ever done for me has been downright amazing.
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Old 08-06-2008, 09:28 PM
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Originally Posted by vendetta View Post
First off check your vacum at idle
divided it in half add one, that is the size you need for your power valve .#2 sounds like you need to go to a larger jet size . Have you checked your spark plugs after w.o.t. sounds like its lean. #3 fuel pressure and volume. Hope this helps
Vacume @ idle good start. Went to larger jets today helped maybe a little but running 74 primary 87 secondary I think that should be big enough. Fuel psi is 6-7 new pumps and regulators.
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Old 08-06-2008, 11:36 PM
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Could tell you what's going on, but since I don't consider myself a carb expert, I'll just shut up.
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Old 08-07-2008, 07:28 AM
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Originally Posted by bcarpman View Post
Could tell you what's going on, but since I don't consider myself a carb expert, I'll just shut up.
Thanks for all of your help. You rock
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Old 08-07-2008, 07:43 AM
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How aggressive are the small blocks? 350/s or 400 plus cid. You may be losing vacum signal at the venturis due to cfm still being too much. Venturi air speed is what creates the the draw to pull fuel thru the jets and into the motor.
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Old 08-07-2008, 07:46 PM
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Originally Posted by Airpacker View Post
How aggressive are the small blocks? 350/s or 400 plus cid. You may be losing vacum signal at the venturis due to cfm still being too much. Venturi air speed is what creates the the draw to pull fuel thru the jets and into the motor.

Thanks I guess from what I was told today that it is normal to gain some speed from pumping the throttles at WOT and hitting the accelrator pumps.
Thanks for the help
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Old 08-08-2008, 07:59 AM
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you really ought to consider putting jet extensions on the secondary jets. fuel tends to run to the back of the float bowl under accelaration.
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Old 08-10-2008, 08:53 PM
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did you ck the fuel pressure at WOT throttle ? first carbs seemed to big....but sounds more like a delivery issue to me, sometimes you can set that pressure 5-6 psi at idle but anti-siph. valves and restrictive marine fuel inlets choke out flow at wot, Rob
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