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Old 03-31-2007, 09:11 PM
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big block spark plug help!!

I have a new 468 big block in a 1956 chevy. Carb, Holley 750. Ignition, HEI.

Have been running same set of AC R44N spark plugs all fall and winter with no problems.

All of a sudden last week, I am gas fouling plugs. I replaced the plugs with new R44N and they started fouling within 10 miles. The tailpipes are black and sooty.

What could cause the problem? Choke is working properly. Air filter is new.

I haven't messed with the carburetor or timing. Could carburetor need adjustment? Power valve bad, if so how do I know? Could spark be weak, if so how to know?

Should I try a hotter plug before messing with carb, if so what plug? Before plugs start fouling it runs like a scalded dog.

thanks boys for the help.

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Old 03-31-2007, 09:25 PM
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Sounds like power valve gone.
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Old 04-01-2007, 07:47 AM
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Quote:
Should I try a hotter plug before messing with carb,
It's running Rich,.......

Why would you Change to Different Sparkplugs,..??..??
When you're dealing with a Fuel Delivery Issue,..??..??......

If your Clutch was Bad, Would you Change the Tires,..??..??.......
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Old 04-01-2007, 11:36 AM
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Bondo:

My thought was that possibly the plug is not hot enough to burn the summer blend of gasoline. How do you confirm that the problem is with the power valve. How hard is it to change the PV.
jt
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Old 04-01-2007, 12:10 PM
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1.)
Quote:
How do you confirm that the problem is with the power valve.
Quote:
Holley ... power valves
If you have a carburetor older than 1992 (or you have experienced
an extreme backfire) and expect a blown power valve,
use this simple test. TEST: At idle turn your idle mixture screws
(found on the side of the metering block) all the way in. If your
engine dies the power valve is not blown.

2.)
Quote:
How hard is it to change the PV.
4150 / 4160 series exploded view.

It's item #121 in this exploded view, right in front of the main carb body. You'll need a fresh pair of front bowl and metering plate gaskets at the very least. Holley's are a pretty simple design. About the hardest thing is making sure that you get the transfer-tube (if equipped) o-rings installed properly. Use a little smear of vaseline on them.

You mentioned "750" ... is it a List# 3310 with center-hung, dual feed float bowls? If so ... you're laughing ... easy. Try to get a 2-stage replacement power valve as well.

Last edited by 66GMC; 04-01-2007 at 12:21 PM.
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