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Old 07-25-2012, 06:44 PM
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idle mixture question

I was hoping one or two of you would be nice enough to let me bounce some logic off you and let me know if what I'm thinking makes sense... or if I'm way off.

SBC, dual quads, Edelbrock RPM Air Gap dual plane intake.

Just had the engine rebuilt and after about 125 miles pulled the plugs. #1 was carbon fouled and fuel actually dripped out of the plug hole. The other 7 were fine, though #3 was slightly carbon fouled.

The last time I drove it, I idled for probably 3 minutes with no throttle before shutting off (lining up back and forth when backing into garage).

The left-side idle mixture screw of the front carb was turned out about 1/2 to 3/4 more than the right side. It would be this idle mixture screw that would control the left-side venturi's and thus putting more fuel into cylinders #1 and #3 at idle. Since there was actually fuel pooled in the #1 cylinder and the last time it ran I'd idled it without throttle for 3 minutes or so before shutting it off, I'm thinking it's just an idle mixture issue and by turning the left-side screw in more (which I've already done), that should take care of it. Does this make sense or is it likely to be more complex and involve jetting, metering and/or float?

I'll know more after the next time I can take it out, but I hoped to get some feedback on whether my thinking was sound.

Thanks!

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Old 07-25-2012, 07:14 PM
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You have a fuel pressure and or carb float height issue. and or dirt is infecting
The carb needle seat assembly causing flooding.
The carb is flooding. remove and repair.
Get a fuel pressure eg or get the right fuel pump. 5-6psi.
eg carter #P4070

5psi at idle max 6psi at idle .
carbs throttles should be both evenly open at idle. idle mix screws should all end up more or less even.

What camshaft?
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Old 07-25-2012, 07:40 PM
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I have a pressure regulator set to 4.75 psi.

Lunati cam: .477 lift, 275 adv dur, 225 dur @ .050.
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Old 07-25-2012, 08:38 PM
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Quote:
Originally Posted by loafing1 View Post
I have a pressure regulator set to 4.75 psi.

Lunati cam: .477 lift, 275 adv dur, 225 dur @ .050.
this cam will want a modified distributor curve. The stock curve will not work.

20-24deg base at idle 34-36 at max advance. 4" or 5" step up springs.
vac advannce use ported. BOTH Carbs throttles base opening must be correct at idle.

remove both carbs and preset the carbs idle throttle opening setting
The idle fuel transfer slot should be jsut exposed at idle on both carbs
at idle.
If the carbs are too far open at idle (lack of spark advance at idle) the idle will be rich

big Cams need more idle base timing

If it is flooding with 4.75psi fuel pressure, there is dirt in the needle seat or the needle seat is defective or the float is out of wack.
Get new fresh spark plugs
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