273 Commando w/front 4 Spark Plugs Black/Sooty

[dibbons]

This is 1965 factory stock 273 Carter AFB, 273 factory intake, 273 factory exhaust manifolds on a stock rebuilt 318 short block with 2.5 inch TTI dual exhaust. Only about 2,000 street miles on re-build which, up until now, had a rock-solid smooth idle but now shaking noticeably at idle. Warm compression check shows six cylinders @ 160 PSI, one @ 150 PSI, and one @ 165 PSI. Wondering how plugs from cylinders 1, 2, 3, 4, could be so dry sooty black while the other cylinders (rear four) have normal whitish/tannish looking plugs? (choke is always tied open permanently by the way)

 

[dibbons]

Photo(s)

 

[valiantwagonguy]

I'd look into the carb

 

[toolmanmike]

This is 1965 factory stock 273 Carter AFB, 273 factory intake, 273 factory exhaust manifolds on a stock rebuilt 318 short block with 2.5 inch TTI dual exhaust. Only about 2,000 street miles on re-build which, up until now, had a rock-solid smooth idle but now shaking noticeably at idle. Warm compression check shows six cylinders @ 160 PSI, one @ 150 PSI, and one @ 165 PSI. Wondering how plugs from cylinders 1, 2, 3, 4, could be so dry sooty black while the other cylinders (rear four) have normal whitish/tannish looking plugs? (choke is always tied open permanently by the way)

I wouldn't be concerned about the compression. Balance the idle mixture screws and see what it des. Screw in and gently seat the needles. Unscrew 2 1/2 turns and tune from there.

 

[RustyRatRod]

This is 1965 factory stock 273 Carter AFB, 273 factory intake, 273 factory exhaust manifolds on a stock rebuilt 318 short block with 2.5 inch TTI dual exhaust. Only about 2,000 street miles on re-build which, up until now, had a rock-solid smooth idle but now shaking noticeably at idle. Warm compression check shows six cylinders @ 160 PSI, one @ 150 PSI, and one @ 165 PSI. Wondering how plugs from cylinders 1, 2, 3, 4, could be so dry sooty black while the other cylinders (rear four) have normal whitish/tannish looking plugs? (choke is always tied open permanently by the way)

That's a single plane intake manifold. If you have the PCV valve in the port in the intake manifold, instead of at the carburetor, that could cause the rear four to run excessively lean which could make the front four look overly rich. The port in the intake is for power brakes and the carburetor port is for the PCV valve. So that's something to look at.

 

[AJ/FormS]

My guess is that you have Multiple problems;
1) are the secondaries stuck partly open
2) the IABs are plugged OR
3) the float level is too high

 

[4spdragtop]

Do those 4 plugs share the same plenums?

 

[toolmanmike]

Do those 4 plugs share the same plenums?

Factory open plenum 4 barrel intake

 

[toolmanmike]

This is 1965 factory stock 273 Carter AFB, 273 factory intake, 273 factory exhaust manifolds on a stock rebuilt 318 short block with 2.5 inch TTI dual exhaust. Only about 2,000 street miles on re-build which, up until now, had a rock-solid smooth idle but now shaking noticeably at idle. Warm compression check shows six cylinders @ 160 PSI, one @ 150 PSI, and one @ 165 PSI. Wondering how plugs from cylinders 1, 2, 3, 4, could be so dry sooty black while the other cylinders (rear four) have normal whitish/tannish looking plugs? (choke is always tied open permanently by the way)

Let's see, it ran good and then started fouling 4 plugs on one side? If it were me I would take the carb off.

 

[Bewy]

Plugs all the same heat range, which is?

 

[dibbons]

All the plugs are new Autolite 66. Distributor is single point

 

[65dartcharger]

I wouldn't be concerned about the compression. Balance the idle mixture screws and see what it des. Screw in and gently seat the needles. Unscrew 2 1/2 turns and tune from there.

I would also check with valve sealing. Are cylinder 1, 2 3 and 4 worn out?

 

[dibbons]

Professionally rebuilt less than 2,000 miles ago. I don"t expect to find anything worn out yet.

 

[teringer]

Check carb base plate gasket, re tighten Intake gasket

 

[dibbons]

Update: Went to remove carb when I noticed the plug that had previously been placed in extra intake manifold vacuum port was missing.

 

[dibbons]

Plugging the vacuum leak and adjusting the carb resulted in reading of 19" manifold vacuum.

 

[RustyRatRod]

Yeah, that could do it.

 

[dibbons]

AFB