So I'm using just the throttle base from a Carter BBD under the mixer after my propane conversion. I've got a miss in cylinder #6 that I've tacked down to what I think is a fuel flow problem. It happens mainly at idle. Is there any way that something could me happening in the base of the old carb---bringing in richer or leaner mixtures? I'm fixing to JB-Weld up the passages I'm not using.

ALSO, and More Importantly, where do I want to attach the vaccuum advance to the distributor?

I feel ignorant, but what exactly is ported vacuum? I understand manifold vacuum, and vacuum above the throttle plates that increase with speed but is very small at idle, but not ported vacuum.

Finally, what should the vacuum for the distributor read at idle? How about at WOT?

Thanks,

Joe

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Joe Hoppe

71 D100 225 Super Six 727 AT on 2008 Crown Vic CopCar frame

64 Valiant Wagon 225 904 AT 3:23 8.75"

Take a careful, close look at the throttle bores. In one or both of them, you will see a small slot that lies just above the top "uphill" edge of the closed throttle plate (be careful not to confuse this slot with the small hole(s) that provide idle fuel). Find the throttle body passage that connects to this slot, and rig a secure connection from that passage to your vacuum advance. On a whole carburetor, that passage leads up through the carb's main body casting and to the outside via a hose nipple to which is connected the distributor vacuum advance line.
That is ported vacuum! The slot I described above is the "port".
Near zero at curb idle, approximately manifold vacuum at WFO.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Thanks very much, Dan. One more question. I've got a solid spacer above the throttle body. Can I just drill a hole through that and use it as the vaccuum source, or is there something special about those ports? The vaccuum would be low or nil at idle, and then increase as the throttle opens, as I understand it.


Joe

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Joe Hoppe

71 D100 225 Super Six 727 AT on 2008 Crown Vic CopCar frame

64 Valiant Wagon 225 904 AT 3:23 8.75"

Use the port for the advance vacuum. Low at idle, higher at part throttle, then low again at 75% to 100% WOT.

For anything else, that needs manifold vacuum, use the carb's manifold vacuum that is simply leads to the manifold if carb have it. Any nipples that is left unused, cap them off.

If you have lean in one of the runners like cylinder 6, you might have manifold leak.

Cheers, Wizard

No, you really want to use the special port. It's very carefully placed relative to the throttle plate to give the correct vacuum signal. It's worth your extra effort to do this right.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Thanks for the replies. I'll do some drillin' to get ported vacuum.

I've checked for vacuum leak w/ the trust WD-40. Idle is rough, but it smooths out very nicely around 1500 RPM.

Joe

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Joe Hoppe

71 D100 225 Super Six 727 AT on 2008 Crown Vic CopCar frame

64 Valiant Wagon 225 904 AT 3:23 8.75"