Spivy

It isn’t necessary to use such a large tie-wrap as in these pictures. Those just happened to be what was available close at hand in that dyno session. The smallest tie wraps work good on 4150 carbs. The AFB booster is from a ’67 440 carb.

A spivy can move the EGT as much as 200°F, move a cold cylinder up 200° and at the same time move a hot cylinder down 200°. It diverts fuel from one place to another. Sort of a Robin Hood deal, take from the rich, give to the lean.

Point it toward where you want the fuel to go. If you have a rich cylinder, aim the spivy toward the runner entrance of the other cylinder fed by the same venturi. If is a lean cylinder, aim the spivy toward it and it will take fuel from the other cylinder on that venturi and put it in the lean one, so be prepared to jet up to make for the amount of fuel diverted if necessary.

The low pressure in the flow downstream of the spivy pulls the liquid fuel in that direction. It is a lot like putting your finger in the side of a stream from a garden hose, it pulls the liquid toward the direction of your finger.

Pretty spiffy.

This is a Mopar marine AFB with spivies on three boosters, primary throttle side at 4 o’clock, secondary throttle side at 1 o’clock and secondary choke side at 8 o’clock.

Had one of those on my gas carb and had a guy ask me why I have a plastic tie on my booster??
I told him that the booster is loose so that is on there so it don't fall out ..He shook his
head and walked away!!!

I've seen notches machined into some of the boosters on the old carbs i work with. Same, but opposite, principle?