Cadillac carbs

[lightning boy]

17056230 What was the idea with the tiny air bypass holes in the base plate. How did they supply air to a 500 cid engine? This one also has primary pullover enrichment. Do these make good performance carbs or would I be better off looking for another?

[Cliff Ruggles]

Primary POE was used on some models to run an even leaner mixture for very light engine load to help with emissions and fuel economy.  The POE very quickly adds fuel with any quick throttle movement, much like the accl pump to help prevent a momentary lean condition.

It really doesn't work all that well and I don't really use it much.

As long as the Caddy carb has the later style APT system that raises and lowers the power piston it is an EXCELLENT starting point for a really nice high performance street/strip carburetor.....Cliff

[lightning boy]

Thanks Cliif.
It does have adjustable APT with a stepped primary metering rod.
I'll call for parts soon.

[lightning boy]

What about the tiny air bypass holes in the baseplate? How is there enough bypass air for a big inch caddy motor? Just curious.

[Kenth]

Idle bypass air is added due to engine design, lots of different Quadrajets thru the years did not use any idle bypass air at all.
Also, most if not all, Quadrajets with hot air choke has a .125" channel adding bypass air and is part of the calibration.

[mcx]

So when converting a hot air choke shove  to a electric element insert  and blocking off  it's vacuum feed hole , should the idle air bypass in the base plate be increased to compensate for the loss of the choke shove  feed ??  Thanks, Mike

[Kenth]

That would be a good idea, if necessary.
Or, leave the fitting open with a small screen inside the choke tube nut (remove tube).
Also, the .125" channel in bowl is restricted by the .092" seal between choke and bowl.

[Cliff Ruggles]

Correct, but it is still a controlled vacuum leak and adds some bypass air to the scenario.
 
I much prefer to block them off and add additional idle bypass air in the baseplate if/as needed.  When blocking them off a simple/easy method is to melt a tiny bit of lead from a wheel weight into the hole in the carb and gently hit is with a flat punch. 

A small split shot from a tackle box works equally as well.  I HATE to see folks drive a steel check ball into the main body, difficult if not impossible to remove later if someone ends up trying to restore the carb back to stock specs......Cliff

[Kenth]

Agreed, i use a 6-32 tap and put a few threads and a set screw in the channel to block it off.
Easy to remove later if needed.