Re: engine vacuum question
The front ported vacuum should be pretty low until you open the throttle. The port for the ported vacuum is located right above the throttle plate, so when the throttle is closed it sees the air above the throttle and when it is open the port sees manifold vacuum. You may need to keep the advance connected to the carb and tee off it to get the right reading, since advance directly affects idle vacuum. The curb idle may be set improperly. How did you set the idle speed and mixture? The curb idle should be set with the vacuum advance CONNECTED and the engine completely warm. If your chilton's shows the procedure for a '68-71 V6 CJ, use that. That Jeep used a 225 cid V6 with the Rochester 2bbl.
The idle speed screw should be set for 650 rpm (7 is ok too), then the left mixture screw set for maximum speed, then the idle speed screw set again, then the right mixture screw adjusted for maximum rpm, then the idle speed screw set again, then the mixture screws turned in (leaned) by 1/2 turn, then the idle speed screw set again. This procedure gives the optimum idle mixture. (I think it's called peak optimum idle method, or something. )Yes, there are two mixture screws. The engine may seem like its idling ok with way too rich a mixture, so it's easy to be fooled if you just turn the screws until it seems right. This is not only bad for fuel economy but also bad for your piston rings due to washdown of the oil.
The manifold vacuum numbers sound just fine, maybe even on the low side for some engines. The idle manifold vacuum on my 1.8L 4cyl Miata is 26 and on my 2.6L Straight-6 BMW is 23. The brief jump is just what it should do. The brief jump number should be 5-10 inHg higher than the low number on let off, and lower on blip, depending on altitude and atmospheric conditions.
The idea behind vacuum advance is to provide better fuel economy at low rpms and part throttle. At idle, the advance is slight, maybe a few degrees. Off idle, as the throttle plate opens, the port sees manifold vacuum and advances the timing to add low rpm power and improve fuel economy. As the engine speed increases, the centrifugal advance adds advance to the vacuum value, because more advance is needed at higher speeds. As the throttle is opened more, the vacuum drops and the timing is retarded slighly by the vacuum advance to prevent knocking from the extra air/fuel mixture. As road speeds are reached and the gas is let off and the throttle closes some, the vacuum builds back up in the manifold, and the timing is advanced more. If the throttle is closed at high rpms, the timing is advanced fully due to the high vacuum and full centrifugal advance and the early firing of the pistons helps compression braking. Vacuum advance makes no differance in full throttle engine power, it is just there for better fuel economy and knock prevention.
I don't know that you need the complexity of the Cagle regulator. A simple pressure regulator set at 4 psi should do the trick just fine. The 2G carb has a good float/needle valve setup that will hold fine as long as the float is not bad. (I ran a 2GC on my jeep with a 225, I just got a Qjet and an Offy manifold) I had one go bad due to a backfire and the carb flooded (literally) and I almost had a fire. I have a mechanical fuel pump. I replaced the foam float with a brass float when I rebuilt the carb.
1955 Willys CJ5 Buick 225 V6 160HP 270ft-lbs, T90 trans, Warn OD, PTO winch, Spicer 18 T Case, RS9000's, Dana 25F/ 44R,
5.38:1 gears, 11" brakes, Bestop Supertop, Hurculiner