This is going to sound really cheesy when you read it, but keep in mind all you need is something to show pressure differences. I've tried to come up with a slightly different design, but so far haven't been able to source materials cheaply enough to suit me. Ok, so here's the general idea. I created a clear cylinder with a loose membrane in the middle separating it into two halves. Each end of the cylinder is sealed except for a nipple where tubing is hooked up to to the carbs in question. If the membrane moves one way or the other, you can tell relative difference in pressure. The pulses are worked bout because the membrane is loose enough so that it can move significantly into one side or the other. Ok, so let me clear up how I made this contraption. I tell you how it works first because you'll laugh at it's construction. I took two 30 mL syringes and removed the plungers. The big ends were stuck together. You should get the idea of the cylinder with the nipples on either end. So what did I use for the membrane? An un lubricated condom. Hey I did warn you you'd laugh. I used little bull dog clips to hold the syringes butt to butt so to speak. Perhaps a poor choice of words considering. In any case you can easily see the condom move toward one side or the other depending on which carb has the greater vacuum. You simply adjust until you get it to sit there nicely in the middle. Pretty darn cheap, too. I should warn you that the condom doesn't last that long and if you only use the contraption every year or two, you'll likely have to use a new one each time. Besides, who wants to re-use condoms anyway?
I thought a person could make something similar and perhaps a bit more elegant out of hard wall clear acrylic tubing using a nicely matched ping pong ball as your separator, but I found it wasn't cost effective for a tool used so rarely. Yeah, there's a condom joke right there for you, too.
