Ok, so I'm trying to synchronize my carbs, for the second time. (The first time it couldn't get the #1/#3 to even out and then realized that some previous mofo must have lost the standard M4x0.5 screw and put in a standard M4x0.7 which had stripped the threads... ) After taking them off and tapping an M5 screw in there I'm back at it again.

Anyway, here's the question: Does the vacuum go up or down if you open the throttle? It goes down, right? (Bigger opening to the atmosphere, more air gets in, less vacuum.) So the proper direction is to close the throttle on the cylinders that have too low vacuum.

This seems counterproductive because if you *open* the throttle, then the vacuums go up. But that's because the engine is speeding up. Since all cylinders are going at the same speed, higher vacuum means too closed throttle.

The reason I'm asking is because I'm having a hell of a time getting to an even point. When I turn the screw that adjusts front vs back, the two back ones also change relative to each other. Turning the screw that adjusts #1 vs #3 doesn't obviously do anything. I don't know if something's loose or whatever, but it's really frustrating.

This is your problem, It doesnt adjust front vs back.

It's not like balancing an inline 4. Where you have 3 screws (one for each pair and one for front / back)

Wth the NC30 Carb #2 is fixed, you can't adjust it, this is the front left carb , it is called the base carb.

You have 3 adjustment screws, On the NC30 each screw adjusts the vaccum on a single carb only. (the carb its closest to)

You set the 3 adjustable carbs so they are the same vaccum as carb 2 that you can't adjust.

This takes a bit of time if they are out as adjusting one carb will have a knock on effect on the others, so you have to go around in circles adjusting each of the 3 carbs one at a time.

I usually find the carb that is the most away from number 2 carb first and bring its vaccum up or down (by turning the screw in or out) to match number 2, then adjusting the others.

Hope that makes sense

Neosophist wrote:This is your problem, It doesnt adjust front vs back.

Well, damn! I looked at the linkage and just could not understand how it would adjust front to back but, since that's what the Haynes says, I thought I must be extra slow today. That makes more sense then. I did eventually manage to get them pretty well adjusted by randomly turning screws trying to figure it out.

Thanks for clearing that up!

I synced mine off the bike there are 3 holes in the Venturi inlets by the butterfly's. 3 carbs are adjustable just set the 3 to the same as the non adjustable carb works a treat my bike runs great and ticks over 1000-1200rpm