I know, this is somthing I'm going to have to tackle, making the modulator on my Cruisomatic C4 work, with the boost. I know that I have to put a check valve in the vac line, so it won't boost to the modulator, but also, the modulator would also have vac all the time, because of the check valve, how do I overcome this? I'v been told to create a slow leak in the vac line, and it would 'work' but I don't think that's a good idea, unless that's the only way to do it.