Questions about the yardstick manometer

[bcgilligan]

I made one of these units several years ago, and it has worked nicely on three diff bikes, vacuum being vacuum. The Keihins on my W650 and Triumph T100 are simple, one screw affairs, and rarely go far out of adjustment. Cable installation would not affect their balance, unlike on our Beemers.

One of the guys on the Triumph forum modified 'our' design by adding vacuum chambers made from automotive clear plastic fuel filter holders to the tops of each tube. Others have inserted used carb jets in the tubing to add some damping. Others use a simple screw clamp around the tubing.

Anyone here done any ot these?? The reason I ask is that I'd like to add enough buffering to keep from sucking the fluid through the engine, especially once I've adjusted the idle balance, and begin attempting to balance (via cable length) in the 3000rpm range. I use red Stabil, and it really creates quite a smoke cloud going thru the engine.

Bob

[20774]

I can't answer your question because I haven't built one of those but I've heard of some of the "fixes" that you mentioned.

But in my understanding, there's no need to try balancing the cables at 3000 RPM...you might want to do a quick check, but the balancing is done at a much lower RPM, just off idle around 1500-1800 RPM. The effect of the differences in cable tension are most noticable here because of how little the slide has moved up relative to the throat volume. At the higher RPMs with the slide raised quite a bit higher, it will harder to detect any differences with slight changes in the cable. If you can get it balanced at the low RPM and it is hugely off at higher RPMs, you should probably investigate what's wrong with the cable. It's either stretching, binding, or giving you a non-linear response.