Topic: Carbtune readings.

[John]

Hey, first, thanks to everyone who helped me with my clutch issues.That is sorted here is problem #2. When balancing carbs with the carbtune, I adjust all four carbs to read almost perfectly in sync. Then i blip the throttle, wait for things to settle down and the relationships between cylinders change. Sometimes slightly, most times enough to where i need to readjust. This also happens if i hit the kill switch and restart. If it weren't for the fact that my engine would become a puddle of aluminum on the garage floor, I feel like i could sit around doing this all day getting slightly different readings each time. What am i doing wrong? The bike is a 71 cb750 which otherwise idles and runs good.Carbtune is assembled per instructions and appears to otherwise work great. Any thoughts?

Thanks,
john

[oldbiker]

This sounds as though the carbs are not returning to the closed position after you have blipped the throttle. Could be something as simple as sticky cables or a tiny bit of grit in the throttle mechanism, or even the return spring being a bit tired.

[MRieck]

Check for vacuum leaks at the intake boots. Spray some brake cleaner around the boots while it is running- if the idle changes you have leaks. Personally I'd replace the boots anyway secondary to age. Valves out of adjustment will also cause what you describe.

[kaysystems]

Are you sure that the carbtune is absolutely vertical. If not the sliders may stick a little in the tubes.

David