Ideal RPM for carb Sync

Got the mercury stick out at the weekend an synced the carbs. Did this with engine at working temp at idle, about 1,200 RPM. Mercury was a little bouncy but all fairly well balanced at around 18-19 cm.

Should I be doing this at perhaps 2,000 or even 2,500 RPM to obtain a truer result?

Thanks.

I've always done it just like that - idle speed on a warmed engine. But then I'm no expert.

The difference will be greatest at the lowest idle speed. At larger throttle openings, the difference becomes much less (as a percentage of total opening).

Also, the device is only accurate near the RPM at which you calibrate the tool.

Thanks JR. Just wondering if the less "bouncy" results I can get at 2,000+ might be a tad more reliable than the 1-2 cm bounce I'm getting at 1,200?

We'll see if anyone else has an opinion.

Actually, setting your idle using the tachometer is often misleading. The tach on many KZs is too inaccurate to use to set idle speed. Get an external shop tach if you feel like you need to get the idle exactly in spec. The bike should idle smoothly when you sync the carbs. 2K rpm is likely a bit high.

Here's how to calibrate your manometer.
The restrictors are just little plastic plugs with a pin hole in them. You enlarge the pin hole (very slightly) on the tube that shows a low reading.




Post edited by: loudhvx, at: 2007/07/02 15:01

When blippling the throttle, often air may show up in the tubes.
Here's how to remove the air bubbles. They affect the reading so should be removed. You can get the syringe (no needle) at any pharmacy, drugstore etc.
While the engine is hooked up and idling, you connect the syringe and pull. The mercurey will drop in all the tubes. Then let the syringe return slowly and the mercury should raise in all tubes slowly. There should no longer be air in the tubes.



Post edited by: loudhvx, at: 2007/07/02 14:59

WG, I may have been unclear? I was just asking whether I should increase the idle to 2,000+ in order to perform a less "bouncy" sync, then fully intending to crank the idle back to 1,000 (ish) once the sync was done? Thanks for the suggestion of using an external (more accurate Tach).

LOUD, thanks for the two suggestions regarding the manometer. Obviously the better dialed in the tool, the better the end result of the sync. I'm in the office 15 miles from the manometer right now but, from memory, my manometer doesn't have a vent "tube" as such, perhaps just a small hole in the rubber cap that goes over the mercury resevoir? I'll get a small piece of tubing and insert it through the hole to perform the bubble removal exersize.

I'm assuming the tube I insert must go all the way down into the mercury.

The vent should NOT go into the mercury. It vents the air above the mercury in the reservoir.

If the levels are severely bouncy, it could be the restrictors are missing or in the wrong place. Sometimes people put the hoses on backwards and the restrictors end up on top of the mercury tubes. That would make the levels bounce more.

Whatever RPM you use to calibrate the tool is the RPM you want to sync at.