Vacuum levels

[anton van tonder]

Can someone tell me what the vacuum levels should be on a cbx1000 1980 model for sync. I use carbtune and the engine is a rebuild bigbore. She fired up first time. This bike is a complete rebuild. My son and I balanced the carbs and set the mixtures with colourtune.

The engine sounds good except slight clutch rattle. This is still the original basket.
All the fundi and experts can probably help me on this matter.

Regards from oz
Anton

[tevan]

I have done several of these bikes and the reading really does not matter. You just need to get all real close or dead on.
There are others on here probably knows a hell lot more then me on this but this is what I have found.

[anton van tonder]

Hi Mate,

Thanks for your help!!! I thought as much.

I have done balancing and carb tuning on my kz1300 (x2) many times, but on the Kawa machine you cannot have low vacuum levels. Normally above 22 cm/hg. Perfect vacuum 24/25 cm/hg on carbtune. I found the cbx carb much harder to work on due to lack of space.

The best vacuum levels for the CBX that I got on the carbtune was between 14 to 16cm/hg. I could not find any info in the manual about the vacuum levels. It is probably the worst manual ever.

Regards from down-under
Anton

[daves79x]

Don't know how it equates, but I usually draw 7-8 inches of vacuum at 1000 rpm when carbs are balanced.

To your other point, most guys think the Honda CBX shop manual is one of the best.

Dave

[EMS]

It doesn't really matter what the level is. What matters is, that they are the same on all carbs. The actual level also depends a bit on the fluid. Mercury would be different than a water mix. I am not familiar with the "carbtune" instrument.
What does the level scale cm/hg represent? One inch equals 2.54 cm. 14-16cm (of mercury?) would be 5.5 to 6.3 inches

[herdygerdy]

I recall in the Carbtune manual, they say it doesn't actually matter what the level itself is, but it is very important you get them all as close to equal as possible.

It's also a good idea to check and adjust your valve clearances (cold) before doing this.

And in some cases, they even suggest inverting the unit to get reasonable readings and movement of the slides. I have had to do this from time to time.

And of course, No. 4 is set at factory, so all the other 5 cargs are set to that carburettor. You set 5 to 4, then 6 to 5 and repeat until as close as poss., then on the other 'side', 3 to 4, then 2 to 3, then 1 to 2 and repeat as needed.

It is a process that can not be rushed, and patience will be well rewarded. A big shop fan blowing on the engine will help keep it and you cool. Don't rush it and take plenty of coffee breaks.

As you get closer to having them equal, you will hear and feel the engine settle right down and even most of the clutch rattle will disappear.

Have done many of these now with my carbtune kit and can not speak highly enough of them.

Cheers..Tony.