At what revs should I sync the carbs? I did it at idle (1000rpm) and when I gave it some throttle (3000rmp) the nr 2 and 3 carb had higher vacuum than 1 and 4. When it settled down to 1000rmp it was OK again.

 

https://cbrforum.com/forum/how-tos-8...ctures-115891/

 

I used the link that Sprock mentioned, great help. I too had some small fluctuations when revving but then at idle all was good. I think as long as your idle is set correct and they sync at idle you will be fine. Just my useless 2cents.

 

i cant see any pix on that link. anyone else?

 

You are right there ^

I 'll pm Naga ask if he can fixit

In any event here's his video on it

 

The vaccum levels will go off when you open the throttles. It's not an issue.

One thing to be careful about .... Don't rev it up too much or you can suck the fluid into the engine. It shouldn't hurt the engine (unless it's an old stick with mercury) but you would have to rebuild your stick.

I find that if I set mine to be even at 1800 rpm I still get a smooth idle but it reduces an unevenness I get at that rpm.
Just a thought to consider.

 

Hey:

Just so you know street bikes all get sync'd at idle 500 -1100 RPM depending on altitude. Only race machines get sync'd at higher RPMs in the max powerband where it is used at. If done by this method, at idle or lower RPMs it will be off and not in sync. Drag bikes done this way are very hard to drive on the street, if even able too at all. Also if you have not purchased a carb stick tool yet, I highly recc the Morgan carb tune Pro, then you never have worries of fluid suck up or issues with bubbles and are by far more accurate over the long haul.

Morgan Carbtune - carburetor synchronizer for balancing motorcycle carbs.

I went from a Motion Pro Professional carb sync tool, to the Morgan Carb Tune Pro and will never go back to another type again. Ive tried the newer electronic battery type and they are dead on ACCURATE when the batteries are new, but accuracy falls off quick when they start to go. Older gauge type vary a lot and not as accurate as the others and need calibration to be keep in tolerance, so are more hassle than they are worth in MHO.
Also check valve clearances are in spec, prior to doing a carb sync. A compression check is the 1st order of checks (with leak down if you can), valves clearence checked, and then the carbs sync'd, for a proper tune and check up, as one may affect the others adjustments if not done this way. Also log and date all the info for future refs.

Dub

 

I have a Carbtune Pro and find it to be an awesome piece of kit. It got the carbs on my 89 spot on.

 

^ Me also Bordo - the Carbtune is the "one" imo too

 

The carbtune looks like the ticket.
Dub I mentioned that I sync mine at 1800 because I have a 1/2 mile of gravel road to my house that has a steep downhill decent. The speed I descend works out to be right around 1800 rpm.
If I sync at 1050 per the book, I get an unevenness and slight surge at 1800 rpm.
If I sync at 1800 it's is gone but I still get a rock solid idle.
It's a compromise I make on my bike that may not be appropriate to anyone else's.