bench sync...

does anyone know which end of the carb do you look at and measure to bench sync a set of carbs before installation?Through the front(by air cleaners)or the rear(by carb holders)?Im thinking rear but want to ask before I screw it up!!Thanks
Tony

The front of the carb at the intake manifolds. Or as you put it the rear.

thanks milkman!

Wasn't there a guide to bench-syncing somewhere? Trying to e-mail a member how it's done, and I coould have done it myself in the length of time it takes to explain. I'd promise to save it in my favorites this time.

Now I found this:
members.dslextreme.com/users/bikecliff/i...carb_sync_notes.html

Here is what the FSM has to offer (first page)....

second page.....

pix are worth $1,000,000.00 ...

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edit: MEH! These pix are the HUGE!!! Diagrams are to the right in the scan image.

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this is from a 78 KZ 650 D1 (SR), but itm was the same on the 78 650b I used to own.

Wrong side - notice the large gap:


Correct side - notice the square cutout:


Scan from the manual :

Bench sync is performed to get the four slides approximately opening and shutting together with the same amount of gap between the venturi and bottom of the slide. The MAIN purpose of bench syncing is to make sure this opening/shutting happens in the middle of the range of adjustment of the idle screw. In other words, if you can't complete close the slides using the idle screw OR open them sufficiently to set the idle speed properly you won't be able to operate the bike. I bench sync hundreds of carb assemblies a year and it is really important to get it right with manual slide carbs; not so much with constant velocity where the bench sync is only to do the secondary purpose and that is to get all four slides working at the same time. In the case of CV carbs, this is done by getting all four throttle butterflies cracked the same amount. Ok... to bench sync mechanical slide carbs, loosen all four locknuts on the sync mechanisms. Then back the idle screw out till one of the slides is completely shut. You can use the adjusters at this point to get all of them completely shut if they are not. Then turn the idle screw IN until you raise all the slides about 1mm. Then use the slide adjuster screws to CLOSE all four slides again. Turn the idle adjust IN till one of the slides is open an eyelash and use the adjusters on the other three to make them LOOK like they are open the same amount. It is actually more accurate to use your eyeball than to use a wire as suggested or at least it is for me. If you use a wire, make sure it is a VERY thin wire as suggested because if you use nails or other large objects as some suggest, the idle adjust range won't be right. Last, put the carbs on your bike and use a manometer to synchronize as they won't be perfect but at least you will be able to open and close the slides sufficiently.

Very helpful information. I just bench synched my 81 550 but my slides have about a two millimeter gap when closed. With this said, it still helped tremendously! Guess I'll be doing it all over again tomorrow.

just subscribing cause im getting my 29's ready to go back on my 78 1000.

Last, put the carbs on your bike and use a manometer to synchronize as they won't be perfect but at least you will be able to open and close the slides sufficiently.

Yeah, no kidding! The CV carbs on my twin were way out just bench synching them, I was surprised how much they were out when I put the manometer on them.