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bench top carb sync process??

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G

Guest

Guest
What's the process to check carb sync on a bench?? I have an 85 GS550L, with 2, two-barrel carbs. I want to verify it's close before installing back on the bike.

also, how much gap should there be from the bottom of the slides to the carb body when the carbs are sitting on a bench?? As I look through the intake ports, there appears to be about 3/8" - 1/2" gap. Is that right??

Carbs are Mikuni BSW30SS, ID # 43510.

Thanks!
 
To do a bench synch reassemble the carbs and bolt them on to the holder. They should be ready to go on the bike. Go to the carb that is fixed to the throttle plate and use the idle adjustment screw to open it so that a small drill bit shank will barely fit through the opening. Then using the synch adjusters set the other carbs to the same opening.

The gap in the slides sounds about right.
 
How small a drill bit are we talking?? Fit through what opening?? I only have 2 carbs.

As you can tell, I'm a newbie at this.

Thanks for the input.
 
Smaller

Smaller

The smaller, the better but it won't be just right without adjusting properly after they're on and running. (The 'opening' is the one between the round 'butterflies' that open and close.)
 
Last edited:
1/16 to 1/8 inch would be fine. Is your right carb the 'master'? The master carb is the one that has the throttle cable attached to it. With the carbs on the bench, adjust the master idle screw until the drill bit will slide through the butterflies with just a bit of drag. Use the sync adjuster screw between the carbs so the other carb has the same amount of drag on the bit. This gets them close enough to run the bike so you can do a vacuum sync.

Don't forget to return the master idle back to about where it was, or you will have one racing engine when you hit the starter. :shock:


.
 
Thanks - i'll give it a try.

of course, you know what my next question will be - I'll be clueless about the REAL sync job on the bike!!

Gotta get a vacuum gage first - is there a particualr reading (vacuum level) I'm shooting for, or just to balance the two to each other??

thanks again for all the help - you guys rock!!
 
Gauges

Gauges

In my experience with duel carbed bikes, I think you can get it very close without going to the expense of getting the gauges; I would certainly try that first.
If you do use them, one will go up a little when the other goes down and so on. When you get them the same, all should be well. You also might try it at a couple of different RPM ranges,while you're at it....and adjust accordingly.
 
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