Carb sync.

[Roy]

When trying to sync the carbs on a Yamaha xs1-b using welding rods, or drill bits, what holds the butterfly in that position?

 

[5twins]

The idle speed adjustment screw. It's the stop for the throttle cable bracket and moving that opens or closes the butterfly plate.

 

[Roy]

The idle speed adjustment screw. It's the stop for the throttle cable bracket and moving that opens or closes the butterfly plate.

Got it. So you DEFINITELY have to keep the idle screws in sync. This whole carb adjustment thing is pretty darn overwhelming. Now I discovered the pilot screw won't kill the engine when I turn them all the way in.

 

[OlFart]

Have not researched XS650 procedure. However, I once had a Moto Guzzi Ambassador. The method for synchronizing the carbs was to use a pull the opposite spark plug wire from the cylinder being adjusted. When the idle speed of each cylinder matched the carbs were balanced. That was with a points and condenser ignition. With an electronic ignition there would be a chance of damaging the system if the unplugged wire was not grounded. This system should not be used without comment from others in the know. The mentioned system is best with the use of a tach meter for exact balance and does not effect balance above the idle rpm range which usually includes the low rpm range.

 

[gggGary]

There's two parts to it; the throttle cable slack adjustments so with enough throttle that the slides are off the stops the carbs are balanced, then set the stops so the sides match when the slides are on the stop screws.. I'm a luddite but hand over the mufflers, matched exhaust pressure works for me.

 

[OlFart]

There's two parts to it; the throttle cable slack adjustments so with enough throttle that the slides are off the stops the carbs are balanced, then set the stops so the sides match when the slides are on the stop screws.. I'm a luddite but hand over the mufflers, matched exhaust pressure works for me.

It has been decades since I had that Ambassador. That sounds correct to me. I did like their method. I had a tach meter. Actually one could get close by ear. I had forgotten about hand over the exhaust. Another seat of the pants approach. You sound old school.

 

[5twins]

Yes, it's a two step process, but you need to do the idle sync first because changing the idle speed changes the amount of freeplay in that carb's cable. That would throw off your "at speed" (slides lifted) sync. So, sync and match idle speeds then sync the cables so slide lift (or in our case, butterfly plate opening) starts at the same time on each carb.

 

[OlFart]

Yes, it's a two step process, but you need to do the idle sync first because changing the idle speed changes the amount of freeplay in that carb's cable. That would throw off your "at speed" (slides lifted) sync. So, sync and match idle speeds then sync the cables so slide lift (or in our case, butterfly plate opening) starts at the same time on each carb.

Hard to believe just how much I have forgotten about that Ambassador procedure. Over the years I have had many different brands and models of bikes. I usually consult repair manuals first before doing anything to a motorcycle and I am not ashamed of that fact. I even consult the manuals as a reminder and double check if I had previously done a procedure because it is easy to recall incorrectly. I have never been perfect. Ha! That I am still alive is mostly a matter of pure dumb luck.