I figured I did the DIY over at another forum, so it'd be fair-game to start spreading the DIY knowledge!
A quick side-note on what this process accomplishes. Being as this type of motorcycle uses two carburetors (one for each cylinder) for maximum efficiency you want to ensure each cylinder is working equally. A sure-fire way to 'check' to see how hard each cylinder is working is by seeing if both of the cylinders are pulling equally. So how do you check to ensure each cylinder is pulling identically
... Carburetor syncing!
First off here's all the parts I used...
(2) Identical glass bottles
(1) section roughly 10'-15' in length of 1/4" ID hose (sold at any hardware store)
(2) rubber corks (also sold at hardware stores). BRING the glass bottles with you so you can find a cork that will fit in the bottle to seal it!
(1) 3/16" 4-way vacuum tee (sold at auto-parts store)
(2) 3/16" vacuum caps
You can use damn near any glass bottle for the task (I liked the tallness of those expensive 'sparkling water' bottles so I used them). Only fill them up a 1/3 of the way with something like vegetable oil (It's preferred to a liquid like water as it won't develop algae). Drill two 1/4" holes in two rubber corks. This is trickier than you'd think as rubber will expand after you drill the hole, so you have to keep drilling in and out into and test fitting until you can slide the 1/4" ID hose in
very snugly. First cut a length of 1/4" ID hose that will go through the corks and touch the bottom of each bottle (So each bottle is connected via this one hose). Then then cut 2-4' long or so hoses to actually hook up to the carburetor ports. Each of those hoses will go into one of the bottles (One for each port) and only needs to protrude slightly past the bottom of the cork (Otherwise that carburetor will suck up vegetable oil).
I've scared up a little diagram of the hose routing as to solidify HOW to route it...
On the bottom of the picture I also used one FOUR-WAY 3/16" vacuum tee (although I used the tee in the project so in the picture is a three-way tee). and two 3/16" vacuum caps.
To begin:
I made 'permanent' vacuum taps for each cylinder and I found it easiest to do on the left side of the bike. This entails that you can easily sync your carburetors in the future by simply removing two vacuum plugs and hooking up the sync'ing rig...
Zooming in you'll see a tee that ties into the right cylinder that tees one way to the fuel shut off and the other way towards the front of the bike.
I took this tee out and added a 4-way tee and simply plugged (with a vacuum cap) thus providing a vacuum port for the right cylinder. SAVE the 3-way tee as you can use it for the other cylinder.
If I zoom out a little bit you can see the new tee with the blue vacuum cap on it. Now for the right cylinder...
Remember that little tidbit about 'saving' the 3-way tee from the left cylinder's vacuum lines? Simply cut an 1-1/2" section of hose from where it connects (see above) add that tee, a vacuum cap and viola!
So now you have a vacuum source from each cylinder that you can use to test how much each cylinder is pulling at idle. Sitting right between each carburetor is a lone screw which you can adjust the bias between each throttle on each carburetor (odd wording I know).
Right about now I'd suggest taking the bike out and getting it up to ideal running temperature (with the front fairings off). Hell I ran out to pick up some cheapy vegetable oil myself for the test rig. Once you return hook up the test rig...
There are various ways to check the vacuum force of each cylinder and the two bottle method is an easy way to visually see this. Here I have a hose going from each test port to each of those bottle mentioned earlier. If you look in the middle of the picture and see a small phillips screwdriver? That's the bias screw for each of the carburetors.
Before you say, "How the heck do you get TO that screw?" I've found the ultimate tool for doing ANY carburetor work on the 250's
Your local hardware store should sell this: The Milwaukee Offset screwdriver. It allows you to get into tight confines and turn things that need to be turned
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I filmed a video of the carbs out of sync and of them IN sync, but the quality was lacking and it was hard to distinguish. I mentioned ONLY filling each of the bottles 1/3 of the way up and here's where this comes in handy. After you hook up the test rig and fire the bike up it can be hard to see what's going on. I let the bike run for a minute to make sure it was at ideal operating temperature and at that point one of the bottles was 2/3 of the way full and the other was empty (The carburetors were very out of sync). I started turning the screw down and slowly a very bubbly (and very visible) stream of vegetable oil began transferring back to it's original bottle). Once the bottles were close to equal in oil again I backed the screw off until the bubbly oil in the transfer hose (between the two bottles) ceased moving. Once the oil is still in the tube connecting the two bottles, your carburetors are in sync. Then after shutting off the engine you can disconnect the rig and put vacuum caps on the open vacuum tees.
You can also adjust your idle if need be as the bike is in ideal running order and fully warmed up. People keep asking how and what to adjust the idle to. The manual says 1,350 rpm, but I found the bike happy at 1,500. To each their own I suppose.
In the above picture is a shot with the fairing back in place of the idle adjustment knob. It's easily accessible although you really don't need to use it often (I KNOW a lot of people love turning things and calling their selves mechanics ).