Balancing your Carbs!


American Infidel
This is a great write-up by our very own Sweatmachine!

1. The bike needs to be warmed up, as in ridden for 15-20 minutes.

2. With the bike running, adjust the idle to around 1500 RPM’s (black knob on left carb near the bottom, turn clockwise to raise, counterclockwise to lower).

3. Kill the bike

4. Remove the vacuum nipple caps from each intake manifold/carb; they are between the carbs and the head. Some folks call them 'squirrel condoms' here is what they look like (thanks Dinqua)

5. With the Mercury already in the tuner, hook one hose to each carb's vacuum nipple.

6. Fire the bike up, check the mercury levels. One will probably be higher, that carb is experiencing more vacuum.

7. Turn the adjuster screw with a Phillips head, tiny tiny tiny tiny tiny amounts at a time. Think 1/16ths of a turn. It might be easier if you raise the back of the tank but I can get my hand in there. here is the adjuster screw (again, thanks Dinqua):

here is what I use, I welded a Phillips tip into a socket:

Once you get the mercury levels right then rev the motor a bit, maybe to 2000-2500 RPM’s, they should rise/fall then settle at even levels.

It's not that bad! Once you've done it you will be fast!

Here’s something I found that I don't think has been mentioned yet, though I only skimmed the thread. The 4 tubes are not going to be exactly the same because the openings in each restrictor are never perfectly matched. In other words, one might show a different level than the next given the exact same vacuum amount. So here’s what I’d recommend, I found it worked for me because i got a different balance after doing this and it was obvious that it was the correct balance.

Leave the cap or hose (which ever happens to be on the nipple you are using) on one side and attach just one hose to the bike on the other cylinder. Start the bike and turn up the idle knob till its high enough to keep a fairly steady mercury level. Note on the gauge where it is staying on average. Now disconnect it and do the same thing with the other 3 hoses until you find 2 of them that are matched closely. Two of them that should the same level on the gauge. Its very unlikely, but if no 2 are close, or you just want to get them even closer than is necessary for peace of mind or just because you are anal, you can use a pin to slightly enlarge the hole in one of the restrictors on one of the tubes that reads lower than others till it matches one.

Anyways, it just goes to show that these gauges are not real accurate. Whether or not they are more accurate than is really necessary or not is a matter of opinion i suppose. But the point is that since our bikes are only 2 cylinder and these gauges have 4 tubes, we have the ability to pick and choose the 2 that are closest and end up with a better balance.
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I use a homemade balancer that consists of a yard stick, some zip ties, clear tubing, a small ball valve, and some 2 cycle oil. Works very well. The small ball valve was added by a member of another site but was a great idea to control the liquid. It goes at the bottom on the loop and can be slowly opened sop nothing gets sucked into the engine. If too far out leave it closed, adjust some and try again. Here it is
A couple of additional comments:

A mini-ratchet with the appropriate bits is great for working on the carbs. I use a 2-inch Phillips bit in the mini-ratchet for the synch adjustment; same effect as Sweat's tool without the welding.

I use a Twinmax electronic synchronizer because it doesn't have mercury. The needle oscillates rapidly from side to side by a few mm when connected, but it's very easy to see when it's centered on the zero mark, which is the goal.


Two Stroke
I find balancing the carbs up at 2500 rpm gets smoother results where it matters. And, like Marty, I use a mini-ratchet to adjust the screw (even in rip-off Britain they're cheap).


Okay, rookie question: Is there one screw that adjusts the balance between the carbs, or is there a screw for each individually? If so how do I know which one to adjust?