With reference to vacuum sync for Mikuni 33 smoothbore carbs,
wiredgeorge wrote: Don't see a reason why you couldn't drill/tap intake runners. I have installed vacuum spigots from an old set of carb holders into a set of larger carb holders. It is kind of a pain to get them out of the old rubber but it can be done. If you drill/tap, you will have to use adapters to do the sync but if you modify the rubber carb holder, you can just shove the hoses from the manometer onto the vacuum fittings you installed.
Sudco recommends only mechanical sync for smoothbore carbs.
Such mechanical sync is also known as bench sync, where the carb assembly has been removed from the engine and is on the work bench with the top caps removed to allow access to the throttle slide adjustments in each carb.
After the bench sync, when a "running sync" with manometer or vacuum gauges might be thereafter performed, Sudco says the detached caps allow air leaks which adversely impact a "running sync."
In summary, Sudco says to carefully bench sync, followed by pilot air screw tuning of the idle circuits with the carbs fully assembled (i.e., caps attached).
However, the stock Mikuni carbs with manual slides and side-located pilot air screws would be expected to have the same "air leak" with their caps removed, as noted by Sudco. Moreover, the Kawasaki FSM details the procedure for both bench sync (basically same as the mechanical sync described by Sudco), followed by a running sync with caps removed and manometer or vacuum gauges attached.
Am thinking most smoothbore tuners, including wiredgeorge, perform both bench sync and running sync, the same as for stock manual slide Mikuni's as provided in the FSM. And I have long enjoyed success in syncing smoothbores by following the FSM stock carb sync procedure for Mikuni mechanical throttle slide carbs. The dreaded "air leaks" with caps removed hasn't been an issue. And in any event, running sync may be easily verified by reading the manometer or vacuum gauges after the top caps are replaced.
Let's say that bench sync has been done, and the carb assembly is now reattached to the engine, and the carb caps are off, and manometer or vacuum gauges are attached, and engine is idling, and sync screws have been adjusted to provide the best equal vacuums in all carbs, and the slide adjustments have been locked. Next, turn off the engine, remove the manometer or vacuum gauges, and replace the caps. Then re-start the engine and proceed with final fine tuning of the pilot air screws.
Remember to have a fan blowing on the engine to keep it from over-heating while the engine is at idle rpm during the running sync process and pilot screw fine tuning adjustments.
Here's a tip about bench sync that might not be mentioned in the FSM.
When setting the slides to equal heights (with paper clip, drill bit, wire, or whatever), be sure to have the idle adustment screw threads in approximate mid-position or at least in a position to assure that the slides may be lowered during the running sync. Neglecting this step may result in being unable to sufficiently lower the idle rpm. For example, when fine tuning the pilot air screws gets the idle rpm too high, it's important to have some threads remaining on the idle adjustment screw in order to reduce the idle speed.
The following user(s) said Thank You: daveo, DobbinsCMA
The air box is always preferable for all weather riding. With my 28's I could tell I was running out of gas at high speeds under load in 5th on the grade going into town. I changed the float valves from 2.0 to 2.5 and that helped. Once I got the 33's working properly kinda, that wasn't an issue. At first the way they were set up it was all on or all off. Now I can cruse through the parking lot or slow streets and when I want to get on it, it's all there.
The two inner ports are hard to get to so I made extensions with short tubing with nipples on the ends. As suggested here I will use solid brake line for my fittings. I can experiment with my old holders to see if I can install ports in them. If so I can have Jeff fill the holes and sync them that way. We'll see.
I'm sure I'll get an argument there but think of this, at speed the air is rushing by creating a vortex in that area. As explained to me so long ago, the frame becomes pressurized allowing more air to be available to the carbs. Aside from issues of air starvation, wet conditions, carb issues, the air box is the way to go to prevent this, that is unless you're on the track doing 10 second passes. IMO