Questions about carb synch on a XII

[Eydugstr]

Are there any special tools you'd recommend as a "must have" to do a carb synch on an XII ? Have a decent set of gauges, but will I need a 90 degree screwdriver or anything like that? Are there any gaskets or O-rings I should go ahead and buy in advance?

[triton28]

IMO a 90* screwdriver would be nice to adjust the idle mixture screws as the screws do have an effect on individual cylinder RPMs, but if the carb idle mixture screws haven't been fooled with, then it isn't necessary. Problem is without a "Color Tune" plug it is really hard to notice the different fuel mixture responses to the changes of the screw positions on a multi cylinder, multi carburetor engine. Although if one is used to the mechanics of an engine and listens attentively it is possible to notice the slight changes in RPM without a "Color Tune".
Adjusting fuel mixture on a single carburetor engine is really easy as all of the cylinders respond to the change in position of the idle mixture screw in unison.
So with a multi carburetor engine, while an individual cylinder's fuel mixtures may be richer or leaner than it's adjacent cylinder, unless it is way out of whack, it won't affect the gauge readings as the readings are of vacuum created by RPM, not mixture.
No other special tools, o-rings, or gaskets are needed.
That's been my experience anyway,
Dave

[Nails]

It's hard to find a 90-degree screwdriver to fit some of the carburetors. The normal one's are way too big. I ended up making my own out of an Allen wrench (photo somewhere on here -- it's gotta be really small). PITA to use, but I don't need to use it very often.
If you take the carbs off, I recommend marking the them so you can be sure of your adjustments. I mean, put the screws 1 1/2 turns out (or whatever), then use a Dremel to make a little mark on each side of the hole that has the screw, in line with the screw's slot. Using a dentist's mirror, you can make sure that you really turned the screw that 1/4 of a turn you intended.

[Nails]

If you plan to disassemble the carbs to clean them, you'll want to have some of the float bowl gaskets on hand. I found cheap aftermarket gaskets that worked fine. It's easy to screw them up during reassemble -- I used a very thin coat of UTV to hold them in place. Don't use much or it'll squeeze out and screw up the floats. (I read about a guy who did that.)
There's a good chance that you'll find other parts in need of replacement, so I'd recommend just budgeting time for making an order. The carbs have lots of plastic Tee's and crap, and almost all of it was rotten on my bike. I mean, rotten with holes.
It's easy to screw up the Phillips screws that hold the carb together. I had to replace a couple. They don't need to be silly tight.
Carb boots are notorious for leaking -- look at them carefully. They're pricey, but don't waste your time on sketchy ones.
I bought a cheap ultrasonic cleaner from Harbor Freight, which was about the same cost as taking the carbs in for cleaning. I'd do that over again.
There's another thread here about setting the fuel levels very carefully. I wish I had seen and done that the last time I had mine off. I think measuring the float height (per the manual) is only approximate. I recommend replacing the float valves.
Consider making the fuel line from the pump to the carbs a little longer, to give you more room to hook everything back up. It's a total PITA to hook up a short fuel line if you have to put the carbs on the boots before it'll reach. Better to have the line long enough to hook up before you slide the carbs all the way into the bike. Also a total PITA to get that lower throttle cable back on (I got good use from a long roach clip, hemostat, or whatever it's called). Everything else is just a routine PITA.
But using the vacuum gages at the end is super easy.

[Eydugstr]

Just to clarify...I'm doing a carb synch...not rebuilding the carbs.

How is everyone else getting to the center adjustment screw? The one that balances the 1 & 2 carbs with the number 3 & 4 ??

[Nails]

Sorry, I wasn't sure. You asked about gaskets and o-rings.
I vaguely remember a hassle with the center screw. Either I didn't need to fuss with it, or I might've adjusted it with the engine off -- turned the throttle to reach it. And then re-checked it.
My memory is what I use to forget things.

[triton28]

I have the upper airbox off when I sync the carbs and I use an 8", (shaft length), # 2 Philips screwdriver for the center screw.
No problem reaching/turning it.
Dave

[voyager55]

Just be sure to put as little pressure on the screwdriver as possible when adjusting the screws. I let it sit on the screw then turn it with two fingers.
To much downward pressure will screw up the sync. Take you time adjusting the screws

[Eydugstr]

You guys are taking the air box completely off and running the bike? What do you do with the igniter box? Have it dangle on the side?

I've been going by the service manual, which is having me remove the air box, get the hoses installed for the gauges, then replacing the airbox and running the bike. Granted with the air box off I can go straight down to the center adjustment screw, but how steady are the readings on the gauge without the airbox installed?

[triton28]

I place the igniter on the frame rail/harness with a bungee cord or a zip tie so it doesn't fall.
The clock type dial gauge readings aren't steady at all to start with regardless of the airbox being on or off, but with the gauge air line dampers adjusted they smooth out enough to use.
As long as the gauges all bounce at the same readings is what one is looking for, as the dial type synchronizers will never be perfectly smooth and steady.
I haven't tried the "Morgan Carbtune" synchronizer but I suspect it would be superior to clock type dial gauges as it uses stainless steel rods to register the vacuum pull.
One thing, make sure all 4 gauges register the same for a uniform vacuum source. I use a hand operated vacuum brake bleeder set each time to the same vacuum reading, 15" Hg. Then I adjust all 4 gauges to the same reading between each other, usually almost 12" Hg on the dial for my current set of gauges.
This calibration of the gauges is critical as all 4 must reflect the same reading for a known vacuum.
I have found the offshore supplied gauge sets to be not very well calibrated when one first receives them.
Dave

[ekap1200]

Having the 90 carb adjusting tool is only the beginning. You need the correct blade end for it. If you ask the tool man' be it snap on - or matco or whoever, there is a blade screwdriver with a sleeve that protrudes around the blade making it easy to get onto the screw and remain there while you adjust it. It won't slip off the screw. it is made for the 90 deg tool and is very short. Right tool for the job always works well..... You should only have to tweek it just a bit. they don't go drastically out of adjustment .
Gene K.

[HMB Don]

The 90 degree screw I used was from Kawasaki. I bought it for use on my 1994 Concours, but it worked on my Voyager1200 and my sons old 600 Yamaha. I bought this tool back in the 90s and it was pricey then.

[Nails]

The 90-degree pup I bought needs about 2 1/8" clearance. (It was specifically recommended here, in some old thread.) I think some of the XII carbs have less than half that -- much, much tighter than normal.

Here's the unit I made, sitting one a saddlebag lid for size. (The first one I made was too long.) It works as long as the motor isn't too hot; and as mentioned I verify the screw setting with a dentist's mirror. (Since I'm at 8K feet elevation, I'll take it with me in case I want to rich-up the mix for the flatlands.)

[Eydugstr]

TY for the responses everyone. Right now I'm using an older motion pro set of gauges that use mercury, which so far have been pretty stable.

Having the 90 carb adjusting tool is only the beginning. You need the correct blade end for it. If you ask the tool man' be it snap on - or matco or whoever, there is a blade screwdriver with a sleeve that protrudes around the blade making it easy to get onto the screw and remain there while you adjust it. It won't slip off the screw. it is made for the 90 deg tool and is very short. Right tool for the job always works well..... You should only have to tweek it just a bit. they don't go drastically out of adjustment .
Gene K.

TY. Because I was able to get to the outer two screws, and already had gone to the trouble of hooking up the vac gauges and re-installing the airbox, decided to just balance the individual (left and right) sets of carbs. Even by doing that much it really seemed to quiet the chain noise down, and better throttle response. What I've learned so far is that the $28 08-0119 motion pro carb tools ( https://www.motionpro.com/product/08-0119 ) will reach and work on the inner screw, but like you pointed out, is something of a PITA. I'll live with the $28 tool for now but what I will do down the road is pick up a motion pro 08-0229 ( https://www.motionpro.com/product/08-0229 )that would let me use a snap on socket with a recessed screwdriver head (https://store.snapon.com/Carburetor-Adj ... 35712.aspx) to make a routine job a little easier.

[ekap1200]

Hello again , Wow that motion pro carb adj tool is long at the end. The one I have is from MAC TOOLS and must be at least .500 shorter at the 90 deg end. But that is the socket that makes the job a snap. practically falls onto the screw....
Gene Kap

[Eydugstr]

Well, ekap...If you're referring to the $28 one, It fell under the category of "This is what the store had available at the time."