Carburetor Synchronization

[Kiwi_XZ]

Hi all - a small story...

I decided I would have a go at sync'ing my carbs today, the bike has now done about 2000 kms and appears to have been going OK but with all the other things I've been doing I just haven't had time to do this.  I also need to get a manometer and as I'm to tight to go out an purchase a mercury manometer (I couldn't find one in New Zealand for under $100.00) I decided to build one using ATF fluid from plans on the internet.

All went well with the building, I used clear tube and mounted it on a piece of 4 inch by 1 inch pine about a yard long.  The tube looped at the bottom and was held in place using cable clips.  I graduated the board in 2 inch graduations so I would have a reference during the sync'ing.  The whole thing looked very professional.

Warmed up the bike and connected the tubes, at idle (1350 rpm) the fluid shot up the rear cylinder tube and started to march off towards the manifold.  Oops, shutdown!  I try a few things.  Thinking that the tubes may be leaking at the manifold ports I try fitting small hose clips, no improvement.  Only after I disconnect the sync rod to the front carb and find that the ATF fluid now wants march off to the front does it dawn on me that my problem is a big split in the manifold vacuums and it is beyond my cheap ATF manometer to measure.

I quick trip to the local Auto Parts Shop and I purchased a couple of cheap vacuum gauges.  At idle they dance all over the show but at 3000 RPM they settle to a steady figure so I set the sync at that point and then when I connected my cheap manometer I could carry out a final fine adjustment (about 1/4 of a turn).

It worked for me!

[h2olawyer]

My first use of the ATF manometer had much the same result.  I used about 20 feet (6 meters) of tubing so I had lots of time to get things shut down - at least I thought so.  As I started the bike, the ATF ran quickly to one cylinder (can't remember which now) & I got the bike shut off just before it went over the top.  I just used trial & error synch rod adjustments to get it closer & finally was able to use the manometer.  Now that it's been so close, I have been able to check the synch on a regular basis & it has never been more than a couple inches difference between the tubes.

ATF is used because if it does reach the cylinder, it will do no harm & burn off.  Probably will make a pretty good smoke screen, though.

H2O

[MotorPlow]

The homemade manometer that Rick G. built for me has a simple shut off valve on the clear plastic tubing. This way, I can leave the bike running, adjust the carb sync rod and then simply open the manometer valve to see where it is. Then if it's close, leave the valve open and adjust the sync rod. If it's not close, I can simply (and quickly) shut the valve and keep the ATF Fluid out of my engine.

[Superfly]

I used vacuum gauges (2 of them) and they work fine for me.

[Kiwi_XZ]

Hi all.

In total I had about 8 metres so that must be around 28 feet, the tube was so long that by the time the metre or so of ATF was drawn thru it had aerated and dispersed along the tube allowing me plenty of time to kill the engine.

The only hassle was waiting for it all to collect back at the base of the manometer.  The valves allowing quick shut-off are a good idea, I think I'll incorporate them in the design.  They'll also help with storage.

The vacuum gauges worked well also, crap at idle but then I can't understand why the manuals suggest it is carried out at idle.  Normal range would be above 3000-4000 rpm anyway.  That were I set it up initially using the vacuum gauges and it worked well.

[Lucky]

the vacuume guages the bike shops use have a metered oriface. a jet could be used in the lines this would give you a smoother reading at idle.  probably wouldn't hurt in the fluid manometer as well.

Chris, i'd like to see the valve Rick used. (great idea!) can you post a pic?

where is it located? at the center of the tube?  i wonder if it'd really matter...

[MotorPlow]

Sorry about the large photos, but I don't have phot editing software on this computer to resize them....

[Lucky]

 i see, fishtank stuff.  twhat's the "T" fitting with the red cap for? filling it? what do you fill it with? squirt can? (i love those old fashioned brass squirt cans, their cool)

[MotorPlow]

Dunno, never had the red cap off. Rick sent it to me pre-filled.

[Extent]

When I sync with the homemade manometer I clamp the tubes shut with a pair of pliers in one hand so I can slowly let off and see if it is really out of sync.  If it is I can just clamp back down again and reach over and kill the engine.  You can also slowly twist the sync rod with your other hand to keep it under control untill you've got it completely released.

[jasonm.]

It appears you have a balance tube set up. You are trying to have equal vacuum. If one side is significantly stronger...the fluid can get sucked out. The old style syncs used heavy mercury. It takes a real error to suck mercury out. I now have a Morgan carb-tune. Uses steel rods in glass tubes. Works exc. You can always try 90wt. gear oil???