Throttle body synch.

[B.D.F.]

I have not see the videos but I would not do it the way you are suggesting because there will be significant changes between each T.B. on each side (in other words, the relationship between T.B. #1 and 2, and T.B. #3 and 4) will change as the balance screw is changed.

Here is how I do it: first note all levels on the manometers. What we are really after here is the difference, not an absolute reading. So suppose you find the following:

#1: 230 mm Hg
#2: 250 mm Hg
#3: 260 mm Hg
#4: 270 mm Hg

First, average #1 and 2 and #3 and 4 like this: the averages of 1& 2 is 240 mm Hg, the averages of #3 and 4 is 265 mm Hg. The mechanical balance screw is between cylinders #2 and #3 and changes the relationship between the opening angle of the throttle plates. So move that balance screw until the averages of #1 and 2 equal the averages of #3 and #4. Now maybe the new readings are:

#1: 245 mm Hg
#2: 255 mm Hg
#3: 240  mm Hg
#4: 260 mm Hg

Now adjust the air bleed screws on each throttle body. The manual states to increase the lower vacuum of each set to the higher vacuum of each set (a set being either #1 and #2 or #3 and #4). This is fine.... if it works. I tend to adjust mine both up and down as required so as not to be turning the screws in all the time. Either way, balance all the T.B.'s using the air bleed screws until they are reasonably close to the same- reasonable being at least w/in 10 mm, and better yet w/in 5 mm of each other.

NOTE: at some point, if the air bleed screws are always turned in to always increase the lower cylinder vacuum, the screw will eventually seat and no longer be adjustable. If (when) that happens, something needs to be done to reset all the air bleed screws to some neutral point: I would suggest something like two turns from the fully closed position or each air bleed screw which should be a decent starting point. After the reset, the synch. will need to be done again. Sorry, there is no way out of this that I know of other than not screwing in all the screws for every adjustment, and that is not a guarantee either.

Brian

Edited to make all measurements in mm; some were in cm and some were in mm.

Slightly confused here,
Fred's video shows adjusting the center screw that balances the left /right banks BEFORE you sync the banks... Wouldn't it be better the other way around? (Sync the left 2 carbs to each other, then sync the right 2 carbs to each other then match them with the center screw?)


*scratches head*

[B.D.F.]

Yeah, you could use some type of adjustable restrictor but I would steer away from any more adjustments than necessary. Solid restrictors are the better way to do IMO and you can probably get them from some place like Motion Pro for a few dollars. Besides all of that, the C-14 has restrictors built into the venturi tubes so I do not think the external ones normally used are even needed on this bike.

The problem with the balance meter is that you have no idea what 1/2" difference between cylinders means- is that very close or too far apart? Another beautiful thing about mercury manometers is that physics controls the height of the mercury and it is easy to quantify the height (in any length units you want).

Again, I am pretty confident that a "4- banger" vacuum balancing tool with a common manifold on the bottom and using something like ATF would work fine, but it would be best to calibrate the difference in the liquid height(s) as it compares with something known like inches of water or mm of mercury (in* H20 or mm* Hg). Once that is done you could scratch in onto the plank that holds the tubing for all time- something like 1" H2O  = 5" Hg so that future generations will know what you were trying to do when they find that thing in an archival dig....    Seriously, the physics of the balance gauge will work fine, and I am a fan of home made tools (or tools used for the 'wrong' purpose like spark plug sockets to remove front axle bolts) but this will require a bit of tinkering and study to get it to be useful IMO. Best of luck and please do let us know how you make out.

Brian

OK, fair enough, though your suggestion only covered the bottom half of the problem.  There would also need to be restricted equalization tube connections at the top.  Ideally, if it had a adjustable restriction (using a thumb screw), then it could be used to adjust the sensitivity as balance was dialed in.

I know it's not a Manometer, but with adjustable sensitivity, it would probably provide for a very accurate synch.

[C1xRider]

Well it's been a while since we've visited this thread, but I wanted to follow up with my test results from the homemade balance gauge.  I must say, if I had known it was going to work as well as it does, I would've taken a little more pride in its construction, to make it better looking for pictures.

I had already planned out several revisions to the gauge in my head, and different fluids to try, but it wasn't necessary since it worked fantastically well first try. The gauge is very sensitive to pilot screw adjustments, as a very small change in the pilot screw has a very noticeable change on the gauge.

I bought 8 feet of 3/16ths inch clear vinyl tubing from ace hardware for $10, and a 4-way tee for $0.68.  The white cardboard backing and plastic strips to tie the hoses on were free.  The tubing was cut into 4 equal pieces.  The fluid is just regular antifreeze.

On the bike I installed high temp red silicone 5/32" vacuum hose.  This stuff is very stretchy and easily seals over the vacuum ports on the throttle bodies, as well as the 3/16" brass hose splices I used.  It fits tight enough, that I didn't hassle with putting clamps over it.  I put the plugs removed from the throttle bodies (and their clamps) on the end of the splices.

I used a mechanical gauge to measure the actual amount of vacuum on each cylinder.  After the valve adjustments, I was not able to balance all 4 cylinders using just the pilot screws.  When checking the values with the mechanical gauge, 1 and 2 where very high, almost 300mmHg.

I gave, up turned all the pilot screws all the way in, then back out 1.5 turns.  I then turned the center balance adjust screw in until the left and right sides were almost equal (between 1/8 and 1/4 turn).  After that the pilot screws dialed it right in.  When I was done playing with the balance gauge, I checked all 4 cylinders with the mechanical gauge, and they were dead on at 260mmHg.

I made a quick video with my phone of the engine running and the balance gauge attached, however I didn't realize my phone would not rotate video like it does with still pictures.  Sorry, you'll have to tilt your head to the left to watch it.

Any questions?

http://youtu.be/2BnWWgjKQpo

[The Pope]

Thanks C1 for posting this!

[pistole]

- ingenious !!

.

[GPzJeffrey]

I've done this method for twenty years now with carburetors:
I have tried using mercury sticks, the problem I had with it was there was no restrictions on the columns, so they bounced up and down about a cm or more with every piston cycle...tuning with them was trying to guestimate the middle point on the jumping mercury high and low point.. Even after I put line restrictors in it was still pretty bad....finally my instrument cracked when apparently it became brittle and cold...so I disposed of it in an environmentally friendly way decided to make my own.

So here's what worked best for me on my '96 GPz that I rode for over 250K miles and 20 years of tuning it, and it's super cheap:  I got like 20 feet of clear plastic tubing...4 mm I guess, it's always fit on every bike I've tried it on...some zip ties and a yard stick and some ATF and you're in business. Zip tie the tubing to the front of the yard stick making a tall "U" all down it's length with like 7 feet of tails hanging off the top of each side, the closer you can get the tubes together the better without kinking the tubing. With a turkey baster or syringe, slowly and patiently put just enough ATF in the tube to come up 18 inches on each tube. Hang it vertically when you do this, and wait for at least a day after to ensure all of the ATF ends up smack dab in the center with no air bubbles...it doesn't have to be precisely 18 inches, just roughly halfway up. (More on this later)

ATF works beautifully because it seems to have just the right amount of viscosity and that wonderful red color that makes it easier to see. If it were to somehow get sucked into the vacuum port it won't cause any real harm either, just get burned up.

So synching carbs I imagine is near exactly like synching TBs. Here's why on this homemade manometer you don't have to be precise on the height: it is comparing vacuum on two cylinders against each other via the side by side column heights, not comparing vacuum on a mercury column against atmospheric pressure.

So you first synch #1 and #2 cylinders against each other, then #3 and #4, then either #1 against #4 or #2 against #3. With carbs and their common linkage there is only ever 3 adjustment screws, between carbs 1&2, 2&3, and 3&4. The screw between 2&3 adjusts both pairs of carbs 1&2 against pairs 3&4. I'd just hang my manometer off of garage ceiling right where I can see it while fiddling with the adjustment screw.

The real advantage of doing it this way, comparing only two cylinders at a time to each other, is you get far better sensitivity on the ATF manometer. For example, and this isn't exact but a guestimate to make a point, a 1mm change in height of a mercury column would be more like a 1 inch change in ATF column height....and for one column to go up one inch means the other went down an inch, so you can see two inches of difference between columns....far greater resolution so you can make much finer adjustments....and on Keihen CV carbs, this really is important, and I imagine it is with the TBs too.

The other thing is that the columns don't jump up and down with each cylinder's cycle.... there's less variation in the timing of the vacuum pulses against each other vs against an atmospheric reference pressure, and again, the ATF seems to have just enough viscosity to resist sudden movements.

The only real disadvantage is that you have to stop the bike engine and move the connections each time you are done synching two cylinders against each other, for a minimum of three iterations. (Again, #1 vs  #2, #3 vs #4, and #1 vs #4.)...and there were times after a carburetor rebuild when I went through more than six iterations.

So I'm looking forward to synching my new C14 TBs here in the future. My old school manometer is well up to the challenge.

Jeff in WA

Yeah, you could use some type of adjustable restrictor but I would steer away from any more adjustments than necessary. Solid restrictors are the better way to do IMO and you can probably get them from some place like Motion Pro for a few dollars. Besides all of that, the C-14 has restrictors built into the venturi tubes so I do not think the external ones normally used are even needed on this bike.

The problem with the balance meter is that you have no idea what 1/2" difference between cylinders means- is that very close or too far apart? Another beautiful thing about mercury manometers is that physics controls the height of the mercury and it is easy to quantify the height (in any length units you want).

Again, I am pretty confident that a "4- banger" vacuum balancing tool with a common manifold on the bottom and using something like ATF would work fine, but it would be best to calibrate the difference in the liquid height(s) as it compares with something known like inches of water or mm of mercury (in* H20 or mm* Hg). Once that is done you could scratch in onto the plank that holds the tubing for all time- something like 1" H2O  = 5" Hg so that future generations will know what you were trying to do when they find that thing in an archival dig....  ;D  Seriously, the physics of the balance gauge will work fine, and I am a fan of home made tools (or tools used for the 'wrong' purpose like spark plug sockets to remove front axle bolts) but this will require a bit of tinkering and study to get it to be useful IMO. Best of luck and please do let us know how you make out.

Brian