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Carb Sync 1979 A1 10 months 2 weeks ago #28593

  • dcarver220b
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Apparently, there’s some interplay between 2 and 3, where if one is grossly out of adjustment, the other won’t respond.
I don’t know and wasn’t going to tempt fate by experimenting.


It's typical for one adjustment to affect the other two. An example would be: Left carb 9"hg - Center 7.5 - right 6.5. I always start with the Highest value and lower that reading (CCW on the adjuster). The other two will, as a rule, rise in vacuum readings. Then adjust the lowest reading (CW on the adjuster) to raise that reading. The other two will change slightly - generally the reading on those two will lower slightly.
Continuing with this example - I will then adjust the middle reading. This may be CW or CCW on this adjuster. (It depends on other variables). This will usually bring all three to within .5" Hg. Then adjust to two lowest (CW on the adjuster) to bring these readings in line with the highest. In doing so the highest and the carb not being adjusted will tend to lower slightly. Then continue to work on the two lowest readings. It sounds like a lot of back and forth.......and it can be. It's purely patience ! As long as it's understood that one adjustment changes the other two, the learning curve is easier. Also: I will suggest that the manuals recommendation of starting with the adjusters "backed off" 1.5 turns can be changed to 1 turn if this basic method is followed. Attempting to achieve the highest readings can lead to over tightening the adjusters which will lead to linkage binding and a challenge to balance at all. There must be some "slack" for freedom of movement within the connecting linages ball joints.
SO....., generally........Increasing the vacuum value on one will lower the readings on the remaining two. And vica versa.

Ended up with these readings at 4,000 RPM. Since 4k is the 'sweet' spot for riding, decided to balance there
and not worry about idle specs so much.


Balance at 1000RPM. At 4000 RPM the transition jet(s) will be in-play and depending on other parameters the sync won't ( can not) be as accurate. Unless the goal is an idle at 4000 RPM for those Rocket Launches :woohoo:


I'm just learning, so please forgive transgressions. If the goal is for a clean, even running engine at normal mph/rpm, would it not make sense to balance at higher rpm than lower? I honestly don't know and don't want to offend, but if 80% of running time is at 4k, does it not make sense sync even fuel delivery at higher values?

Please, Please, Please don't take offense. Honest question from apprentice perspective!

Don

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Carb Sync 1979 A1 10 months 2 weeks ago #28602

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Good day carver. First time I think, that this question has been raised.

Syncing at 4K involves much higher air velocities and will be incorporating the transition jets and possibly subtle variations in that amount of fuel, depending on how these ports are behaving relative to that vacuum and air velocity. At 1000rpm the single idle port is the only source of fuel. (a fuel/air mix). This is controlled by the pilot needle which is usually somewhere in the 3 turns area. The throttle plates are barely "cracked". The filtered air going through the venturi will have a more consistent velocity through this small area and with the vacuum created, draws the fuel out of this port at a more consistent rate. This is a relatively precise adjustment. Sync'ing at 4K will possibly involve to some degree, the transition jets. For example: At 4000 you may very well be getting additional fuel from the first transition port with the second transition port trying to supply some. It's this "transition" between ports that are trying to supply fuel that makes sync'ing at high RPM's, not as accurate as a 1000RPM idle sync.
Although you may believe you've have had some success sync'ing at this RPM, it's not as accurate. Sync'ing, as the manual indicates, is to provide a smooth idle. Assuming that the carbs are clean, everything else as it pertains to the fuel delivery (Transition ports to Main-jet), looks after itself......or should.
If you can not sync at 1000 then you likely have a blockage or restricted idle jet. I have experienced many carbs that I've rebuilt that the owners claimed to be squeaky-clean, but un-tuneable. This was the case with a recent carb job I did for a local 1300 owner. I cleaned these carbs with "the Tool" and the owner was stunned by what got flushed out. The carbs tuned beautifully after that !
Hope this makes more sense.
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Last edit: by scotch.

Carb Sync 1979 A1 10 months 2 weeks ago #28603

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Good day carver. First time I think, that this question has been raised.

Syncing at 4K involves much higher air velocities and will be incorporating the transition jets and possibly subtle variations in that amount of fuel, depending on how these ports are behaving relative to that vacuum and air velocity. At 1000rpm the single idle port is the only source of fuel. (a fuel/air mix). This is controlled by the pilot needle which is usually somewhere in the 3 turns area. The throttle plates are barely "cracked". The filtered air going through the venturi will have a more consistent velocity through this small area and with the vacuum created, draws the fuel out of this port at a more consistent rate. This is a relatively precise adjustment. Sync'ing at 4K will possibly involve to some degree, the transition jets. For example: At 4000 you may very well be getting additional fuel from the first transition port with the second transition port trying to supply some. It's this "transition" between ports that are trying to supply fuel that makes sync'ing at high RPM's, not as accurate as a 1000RPM idle sync.
Although you may believe you've have had some success sync'ing at this RPM, it's not as accurate. Sync'ing, as the manual indicates, is to provide a smooth idle. Assuming that the carbs are clean, everything else as it pertains to the fuel delivery (Transition ports to Main-jet), looks after itself......or should.
If you can not sync at 1000 then you likely have a blockage or restricted idle jet. I have experienced many carbs that I've rebuilt that the owners claimed to be squeaky-clean, but un-tuneable. This was the case with a recent carb job I did for a local 1300 owner. I cleaned these carbs with "the Tool" and the owner was stunned by what got flushed out. The carbs tuned beautifully after that !
Hope this makes more sense.


Thank you Scotch for your response. Makes total sense to me... After doing some research, and from your reply, I know understand the error in my logic. I'm confusing idle sync on carbureted engine vs idle sync and butterfly alignment on a fuel injected engine (Yamaha FJR 1300).

What started all this happiness is my very good idle sync wasn't so good at 4k rpm as measured on the CarbTune. Then, recalling the FJR procedure, tried to adapt apples to oranges. By that I mean the FJR's FI engine has 1 injector per cylinder and one throttle body butterfly per cylinder. The KZ carbureted engine has one diaphragm per 2 cylinders. To apply the FJR procedure to the KZ is a mismatch, a mistake.

The FJR procedure is to essentially close down the air bypass screws, then manually, mechanically, adjust butterfly's for equal opening per throttle setting as measured by equal vacuum levels. Then bring the air bypass screws back into play.

Here's a copy and paste of the that procedure, just for additional mental gyrations! :) If you want to see pictures, CandyButt.org

Kawboy and Scotch, Thank You, Thank You, Thank You!
7/6/2015 - It has been reported that reading all of the comments and discussion in the replies to this thread can be a bit confusing. All of the information required to perform the RDCUA TBS procedure is contained in this first post, or at the procedure linked to immediately below. This post has been updated to reflect the best working procedure for first and second gen FJRs.

(note that the RDCUA TBS cannot be performed on 3rd Gen FJRs)

3/2013 - I have captured and compiled a complete html version of this procedure and am hosting t at my fjr.nerds web space for posterity here: The Really, Definitely, Completely Un-Authorized Throttle Body Sync (TBS)

Re-edited 10/2012
This version of the UnAuthorized TBS procedure is based on a premise; that the ideal throttle synchronization is when the throttle plates are aligned with each other and parallel.

After a large number of uses, this procedure has been found to be very effective. Nobody who has used this procedure has ever said that it made their bike run worse. Most people say that their bike ran smoother (less vibration at ~4k-5k rpm ranges.

You will see some discussion in other posts about alternate ways to adjust the throttle plates. Some folks believe that you need to rev the engine. Some think that you need to load the engine and rev it. None of these other methods have been shown to be any more effective than doing it the way detailed here. And this way is a lot easier to do.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The Really Definitely Completely UnAuthorized Throttle Body Sync

I decided to start a new thread to document this procedure. Not because it is so much different than any of the other UA TBS procedures, but because there are so many Throttle Body Sync threads. I'm hoping that this procedure becomes the new standard non-standard. The concept for this TBS procedure came from a thread / discussion I had with a short duration forum member from Maine, Alekso last year. The idea was to make a procedure that wasn't so convoluted and difficult to follow and understand as the original Unauthorized sync procedure.

For those just tuning in, what's going on here is that the "official" throttle body sync procedure, the one called out in the Factory Service Manual (FSM) and specified as a "required" procedure at 4k mi. intervals (what?) is simply an adjustment of the air bypass screws at idle speed. These bypass screws have their primary effect on vacuum at idle speed, and have very little to do with how smoothly the engine runs at anything other than at idle or just above. As the throttle butterfly plates open, the tiny amount of air contributed to the total intake by the bypass circuit becomes increasingly less significant so that by the time you are at 3-4k rpm these screws are pretty insignificant. What is significant at larger throttle openings would be the relative angles of the throttle plates.

The problem is that the FSM doesn't specify a procedure for properly aligning the throttle plates. They just say that the plates are set at the factory and to leave em the hell alone... huh.gif Being gearhead dweebs, we know that to achieve the smoothest possible running engine it is our goal for each of the 4 cylinders to contribute the identical amount of power per stroke. With Electronic Fuel Injection and Electronic Ignitions, the likelihood of balanced fueling a nd perfect ignition timing is much better than in the days of carburetors and points of the past. So our best tuning opportunity is to try to balance the air intakes, which can be best measured by the intake vacuums.

Prior "Unauthorised" TBS procedures suggested that you just open the throttle while observing the vacuum gauges and make the mechanical adjustments to the throttle linkage quickly. Surely that will work, but at what rpm do we need to go before the air from those bypass screws is nullified? And how sadistic is it to continually rev your engine while making these fine adjustments? (hint - they aren't all that quick)

Enter the RDC (Really Definitely Completely) Un-Authorized TBS.

The concept here is pretty simple. To align the throttle plates and eliminate the air contribution from the air by-pass screws, we just close them all the way before starting. Yep... it's just that simple.

So, to prove the concept I documented my most recent RDC UA TBS using a new (to me) Gunson Carb-tune vacuum gauge that I picked up over the winter:


After propping the tank up out of the way, here are the important adjustment points
(note - your under tank could look this uncluttered after installing the WynPro PAIR Block-Off plates and removing all the PAIR crap):

100_1211.jpg

V1 thru V4 are the 4 standard vacuum take-off points for hooking your vacuum gauge of choice to.

1-2, 2-3, and 3-4 are the mechanical linkage adjustment screws to adjust the relative angles of each cylinder's throttle butterfly plate.

Before I began, I documented what I had for vacuum at idle:
IdleB4.jpg

Not bad. Notice that #1 is a bit low and #4 is a bit high. Now, without making any adjustment I then revved the engine to ~3-4k rpm and used my Vista Cruise to hold it long enough to snap a picture:

3krpmB4.jpg

Hello! What's that? Now cyl #1 is high and #4 is low!! This is not good. No, not good at all...
(well really these aren't all that bad, but you get the idea...)


Procedure:

Close down (lightly) all 4 of the Air Bypass screws:

100_1217.jpg

100_1218.jpg



Depending on how open they were before, your engine may not want to idle. You can either crank the idle adjustment (under the right side of the tank) or use your Vista Cruise to hold a reasonable idle, like I did.

Now that the air screws are out of the picture, you can adjust the throttle plate linkage screws (at idle, not while winding the piss out of your poor engine) and balance the vacuums with the throttle plates angles.

Important: Start by balancing cyl 2-3 since 1 and 4 are effected by that adjustment. The only tricky part is if 2-3 needs adjustment you can't get a screwdriver on the adjustment screw. So, take a guess, shut the engine off, and open the throttle enough to get at the screw head. Adjust it one way and then restart the bike to see if you guessed right.

Once 2-3 is good, the 1-2 and 3-4 adjustments can easily be made invivo. If you want to rev the engine to various RPMs to see how much things vary (or don't), knock yourself out (I did). In fact I was a bit nervous of running the engine in the garage for so long, even with water cooling.

When you are completely happy with the balance, I suggest shutting the engine down, and then dialing in ~ 1 turn CCW (open) into each air bypass screw. Restart the engine and adjust your idle to ~1100rpm.
Now recheck your vacuum gauge. Since the throttle plates are now aligned, if there is any mis-balance simply adjust the bypass screws until it is balanced at idle.

When I completed this procedure I had dead nutz balance at idle, and it varied very, very little at any throttle opening. I have not ridden the bike yet after adjusting. It may not amount to a hill of beans, but at least I now know that, unequivocally the throttle has been fully balanced and any vibration that remains is not being caused by an intake mis-balance.

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Carb Sync 1979 A1 10 months 2 weeks ago #28606

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I'm glad you could make some sense from my attempts at explaining. What I take for granted in terms of my being able to "just doing it" was actually more difficult to put into actuall words. The bottom line is: Syn'c for the maximum Vacuum but it must be kept in mind that adjusting for this maximum can easily lead to the adjusters being turned in too far, which can cause binding. This is usually indicated by an idle that is slow to return or won't at all.. That's the point of the manuals recommendation to start with the adjusters backed off 1.5 turns. My suggesting that the sync be started with the lowering of the highest reading (lowering the reading to match the remaining two) maintains this margin to avoid binding. Arguably, one could start with all the adjusters at .5 turns out from being tight as long as this limit is kept in mind.
1980 KZ 1300 sr# KZT30A-009997
Always High - Know Fear !
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Carb Sync 1979 A1 10 months 2 weeks ago #28654

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Follow up - carb resync at 1k rpm. Much smoother at idle, at 4k manometer, unlike the first time, is very close.


My CandyButtAssocation blog post
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Carb Sync 1979 A1 5 months 3 weeks ago #29249

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What did you use for carb sync adapters?  Are they 5mm or 6mm?  I see Z1enterprises has a 5mm set.  I recently acquired a 1300 myself and will need to sync when I get the carbs out of the shop.
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