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Old March 16th, 2015, 02:51 PM   #1
RcTechnologies
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Full service manual says to turnout one carb pilot more than the other....why?

And for good reason. Were at 9,000 mi and doing all maintenance items on the list, incl carb cleaning and valve checks. ALL is good.
For curiosity we welded up a "tuning purposes only" exhaust system that isolated the cylinders and housed O2 sensors. After syncing within 1 mm Hg one side had to be enrichened drastically to make the O2 sensors match, as the full service maual says "Pilot Screw Setting: #L: 2 1/2 #R: 1 3/4" (pg 3-16). Plugs look great now. But the question still burns, Why'd the engineers at Kawi do this, and why do the O2 sensors concur?

Note: the factory setup and tune (sync and pilot turns) makes one cylinder work substantially harder than the other.

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Old March 16th, 2015, 03:29 PM   #2
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Did you bench sync, or running on the bike sync?

Here's my personal write-up on synchronization, once you understand what you've done, the answer will be clear.

Quote:
You can get a reasonable sync with the carbs in hand. Back the idle adjustment off to close that carb then match the second carb to it with the sync screw. You can then turn the idle adjustment up while using a thin feeler gauge (maybe .002") between the throttle plate and the throttle bore, adjust to just fit, and then check the second one and adjust to match. If you have good feel for this it will run fine once installed.*

It would do folks well to take a minute to review and understand what a sync tool does, how it works. And take another minute to look at the carb linkage and sync adjustments available to fix irregularities that might occur. It can help take some of the mystery out of this as well as stop unnecessary carb sync screwups.*

Meaning, that the carbs were right once, the butterflies were matched and it performed well, but then changed. Undecided And the problem somehow occurred in the butterfly direct shafts, or the sync screw turned or wore that pad that it rests on, or the carburetor pairing/ bridging brackets twisted in relation to each other, and enough so that the butterflies no longer operated in sync, such that performance noticeably suffered. And a fix will be accomplished by changing the butterfly position, the only thing the sync adjustment does. Hmmm. Really? Undecided*

Meanwhile, the tool measures vacuum at each individual runner. That's all it does, how it works. And vacuum is effected by a huge list of things, butterfly position being only one of them, and the only one addressed with that tool while turning those sync screws. The rest of that list includes, valve adjustment, jetting, float level, compression differences between cylinders caused by wear as well as factory CC differences in the head, intake runner, as well as flow by port variations, etc. Variations in cams, wear or factory tolerance. Then there's the potential big one, pilot jets and pilot screw mixture settings. All of those effect the vacuum and will be read by the sync tool, accurately identifyng the difference that exists, and with the only adjustment being used to "correct" the problem, move the butterfly relationship, one to the next.*

It's that clear understanding that has me of the opinion and long time practice to not touch the sync screws on a set of carbs that were right once and were never dismantled from the rack. And jet cleaning as well as float needle changing doesn't require that they be dismantled. And further, if I DID dismantle a set of carbs, I just matched the butterflies on the bench at assembly, using a feeler gauge, and then never touched them again, never gave them another thought.*

That method, properly executed, will have THAT portion of the complete equation, balanced flow to each cylinder in a multi-cylinder/ carb application due to butterfly position, satisfied entirely adequately. And in fact, it has worked for me every time I've done it on every bike (as well as individual runner/ butterfly V-8 intakes, all eight) that I've ever owned or any that I've fixed for others. And the times I fixed for others was usually after an attempt by others to sync the carbs, chasing a problem, or sometimes not even chasing a problem, but one they created wth a sync tool, chasing a problem from that list, that was never a butterfly position change problem. Those linkages are so direct and simple that they don't know how to screw themselves up. Not enough to care about.*

I'm sure this will start a lot of controversy so I won't argue it, just offering it for those who understand the whole picture that I outlined and might make good use of it. It is what I've done, on every engine I ever worked on, including blue printed racing engines as well as regular old, high mileage street stuff. I've had at least four, four cylinder bikes with over 100,000 miles that ran quite well, the whole time, and never had a carb sync performed. When they did finally get a total disassembly, this is how I set them up, on the bench. Over the years I've straightened out at least a half dozen messed up ones, probably more, and on the bench, after fixing the original problem which was fouled pilot jets.*

I only posted this because it seems like its coming up fairly often, especially with problems from a sync gone bad. One I would suggest was never a sync problem to begin with. A big or sudden change in performance is NEVER a sync problem. NEVER. Remember that. Cool If there is a problem, and you connect the gauges? YES, there will definitely be an imbalance indicated. But because that hole has a problem that is from the rest of the list. A bad plug, a plugged pilot jet, a screwed up float, a bad valve or setting, etc. Every one of them effecting the vacuum in the intake but NOT from a sudden move of a butterfly position, a sync adjustment.

Also here is my write-up on pilot screws tuning,

Quote:
Warm it up, turn 1 side pilot screw in until the rpms drop, then back out till RPM's peak (and no further)* Twist throttle...see how it reacts...tweak to taste.
Repeat on other side... test ride. You're looking for best throttle response and transition from just cracked to 1/4 throttle opening or so.*

Thats a quickie, 10 cent tutorial on setting pilot screws.**
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Old March 16th, 2015, 03:53 PM   #3
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Welcome Russ!

So you're saying the factory pilot adjustments make the bike run more efficient? Wen I was tuning te bike, I found out that the pilot needles are not at equal heights if you set it at 2.5 turns out. Adjusting it to factoring settings equated it equal heights. My thought was the flow of fuel from one end to the other carb probably had to be compensated.
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Old March 16th, 2015, 04:03 PM   #4
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Both actually. It was my idea to bench sync with wire feelers, and my coworker insisted on a manometer (multiple rpm test points). The question is why have one cylinder work so much harder than the other at low load conditions? Does it have something to do with two cylinders firing immediately after each other?

Update. Finished lab setup and put the leovince back on. Sounds audiophilicly eargasmic! You can hear an incredibly consistent "buda-buda-buda-buda". throttle response beautiful with a .30 second hang at 3000 rpm when you snap it closed (to reduce engine braking effects). Must ask oneself "did I just set myself up for a blown piston/thrown rod later on?" Is there a reason the factory and manual have one carb richer than the other, resulting in crazy EGT differences between cylinders (at idle/low load)?
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Old March 16th, 2015, 04:14 PM   #5
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thanks nutz. funny thing was, the rich side was the carb closest to the fuel inlet hose (from tank)
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Old March 16th, 2015, 04:32 PM   #6
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Do you still have the stock needles? IIRC, the needles are slightly different from left and right due to having different part numbers but do not know physically if there is a difference.
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Old March 16th, 2015, 10:07 PM   #7
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perhaps it is an unintentional defect from manufacturing processes, and the adjustment is simply to account for the known defect
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Old March 16th, 2015, 10:17 PM   #8
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I know from personal experience from doing the idle mixture screws modifications, removing the anti-tamper caps, I've never found both of them the same, not even close.

Some of the worst ones are at least a full turn difference, or not more in extreme cases.

As I stated earlier in my quickly pilot screws tuning, you adjust each one separately for best performance. For the most part they are pretty close to each other, but never exact In the end.
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Old March 16th, 2015, 10:59 PM   #9
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When one wants to do this right, it needs in each pipe of the header a hole (which can be closed with a screw) from where the co measurement is done separate for every single cylinder.
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Old March 17th, 2015, 09:40 AM   #10
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The reason each cylinder is different is because Kawi designed cylinder 1 to be the "torque" side, and cylinder 2 to be the "power" cylinder.

The 250 is down on power, we all know this. To keep things cheap it was easier to split the power load between the two cylinders to make a more rideable bike, providing more power down low compared to the pre-gen 250's.

I'm sure you noticed the headers are different lengths between the two cylinders. When adding on an aftermarket header, which has equal length headers it's best to replace the needle and idle mixture screw on cylinder 1 with a set/part number intended for cylinder 2.

Example:
So, cylinder 1 is the torque cylinder, with a longer header tuned for more torque.

Cylinder 2 is the power cylinder, with a shorter header tuned for more top-end power.

If top end power is what you're after, with an aftermarket exhaust system with equal length headers, you should match the internals of cylinder 1's carb with those of cylinder 2. IF you're tuning for torque down low to make get the bike more pickup below 4K RPM's, you'll have to weld up your own header, equalizing pressure and tuning for more torque and match the internal of cylinder 1's carb.

Now this is all applying to the inifinite degree. What most people do with aftermarket headers is to go to the dynojet needles and to not worry about the idle mixture screw in cylinder 1's carb and fudge it close enough, however, you seem to be going to the infinite degree, so I would recommend to also match the idle mixture screws to those found in Cylinder 2's carb.

I hope all of that makes sense.
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Old March 17th, 2015, 09:58 AM   #11
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Quote:
Originally Posted by spooph View Post
The reason each cylinder is different is because Kawi designed cylinder 1 to be the "torque" side, and cylinder 2 to be the "power" cylinder.

The 250 is down on power, we all know this. To keep things cheap it was easier to split the power load between the two cylinders to make a more rideable bike, providing more power down low compared to the pre-gen 250's.

I'm sure you noticed the headers are different lengths between the two cylinders. When adding on an aftermarket header, which has equal length headers it's best to replace the needle and idle mixture screw on cylinder 1 with a set/part number intended for cylinder 2.

Example:
So, cylinder 1 is the torque cylinder, with a longer header tuned for more torque.

Cylinder 2 is the power cylinder, with a shorter header tuned for more top-end power.

If top end power is what you're after, with an aftermarket exhaust system with equal length headers, you should match the internals of cylinder 1's carb with those of cylinder 2. IF you're tuning for torque down low to make get the bike more pickup below 4K RPM's, you'll have to weld up your own header, equalizing pressure and tuning for more torque and match the internal of cylinder 1's carb.

Now this is all applying to the inifinite degree. What most people do with aftermarket headers is to go to the dynojet needles and to not worry about the idle mixture screw in cylinder 1's carb and fudge it close enough, however, you seem to be going to the infinite degree, so I would recommend to also match the idle mixture screws to those found in Cylinder 2's carb.

I hope all of that makes sense.
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Old March 19th, 2015, 08:32 AM   #12
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Hi,

today i am trying to sync my carb using bench sync. I am using a couple wire steel do this and gues what? my stock ninja with stock mixture screw diffrent left and right, now my 7dle very smooth, needles tach not bouncimg....very amazing guys. Before I go to dealer to sync my carb but idle not smooth as now.
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Old March 19th, 2015, 08:40 AM   #13
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Quote:
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Hi,

today i am trying to sync my carb using bench sync. I am using a couple wire steel do this and gues what? my stock ninja with stock mixture screw diffrent left and right, now my 7dle very smooth, needles tach not bouncimg....very amazing guys. Before I go to dealer to sync my carb but idle not smooth as now.
Another testimony for bench sync, another important factor is float height, and idle needle tuning.
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Old March 19th, 2015, 06:16 PM   #14
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Thumbs up

Quote:
Originally Posted by Ghostt View Post
Another testimony for bench sync, another important factor is float height, and idle needle tuning.
Float height was stock and idle mix stock. Honestly My bike newer idle better with stock, even sync on dealer. So...I trust hand sync then manometer or bottle sync haha. Very happy.
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Old March 20th, 2015, 01:35 PM   #15
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Aren't the cylinders also inherently unbalanced by the ignition sequence? Unlike most three- or four-cylinder engines, the sequence is uneven for a two-cylinder (not all but most commonly). I guess this has most effect on the exhaust side, so with lucky timing the gasses from cylinder 1 has just blown by when cylinder 2 valves open, helping to evacuate gasses from cylinder 2? At high revs?

Not that I can make any sense of this myself. Cylinder 2 is right? So would need more fuel? Or could have a slightly longer intake and still make same power at high revs.

Of course the opposite is also possible that at some point the gasses from cylinder 1 are just bouncing back from the exhaust when cylinder 2 valves open. At medium high revs possibly. Or on the intake that when cylinder 2 wants to take air the airbox has just been emptied by cylinder 1.
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Old March 24th, 2015, 08:43 PM   #16
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Well done everyone.

After EXTENSIVE analysis, a number of things have become evident and a little lab work was required to prove them as well. Ghost, thanks for pointing out the specifics of syc, not very many know that, and neglect other factors that influence vaccum.

Spooph, from what we can tell you are most likely correct. The design of the header does in fact maximize use of exhaust pulse from the cyl #1 to generate low end torque in cyl #2. (firing 1-2-1-2). Manufacturing defects not withstanding, header design will have a profound effect on the amount of A/F charge at low rpms, especially with 13.25" (ver?) header length. And, of course, our mains kick in past certain throttle positions, rpms etc...

Finally , we filled the header with mineral spirits and did volume measurements.
Just from the math, it is the case that to make useable power below 4K rpm and beyond 2nd gear, extensive low end tuning had to be performed on a motor that is realistically only effective at high rpms (due to its displacement).

Well done to all of you!
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Old March 24th, 2015, 09:12 PM   #17
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Quote:
Originally Posted by RcTechnologies View Post
After EXTENSIVE analysis, a number of things have become evident and a little lab work was required to prove them as well. Ghost, thanks for pointing out the specifics of syc, not very many know that, and neglect other factors that influence vaccum.

Spooph, from what we can tell you are most likely correct. The design of the header does in fact maximize use of exhaust pulse from the cyl #1 to generate low end torque in cyl #2. (firing 1-2-1-2). Manufacturing defects not withstanding, header design will have a profound effect on the amount of A/F charge at low rpms, especially with 13.25" (ver?) header length. And, of course, our mains kick in past certain throttle positions, rpms etc...

Finally , we filled the header with mineral spirits and did volume measurements.
Just from the math, it is the case that to make useable power below 4K rpm and beyond 2nd gear, extensive low end tuning had to be performed on a motor that is realistically only effective at high rpms (due to its displacement).

Well done to all of you!

Well thx u for understanding my carburetor synchronization write-up.

I have also done some research and have found that the NewGen uses two different main jet needles, one for the left, and one for the right,.

Would you happen to have the measurement/micrometer data on the differential of the two?

Also the NewGen uses a different style main jet holder with what seems to be less emulation holes? What you happen to have any data on this as well?

I'm curious if one could use them in a PreGen carburetor, and if it would be a better design, than the multiple emulation holes? Less chances to clog? Etc....
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Old March 25th, 2015, 09:45 AM   #18
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Quote:
Originally Posted by RcTechnologies View Post
After EXTENSIVE analysis, a number of things have become evident and a little lab work was required to prove them as well. Ghost, thanks for pointing out the specifics of syc, not very many know that, and neglect other factors that influence vaccum.

Spooph, from what we can tell you are most likely correct. The design of the header does in fact maximize use of exhaust pulse from the cyl #1 to generate low end torque in cyl #2. (firing 1-2-1-2). Manufacturing defects not withstanding, header design will have a profound effect on the amount of A/F charge at low rpms, especially with 13.25" (ver?) header length. And, of course, our mains kick in past certain throttle positions, rpms etc...

Finally , we filled the header with mineral spirits and did volume measurements.
Just from the math, it is the case that to make useable power below 4K rpm and beyond 2nd gear, extensive low end tuning had to be performed on a motor that is realistically only effective at high rpms (due to its displacement).

Well done to all of you!
Awesome, thanks for confirming my theory! I'm guessing you're not going to be posting any of this data up here?

Regardless, keep up the good work, very interesting stuff this...
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