Carb Syncing

[RagunCajun]

Very well put. It was a good $50 in investment for me. I must have a crisp engine. So along with some good aftermarket reeds, the sync tool is a must for me.

 

You can split the cost with another banshee buddy if money is tight. These days I know it can be rough to set aside money for toys.

[TeamRealtreeHD]

Very well put. It was a good $50 in investment for me. I must have a crisp engine. So along with some good aftermarket reeds, the sync tool is a must for me.

 

You can split the cost with another banshee buddy if money is tight. These days I know it can be rough to set aside money for toys.

 

[muggzy]

My idle is smooth and even, starts easily and pulls pretty good and I've never noticed one cylinder running hotter than another. But I'll likely invest in a tool soon b/c I think it could possibly have better power in the low end. My real surprise is that you guys are telling me that the performance (at low throttle) is so sensitive to extremely minor differences in slide position.

 

I still say that if using the tool results in a visibly noticeable difference in the slides, then you're compensating for something elsewhere in the engine. Possibly as simple as air screw adjustments or as bad as a leak somewhere else.

 

Since I don't have the tool yet, I don't know what the procedure to using it is, so the rest is pure speculation. But has anyone ever tried to adjust the air screws base on the tool? As I think about it, if the slides are being finely adjusted and assuming the rest of the engine checks out on compression and leak-down tests, then isn't it possible that adjusting the air screws is where the adjustment ought to be?

Edited August 9, 2010 by muggzy

[RagunCajun]

I adjust my airscrew based off off idle response.

Edited August 9, 2010 by RagunCajun

[FASTOYS]

Mugzy, air screws have nothing to do with carb sync as far as idle and slide lift. They do have to be adjusted to get the correct idle speed and off idle response for your motor but you still have to set idle sync and off idle slide pull sync correctly to get the most out of your bike. The sync tool does not compensate for anything other than the inability to sync carbs to the nats azz.

[muggzy]

Mugzy, air screws have nothing to do with carb sync as far as idle and slide lift. They do have to be adjusted to get the correct idle speed and off idle response for your motor but you still have to set idle sync and off idle slide pull sync correctly to get the most out of your bike. The sync tool does not compensate for anything other than the inability to sync carbs to the nats azz.

 

I'm sure you're right, your experience is far more extensive than mine. I'm just having a hard time accepting that adjusting the slides so finely that you can't see the difference can have such a significant effect on performance. OR if you can see the diff. it's just compensating for a difference or a problem somewhere else.

 

It makes sense that it will affect the idle way more than WOT. I mean just thinking about it;

a 0.5mm diff on a 2mm opening (~ at idle) is 25% of the opening, and at WOT 0.5mm on a 25mm opening is 2% . So a 0.1mm (barely noticeable) at idle might be as much as 5% and yeah, we all know 5% is usually noticeable. OK it makes sense , thanks!

Edited August 10, 2010 by muggzy

[CarvedArt]

My idle is smooth and even, starts easily and pulls pretty good and I've never noticed one cylinder running hotter than another. But I'll likely invest in a tool soon b/c I think it could possibly have better power in the low end. My real surprise is that you guys are telling me that the performance (at low throttle) is so sensitive to extremely minor differences in slide position.

 

I still say that if using the tool results in a visibly noticeable difference in the slides, then you're compensating for something elsewhere in the engine. Possibly as simple as air screw adjustments or as bad as a leak somewhere else.

 

Since I don't have the tool yet, I don't know what the procedure to using it is, so the rest is pure speculation. But has anyone ever tried to adjust the air screws base on the tool? As I think about it, if the slides are being finely adjusted and assuming the rest of the engine checks out on compression and leak-down tests, then isn't it possible that adjusting the air screws is where the adjustment ought to be?

 

The air screw is effective across the entire range of circuits, however, has most effect on the pilot circuit (0 - 1/4). So based on your comment that your "idle is smooth and even, starts easily and pulls pretty good," I'd say your air screw and pilot jet are correct.

 

You may very well be right about compensating for something elsewhere, at least a little bit, you're compensating for machining/casting tolerances within the carbs and intake tract; the manufacture has allowable tolerances for each of the parts that they machine/cast plus or minus x-number of thousandths. No two carbs are exactly identical, one might have an extra little indentation in the bore that equates to increased volumetric capacity, while another might have an extra little flashing interfering with flow. Also, typically slides will not rise perfectly square with the bore as the cable pulls the slides will usually drag slightly on one side. So while measuring the slide height that you can see with your eye will get you close enough to start and run it will NEVER be at the top of its game. So I really wouldn't say you were compensating for problems as much as calibrating your intact tract for optimal volumetric efficiency. The higher the volumetric efficiency the greater the potential for running higher RPMs which equates to potentially higher HP. Its not as simple as saying get a sync tool and get more HP. There are TONS of factors that play into these equations to include calculating the optimal resonance amplitudes and frequencies to design your expansion chamber accordingly to attempt to create a volumetric efficiency as close to 100% or higher as possible; which is no simple task. All that being said, I have a sync tool and swear by it; but if you can't afford or borrow one your not going to suffer from major damage. I should reiterate though, if you can, you should! You will notice a seat of the pants difference.

 

To piggyback on dajogejr's comments about...

A drag racers blips the throttle a few times and holds it WOT till the end. As long as both carb opens all the way, you're good.

 

But for the duner trail crowd, you'd be surprised how off you can be by eye.

 

I'd say you'll suffer from performance loss at any level of riding, my point about the drag racers is purely referring to the fact that the only reason your racing is to win and if you can't deliver power down low before WOT you will lose tenths and that could cost you a win. If your "just" riding around the dunes/trails you can't lose any race that your not in. My original post was intended as more of a warm fuzzy to those that can't afford one or can't borrow one. I wouldn't ride mine without syncing and if you can get your hands on one it's well worth your while. It's one of the easiest Banshee "upgrades" available.

[AKheathen]

there is actually a good way to sync the idle, if you don't have, and can't get the tool. start by syncing the slides. i think i used a 3/16" screwdriver to do it on an initial setup. then the cables, and wherever you think the airscrews will start best at. get it warmmed up to operating temp and tune the airscrews evenly to the highest idle, letting it catch up for a bit, then back in 1/8 turn. this is generally a good setting. now bip it again to keep it running hot. next, go back to the silencers and feel the output with your hand. if one side is not firing all the time, fine tune the airscrew in small increments untill it does. if one side fires stronger, then fine tune the idle screws to make them match and you will likely need to do the airscrew again. that will ballance cylinder putput/power at idle. resync the cables again to match the new settings. i'm sure you could probably dick with like 1/4 throttle with the exhaust, but i don't really bother, and the tool is still a better way to get the full sync.

[dajogejr]

That's a great post AK.

 

Folks need to keep in mind, two things...

One, each cylinder might not be 100% the same as other (port specs, wear, etc.) and

Two, one carb might not be the 100% exact same as the other.

 

That's why I've recently learned to tune carbs per cylinder instead of making it an exact copy of the other carb.

I'm not talking leaps and bounds difference, but just enough to make a small difference.

 

The reason the sync tool is so nice is because it mimics what the carb is doing per cylinder, sucking in air and fuel.

That is the carb's job...supply air and fuel.

 

Get that the same first then you can fine tune jetting...

[RagunCajun]

That's why i use one. It measures vacuum on EACH cylinder. My ported were done by hand, not CNC machine. So that means each is slightly different. The naked eye can determine the difference.

 

Basally the sync tool is the best option but there are cheaper options that are still good.

[J-Madd]

To piggyback on dajogejr's comments about...

 

 

I'd say you'll suffer from performance loss at any level of riding, my point about the drag racers is purely referring to the fact that the only reason your racing is to win and if you can't deliver power down low before WOT you will lose tenths and that could cost you a win. If your "just" riding around the dunes/trails you can't lose any race that your not in. My original post was intended as more of a warm fuzzy to those that can't afford one or can't borrow one. I wouldn't ride mine without syncing and if you can get your hands on one it's well worth your while. It's one of the easiest Banshee "upgrades" available.

 

 

In drag racing (on dirt) your always WOT - like Dave said. There is no power to be made at less than WOT. However, I can see where badly unsync'd carbs would affect a run due to one cylinder loading up, or not cleaning out as good as the other in pre stage.

[CarvedArt]

To piggyback on dajogejr's comments about...

 

 

I'd say you'll suffer from performance loss at any level of riding, my point about the drag racers is purely referring to the fact that the only reason your racing is to win and if you can't deliver power down low before WOT you will lose tenths and that could cost you a win. If your "just" riding around the dunes/trails you can't lose any race that your not in. My original post was intended as more of a warm fuzzy to those that can't afford one or can't borrow one. I wouldn't ride mine without syncing and if you can get your hands on one it's well worth your while. It's one of the easiest Banshee "upgrades" available.

 

 

In drag racing (on dirt) your always WOT - like Dave said. There is no power to be made at less than WOT. However, I can see where badly unsync'd carbs would affect a run due to one cylinder loading up, or not cleaning out as good as the other in pre stage.

 

I noticed that you've caveated your reply with "(on dirt)" and so I have to admit I'm NOT an expert in 2-stroke dirt drags, most of my drag experience is on the pavement; both bikes, to include an 87 Kaw Mojave with a .40 over KZ1000, and cars (currently running a Z-28 in IHRA Super Rod (9.90 1/4mi)). I used to run an Inglese manifold on a BBC 461 with 8 51mm EMPI's which is where I REALLY learned what syncing carbs was all about; not a Banshee but sure ran like one! I can tell you first-hand when those babies were out of sync, I staged with a 4500 stall, the moment I let the transbrake go @ 5000 she would hesitate before the wheels lifted; mind you that setup took more than a few minutes of my life to tune and sync. I work in aerospace and I'm pretty steeped in theory, design, and test and I've taken what I've had the privilege to observe/learn and applied it to my motorsport hobbies. So please take what I say with a grain of salt, folks like Dave and yourself actually have the hands-on 2-stroke drag experience and that's something that math can't always predict. You've definitely gotten my curiosity up though, I'd be very interested in real-world results of ETs between a drag motor with carbs synced vs. carbs unsynced (or synced by eye); something like 3-5 runs unsynced vs. 3-5 synced (same bike of course). Might even be worthy of its own topic to see what real bikes run within a specific distance capturing actual numbers before and after sync. Thanks for adding your experience/expertise on this subject, I'm huge fan of learning from the experiences of others; it many times save me from misallocating my own hard earned cash! Seriously, you guys are the reason people are still riding/racing Banshees around here, without you guys we'd all be doing a lot of head scratching and guessing.

[dajogejr]

I can tell you I'm not willing to "unsync" my carbs to test that out...LOL.

 

Interesting and impressive resume. There is a ton of math put into these machines people don't think about.

On the other side of that coin...and you mentioned, sometimes math doesn't equate to real world experience.

 

I can appreciate both!

 

That being said....it's possible mine are out of sync a hair now. I don't know if I borrowed my sync tool to someone and never got it back or if it's in the deepest, darkest corner of my garage and I just can't find it.... It has been a while since I've done mine up to be honest.