Carb synch, How mutch less

[Guest]

I understand that the center 2 cylinders should read a little less vacuum than the outer 2, but by how mutch. I have an OLD set of motion pro merc tubes I use. All the manuals talk about setting the center 2 one line, or whatever it is, less than the outer 2, but what does that " one line" equal?

The merc sticks I have are graduated in cm.(actually 20cm increments). I don't know what the Suzuki one the manuals mention is graduated in.

Thanks,
Don

[Steve]

Well, since there are no numbers on the "official" gauges, you have to go by the pictures.

The picture shows "half a ball".

I will usually shoot for 1-2cm lower, if I am going to bother with that.
Before I joined this forum, I did not know any different and always set them all the same.

.

[don]

Thanks Steve,

1-2 cm seems like alot to me, thats like .400-.800 inches. I currently have them set all even. It seems to start and run fine but the idle seems to have a little lope to it. I was jus wondering if I should set those center 2 to "less" before I go looking for other problems.

Don

[hikermikem]

Thanks Steve,

1-2 cm seems like alot to me, thats like .400-.800 inches. I currently have them set all even. It seems to start and run fine but the idle seems to have a little lope to it. I was jus wondering if I should set those center 2 to "less" before I go looking for other problems.

Don

I think Steve means 1-2 mm, not cm...

I set mineinside ones a couple of "eyeballed" millimeters lower than the outside ones. I don't think it would mean a hoot towards the idle.

Keep in mind that scheme is for a stock exhaust, set them even if you're running a pipe.

If all else is good, I would play with the mixture screws to eliminate that lope. It doesn't take much to affect the carb function at idle

[Steve]

I think Steve means 1-2 mm, not cm...

No, I meant centimeters, as in "one-hundredth of a meter".

There are no numbers on the Suzuki gauge. They use steel balls in tubes, so there is absolutely NO reference to the real world with that gauge. However, given the range that those steel balls are allowed to move, I am guessing that the 1/2 of a ball diameter might be close to about 1 or 2 cm of mercury.

.

[tkent02]

Dead even, or an inch different, it doesn't really matter as far as how it runs.
Just set them however it makes you feel good. If you don't like it, try something different.

[don]

Thanks fellas, but......

Now I'm completely confused......EVERY question asked about carbs here is answered with the regimented " intakes - o rings - airbox boots - set the screws to X turns out - and a proper synch with a guage of some sort " . I'm not questioning anyones experience, but if these things are the basic necessities for proper diagnosis of other issues and the path to carb bliss, how can it not matter that the synch part could be "an inch different" between pairs? I do know that an ill-synched set of carbs can make your motor sound like it has rocks in it, but I don't know how far off they would need to be for this. As Steve said, he used to set em' all the same before he knew about it. That's where mine are currently.

I guess I'm just trying to understand the physics/reason why Mr. Suzuki would set the center two at a different vacuum level and if it makes that big of a difference.

I have a habbit of asking simple questions that can have verry complicated and varried answers. I can get REALLY complicated by installing manometers on the intakes and exhausts then adjust the carbs to match the readings of the meters with the calculated air flows for the compression, pressure at a given speed of the piston, and breaks specifics calculations, .........but I ride the thing to work and around country roads. Just want it to as correct as it should be.

Hope I don't sound too harsh or anything, just asking obvious questions, no insults etc intended here.

Again, thanks for sharing your experience/knowledge.

[Steve]

I guess I'm just trying to understand the physics/reason why Mr. Suzuki would set the center two at a different vacuum level and if it makes that big of a difference.

That's OK, Don, I have always wondered exactly the same thing.

Personally, I can not think of any logical reason why they should be different. Strangely enough, it is only on the models that have a crossover tube in the exhaust, which also happens to co-incide with the switch to CV-type carbs. Not sure if ALL models got the crossover tubes in '80, along with the CVs or not, but every manual that I have had to look at for information only shows that vacuum difference for the '80-and-up bikes with the CV carbs and crossover tubes.

.

[Suzuki_Don]

If they are all level/even leave them there and just ride the bloody bike. Best advice I can offer. I did mine a few weeks ago and I could not get them perfect, every time I tightened the locknut the bloody thing moved and I could not get them perfect. I got them within one line of each other and it's running fine. I haven't even got around to doing the fastest idle thing the guys on here talk about yet. Just trying to get the motor run in.

[don]

Well then.....now that I have my scientific/technical rant out of the way.......

Basicly either set them all the same and leave it, or get them all the same then adjust till it sounds smoothestest/besteses, without opening one of them so far the idle is way up, of corse.

"Use the force" ... " feel the bike " ... " be the bike " ... " naa-naa-naa-naa-naa-naa-naa-naa ". (Chevy Chase in Caddy shack)

Thanks folks.

[don]

Suzuki-Don,

I know your pain. Every time I do a synch, I try to get them perfect. The best I've been able to get is all within a bout 1mm, (for you metric Kiwis).


Steve,

From my stock car days, the crossover, (position of), simply changes the shape of your torque curve. Closer to the head = lower rpm power...farther from the head = higher rpm power. If you have no crossover then add one, reguardless of where along the exhaust system you put it, you will add torque somewhere. Something to do with the scavenging effect by using the adjacent connected cylinder's exhaust air or relieving the pressure from the other cylinder or something, (oooooooo....my brain is starting to itch). Too scientific .......... even for me...............LOL

[don]

P.S.

As Hikermikem has heard, my 550 is smooth as silk, (unless I have wishfull/biased hearing), like a modern fuel injected bike. brbrbrbrbrbrbrbrbrrr - wwaaaaah - wwaaaa - brbrbrbrbrbrbrbrbrrr.

Tryin' to get the "big boy bike " to run the same with the exception of BRBRBRBRBRBR - WWWAAAAA - WWWAAAAA - BRBRBRBRBRBRR.

[BassCliff]

Hi,

FWIW, this is what I ended up with for my last carb sync.



Roughly 24 for the high and 23 for the low. This is at about 2000 rpm.


Thank you for your indulgence,

BassCliff

[don]

Must digest info before commenting.......Flippin' excelent photo Cliff!!!!!!!!!!!!!!! Nice!!!

[Steve]

Steve,

From my stock car days, the crossover, (position of), simply changes the shape of your torque curve. Closer to the head = lower rpm power...farther from the head = higher rpm power. If you have no crossover then add one, reguardless of where along the exhaust system you put it, you will add torque somewhere.

Yeah, I understand the concept of a crossover pipe, but why did they add it between cylinderd 2&3 and not just before the mufflers like others have done? And the question remains, why the difference in vacuum levels because of the crossover?

.