Carb synch... air bleeders?

[Guest]

So I've replaced the o-rings in my mikuni bs32ss carbs, and now I want to sync them. I bench synched them a while back, but I'll recheck them.

The synching procedure with the vacuum-ports and everything relies on the linkages between the carbs to work, from what I can tell. So, what are the air bleeder screws for? The tiny adjustable ones on the engine side of the carb that you're supposed to start around 2 turns from lightly seated. Which do you adjust first, and are they even related?

Cheers

[Agemax]

they are used for setting the air/fuel mixture at idle. they have no bearing whatsoever synching carbs. do not touch them once they have been set correctly

[luvmy40]

There is a connection between the pilot mixture adjustment and the synch.

With your carbs bench synched, use a colortune to set the pilot mixture to just rich. Take it lean then enrichen it until the fire is just yellow on each cylinder, remember to adjust the idle set screw as needed.

Then perform a vacuum synch procedure. After the synch recheck your pilot mixture. It may be fine and it may need a bit of a tweak.

Repeat until synch and colortune no longer require tweaking.

Make sure to run a cooling fan during the procedures.

[Agemax]

There is a connection between the pilot mixture adjustment and the synch.

With your carbs bench synched, use a colortune to set the pilot mixture to just rich. Take it lean then enrichen it until the fire is just yellow on each cylinder, remember to adjust the idle set screw as needed.

Then perform a vacuum synch procedure. After the synch recheck your pilot mixture. It may be fine and it may need a bit of a tweak.

Repeat until synch and colortune no longer require tweaking.

Make sure to run a cooling fan during the procedures.

Carb synching is a mechanical adjustment. it sets all the throttle valves to the same opening start point. yes, if one is open more than another then it will let more air in, which is why you should synch your carbs FIRST before altering any fuel/air mixture settings

[luvmy40]

Synch or mixture first, my point is they are related and you need to check both if you adjust one or the other.

I've had good results with my procedure. That doesn't mean it's the only way, just one way.

[Agemax]

synch first, then adjust mixture. adjusting mixture screws will not alter synch, whereas synch will alter mixture.

[Steve]

There is a connection between the pilot mixture adjustment and the synch.

With your carbs bench synched, use a colortune to set the pilot mixture to just rich. Take it lean then enrichen it until the fire is just yellow on each cylinder, remember to adjust the idle set screw as needed.

Then perform a vacuum synch procedure. After the synch recheck your pilot mixture. It may be fine and it may need a bit of a tweak.

Repeat until synch and colortune no longer require tweaking.

Make sure to run a cooling fan during the procedures.

I will have to partly agree and partly dis-agree with all of this.

There is a relationship of sorts, but no 'connection' between the two.
Adjusting either one does not affect the other.

A question for you, luvmy40, did you actually see a good color change with your Color Tune? Many of us have tried, but results have been mixed. There has been no problem at all using one on the VM carbs, but the BS carbs are not so good. I was going to get a Color Tune until I tried one and found no color change on my BS carbs.

Back to technique: personally, I prefer to do a vacuum sync before a mixture adjustment. If you happen to have a bike on which a Color Tune works, it might not matter, but if you use any of the other methods, which usually rely on detecting changes in engine speed, you need to have all the carbs contributing to the smooth operation of the engine. After the carbs are synchronized, go ahead and check your mixtures. Simply adjusting your mixtures should not affect the carb sync, but I usually leave the gauges connected throughout the whole procedure.

[luvmy40]

Steve,
I haven't started on the GS yet. It's still in several pieces in the garage!

I use this method on My Yamaha Seca 750 with excellent results. And yes, with the Hitachi carbs I get a very visible and easily noted change in combustion color. It's quite easy to adjust to just this side of lean.

I have not had the need to do any carb adjustments on my Katana to date. The pilot adjustment screws on it are still capped.

Have you tried doing this in a very dim environment? Is there no difference at all in combustion color with the BS carb? Is the range of adjustment too small to be visible?

[WilliamGLX81]

Short of a Colortune, how do you know when your carbs' mixture is right? Starting at a consistent 2.5 turns out, do you check for engine speed or exhaust tube temp or read the plugs or...?

[Steve]

Have you tried doing this in a very dim environment? Is there no difference at all in combustion color with the BS carb? Is the range of adjustment too small to be visible?

Yes, it was in a garage, with controllable lighting. What most of us have observed is that, as you lean out the mixture, the flame never changes color. It only starts to sputter out occasionally, then more often, finally going out completely. As you richen it back up, the flame will start to come back occasionally (but always the proper color), then more regularly, then all the time. As you richen it even more, the flame still does not change color.

I usually start with the mixture screws out three full turns after a carb rebuild. The behavior just described happens as the screws are turned down past one turn, then back out to about five turns, so I would not call that a "narrow range of adjustment".

We had just done a set of VM carbs and I was VERY impressed with the results, so I took the Colortune home to do a set of BS carbs, and was very UNimpressed.

.

[Badooka]

Yes, it was in a garage, with controllable lighting. What most of us have observed is that, as you lean out the mixture, the flame never changes color. It only starts to sputter out occasionally, then more often, finally going out completely. As you richen it back up, the flame will start to come back occasionally (but always the proper color), then more regularly, then all the time. As you richen it even more, the flame still does not change color.

I usually start with the mixture screws out three full turns after a carb rebuild. The behavior just described happens as the screws are turned down past one turn, then back out to about five turns, so I would not call that a "narrow range of adjustment".

We had just done a set of VM carbs and I was VERY impressed with the results, so I took the Colortune home to do a set of BS carbs, and was very UNimpressed.

.

Noticed my Colortune flame was more white than blue- if I hit the throttle I could see the bunson blue- but really tough to tell much difference in color change during a tune.

[jsandidge]

I watched a youtube video where the guy "syncs" the mixture screws by checking the temperature of the exhaust on each cylinder. He used one of those electronic "point and shoot" thermometers pointing at each exhaust pipe about 3 inches down from the head. This should work, since a cylinder with a lean mixture will run hotter than a richer one. I've heard the inboard cylinders naturally run hotter than the inner ones, so I'm not sure how exact this process is. This was done after a vacuum sync, then the vacuum sync was re-checked. The mixture sync did affect the vacuum sync and vice-versa, so it took a little back and forth tweaking. I will be trying this after I finish my carbs and check my valve gaps, so I will post results in a week or two.

[luvmy40]

Suzuki's "YICS"?

Do the GS engines have an internal equalizer? My XJs are YICS(Yamaha Induction Control System) engines. They have an internal passage that homogenizes the intake from cylinder to cylinder. There is a tool that must be installed to block these passages when tuning the pilot mixture.

If the GS has a similar system it would make the color tune ineffective unless it can be blocked off as well.

[Steve]

No such animal on the GS.

.

[Steve]

I watched a youtube video where the guy "syncs" the mixture screws by checking the temperature of the exhaust on each cylinder. He used one of those electronic "point and shoot" thermometers pointing at each exhaust pipe about 3 inches down from the head. This should work, since a cylinder with a lean mixture will run hotter than a richer one.

In theory, yes, this will work.

In practice, I will have to say "maybe".

If you have stock pipes, they are double-walled, making any temperature readings rather cumbersome. Because of the double walls, there is quite a time lag in any exhaust temperature readings, which would make it a VERY long process. Might be quicker to just gear up and hit the road to do some plug chops.

If you have an aftermarket exhaust system, the temperature method of tuning might work, but there are still questions. For example: what temperature is your goal? It might be easy enough to get them all reading the same, but who is to say that it's the "right" temperature?

Then there is always that question about the choice of words. You do not "sync" the mixture screws.

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