Syncing carbs after valve adjustment

[Guest]

Does this order sound okay?

Start with:
(from a Chuck Hahn post)
Adjust carb 4 to match what carb three is showing, then 1 and 2. Note that as your turning the sync screws that carb 3 WILL in fact change. Make slow adjustments and get all 4 as close to each other as is possible.

Although on my bike, I want #2 and #3 to be one notch below #1 and #4 on the vacuum gauges because of my exhaust crossover.

Once carbs are synced then use the highest idle method for fine tuning?

[growler]

Or is the throttle response method the way to go?

[Steve]

The sync sequence is good. In the Suzuki manual, they adjust #4 first, then #2, then #1.
Note that #1 is slaved off #2, so if you adjust #2, you will also affect #1.

The manual also suggests putting the vacuum on 2 and 3 just a bit lower, but nobody has ever given me a good reason why.
That change happened at the same time that CV-type carbs were introduced on the four-cylinder GSes, and the exhaust
systems also got crossover tubes, but nobody has ever explained whether they are the reason.
I recently saw a post on anothoer forum that said "if you have the stock airbox, adjust the two inner cylinders lower. If you have pods, make them all the same."
Again, I don't know what difference it makes, I have always done mine straight across

As for the mixture tuning: if you know what you are listening for, the throttle response method can work quite well, but there are so many variables, it's highly subjective.
I prefer to use the 'idle-drop' method, which is much easier to do while the vacuum gauges are still connected. Once the carbs have been synchronized, turn one of the mixture screws (I usually start with #1, but it does not really matter). Which way to turn will depend a bit on where you are starting. I start with them three full turns out, which ensures a rich mixture to start with. Slowly turn the screw IN, listening for a change in idle speed and watching the gauges. When the engine speed drops, so will the vacuum. It can usually be seen on the gauge before it is heard. When the gauge drops, turn that screw back out about 1/4 turn, move to the next one. When you are done, go back, do them over, just to make sure that the engine speed drops within that 1/4 turn, then back it out 1/8 turn, so it's running smoothly. A quick blip of the throttle to evaluate the response will confirm a proper mixture.

Regardless which method you choose to use, do the carb sync first. It's hard to tweak the mixture on a carb that might not be open far enough to be contributing to the output.

.

[gustovh]

The high idle method sets your pilot circuit up for lean best idle, then sync the carbs.

V

[Steve]

The high idle method sets your pilot circuit up for lean best idle, then sync the carbs.

V

BUT ... if your sync is off and you are basically running on three carbs, adjusting the mixture on that carb won't make any difference at all, which is why I prefer to do the sync first, then the mixture.

Your bike, your call, just saying why I do it my way.

.

[growler]

Thanks Steve. I think I will try this method.

The sync sequence is good. In the Suzuki manual, they adjust #4 first, then #2, then #1.
Note that #1 is slaved off #2, so if you adjust #2, you will also affect #1.

The manual also suggests putting the vacuum on 2 and 3 just a bit lower, but nobody has ever given me a good reason why.
That change happened at the same time that CV-type carbs were introduced on the four-cylinder GSes, and the exhaust
systems also got crossover tubes, but nobody has ever explained whether they are the reason.
I recently saw a post on anothoer forum that said "if you have the stock airbox, adjust the two inner cylinders lower. If you have pods, make them all the same."
Again, I don't know what difference it makes, I have always done mine straight across

As for the mixture tuning: if you know what you are listening for, the throttle response method can work quite well, but there are so many variables, it's highly subjective.
I prefer to use the 'idle-drop' method, which is much easier to do while the vacuum gauges are still connected. Once the carbs have been synchronized, turn one of the mixture screws (I usually start with #1, but it does not really matter). Which way to turn will depend a bit on where you are starting. I start with them three full turns out, which ensures a rich mixture to start with. Slowly turn the screw IN, listening for a change in idle speed and watching the gauges. When the engine speed drops, so will the vacuum. It can usually be seen on the gauge before it is heard. When the gauge drops, turn that screw back out about 1/4 turn, move to the next one. When you are done, go back, do them over, just to make sure that the engine speed drops within that 1/4 turn, then back it out 1/8 turn, so it's running smoothly. A quick blip of the throttle to evaluate the response will confirm a proper mixture.

Regardless which method you choose to use, do the carb sync first. It's hard to tweak the mixture on a carb that might not be open far enough to be contributing to the output.

.

[growler]

I did have some problems loosening the lock nut on 2 of the 3 sync screws. I even have the "magic" tool, and that didn't make them budge. I'm not sure I have a deep socket that size...6mm or 7mm? I'll take my time and try again today after work.

[Steve]

8mm. .......

.

[rapidray]

I always sync first & then do the mixture screws.
Ray.

[growler]

Here's a short video of how I had them last night. Made an adjustment though and sent them a little wacky, so going to start over tonight using the method above. I was close. Noticed #2 didn't move much when blipping throttle. Hmm.

https://www.youtube.com/watch?v=4K9Z9TkVbRo

[Steve]

Looks like the damper on gauge #2 needs to be opened up a bit. Looks like it's responding, but VERY slowly.

Just out of curiosity, did you connect all four gauges to one source (preferably with a manifold) before connecting to the engine? Those gauges don't always agree with each other, so it's nice to compare them to make sure they are all reading the same before you introduce the variable of engine vacuum. Once you know that the gauges agree, you will then know that any differences you see are actually differences in the engine.

Nice video, engine sounds real smooth.

.

[Grimly]

The middle two pots run richer to cool them slightly. When I first saw the settings of the standard carbs it puzzled me at first, then the penny dropped. I've known several engines where the middle cylinders were inadequately cooled and they always burned their valves first.

[Steve]

I understand that theory, but can't comprehend the method.

A lower vacuum reading is caused by the throttles being OPEN a bit more. That means that those two cylinders are working a bit harder, probably causing a bit more heat in the process.

I know that the 1150s and, I think, the 4-valve 550s had larger main jets in the inner cylinders to cool them a bit. THAT I understand, but not opening the throttle more.

.

[growler]

Finished the sync last night. Ready to take her out this weekend for a ride. Then on to the oil pan gasket and other misc things I need to do.

Thanks for your help!

[Grimly]

I understand that theory, but can't comprehend the method.

A lower vacuum reading is caused by the throttles being OPEN a bit more. That means that those two cylinders are working a bit harder, probably causing a bit more heat in the process.

I know that the 1150s and, I think, the 4-valve 550s had larger main jets in the inner cylinders to cool them a bit. THAT I understand, but not opening the throttle more.

.

What's really needed is a set of EGAs, one on each header, to see exactly what's happening. Such a thing was so expensive as to be impossible for the average owner 30 years ago, but can be done fairly cheaply now. I suspect the balancing act in the middle venturis is by design allowing the middle two to have just enough extra air to compensate for the bit of extra fuel so that it burns cleanly, but is still rich enough to apply the cooling effect, without making it run unevenly.
The designers were on the ball, there's no denying that - and the fact is, they (and other Japanese makers especially) managed to produce a series of engines which produced good power to weight / size and also ran very efficiently *unless the power was used wastefully* and on the borderline of being too weak but ran reliably for years and decades - a feat very few other manufacturers of the day managed to accomplish without badly damaging their engines. I was always slightly concerned whenever I looked at the plugs, but everything was set up to maker's specs and nothing burned out.
I'm reminded of my XS750, which returned 48mpg no matter how I rode it and that was every bit as heavy as the GS850. Best I ever had out of the 850 on CV carbs was 60mpg, driving like a granny. 48mpg average from that would have been good.