Carb Synchin' my gs850

[Scudder]

My 1980 gs850 is still not running right. Much better than before dipping and rebuilding the carbs, but I'm thinkin' I'm up for a carb synch this weekend.

My question. I have two synch kits that I borrowed. One is an old suzuki on with the ball bearings, and the other has the gauges/needles. Does it matter? I'm leaning toward the old suzuki one.

Also, I've read in the gauges/needle carb synch kit that the choke should be all the way open when synching the carbs. I've watched tutorials on you tube and this step was not mentioned. They just say to have the bike warm and keep it at 2000 rpm while doing the synch procedure.

Any help is appreciated.

Scudder

 

[Dogma]

Uh, if you balance it with the choke open, won't it be smooth only with the choke open?

When Steve balanced mine, the requirement was that I had ridden it to his place so it would be warmed up (normal operating temp). I do seem to remember he raised the idle during the sync. Best to do that with the idle adjust screw, not by adding fuel to the mix from an unbalance device (all the linkage in the "choke" mechanism).

Lots of people are skeptical of the gang of four gages type balancer. Each gage has to be calibrated exactly the same. The other types, especially with fluid, are much more likely to read exactly the same for the same vacuum. If you do use the gages, connect them to a single vacuum source to see if or how they might read differently from each other.

 

[Steve]

Either gauge should work fine, just be sure to check the gauge before using it. If I remember reading the Suzuki manual correctly, it says to apply the same vacuum to each column to make sure they read the same before connecting to the engine. Easiest way is to make a manifold (aquarium air supply manifold works well) to apply the vacuum to all four at the same time. Might need to do that to the other gauge, too, not sure what you have.

The "choke" should be turned OFF, whether you consider that open or closed. The bike should be fully-warmed up, as in "ready to ride", so no "choke" should be involved.

Suzuki manuals call for engine speed to be between 1500 and 2000 RPM. Before I read that specification, I had always done a sync at about 12-1300, and, in fact, I still do. The higher speed might smoothe out the pulses a bit, but I have found minor differences in vacuum sync between the two speeds. Since I am looking for smoothness at idle, and even pulling as I open the throttle, I sync at basically idle speed.

Have you adjusted your valves yet? If you sync your carbs before adjusting the valves, then change some shims, you will change how much air that cylinder(s) is (are) breathing, which will affect the vacuum level for that carb, and you will have to re-sync.

.

 

[mike_of_bbg]

Wow, you got a hold of an original Suzuki tool? I'd use that. Please bear in mind that the "official" sync is not flat, but with the outboard cylinders pulling one "half ball" more vacuum than the inboards.

No choke: the choke allows an enriched air/fuel mixture it, so it can affect the flow and thus the vacuum through the carbs. Warm the bike up first, point a fan on it while running it stationary. My philosophy is to sync as close to idle as the smoothness of the tool will allow (at idle generally there's some "bounce" to the columns). The theory being that as the throttles open the minute differences in throttle openings will diminish. In the later sections (after change to CV carbs) in my manual it says 1500-2000 RPM.

Make certain to cap the vacuum tap for the petcock.

Good luck.

My 1980 gs850 is still not running right. Much better than before dipping and rebuilding the carbs, but I'm thinkin' I'm up for a carb synch this weekend.

My question. I have two synch kits that I borrowed. One is an old suzuki on with the ball bearings, and the other has the gauges/needles. Does it matter? I'm leaning toward the old suzuki one.

Also, I've read in the gauges/needle carb synch kit that the choke should be all the way open when synching the carbs. I've watched tutorials on you tube and this step was not mentioned. They just say to have the bike warm and keep it at 2000 rpm while doing the synch procedure.

Any help is appreciated.

Scudder

 

[Steve]

When Steve balanced mine, the requirement was that I had ridden it to his place so it would be warmed up (normal operating temp).

Couple of reasons (excuses) for that "requirement", fine sir.

1. Yes, it needed to be fully warmed up.
2. You were looking for an excuse for a ride.
3. It was easier for you to come to me than for me to take my mercury sticks to you.

.

 

[Scudder]

Seems odd to me too. This is exactly what step one says for the Instructions for use:

1. Run the engine until operating temperature is reached. Carbburetors must be adjusted with engine warm and choke fully open.
CAUTION: Choke operation may damage vacuum gauges.

Seems that the instructions contradict themselves. Choke fully open in my book means to have the choke on all the way. However then it says if you operate the choke, it could damage the vacuum gauges.

I'm confused.

Scudder

 

[mike_of_bbg]

Well, real "chokes" are plates that close the incoming air, causing more vacuum to pull more fuel. So it makes sense that a real "choke" would need to be "fully open", as in not blocking the air flow at all. Our Mikuni carbs don't have real "chokes", they have "fuel enrichment circuits", which provide an extra amount of enriched mixture in (that's why the RPMs go up so high under full choke: there's more AIR in there, too).

 

[Dogma]

Couple of reasons (excuses) for that "requirement", fine sir.

1. Yes, it needed to be fully warmed up.
2. You were looking for an excuse for a ride.
3. It was easier for you to come to me than for me to take my mercury sticks to you.

.

I wasn't complainin' or anything!

 

[Scudder]

Yes. I've adjusted the valves. Seems to me synching is the only things left as far a fuel/carbs go. I've never synched any carbs before so this will be a good learning experience.

Scudder

 

[mike_of_bbg]

And tuning the idle screws using the "highest idle" method...

Yes. I've adjusted the valves. Seems to me synching is the only things left as far a fuel/carbs go. I've never synched any carbs before so this will be a good learning experience.

Scudder

 

[Scudder]

My rpms don't go any higher than 2000 even at full choke. This has always been a frustration, because it takes a long time to get the bike ready to ride. Will synching the carbs help my choke issues?

Scudder

 

[mike_of_bbg]

It may. I'd suspect you have a butterfly or two that's completely closed. You could also be running a bit lean.

Highest RPM method for idle screw tuning:

http://members.dslextreme.com/users/bikecliff/images/highest_rpm_plug_chop.html

 

[Steve]

My rpms don't go any higher than 2000 even at full choke. This has always been a frustration, because it takes a long time to get the bike ready to ride. Will synching the carbs help my choke issues?

Synchronizing the carbs won't do anything to speed your warm-up time, but ensuring a proper mixture will. What settings do you have on the mixture screws? To help start the bike and ensure a good sync job, I will have the mixture screws on an unknown set of carbs set to three full turns out from lightly-seated. After the bike is warmed up, sync the carbs to get it running as smoothly as possible, then slowly turn each mixture screw in, listening for a drop in engine speed, then back up about 1/8 turn.

If you start with the screws farther in, you might be running too lean to run effieicntly, so it won't be easy to distinguish between mis-firing and not-firing (due to closed (non-synched) carb). The little bit of extra fuel that is provided by the mixture screws will not be enough to foul the plugs during the sync job, and makes the job go that much quicker.

I agree with the confusion about the "choke" circuit. That is one reason that I ALWAYS put that in quote marks when I mention it. As Mike mentioned, an old-style car choke has a plate that physically blocks (chokes) the intake of the carb, so it is easy to refer to that as being 'open' or 'closed'. The enrichment circuit on our carbs involves a little plunger that, when engaged ("choked") actually opens an extra air passage and a fuel passage to provide the rich mixture for starting a cold engine. When you CLOSE the extra ports, you go back to running on the 'normal' circuits in the carb.

Just one more time for clarification: Your "choke" knob should be pushed IN while doing your carb sync.

.

 

[Scudder]

Thanks. My mixture screws are at 3 turns out from lightly seated, now. So... I should be good to go as far a carb synch goes.

The choke issue (2000 rpms only at full choke) is the real puzzlier in this whole thing to me. I've been down the road of carb issues, etc. with my other bike (gs750), but I've never had a choke that when fully open is topped out at 2000 rpms. I have to adjust the idle screw at start up and after it is warmed up. After the bike is warmed up (5 minutes of riding) it runs pretty well, but doesn't have very good, acceleration because of missing, etc. Don't think that has anything to do with the choke, but there is an obvious fuel/air problem.

However, the missing that was taking place with my 1978 gs750 was ultimately solved with a replaced condenser, thanks to Big T's excellent problem solving skills. That was a huge day. I'd been chasin' my tail for a long time with the fuel/air issues, and it was solved with a $1.99 condensor. Think I may have gotten luck on that one.

Scudder

 

[Steve]

While I was home a couple of weeks ago, we got my son's 650L going with the usual stuff, clean carbs, new boots, o-rings, valves, etc. That bike never goes over 2000 on "choke" either, but that's OK. I always try to find the 'sweet spot' in the "choke" that allows starting but keeps the engine speed down, anyway. His bike requires full "choke" (the only one of our bikes that does that), but can almost immediately be taken to half-way. Never gets over 2000, can be ridden away within a minute, like all the other bikes.

.