So I am trying to perform a carb synch on my 98' gs. Here's the problem, my layout looks nothing like what's in the pictures in the wiki guide. For one the choke cable spring is on the other carb and the spring goes outward and the cable noodle is on the inside. Also the second vacuum port with the rubber piece on it is one the exact same carb with the port of the bottom, that can't be right!!! Pics soon

Ok I had to go buy some vacuum gauges. And I found the youtube video guide which shows to connect them to the black plastic nipples on top of each carb. So I did that. Hears the thing, my gauges are jumping all over the place at idle, I cant seem to get a reading. What am I doing wrong?

I haven't synced yet but I was under the impression it wasn't supposed to be done at idle.

Yea I kinda figured that out, higher rpm means higher frequency and less gauge bouncing. 2 new problems though, one I have white smoke coming out of the valve cover breather tube and it doesnt appear that my carbs have an overlapping vacuum range. When I turn the sync screw I can make one of the carbs change its vacuum reading but the other doesnt move.

The simplest, and so far quite reliable method for me is free. Also, your setup is fine. Choke is fine and the vacuum tube is ok as well. The Wiki is showing you a much later model as indicated in the heading.

To sync the carbs...free method:

1. Remove carbs from bike.
2. Find a paper clip
3. Straighten paperclip
4. Cut paper clip in half
5. Open throttle and insert one paperclip under one butterfly valve, and allow to close
6. Unscrew sync screw so second paperclip fits under second valve
7. Slowly turn adjustment screw until you can just barely NOT pull the paperclip out of valve

DONE

Notes: DO NOT let the valves slap shut on paperclips, you can dent the valve flaps
           DO NOT drag paperclips through valve flaps any more than necessary....same reason

Whenever I do this, I use single strand 18ga copper wire simply because it's softer and won't ruin the valve flaps, but people sometimes don't have that lying around.

Quote from: Soloratov on August 17, 2014, 05:31:47 PM
The simplest, and so far quite reliable method for me is free. Also, your setup is fine. Choke is fine and the vacuum tube is ok as well. The Wiki is showing you a much later model as indicated in the heading.

To sync the carbs...free method:

1. Remove carbs from bike.
2. Find a paper clip
3. Straighten paperclip
4. Cut paper clip in half
5. Open throttle and insert one paperclip under one butterfly valve, and allow to close
6. Unscrew sync screw so second paperclip fits under second valve
7. Slowly turn adjustment screw until you can just barely NOT pull the paperclip out of valve

DONE

Notes: DO NOT let the valves slap shut on paperclips, you can dent the valve flaps
           DO NOT drag paperclips through valve flaps any more than necessary....same reason

ive already done this using some pieces of cut up close hanger.... it is not very precise. I was hoping to do a legitimate carb sync

Cloths hanger is far to large, thats the issue. Using smaller wire works great, and so far, I had it rechecked by the shop twice...for these motors, they said it was well within spec.

If you are having issues with your meter, then it is either the meter, or you may have a vacuum issue.

No offense but thats not particularly helpful besides I really would rather use the gauges to make this work...it should be more accurate. I just bought brand new gauges they should be fine. What kind of vacuum problem? Also I am having to rev up to 6-7k rpm before the gauges stop bouncing.... everyone else seems to have them level out at about 2k rpm.

At 6-7k rpm one gauge reads 3.5 in HG constant regardless of where I put the adjustment screw. The other can adjust between 10 in HG and 5 in HG depending on where I put the adjustment screw... however I cannot get it lower than 5 and since the other one doesnt seem to be able to adjust then it is impossible for me to synch these.

Maybe we need to back up. Your carbs look nice and clean, so thats good, but I am looking at that picture again, and usually that rubber cap...on the side there is a hose that runs to the petcock to control the fuel flow. Do you not have that? It's shouldn't effect the sync, just asking.

The point of using my method is that it gets them synced close enough so that unless you really are going for dead on perfect, your motor should run fine assuming no other issues. If your meter is showing one carb is doing something very wrong, then my method gets you close enough to look for a DIFFERENT issue than sync. If you can get the motor idling steady, then spray all over the carbs with carb cleaner. If the idle fluctuates, you have a vacuum leak.

Quote from: Soloratov on August 17, 2014, 06:05:32 PM
Maybe we need to back up. Your carbs look nice and clean, so thats good, but I am looking at that picture again, and usually that rubber cap...on the side there is a hose that runs to the petcock to control the fuel flow. Do you not have that? It's shouldn't effect the sync, just asking.

The point of using my method is that it gets them synced close enough so that unless you really are going for dead on perfect, your motor should run fine assuming no other issues. If your meter is showing one carb is doing something very wrong, then my method gets you close enough to look for a DIFFERENT issue than sync. If you can get the motor idling steady, then spray all over the carbs with carb cleaner. If the idle fluctuates, you have a vacuum leak.

The vacuum line to the frame petcock connects to a long brass nipple that comes out the bottom of the left carb. When looking for a vacuum leak where should I check? Maybe I can do a quick visual inspection... maybe I missed something.

Um, the vacuum line should definitely NOT be connected to anything on the bottom of the carb. 


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Those brass lines in this picture, should wrap right around and go back intot he carb. If either one is not...that's your issue. Has the bike been running?

Note the vacuum port labeled in the middle of the picture, that is the petcock port.

yea mine has an extra port that isnt in that picture here see... it is next to the drain plug on the left carb. And no it hasnt been running, it has been disassembled for a long time.

Carb syncing is done at an idle or just above an idle if you want @1500 Rpm. It's been decades since I have used vacuum gauges, they are a pain to watch fluttering around, the main reason I went to a mercury manometer.

is it running from a port BETWEEN the carbs? If so, yeah, that's not right either. That hose is far too large to be a vacuum line...vacuum line should be about...1/4-5/16 maybe

I use vac gauges but you need aquarium  check valves to stabilize the needles

Quote from: Soloratov on August 17, 2014, 06:50:47 PM
is it running from a port BETWEEN the carbs? If so, yeah, that's not right either. That hose is far too large to be a vacuum line...vacuum line should be about...1/4-5/16 maybe

No I had it running from the vacuum port on the back of the frame petcock to that port. And it is the right size tubing (1/4 if I recall... 5/16 is the fuel line size)... the tubing just has thick walls so it looks bigger but the ID is correct. looking at the hose routing diagram for my year it does appear that it goes into that upper vacuum port (the one that had rubber cover on it)... so I moved it to there and moved the rubber cap to the other side. This pretty noticeably stabilized the vacuum gauges but they were still too bouncy to read even at 2k+ rpm. I ended up giving up on the stupid gauges (what a waste of cash) and built one of the home made manometers with some aquarium tubing, zip ties, a broom handle and some left over fork oil. It didn't take but a few minutes with this device to get them synced. It really purrs right now... sounds effing amazing.

One thing I am noticing but I don't think it is a problem, but when I lift off the throttle I do get occasional and minor backfires (just an off key pop, no smoke or other symptoms). Considering the ignition advance, the aftermarket exhaust, lunch box filter, and carb rejet I think this is pretty normal... what do you guys think?

Quote from: Nakedguy on August 17, 2014, 09:06:49 PM
I use vac gauges but you need aquarium  check valves to stabilize the needles

good idea for the future

Ideally to eliminate the fluttering you need constrict the tube running to the guages. In my fathers permanent set up he has a copper tube squeezed to give a small opening.
I have tube clamps that I use to squeeze the plastic tubes to eliminate the fluttering.
I don't have the manual handy but don't they instruct the test at a few thousand rpm?
Regards.
Bmf