Carb Sync Jam Nut Frustration

[danny01975]

82 GS1100 GK. I got a carbtune so I could sync the carbs since I changed the exhaust. Works well and I was able to get them all very close. That is until I try to tighten the jam nuts holding the adjustment screws. Especially the #2 which is directly below the throttle cable bracket. It was an exercise in futility.

Is there a special tool for tightening these? Or a trick for doing it? It’s way too crammed to get an 8mm wrench in there.

[Nessism]

Motion Pro sells a nice tool. It's true that tightening the nut can affect the sync. Some trial and error involved, and the tool makes that easier.

[danny01975]

Motion Pro sells a nice tool. It's true that tightening the nut can affect the sync. Some trial and error involved, and the tool makes that easier.

Are you talking about the 90 degree tool or something else? That 90 degree tool would be useful but it won’t allow me to hold the screw while tightening the jam nuts holding

[dgates1]

Are you talking about the 90 degree tool or something else? That 90 degree tool would be useful but it won’t allow me to hold the screw while tightening the jam nuts holding

It is essentially a long tube with an 8mm socket on the end with a long screwdriver that goes down the middle of the tube.

[dgates1]

Funny.. I was just researching this as I am getting ready to sync my carbs. From what I read it is easier to access the 2-3 adjustment screws if you move the choke cable mount out of the way, but still a little difficult. This give you just enough room to get that tool in there, but may still be a little angled.

I have read the "Famous Nert Sync Screw Solution" and it seems a little extreme but I guess it works -

http://bwringer.com/gs/syncmod/NertSyncKit2.pdf

My question is if anyone ever came up with a replacement screw and spring for these to eliminate the nut?? I read several old threads on it but seemed to die on the vine.

https://www.thegsresources.com/_forum/forum/technical-forums/old-technical-info-forum/18440-replacing-the-cv-carb-sync-screw-locknut-with-something-better

I can get a pack of (3) 5mx20mm (0.5mm pitch) hex head screws from eBay for only $5.90 shipped.

Did anyone ever figure out what size spring would work for this?? I'm assuming a 7 or 8mm OD spring would work but what length? I'm thinking 10mm length would do the job...

[Nessism]

Sadly, Motion Pro may have discontinued the tool in question. This is a knockoff that should work, though.

https://www.z1enterprises.com/carb-adjustment-tool-set.html

[danny01975]

Sadly, Motion Pro may have discontinued the tool in question. This is a knockoff that should work, though.

https://www.z1enterprises.com/carb-a...-tool-set.html

Thanks! I agree, the spring / replacement screw solution would be best. I might just give that a try!

[salty_monk]

Would be pretty interesting to see if the spring works. I bet you'd need a pretty strong spring. Also makes you wonder why they didn't do it that way originally, my guess is that it would creep.
Yeah, pretty impossible to do without that tool....

[dgates1]

Just sharing this here from another thread I posted this on.

I did end up changing out my Carb Sync Screws for hex-drive cap screws with a washer and spring on them. Found the M5x0.5 pitch screws on eBay from China (search for "M5 fine thread"). Had ordered 20mm length and they were too long and interfered with the choke rail. The 16mm length ones I ordered next were just right. Also ordered 7mm OD x 5mm ID x 15mm Long SS springs. These were good on the 20mm screw but too long for the 16m screw. Ended up cutting them to about 10-11mm length and installed with a SS M5 washer at the top of the screw.





I had done a vacuum sync right before this with the 11" long "special tool" that is suppose to work and it was difficult to get them balanced really good. Used a micrometer to crudely "measure" where the throttle valves were. I installed the new screws/springs and tried to match with the carbs still on the bike. It started but was not very happy... might be better to pull the carbs and do a bench sync.

After they were installed and I did the sync again, it was really easy to dial them in to be just about perfect with a 4mm ball end bit on a 6" bit holder. Yes.. I know everything is really dirty right now (she just woke up from an 8 year nap) and I did replace my O-rings in the boots.

Time will tell if they hold their position.

[danny01975]

Nice! That's exactly what I was thinking about doing. I eventually ordered the long screwdriver tool and got them sync'd. But even with that, tightening the jam nut while holding the screwdriver, while easier than before, was still hard to get it exact.

I found myself "pushing" on the tool when tightening the nut which affected the idle position slightly, throwing off the sync a little. And the tiniest screw turn makes a big difference.

If this works, it will be a much better way to do the sync. Please keep us posted!

[bonanzadave]

I was not that scientific. With the nut just loose (1/16th turn) I got the screw where I wanted it on the carbtune then backed it off a tick. When I tightened the nut it turned the screw back where I had it. Good for me !