Nert's Famous Sync Screw Solution

[bwringer]

This popped up in the tech section from a forum member called "Nert", and it's a simple and ingenious solution to the biggest problem with synchronizing CV carbs -- it's impossible to tighten the lock nuts without affecting the adjustment, and it's nearly impossible to reach the middle sync screw.

The engineering and the PDF are from a forum member called "Nert". I am only providing the hosting for the PDF file.

It's a 2.3MB PDF, so you may want to right-click the link and choose to download the file.
http://bwringer.com/gs/syncmod/NertSyncKit2.pdf

 

[8trackmind]

Thanks, Brian. :-D

 

[Guest]

Hmmm, very interesting... Good read

 

[Tom MLC]

Ingenious. Practical, and easy.

How does one manually sync the carbs? (is the procedure in my Clymer's, I wonder?)

 

[bwringer]

Ingenious. Practical, and easy.

How does one manually sync the carbs? (is the procedure in my Clymer's, I wonder?)

I think the manual uses the term "bench sync" -- basically getting the throttle butterflys somewhat in the same ballpark, at least enough to start the bike and do a proper sync using vacuum readings.

Basically, you stick a thin round metal object, such as a drill bit or thin rod of some sort (the size doesn't matter much), into one of the throttle butterflys and then open the throttle with the idle speed knob until it just falls out.

Then follow the same sequence as a normal sync and adjust all the sync screws so that all the throttles are opening and closing together.

Adjust the idle screw back down, then start the engine and adjust the idle speed until it runs enough to do a vacuum sync.

This is a rough adjustment procedure you only need if you have disassembled the carbs. You can probably manage to do the modification on an assembled rack of carbs without moving the sync screws much at all.

 

[t3rmin]

Anybody done this mod with the carbs in place? I *hate* taking those suckers off (well actually it's the putting back on that sucks...).

 

[t3rmin]

Here's another idea that I might try for those of us too squeamish/lazy to drill our carbs. What about a drop from a hot glue gun on each sync screw? Remove the jam nuts, sync it up, then put a drop on each one. Should be easy enough to knock off next time you need to sync. Maybe couple it with a bit of removable grade loctite on the threads?

 

[terry]

I don't want to disparage "Nert"s idea at all, but it seems to me that replacing the set screw and locknut with a pan head screw with a stiff spring underneath (same principle as your idle adjustment screw, mixture screws etc) would be a lot easier, with no requirement to remove the carbs, or drill any holes? The spring would stop the screws from moving under vibration, and would be a little less "fiddly", I reckon? Cheers, Terry.

 

[Jethro]

Im sorry, but anyone who speds any time synching carbs is FOOLISH not to just pony up 20 measily dollars for this brilliant tool, which makes it an absoulte no brainer to adjust the set screw and tighten the lock nut in one tool, easy as can be...
http://www.motionpro.com/motorcycle/tools/carb_adjusting_tool/

 

[bwringer]

Im sorry, but anyone who speds any time synching carbs is FOOLISH not to just pony up 20 measily dollars for this brilliant tool, which makes it an absoulte no brainer to adjust the set screw and tighten the lock nut in one tool, easy as can be...
http://www.motionpro.com/motorcycle/tools/carb_adjusting_tool/

I've had one of those MP tools for years, and it's STILL a major PITA to tighten the locknuts without drastically affecting the sync screw setting. You have to develop a feel for how much tightening the locknut will change the setting, and then compensate. The MP tool makes the project just barely possible, but it doesn't address the basic weakness of the whole idea of using locknuts.

Also, we just found out the hard way that the socket on the tool, at least the example I have, is not deep enough to reach the locknuts on some carbs. Aaaaarrrggghhh!!!^%$##@!!!!!!!! (The patient is a 1982 GS850GL - the tool works fine on my 1983 GS850G. Go figure.)

 

[nert]

I don't want to disparage "Nert"s idea at all, but it seems to me that replacing the set screw and locknut with a pan head screw with a stiff spring underneath (same principle as your idle adjustment screw, mixture screws etc) would be a lot easier, with no requirement to remove the carbs, or drill any holes? The spring would stop the screws from moving under vibration, and would be a little less "fiddly", I reckon? Cheers, Terry.

Terry
I agree, that was the direction i started in. I could not locate screws with the same thread pitch and thread count with the length and head style i needed. Decided to tension what was there instead with locally available and common hardware. No problems so far. And the modification isn't that tough. Yes the carbs need to be off. Some of us anal people do that anyway in the off season just to have our hands in her.

 

[jimcor]

Here's another idea that I might try for those of us too squeamish/lazy to drill our carbs. What about a drop from a hot glue gun on each sync screw? Remove the jam nuts, sync it up, then put a drop on each one. Should be easy enough to knock off next time you need to sync. Maybe couple it with a bit of removable grade loctite on the threads?

Maybe it's just my bad luck, but that hot glue never sticks to anything you want it to. Don't think I'd waste my time.

 

[t3rmin]

Im sorry, but anyone who speds any time synching carbs is FOOLISH not to just pony up 20 measily dollars for this brilliant tool, which makes it an absoulte no brainer to adjust the set screw and tighten the lock nut in one tool, easy as can be...
http://www.motionpro.com/motorcycle/tools/carb_adjusting_tool/

I'll chime in with bwringer on this. I've got the tool, and while it does make the process manageable, it's still by no means as easy as it should be. Tightening that locknut always throws it off so you have to compensate...

 

[Nate_uk]

newbie alert..
..I've always used the blue medium strength loctite and never had any problems with the carbs going out of sync. Way easier than fiddling around with the lock nuts. I do apply a liberal amount to the tops of the thread though.
Just my two pence (or cents, depending upon where ya from) worth

Nate 8-[

 

[t3rmin]

Terry
I agree, that was the direction i started in. I could not locate screws with the same thread pitch and thread count with the length and head style i needed. Decided to tension what was there instead with locally available and common hardware. No problems so far. And the modification isn't that tough. Yes the carbs need to be off. Some of us anal people do that anyway in the off season just to have our hands in her.

Off the top of your head, any idea what the pitch is? Seems like it looked like 0.50 or 0.75 as I recall. And it's a 5mm screw, right?

I managed to find a 6mmx0.50 tap the other day (for reaming out a messed up mixture screw hole), which was quite a feat, so maybe I'll try my luck on this...

I didn't even think of replacing the screw and putting a spring in there. It's so obvious, duh. ;-)

 

[t3rmin]

Maybe it's just my bad luck, but that hot glue never sticks to anything you want it to. Don't think I'd waste my time.

Well I have my doubts but it was the only thing popping into my head and I figured it was worth a try, or at least it would spark some conversation and land me a better idea. And it did! ;-)

newbie alert..
..I've always used the blue medium strength loctite and never had any problems with the carbs going out of sync. Way easier than fiddling around with the lock nuts. I do apply a liberal amount to the tops of the thread though.
Just my two pence (or cents, depending upon where ya from) worth

Nate 8-[

Blue loctite + new screw with head and tension spring would be sure to work. It's my new mission in life to find the appropriate screw.

 

[t3rmin]

Anyone interested in a group buy or something if I can special order the right type of screw to implement the "spring and panhead screw" mod?

 

[bwringer]

Anyone interested in a group buy or something if I can special order the right type of screw to implement the "spring and panhead screw" mod?

Absolutely.

You'll need to scare up the springs, too. There's nothing that will work in the extensive selection at my local hardware stores, and it's impossible for me to figure out what will work from the simple printed specs at McMaster-Carr. ( http://mcmaster.com ) .

I also need to contact Nert to see if he's still interested in selling the materials for his conversion. Seems much easier than finding the stuff myself.

If you're using Loc-Tite, use the low strength green stuff instead of the medium-strength blue. It won't mangle the threads, and it's touted to penetrate the threads on assembled fasteners. The only problem is that you should probably let the bike sit for a couple of hours following a carb sync to let the thread lock goop set up.

 

[t3rmin]

Can anyone who's got immediate access to their bike give me the sizing on that screw? I won't be able to check it myself until this evening and I'm impatient to get some pricing.

*EDIT* I'm going to start a thread on this in the Tech section to get some more exposure and since this is more of a discussion than a tip now...
http://www.thegsresources.com/_forum/showthread.php?t=100721

 

[terry]

Terry
I agree, that was the direction i started in. I could not locate screws with the same thread pitch and thread count with the length and head style i needed. Decided to tension what was there instead with locally available and common hardware. No problems so far. And the modification isn't that tough. Yes the carbs need to be off. Some of us anal people do that anyway in the off season just to have our hands in her.

No worries mate, absolutely no offence intended, your idea works, and I can't fault your instructions, I wish all the instructions I read could be so clear, ha ha!

I'm an incredibly lazy bastard though, so I always look for the easiest way out, while still achieving the aim, of course, so if I don't have to pull something apart, drill, tap, etc, then I won't.

Metric screws are relatively easy to find here in "Metrificated" Oz, I'm thinking that a nice set of stainless steel "Allen head" screws might be the go, I think standard 5mm screws are .75 pitch, and fine are .50, but I'm guessing that they're .75.

I'll check it out tonight, I think I've got a spare set of carbs in a box somewhere? I was just going to pull an old set of carbs apart and take the springs off the idle mixture screws? Cheers, Terry.