Oldbike: Sync the Carburetors

With the unseasonably warm weather I have found renewed motivation to work on OldBike.  I decided that it was time to vacuum sync the carbs.  This was not my first rodeo when it came to carb syncing; I have been doing this on my SV650s regularly for years.  After looking through the Clymer manual I realized that there are some slight differences.  Whereas the SV650s process has you attaching the sync tool to fittings on the carbs, the GS has holes drilled and tapped into the barrels of the engine directly after the intake spacer where you measure the vacuum.

I had always wondered what the brass threaded tubes that came with my carb sync kit were for.  I am sure glad that I never lost them.

 They thread into the holes that were drilled and tapped into the barrels of the engine giving you a place to attach your tubing.  Once you have the tubes attached you can fire up the engine and start syncing the carbs.  In the Clymer manual they go through a whole thing about setting up the synch tool to test at 2000 RPMs this is if you have the mercury filled monometer type tool.  As far as I know the dial type that I have is not adjustable.  I have always just revved the engine to a point where the needles settle down and try to match them by turning the adjuster screw.  If I am wrong about that feel free to let me know on here.  It didn’t take too much fiddling to get them matched, check out the video below to see the results.

After I did that I washed NewBike and took both of them for a spin around the neighborhood, by far the best riding weather I’ve ever experienced on a March 13th!  When I got out of the driveway with OldBike is stalled and upon closer inspection I noticed that the vacuum connection to the left carb that tells the petcock to send fuel had worked its way out and was VERY loose and kept popping out.  My hypothesis is that when in the bath of carb cleaning solution enough material was eaten away on the carb bodies that the brass part of the elbow fitting no longer fits snugly.  I even tried the extra elbow fitting from my other set of carbs and the same issue.  My solution was quite shad-tree if I do say so myself.  I fished a Blatz can out of the recycle bin and cut a small ¾” long strip of aluminum,  I stuck it into the hole that the elbow fitting goes into as deep as the brass portion would go and bent the remainder over 90 degrees.  Having done that, for good measure, I put a small rubber o-ring on the brass portion of the fitting so that and air that might try to sneak out would be stopped.  I used a tuning hammer to tap the elbow fitting back into the hole (with the strip of aluminum still in there) and the fit was much more sung.  Snug enough that I got good squish on the o-ring, allaying any concern of a vacuum leak.  Problem solved!  Can you see the Blatz can in the picture below?!?

One thing that I will need to look at is that the OldBike seems to not want to idle when it warms up, I have to keep revving the engine and eventually that doesn’t even help.  In my next post I will try and do some diagnosing of the cause!

'Til then thanks (as always) for checking out the Blog, if you ever have questions or suggestions please post them below!

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