Hey Everyone,

[edit: Warning if you're going to use the technique here, do *not* do it by disconnecting the spark plugs as I did. Go for disconnecting the coils. The Haynes manual warns profusely not to run the engine w/ the plugs disconnected as it can damage the coils.]

I just thought I would share with the world a rudimentary but very easy technique I just developed for syncing carbs. I was in a jam b/c the attempt I made last week to do it without the proper fitting for the front cylindar was so far off that my bike has been getting about 18 mpg since then (and I don't ride hard). So, I wanted to get it at least close while I'm waiting for the fitting and a real carb sync gauge.

*Warning* - this procedure could make your bike explode and kill you. Don't say I didn't warn you.

That said, the benefit of it is that it doesn't require anything you don't already have. You could do it in the middle of the desert if you had your bike's stock toolkit.

First, the theory:

The purpose of carb syncing is to make sure both cylinders are sharing the load evenly, thus minimizing excessive work on just one of them. The question is how can you do this without vacuum gauges (or equivalent) and also without the key fitting in place of the blanking bolt.

When I reinstalled my carbs after cleaning them, and broke one of my choke attachments, I started the engine up anyway, and found that I got it running on one cylinder. Not a good thing at the time, but it hit me, if the engine can run on one cyl, then if you compare how it runs on one cyl to how it runs on the other, you are doing roughly the same thing as comparing the vacuum pressure in the two cylinders.

So, basically what I did was this:

• Warm up the engine
• Unbolt tank & lift vertical (I used a shock cord to keep it upright & out of the way, but that's not actually necessary)
• Set the idle to about 2200 rpms
• Shut the engine off
• Pull the lead off of the rear spark plug (and take special care to make sure it is insulated from anything metal, and that there isn't any loose fuel around
• Start it up again so it is running off of just the reference cylinder
• Watch the tach for a few seconds, and carefully note the rpm range. In my case it fluctuated around 1300 rpms
• Shut the engine off
• Reconnect the rear plug and disconnect the front plug
• Start up again
• check RPM range again, and adjust sync screw until it is the same as it was when running off of the other cylinder.

A couple of important notes. First, it is a bitch and a half to adjust the sync screw with just a screwdriver, it's really hard to get to. I actually got an elbow joint to go with my socket set and used the 7mm socket. So technically I lied, this doesn't come with the bike. But this obstacle is independent of the need for the vacuum gauges & fitting, and it's not impossible, it's just a pain.

Second, there's a decent chance you're going to get a backfire when you reconnect a disconnected cyl, since there is likely unburnt mixture in the path somewhere.

Third, when I disconnected the front plug and started the engine, I could clearly hear arcing somewhere. I couldn't see it, it wasn't right at the lead, which I had insulated with a glove anyway. The rear lead didn't do this. I never did get this to go away. Either way, it probably would have been a lot smarter to disconnect the coils than the plugs, since the coils only get regular 12 volts, not the supercharged current that is on its way to making a spark, and therefore much more capable of starting a fire.

Fourth: You want to minimize theh time you are running on one cyl, since it is effectively the most extreme example of "carbs being out of sync" imaginable - and the whole reason we are doing this is to minimize the negative impacts of that. But I figure that doing it for 10 seconds under no load is better than riding around w/ way out of sync carbs

And last, I still don't have my actual gauge or fitting yet - so I cannot tell you how far of it is, or even whether making the two cyl's rev equally on their own is the correct target. it's conceivable that there could be some kind of differential required, although I don't think so.

Anyway, if you've planned ahead, then you don't need to do this b/c you already have ordered the fitting for the front cyl or an equivalent adapter, and you already have a gauge that you trust. Also, if you've really planned ahead then before you put the carbs back in in the first place, you created a permanent vacuum hose test harness that is easily accessible without having to take anything apart. (Just my humble advice). But just in case I'm not the only person who ever found myself w/ a need to sync carbs but not the necessary gear, I am guessing this is better than doing nothing. However I doubt that it's better than simply not riding your bike until you get the right gear, so I would still say don't do this unless you can't (or won't) not ride your bike in the mean time anyway.

 

Well... I can tell you, you are way of on sync...

Why not make a simple sync tool out of clear tubing and oil like the rest of us? It's not neccessary to reinvent the wheel...

The only special part really needed is the fitting to the front cylinder... Then you need tubing oil and a ruler...

 

Tweety, did you mean way out of sync? (way of on sync is confusing)

 

I think Tweety meant way OFF on sync. Whatever, I knew what he meant. I think he's correct as well.

 

I did make a sync tool. I still couldn't get a proper sync without the fitting. It's on order. I wanted to be able to use my bike while waiting for the fitting.