Sync. Carbs by shorting plugs

[badgertom]

Has anyone tried to synchronize the carbs by the shorting-of-spark plug method as suggested on bmwmotorcycletech.info/syncharbs.htm ?Since you are shrting out one carb at a time can this result in damage to the engine...esp. if one cylinder runs for a longer time? My understanding is that you basically hold a screwdriver from an exposed spark plug connection to the cylinder or any other ground. Will the spark cause damage? I'm a little concerced about this method.

[Barry]

You will only risk damage to the ignition by open circuiting a plug not by shorting it out.  There is more risk of damage to you and the bike with electronic ignition as the HT voltage is higher. Maybe 35,000 volts instead of 25,000 for the points ignition. Also the energy behind the spark is higher.

The spark created when shorting doesn't do any harm in fact it's reassuring to see you have a healthy spark.

The problem with an open circuit is with the absence of a spark gap to limit it, the coil will generate the highest possible HT voltage it is capable of which can weaken or  breakdown the insulation of the windings.

I did once inadvertently crank the engine with the ignition leads open circuit. Following an oil filter change I make a habit of priming the filter by pulling the plugs and cranking the engine until the oil pressure light goes out. I pulled the caps but forgot to remove the plugs and lie them on the heads connected to the caps. I seem to have got away with it as it was 4 years ago now so it's not necessarily instant death to the coils. The reason no harm was done was probably because The coils only saw cranking voltage approx. 10 Volts which would limit the HT voltage generated.  

I do get slightly concerned about possible bearing damage to the engine when it's firing on one cylinder so I keep it to a few seconds at a time. The uneven torque pulses sound a lot like lugging.

[Mike V]

Badger,

Some excellent info in Barry's post.  

Keep in mind the shorting method is for idle-mixture adjustment only.  

I use two snipped off spokes, press a spark plug tip (nipple) on the smooth part of the spoke with the threaded part of the nipple outward. Remove the spark plug cap, attach the spoke with nipple by threading it on the end of the spark plug. Attach the spark plug cap on the threaded part of the spoke.  Now assemble a short jumper cable with clips well insulated.  It hurts like hell to get zapped by our ignition system.  I wrap my jumper cables with friction tape.  Clip one end of the jumper cable to the spoke and the other to a cylinder fin - that cylinder will now be grounded and will not fire.  With the engine idling adjust the mixture screw (clockwise = lean) on the firing cylinder until the engine just wants to quit, then turn the mixture screw counterclockwise to enrichen until the highest idle is accomplished.  Normally only takes about a screwdriver blade width or so.  Note the idle speed, it should be at the lowest operational rpm.  Duplicate this mixture process on the opposing cylinder and carburetor matching the first rpm value of the carburetor first adjusted.  With both cylinders firing and idling adjust your final rpm value to the appropriate range or speed.  After a good ride (±5-10 miles) recheck the idle and adjust each idle seed screw equally until you meet the recommended idle speed. Make sure you have adequate slack in your throttle cables before attempting this process.

Now it's time to balance your cables with manometer or like device.

This is an old-school method, some like it some don't.  I've done this for many years and am comfortable with it with good results.  Balancing and adjusting takes some practice and patience.  It's good practice to have a fan operating over the cylinders while performing carb balancing.  Don't let the bike idle for too long and never attempt a balance on a cold engine that hasn't been adequately warmed up - that means a ride, not just a start up.  And never rest on an adjustment until you have gone for a good healthy ride and recheck.

Maybe Monte can give us his opinion after he gives this a try.  I just sent him some spokes to try for himself.

Some of the newer carb balancing tools out there seems to be able to accomplish good results without using this method, especially the ones that messure vacuum and rpm values simultaneously.

Just my personal opinion.