The New And Improved Unofficial R65 Forum V2

Technical Discussion => BMW Technical Q&A, Primarily R65 => Topic started by: montmil on August 29, 2009, 03:52:30 PM

Title: Balancing carbs with shorted spark plug
Post by: montmil on August 29, 2009, 03:52:30 PM

This topic pops up now and again... even Bengt Mike and I were discussing it couple weekends ago. Interesting article regarding the dangers of doing this with electronic ignition Airheads.    Monte

"In my own humble opinion, NEVER, EVER balance your carbs by using the shorted-spark method!"
     –John Petty

http://www.ibmwr.org/r-tech/airheads/parklotbalance.shtml

Title: Re: Balancing carbs with shorted spark plug
Post by: Bob_Roller on August 29, 2009, 05:34:50 PM

I've heard this for about 25 years, and I always wonder, what damage will be done ?

Same with the ICU, being damaged if you leave the plug leads disconnected from the plugs, and rotate the engine with the starter .

No one has ever explained this 'myth' .

Title: Re: Balancing carbs with shorted spark plug
Post by: Motu on August 29, 2009, 08:39:37 PM

I just put another plug on the lead - one cyl is out,and the spark still jumps a gap.

Title: Re: Balancing carbs with shorted spark plug
Post by: Justin B. on August 29, 2009, 11:17:16 PM

I've never had the theory behind this causing failures explained to me either, but there does seem to be quite a bit of anecdotal evidence pointing to it not being a good idea.  I especially can't see it buggering up the hall-sensor but many swear it does...

Title: Re: Balancing carbs with shorted spark plug
Post by: Bob_Roller on August 30, 2009, 11:04:11 AM

I have a 'slack' day at work today, I went to the local resident electronics expert on shift, and put forth the question to him .

His response was that with the spark lead disconnected, you now have a larger 'air gap' to jump across, and the secondary circuit, may well find a weak spot in the coil insulation between the primary and secondary windings, and arc back to the primary windings, putting 30,000 or so volts into the primary circuit, frying the ICU and the Hall sensor .

Best explanation I've heard so far .

He had no explanation for the issue of shorting the spark plug lead, causing a problem with other components .

Title: Re: Balancing carbs with shorted spark plug
Post by: montmil on August 30, 2009, 12:53:37 PM

Quote

...Best explanation I've heard so far .

I'll drink the Kool-Aid. Of course, y'all heard it first here on R65.org.  Thanks, Bob.

Monte

Title: Re: Balancing carbs with shorted spark plug
Post by: MrRiden on August 30, 2009, 02:11:04 PM

Ive tried both ways and to tell you the truth really can't find an advantage to the shorted [grounded] spark method other than it is more fiddly, leaves more room for error and mishap. I'll be sticking to my Monte approved "El cheapo" manometer.
http://i101.photobucket.com/albums/m70/mrridden/P1010001.jpg
http://i101.photobucket.com/albums/m70/mrridden/P1010007.jpg