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Old 06-12-2011, 11:47 AM   #12
supershaft OP
because I can
Joined: Sep 2010
Location: San Francisco Bay area
Oddometer: 9,116
Originally Posted by Lornce View Post

I've never taken an electronic bean can apart beyond prying the inspection door off and spraying the guts out with contact cleaner. Planning to dual plug the GSPD when it goes back together (using a pair of brown Dyna 1.5ohm coils because A. I have them [thanks Rapid Dog] and B. The GSPD has run for 40k miles with a 3ohm Buell coil without issue) and am wondering how to achieve the necessary advance curve to suit dual plugs. My only experience with dual plug ignition involved the pre '79-style whose exposed advance weights and springs were fairly easily modified to suit.

Can similar simple spring and post tricks be played with the advance mechanism in the bean can electronic ignition units?

My limited understanding (based solely upon what I've been told and what I observed through my arse at tracks like Grattan, where I was sure my single plug engine pulled harder at the top end, though softer off the bottom) is that the stock curve is useful from idle but needs to be contained 4 degrees or so at maximum advance.

I am at your mercy. Do your worst.

The advantages of dual plugging are really the advantages of running higher compression. It improves off cam performance and midrange the most but it surely doesn't hurt high rpm performance either. Snowbum claims that single plugs work better at high rpm and they don't. Most dual plugged race engines are not that concerned with low rpm performance. XR750 Harleys are a perfect example. Absolutely everyone has been dual plugging them for decades. Drag race engines are another perfect example.

Restrict (don't extend it like Snowbum suggests) the curve by bending the weight stops. Extending the curves rpm range is tougher because the weights still need to hit the stops but you do it the same way by removing weight and testing.
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