Ignition, Window of Opportunity...

[DKWRACER]

Friends, being the open forum that we have, I would like to open the question of ignition timing.In looking at the KTM and Sachs manuals, I find that there is a window of suggested BTDC timing for ignition. How is it that the engineers wound up with this window? I can argue that on standard bore, does it make sense that tighter ignition towards BTDC will not cause problems because of the knowns about total volume compressed. As the bore increases, does not the total volume increase? And so should we retard the ignition related to BTDC??? Given our non-mappable ignitions, does it make sense to slightly keep our ignitions retarded in relation to bore size? Do we need to keep fuel flamability in the equation? Would Kevin Cameron please step forward....
Tom...

 

[Doug Wilford]

Only speculation and past knowledge, if you have ever seen or heard of how many different ways people go about setting the timing on their engines, it is scarier than Halloween.  Knowing this, I am sure the engineers created the window to say if you set your timing somewhere in the window the engine will run and perform at a reasonable level.

 

[john durrill]

Boy are you right Doug.
 We found that 3mm instead of 2.7 made our 175 conversion into a different bike. at 2.7 it was very pipey . at 3 to 3.1 mm it had power from 2000 to redline.
 Both settings would run and start fine. just one setting is a great trail/ enduro engine and one is an MX . ( This is with a Bosch Mag not a motoplat)
The only way to know what you really have with a motoplat for timing is find and mark TDC on the flywheel with a deg. wheel . from that mark  useing a dial indicator, scribe.1mm incraments on the flywheel. then use a timeing light to see what you really have.
John.


 

[rickf22]

Speaking of timing lights... how does one connect the typical automotive timing light to a cycle that has a magneto? Where do the leads that would go to the battery go? Or does this sort of light not work, and there is a different version intended for use with magnetos?  And CDIs?

 

[paavojaelvis]

Rick,
You must use auxiliary power source, eg. a battery or a charger, 12 V DC. Red one to positive, black one to negative. The pick up lead for the spark plug cable is connected normally. DO NOT connect coil lead (usually green) at all (you might ruin your Motoplat or CDI).  Tadaaa...it's flashing. =)

Paavo