If youre talking about Timing a Wico C Mag, there is the advance run time and theres the static start timing. That mag does NOT have any variable RPM based run time advance curve like a distributor, ONLY a static start impulse timing set point (rear lag angle adjustment) so she will start without kicking back and then once she gets to 250 RPM the fixed run time advance takes over all at once (impulse becomes inoperative). She can be set to start at a certain time (which is near TDC) by adjusment of the rear Lag Angle and which rotation of the mag in its flange also changes, but after that the advance run time is a function of the drive cup (most have like a 25 or 35 advance degree drive cup),,,,,,,,,the points gap,,,,,,,,wear n slop in the drive,,,,,,,,and the rotational position of the mag in the flange which can be moved around 10 degrees or so, forward CW retards timing, backwards CCW advances it.....on Deeres at least
The way I tune and time one is to install a set of points gapped at 0.015 on high cam (also a new condensor as necessary),,,,,,,,,,,,set the rear lag angle to match whichever drive cup is used (like if you have a 25 or a 35 degree drive cup) ,,,,,,,,,install the mag in the governor flange,,,,,,,,fine tune the static start timing by rotating mag forward CW to retard or backwards CCW to advance so she fires (impulse trips) right at TDC when the engine is slowly rotated up to TDC NOT running,,,,,,,,,,start her and use a timing light to see where shes firing at under high RPM,,,,,,,,,and if its near 20 to 30 BTDC I let her go.
NOWWWWWWWWW if one is gonna pull it or you just gotta have the absolute max HP so wanna fine tune the advance run time to a certain place (like 27 BTDC etc) you have to use a timing light and when shes running loosen the mag in its flange and turn it CW to retard or CCW to advance till you get it where you want if possible (still dependant on drive cup and wear and points remember) ,,,,,,,,,,,mark the exact location of the mag in the flange,,,,,,,,,then re set the static start impulse timing to TDC by removing the mag and adjust the lag angle and reinsert the mag back in the mark.
BOTTOM LINES:
Adjustment of the lag angle (in rear of mag) affects ONLY the start/impulse timing.........Rotation of the mag in its mounting flange affects BOTH the advance run timing PLUS the start/impulse timing.....
Advance run timing is a function of which drive cup you have like 25 advance or 35 advance, plus the adjustable rotational position of mag in the flange (CW to retard CCW to advance if on a Deere), plus points gap,,,,,,plus wear n tear
Static start impulse timing should be around TDC and NOT too fast it kicks back and is set by adjustment of the rear lag angle and rotation of the mag in the flange (which I use to fine tune it) would also change it, but also change the run time advance remember.....
I was asked to write a series of Wico C and X mag articles (timing and troubleshooting) for a national Deere magazine but havent got at it yet, and spend like 90 minutes explaining this in seminars I give, buttttttttttt theres just wayyyyyyyyyyyy tooooooooo muchhhhhh to write in a couple paragraphs here, yet hopefully this may give you some basics, post back any questions
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