panic wrote:I'm surprised at the 32° spark timing; Branch used 36° for the KR in 1965 (the Cycle World interview). Was this modified in later years? Ideas?
I suspect the answer to your question is YES, since the later competition manuals I’ve seen call out KR valve timing of 36 deg at 7/16” BTDC. The 11/32” value was a familiar value called out for KK, KH, and KHK engines of that era, when I believe the only performance cam available was the KK/KR/KHK cam set 25499-53R. Ignition timing for the K/KH engines trended with cam duration, i.e., the engines with shorter duration cams employed later ignition timing, and the larger cammed engines employed earlier ignition timing, and there were only short duration cams available circa 1954. With the evolution over time of higher duration cams leading to higher engine speeds, I suspect the MoCo increased ignition timing to 36 deg BTDC for KRs.
There are certainly ignition timing discrepancies in the HD literature, e.g., in the early competition manual the KR ignition timing is shown pictorially and stated to be 36 BTDC which was 7/16” BTDC piston position. In the later competition manual, the text portion of the specification (up front in the manual) gives ignition timing as 38° BTDC, whereas in the image of the “timing mark in hole” the same image as used in the older manual shows 36° BTDC. In both instances (old and new manual) they quote 7/16” as piston position for ignition timing.
Likewise, there are examples of KHK cam timing given as both 11/32” (1955 KH Riders Hand Book) and 13/32” BTDC (MoCo factory timing chart).
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