RE: Engine timing, Confusing or what??

[Doug Rasmussen <76075.2276@domain.elided>]

Just when I thought I understood  timing an IH engine.  I have 2 copies of
Scout manuals.  Anyway, from one manual (page 20, cts-2481-K) "adjust
carburetor to obtain specified engine idle speed".  Unfortunately, I can't
find any place in the manual where they define the 'specified engine idle
speed'.  For some reason I've always assumed that the idle speed should be
around 750 rpm, I don't know why I think that, but that number has always
been in the back of my mind.

  From the other manual, (page 20, cts-2481) "The engine should idle at
approximately 300 rpm for timing purposes".  300 rpm!!!!!!!......  I'm not
sure  I can get my idle down that low.  After studying both manuals, this
(300rpm) scenario makes sense based on the way IH setup the mechanical
advance curves of their distributors.  From the "Distributor Test Data"
section of the manuals, I see that all the Scout distributors start
mechanical advance around 400 rpm.  At around 600-700 rpm, the mechanical
advance will be from 4-9 degrees, depending on the distributor number. 
This explains that business of setting initial advance at TC (Top Center). 
By setting it at TC at 300 rpm, you WILL see the 4-9 degrees at the normal
rpm where most of us time the engine, probably around 750 rpm.

  Does this make sense?  Why don't they just tell us to time 4-9 degrees at
normal idle speed (750 rpm) instead of TC at 300 rpm.  This explains to me
why my engines run better with around 8 degrees advance at idle (750 rpm). 
I've never paid much attention to IH timing specs, but now I think I've
always been close to what they recommended without even knowing it.  

  So in summary, if you time at near 750 rpm, set advance around 7-8
degrees BTC .  In a roundabout manner this is what IH is recommending.  

Doug, 
'67 800, 304, 727, soon to have a Mallory, and Rancho overdrive on the shop
floor ready to install.