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Discussion Starter #1
I asked this question before but never got a clear answer. The 99 670 h.o. ignition timing is set at .126 btdc. The other 670's are set around .076. Why the difference? I'm guessing they're different ignitions. Does anyone have a clue?
 

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I think it would have somthing to doo with the different piston and cylinder head disign, Flat top vs domed. .126 and .076 are just initial settings a chart of the timing curve, (advance vs rpm), would tell the hole story.
 

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I have found those numbers are at full advance. At least on my 809 it was.

That is a big change in timing though. You are looking at a 17 deg of timing to 19. On my 809, 3 deg of timing made 8 HP
 

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Mr670 what the $%# , when I read the post i almost posted the same thing,and.. a dome always lends itself to detonation, b ut there may very well be more to this than meets the eye, the porting is different too? or not? low cylinder pressures below the max rpm could want high timing too, just a thought. I didnt know about the big diff in timing and I owned a 96 that I advanced. It was edgy not a sled to doo it on trail riding. The other thing is there isnt any actual advance, if you watch with a light it stmbles at around 6000 rpm, back and forth, but immeadiatly goes to full advance right after that and stays there to max rpm.
 

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The HO engine also has the higer compression ratio so that probably has something to do with it.
 

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Discussion Starter #7
On the h.o. the marks should align at 3500 rpm with lights on. On the standard 670 they should align at 6000 rpm with a cold engine and lights on. Could the dpm have anything to do with it?
 
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