On Mon, 21 Jul 1997 23:00:33 -0400 Trevor Boicey <tboicey@brit.ca>
writes:
ck to normal
>
> Is there a chance that your timing was SO retarded that
>still-burning
>fuel was being sent down the exhaust? Or that combustion was not
>occuring causing raw fuel to get to the exhaust and burn later?
>
> The conventional viewpoint is that as long as combustion is
>normal, advanced timing causes more heat for a few related
>reasons.
>
> The burning fuel/air stays in the cylinder much longer, since
>it becomes hot sooner but doesn't leave any sooner.
>
> As well, the fuel air mixture is hotter while the cylinder
>is still at high compression, which allows the mixture to impart
>more heat on it's surroundings.
>
> And finally, the cylinder doesn't enjoy as long of a
>cooling interval where unburnt fuel mist and "cool" air are in
>the combustion chamber.
Again,I don't know the answers, Trevor, but what you say makes sense.
The Harley had a great deal of "advance" between the two extremes on the
dizzy. So at full retard, it could well have been burning out the pipes.
I do know from other experiences (mine and friends) that excessive
advance will induce heating, but likewise have found that the reverse is
also true, possibley due to the greater throttle opening (more fuel/air
mix) to achieve the same level of performance. I know that if I have to
retard my timing too much, because of fuel inadequicies, etc, my heat
gauge will "normalize" higher than normal. Whether this is a direct
result of the retarded timing, or a consequence of less than great fuel,
I don't know, 'cause I try to avoid that situation like the plauge by not
using that brand of gasoline if at all possible.
It would seem that overheating isn't a problem within a range of
retarded/advanced timing, but that gettin beyond that range in either
direction, leads to overheating.
Like I said, I havent got all the answers, just a bunch of WAG's.
Rick Morrison
72 MGBGT
74 Midget
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