Two-TR6-Paisley writes:
> But why would a vacuum retard reduce performance?
It slows throttle response.
> When I stomp on the gas, there's very
> little vacuum left, and the advance on the distributer would be
> advancing with engine rpm.
Correct. But it's advancing from the retarded state it had reached just
*before* you stomped on the gas. IE, at idle, instead of sitting at around
4 BTDC, all that vacuum retard (full retard available on my unit is 16
crankshaft degrees) has pulled the timing to around 12 ATDC. My mechanical
advance has a lot of work to do to catch up! I get a little for free,
because stomping on the throttle releases the vacuum and the return spring
on the backing plate will hopefully (assuming I cleaned and lubed everything
well enough last night...) bring me back to 0 retard relative to wherever I
timed it.
> I'm tring to think how a vacuum retard
> would hurt performance. I guess from a dead stop it wouldn't be so
> great, but hey, just advance the entire distributor! Anyone got any
> insight on this?
You're right to an extent. But when I drive around town on partial
throttle, I'm still going to have a lot of retard sucked in by the carb.
I've got to shove my foot all the way in it to overcome the retard--at part
throttle, it's still there, fighting against my mechanical advance. If I
advance the timing very much, punching the throttle will release all the
retard, and all the sudden I'm *way* advanced, pinging my way down the road.
Until you reach cruising speeds, where the mechanical advance has come in
and there's not enough vacuum for the retard can to fight it, that retard
is in the way, every which way you turn.
On the positive side, the retard is supposed to give much better combustion
on trailing throttle and at idle. I forget if I read this in the Haynes
carby manual or somewhere else, and I've obviously forgotten the theory
behind it, too.
I've solved this problem, though, by replacing my wheels with cinder-blocks.
Kevin "No, don't feel sorry for me, I've just been bonding with my car for
the last 4 years" Riggs
'72 TR6
rkriggs@ingr.com
Huntsville, AL
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