Hey guys, (and the few gals out there too)
I know we've talked about these types of issues before on this list, but after
some recent . .uhh .. . experiments. . I've got some more questions.
Excuse me if they are repeats.
Concerning the vacuum control of the timing on out cars.
I was playing with the mitivac and found out that the vacuum advance on the TR4
distributor doesn't work.
This was news to me. . . . I have one on another engine in the garage that does
work (or at least holds a negative pressure) is this an easy thing to swap
between distributors?
The Vacuum advance and retard on the 1970 TR-6 distributor does work, although
the retard has been capped off since I got the car.
I set forth to play with this stuff while driving down the road, and was having
great fun and eventually decided that I wanted to know what level of vacuum the
engine was giving to the distributor under various conditions.
So I pulled the plug on the rear carb (The TR-6 has weber down drafts) and
hooked up the mitivac to that and headed off down the road.
With the foot off the pedal . . throttles closed. . .no vacuum. OK
Press the pedal down a little and . . VIOLA . . some vacuum. OK
In general, and up to a point, the more I pushed on the pedal, the more vacuum
I'd get until the engine sorta caught up to the speed I wanted it to go. The
Vacuum would gradually taper down as there was less demand (by me) on the
engine. OK . .that all seems to make sense.
What I don't get is that when I dropped the hammer on the accelerator. . .the
vacuum would disappear.
I can understand WHY this happens. .. that is no mystery.
Now to the question (finally)
. . . because there is no vacuum to the advance unit on the distributor at wide
open throttle all I'm gonna get is centrifugal advance.
Why would I want some advance at a partially open throttle and none at wide
open throttle?
I haven't had a chance to check out the TR-4 with the strombergs, so I don't
know if it's vacuum advance behavior is the same way.
Actually, I'm wondering if the vacuum leak is causing some of the problems I've
been having. . . the occasional backfiring through the carbs on initial
acceleration.
I guess I should pull the spark plugs and see if the ones on the carb with the
vacuum port look different.
thanks in advance for the info I'm going to get.
Scott Tilton
Driving a Triumph everyday in Leesburg, VA
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