> I have fairly bad backfiring (through the carbs) under load when
> accelerating. I have balanced the carb inlets, the mixture
> seems OK,
Just a thought, have you tried to check the mixture under the conditions
where the problem happens? I'm wondering if perhaps you have a fuel
delivery problem that is causing the mixture to go lean under load.
I would also be looking at the wires inside the distributor. They flex
constantly, so sometimes can break inside the insulation and be intermittent
without being visibly bad. The test is to hook up an ohmmeter and gently
tug on the wires. Note that there should be a ground wire between the
moving point plate and the distributor body. You'll need to undo one of the
mounting screws to check it.
> My big question is: how much should I be able to rotate the
> distributor
> rotor? A little? A lot? 15 degrees?
15 degrees is about right.
> Should it snap back to a
> position at rest or just flop around?
It should spring back at least partially. I wouldn't describe it as a
'snap' though, and usually it won't go all the way.
> I am trying to tell if the
> centrifugal advance springs need replacement.
One good overall test is to put a timing light on the engine while you
slowly rev it up and back down. It's not even really necessary to mark the
pulley for the various advance points, just watch that the TDC hole moves
smoothly to the right as rpm increases, and back to the left as you let it
down. If it flops to full advance, or jumps around all over the place, or
doesn't move at all, you've got a sick distributor.
The main point is how the mark behaves, I generally don't bother trying to
check the amount of advance. But if you want to, I've put some curves up at
http://goo.gl/4LcFq
for a few of the various TR distributors. (The list is not exhaustive, so
your car may be wearing something else.) Note that the figures given are in
distributor degrees and rpm, which is one half of what you will measure at
the crankshaft. IIRC each 1/4" on the edge of the pulley is roughly equal
to 5 (crankshaft) degrees of advance.
Also, if the car has been stored a long time, it is probably worthwhile to
disassemble the distributor to clean and lubricate it. Putting a few drops
of oil under the rotor will keep it lubed if done on a regular basis, but of
course that didn't happen while it was stored. I like to put good quality
grease inside the pivot points and where the weights rub on the support
plate.
I'm kind of sour on electronic ignitions at this point. They do have some
advantages of course, including less maintenance required but the overall
reliability seems about the same as points to me. I am currently running
points in my "daily driver" TR3, after having some weird problems with the
Pertronix. The Pertronix will apparently not fire the plugs when the
battery voltage is way down (but still high enough to turn the starter).
The root cause was a bad battery, but it started fine on points while it
would just crank and crank with the Pertronix. That's not my only
misadventure with electronic ignition, just the most recent one.
Points will still fire even when the battery is way too dead to turn the
engine. I proved that again just a few weeks ago, when I accidentally left
the lights on while I went in to work. By the time I tried to leave, the
(gear drive) starter would only grunt. Even the warning light on the dash
was way dim. I set the choke, pushed the car up to walking speed, jumped in
and popped the clutch. It caught first time, and I drove it home.
Of course, not long after I switched back to points, the condenser died.
Guess maybe I should have put a new one in to begin with, instead of keeping
the 40+ year old one that was with the car when I got it. <g> But a spare
set of points & condenser are a lot cheaper (free if you save the "known
good" ones from your last tune-up) than carrying a spare electronic
ignition.
-- Randall
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