Thanks for responding. I was beginnging to think that only
bling-bling kids wanting to know what polish was best on their WRX wheels
were the only ones on the list...
: You're in VA, basically at sea-level? Set it to 8-10 BTDC @
: 800-1000RPM. Vac advance _is_ a port on the carb; venturi vacuum just
: above the butterfly IIRC. Won't do anything 'til you get some flow
: happening. There are some thermo-vacuum valves in this circuit as
: well, but I think they simply block the "advance" signal until the
: engine/intake manifold warm up. The mechanical advance does most of
: the work anyway, and I wouldn't think that ~35 degrees of advance at
: 4000-4500RPM is unreasonable.
A few things. I'm actually in southwest virginia. Field
elevation here is 2132' (I'm also a pilot) and it gets warm... routinely
over 4000 effective altitude (density altitude) in the summer. It's not
the southwest though, to be sure.
I've done a bunch of reading on ported vs. manifold vacuum. I
know now that my car has ported, but I've found conflicing definitions of
that. One school of thought is that the port is right above the
butterfly, so it's basically manifold vacuum except at an idle, where
there's very little. The other information I've found is that the ported
vacuum is taken from the venturi area. If that's the case, then the
vacuum it produces would be more a function of mass air flow. Subtle
difference, but it would also mean more advance at WOT, high RPM.
My particular setup has a thermo in the circuit, but not for the distributor
diaphram. It's connected directly to the ported vacuum. I have tested the diaphram
and verified that it does move, but it leaks down. I have been unsuccessful finding a
replacement shy of buying a whole rebuilt distributor.
: None of this is likely to get much of your "lost" power back, the
: EA-81 is pretty much a stone axe, and not very sensitive to trimming
: ignition timing, or even FA ratio when you get right down to it.
: Be sure that you have a clean air filter, and good ignition parts;
: plugs, wires, cap, and rotor.
That's why I'm trying to get it more or less right. At 16 BTDC with the
vacuum ineffective it was gutless. When I timed it back to 8 BTDC as per the book, it
was extra-gutless. I've redone the rest of the ignition awhile back (to try to get a
little more poop back).
: Check engine compression. You'll want to see at least 120PSI all
: around; 140+ is better. Should be consistent between cylinders, too,
: not more than a 5PSI variance. Check manifold vacuum at idle; should
: be fairly high (25in or so) and steady. Set the timing as above.
I'll try that when a get a chance. The boob who had the car before me
partially cross-threaded a plug. It took me 1/2 a day to get it threaded back in
correctly when I replaced plugs awhile back. Maybe I'll get 3/4 of the compression
checks.
If
: your engine doesn't have hydraulic lifters, adjust the valves. (Some
: got 'em, some didn't; it will say "do not adjust valves" or something
: to that effect on the valve cover(s) of a motor with hydraulic
: lifters.)
Lifters are allegedly hydraulic... has the "don't adjust me" sign on the
covers. Yay...
The CAT on these cars is at the junction of the Y pipe, and
: for various reasons can become plugged. I can't recall if it's
: possible to see the element on these, but if you can it should be
: whitish, definitely not dark colored. You might just swap in another Y
: pipe if you can find one. If this results in a dramatic improvement,
: do _not_ keep driving the car. Something caused the CAT to plug, and
: unless you fix it you will shortly plug up another. Check your air
: suction valves, and the "duty valve" indicator on the ECU. (The LED
: should flicker if the engine is held at a constant 2500-3000RPM;
: steady-state on or off is bad.) Rebuilding the carb may be necessary,
: but it's a pain, and the kit costs $65 or so, so I'd hold off on that
: until you've checked everything else.
I just looked inside the CAT... seemed fine. The pipe right in front of it
sheared off (sounded like a go-kart for a week or two). The rest of the exhaust is in
good shape, so I just repaired the rusted spot. I was tempted to remove the CAT to
try to get a bit more poop, but it was easier (and more legal) to leave it on.
Mine doesn't have an ECM.
: >Will replacing
: >the diaphram likely do all I need, or should I be looking at the flyweights as well?
: Probably have to replace the entire thing. Unless it's leaking oil
: (oil fouling inside of dist cap), or really rusty to the point where
: the weights/springs are frozen, I wouldn't worry about it.
: I have a fair bit of experience with these motors. Feel free to
: contact me directly if the above doesn't help.
My current plan is to rig a digphram from a comodity engine onto the
distributor. Something like a smallblock Chevy. I know that the force/distance may
be a bit off, but as long as the mechanical/centrifugal timing is correct the
high-power timing should be correct. I wouldn't think I'd have to worry too much
about detonation even if the vacuum comes in a bit early/late.
For the time-being, I've connected the leaky stock diaphram to manifold
vacuum through a long restrictive hose. It's got a lot more flow capacity than the
port so it can tolerate the leak better. I've also got my vacuum gauge inside the car
rigged in to read the diaphram vacuum while driving and set the base timing to 10
BDTC. Much more responsive, so I'll probably try to rig in a non-broken diaphram this
weekend.
Sound reasonable (albeit longwinded)? How much timing could I get away with
running 87 AKI fuel?
-Cory
--
*************************************************************************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
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