In a message dated 8/3/2006 7:13:53 PM Central Standard Time,
jimhearn1@comcast.net writes:
> Hi, this is my first time on this board. I just picked up a '74 TR6. I
> am quickly learning things about it but I have a running on problem that
> I would appreciate some feedback on. I'm in California but '74s don't
> need to be smoged even here. I am also wondering if any of the smog
> items are best removed only because they can sometimes cause more than
> their share of problems. I am also aware that some systems are made to
> run as they are and should not be altered. My '74 has 84,000 on it and
> was neglected mechanically by the owner for the last several years. I
> am cleaning up everything, one piece at a time, but would appreciate any
> help on the running on problem. It was being run for some time without
> a thermostat so the first thing I suspected was carbon causing the
> running on. Reading on I see the evaporation system has a no run on
> devise so now I am looking hard at the smog items on the car.
The 74's had pretty low compression so unless someone has shaved the head you
probably do have a carbon buildup. Many folks solve that problem by putting
the car in gear and releasing the clutch when switching off. Problem solved.
But part of the missing evap system is designed to eliminate (or at least
reduce) run-on. There should be a solenoid valve that will switch vacuum from
the intake manifold to the charcoal canister. Since the carburetor float bowls
are plumbed to the charcoal canister this will put a mild vacuum on the top
side of the fuel in the float bowls pulling the fuel away from the jets and
shutting off fuel flow to the carburetors. No fuel, no run-on.
Since your car has been tampered with all bets are off as to how much of the
wiring and plumbing is still there, but it sounds like you need it. At least
until you can decarbonize your engine.
A quick way to check to see if your head has been shaved is to measure the
distance from the block to the valve cover seating surface. Kas Kastner's book
has values for stock early (8.5:1) and later (7.75:1) compression ratios. If
yours is significantly less than the later value then your head has been
reworked and your run-on will never cease unless you try high octane fuel.
Or let the clutch out in gear when shutting down.
Dave
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