I had the same problem with mine many moons ago. It turned out the heater
valve was leaking into the distributor.
Thomas Pokrefke
1970 MGB
-----Original Message-----
From: owner-mgs@autox.team.net [mailto:owner-mgs@autox.team.net]On
Behalf Of Christian, Wellner L. CIV COMNAVAIRSYSCOMPATUXENTRIVERMD AIR
4.1.1.4
Sent: Thursday, January 08, 2004 6:10 AM
To: MG Digest (E-mail)
Subject: 1974 MGB Died While Driving
Group,
On Tuesday afternoon, after prolonged cruising at around 4200 RPM, car
started to break down when RPM dropped below approx 3000. Above 3000 RPM,
not even a miss - ran perfect. Eventually I let the RPM drop too much and
the car died on a CD Beltway off ramp. Would crank fine (fast) but no
start. Acted like either out of gas or absolutely no spark. While on ramp,
checked:
Fuel Pump (prime suspect) wasn't clicking. Disconnected outlet line at
pump, applied power and pump clicked away and dumped a bunch of gas on
ground.
Removed fuel filter (to eliminate filter blockage as possible cause).
No
effect.
Removed carb bowl vent lines to check for stuck needle valve. No
overflow.
Spark at coil - good.
Fuel filter had sediment in it, so I removed the filter. No effect on
starting.
Point gap - fine. Points showed no pitting.
Distributor rotor turned when car pushed in fourth gear w/ clutch out.
Carb oil level good.
Raised carb pistons while cranking to richen mixture. No effect.
Car towed to Saturn dealer (where I was originally headed). New fuel
pump
installed - no effect. They managed to start the car using ether, but below
around 3000 RPM engine would not run. No difference whether engine was hot
or cold (cold engine started fine using choke and ether).
Bottom Line: Engine runs PERFECT at high RPMs, but absolutely will not
run
below 3K RPM. Once its been below 3K RPM, acts like someone turned off the
ignition switch - gas pedal has absolutely no effect.
Engine rebuilt completely stock, has 6K miles since re-build, and was
last
tuned 5K miles ago (about six months ago). Tune up included a valve
adjustment. Carbs re-synchronized and mixtures adjusted Sunday.
Question: If I remember correctly, there is some kind of oil pressure
triggered anti run-on valve on this car. Is the oil pressure switch (for
the anti run-on valve) the one on the passenger side at the end of a short
hose ???? If yes, is the switch activated by completing the ground circuit
or by breaking the ground circuit ??? I want to by-pass the switch in case
its some how activating at too high an oil pressure.
Background - Previously have had intermittent problem where after
prolonged
(30 seconds) of full throttle acceleration, engine would start breaking
down. After letting off gas pedal, engine would idle. Would not accelerate
without breaking down until about 2-3 minutes of very light load operation.
Prolonged accelerating using 2/3 throttle never caused this problem.
Any other ideas ????? Anything at all. I need to get this car home and
its about a $200 tow job away.
Thanks In Advance, Skip
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