It can be just the result of the compression ratio being fairly high for an
iron engine running on standard fuel. I had a tuned A-Series that did that -
I just got into the habit of flooring the throttle as I switched off. The
later A-Series motors (in Metros, Minis etc) had a solenoid activated valve
to achieve the same thing (actually vents the inlet manifold so the engine
sucks pure air and therefore has no option but to stop). I think the valves
are no longer available from Rover, but you should be able to get one
second-hand.
Neil
----- Original Message -----
From: "marcel chichak" <chichm@planet.eon.net>
To: <british-cars@autox.team.net>
Sent: Sunday, October 15, 2000 5:23 PM
Subject: B series run-on problem
> LURK_MODE=OFF
>
> SOL mates!
>
> OK, here's the background:
>
> BMC B series engine with shallow dish pistons, modified head at 9.75:1,
270
> Piper cam, twin HS6 with K&N filters, Maniflow LCB, Hitachi electronic
> distributor. The power plant has about 2000 miles on it and I've been fine
> tuning it all that time. It now makes excellent HP, excellent MPG, about
30
> mi/imperial gallon but it simply will not stop running-on when shut off!
>
> The plugs are perfect tan colour, it's not over heating at all even with a
> 195 F thermostat (max temps around here are in the low teens C), it's not
> over advancing anywhere in the range and there's certainly no carbon
> buildup in the chambers yet.
>
> I've tried going from BP5ES to BP6ES plugs with no improvement although
the
> colder 6's show darker brown around the body so I switched back. Leaning
> the carbs off a couple of flats initiates lean surge at highway speed, a
> couple of flats more fuel colour the plugs too dark so I figure I'm THERE
> with the mixture. I recurved the dizzy to give me more advance all through
> the range (I have a SUN machine :-) which greatly improved the part
> throttle manifold vacuum and still showed no sign of over advance, but
> changed nothing on shut-off. Right now I've got an initial timing of 10
> BTDC and it maxes out at 35 BTDC at 4000 RPM. It hauls butt!
>
> Obviously something in the combustion chamber is over heated causing it to
> diesel, but it's not the plugs, it's not carbon and I paid particular
> attention to eliminating sharp corners in there when I built it.
>
> Anybody got any other ideas on what I can try?
>
>
> --Marcel Chichak chichm@planet.eon.net
> Edmonton Alberta Canada, eh?
> Peek into my world: www.planet.eon.net/~chichm
>
>
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