Been thinking: Anti run-on valve - what is it's real function?
Turbo Mini Forums

We've all called it an 'anti run-on valve'... I noticed it's reffered to as the 'carb vent valve' in Austin Rover literature however.

As we know, This doesn't stop your car ticking over, or even revving - but does prevent it fuelling properly on boost! So, what is it's REAL function?
I'm suspecting it's actually designed to reduce hot start problems resulting from fuel evaporation in the float chamber, which then fills the inlet and plenum with fuel 'vapour'.
By opening the float chamber to atmosphere, the vapours would take the easy way out, along this open pipe. When the ignition is next switched on, the valve shuts, and the float chamber fills with fresh fuel.
Does this sound reasonable to you guys?
Have we been getting it wrong all this time?


D

Sounds feasable, it will be interesting to see what others think ?

Phil.

WWW.TURBO-MINI.COM

Does make sense.

Think dave is right.

I think the valve the Metty turbo has is for venting the boiling petrol to the atmosphere. (After shutdown). We all know the starting problems 10minutes after shutdown. If all fuel evaporates there would be space for fresh cooler fuel at the next start. Never thought of that before - I think I will try to install the valve again. Maybe this cures my hotstart troubles. (Removing the bimetallic part of the jet holder did not change anything to my hotstarttroubles)

We dont have many Metros in Austria - is the Anti run on valve on na engines connected to the inlet manifold? I always thought this valve opens when you switch your engine off and leans (the still sucking engine) mixture that much, that the engine doesn't run on anymore.

Aren't the Anti Run on valve and the vent valve of a Metro turbo of complete different design?

Bimmer Twinky headed and turboed A-Series:
http://www.minifreunde.at/harry/projects.htm

this is interesting. mine takes for ever to start when its hot.
ive noticed on the era turbo that the valve has a pipe on it that dissapers under the subframe (i think) so i assume thats to disspose of the vapour underneath the car safely?

no longer a series, but still 1.3 turbo.

Fitted the carb vent valve today! Did not try a hot start, because it was raining all evening and the car is washed/clean. But what me makes worry is: The valve, when powered, becomes hot after about 5 minutes - I guess 60-70?C, a little too hot to touch! Has anyone a similar experience? The valve is open unpowered and closes when powered with +12V. Does the Metty Turbo have a "peak and hold" circuit for this valve like some modern fuel injectors work?

Bimmer Twinky headed and turboed A-Series:
http://www.minifreunde.at/harry/projects.htm

i am not sure about this valve but where i come from we use solenoid valves to keep a valve always open under power, this is a fail safe installation and the valve closes upon loss of power( wich means in practice twice a year to check the function)
These valves create a lot of heat also, and consume power, nevertheless they keep on working.
Guess this does the same as it should be closed as long as the car runs, says so in the metro haynes manual.

Yes, it should be closed when the car is running.
(Connected to ignition +) If it fails (and opens) the car will stall on boost, because no pressure can be built up in the chamber. I am afraid of burning out this valve, because I only have this one. If I read the wiring diagram correctly there should be only ground and + 12V (fuse protected) to the valve.

Bimmer Twinky headed and turboed A-Series:
http://www.minifreunde.at/harry/projects.htm

replacement valves are a pneumatic component to be obtained with most pneumatic suppliers.
for example: http://www.bci.buerkert.com/Products/PDFil..._3_2_Way_EU.PDF
if you want more, than let know, solenoids give always heat when powered. If yours is to hot its knackered anyway. Try it, you have nothing to loose.

Harry, I use a 'anti run-on valve' for a several years. It always become hot- very hot when it is powered. but it works! i did not have any problems with it since 1998. but 'anti run-on valve' does not help me with the hot start problem.

Its a solinoid, so it will get hot during constant operation. Thats why its mounted to the bulk head to act as a heat sink.

I ran one on my last mini without any problems, but decided not to run one on my latest car after reading posts on them failing. Plus everyone seems to just block the pipe.

On my latest engine, it doesn't like the hot start and I've been thinking of re-fitting it for a while now. This seems like the perfect time to do it.

As Arno said: Nothing to lose! I will take a suitable bolt with me to block the pipe if the solenoid fails!
Thanks folks!
Harry

Bimmer Twinky headed and turboed A-Series:
http://www.minifreunde.at/harry/projects.htm