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Old Today, 08:47 AM   #811
Marvel
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Quote:
Originally Posted by Last Triumph View Post
Which bit?

The WUR works perfectly so that leaves the metering head - a rebuild of which is a last resort operation.

I've now read on a couple of Porsche forums that rebuilding these metering heads has about a 30% success rate - in that they leak, or perform worse than before or whatever, due to immense sensitivity.
We know the vacuum advance can leaks so the distributor is only generating centrifugal advance. Probably a red herring but worth fixing.

Lots of info stating the metering heads corrode, leak and don't work properly after being left standing and using ethanol fuel. And you've eliminated everything else.
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Old Today, 09:48 AM   #812
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Hmm, So the removed AAV test showed higher but still lower than warm idle speed?

And you say the WUV warm up period is shorter than the engine getting up to temp and then idling well?

Now the metering head is well removed from the engine so any heat it gets will be under bonnet heat and that's no the case at present so heating of the meter head I don't think is the problem. Tarnishes may be present in the meter head but petrol draws heat from a surface so probably not sticking. Oh, wait a minute. Warm up fuel enrichment by the WUV.

If you can remove the injectors and measure the volume they flow during the WUV warm up and then the same time period measure the volume flowed once the WUV has switched off. Just by roughly saying the cold idle should be 25% higher (or whatever it is) then fuel flowed should be roughly the same. As we don't have any figures to work from then tis a best guess unless you want to figure some calculation out regarding 14.7:1 ratio. Either way, if it flows a fair bit more then you know it can't be the WUV or metering head.

YOu also say that increasing the mixture at idle improves it's running but then it's massively rich at warm idle.

Well my idea of increasing the metering rods relationship to the air flap of the meter head at idle would increase fuel delivery at cold idle and then by closing down the throttle butterfly once warm you will decrease air flow to the engine and hence fuel delivered too.

But the cheapest option may be to try a new coil. My 36hp 6v idled fine till the cows came home but driving it caused it to be jumpy n jerky and eventually stall and not restart for a good few minutes. I changed the inlet manifold, cos it was similar to carb icing, and cleaned the carb over and over etc etc until I fitted a second hand coil and problem solved. I had a coil that overheated under driving conditions but coils are funny things and sometimes electrics work better once warmed up. Heck it could even be due to oxidation in the feed wires from the ign switch and not enough current getting to the coil until the wiring warms up. Just cos voltage gets to where it should does not mean enough current is getting there too.

So that's my few thoughts on your issue. If the fuelling is working as it should and we know enough air is getting to the engine then what parts get better once warm?

Engine internals can move more freely.
Electrics can be better or worse once warm. Maybe better when warm in your case.
What causes drag on the engine that would get better once warm? Gearbox input shaft?

Hmm, coil first me thinks and then the fuel volume test to rule the meter head out.
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Old Today, 10:32 AM   #813
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Send me your email address and I will send you a scan of this that I found in my desk at work



Edit: that is if you don't already have it

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Old Today, 11:29 AM   #814
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http://www.ebay.co.uk/itm/Porsche-92...4AAOSwpzdWryzB
he may have the other bits to swap over.

or a complete injection set up tho its for a turbo , so may or may not be the same would need to check part numbers
http://www.ebay.co.uk/itm/Porsche-92...cAAOSw9GhYe8NJ
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