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Re: [T3] Fuel in oil

> It's the flow that gets split, not the pressure.

Yes you're right Jim, but the flow is double when both valves are open
therefore the pump needs higher pressure to have the same response

> A dual carb 1600 uses only slightly more fuel than a single carb 1600,
> the only difference is that there is SLIGHTLY less air flow resistance in
> dual carb setup, so the dual carb car can suck just a bit more air. It's
> nothing close to a factor of 2.

Of course you're right in that the twin carb engines don't use twice as much
fuel per mile (though mine seems to try  ;-)) I didn't mean that. What I'm
getting at is that there must be some histeresis in the needle valve- a
response time between the level in the chamber going down to a level that
the valve opens and lets in more fuel. This will give rise to changing
characteristics in the carb as the level changes which needs to be
minimised. It is possible and will happen that both valves will be open at
the same time. To keep the same characteristics as a single carb engine, the
pump will have to deliver twice as much fuel in this period (only when the
valves are open) as a T1 pump. Now each individual carb will get through
half as much fuel/time as it only supplies 2 cylinders, so in theory the
valve should open 1/2 as often and fuel consumption will not suffer. I still
think this makes sense- but I might well be wrong. Its just strange to me
that my car should have a (just) noticeably different character with the
right pump. Might be psychsomatic though- the new pump sure looks nice ;-)

> Here something I've been wondering about in this thread: Don't the mixture
> screws control JUST the idle mixture, while the main jet controls the
> across the open throttle range? So I don't see how misadjusting the
> screw could make much difference unless the engine spend all its time at

The idle jet doesn't stop working just because you are no longer idling- it
still sources fuel and it really does seem to make a difference (on my car
at least) to the running of the engine throughout its range.

> The higher pressure will certainly raise the fuel level in the float bowl
> somewhat, but someone will have to send me a carb before I can tell how
> this might change: I suspect not  much.

This might well be the answer- but surely this means that the effective pump
pressure has been diminished by feeding 2 carbs as otherwise a single carb
pump would do, and too high a float chamber level would be a bad thing so VW
wouldn't have spec'd a higher pressure pump?!?

> Didn't someone suggest that the change might have been to compensate for
> pressure drop in that special little valve some of these cars had--the one
> the crossover connection between the intake and output lines from the
> That's the best idea I've heard so far.

No idea what this valve is- I know the earlier pumps had an antisyphoning
valve built in- is that what you mean?

I don't know, I thought I had it sussed in my mind, but now I'm wondering

Mark Seaton
'73 1600TA London

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