Quote:
Originally Posted by Othen
How are you getting on with that 244? Did you get the carburettor, leaks, transmission, ignition timing sender etc all sorted?
I was looking at the carburettor on the RB today (a Peirburg 175CD - sort of similar to yours) and had an idea that might completely get rid of the drop in revolutions when one puts the auto box into gear. It looks like your car had an anti-dieseling solenoid (as does mine). I was thinking that instead of just switching the solenoid when the ignition is turned on, it could be switched (by the starting inhibitor switch - backwards though, so there is a signal when the car is in gear) that would then open the valve and use the solenoid circuit in the carburettor to increase the fuel/air mix a bit - increasing the engine speed.
The anti-dieseling circuit probably wouldn’t do that job any more, in that one would have to use just the idle circuit to set the tick-over. speed in P or N
I might try it out on the RB.
Alan
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Alan, I would advise against re-purposing the “anti-dieseling” solenoid. On the Volvos and the side-draught carburetors, these open a channel from the air side of the throttle valve to the engine side, which has an effect very similar to opening the throttle valve by the same amount (by pressing the accelerator pedal for example). On down-draught carburetors, the solenoids block off the idle jet when the ignition is switched off. In practice, their main purpose is not to prevent dieseling, as this shouldn’t really be an issue in a properly set up spark ignition engine: The compression is not high enough for compression-ignition of the fuel/air mix, the ignition is switched off so there is no spark, and the cylinder head/valves/etc should really not get that hot to ignite the mix. But what is a real problem is that the passive “flywheeling” of the engine to a halt still creates vacuum on the intake side, which sucks in a small amount of fuel/air. This does not get ignited (normally), but remains in the cylinders, washing down the cylinder walls and eventually ending up in the sump, contaminating the engine oil and greatly increasing wear next time the engine is started. The solenoids reduce the amount of fuel ending up in the cylinders after the ignition is switched off. On down-drought carbs, the solenoids have nothing to do with idle speed (at least until they break).
But in our Volvo, the channel they control is adjustable. This is best left as is, but your excellent idea can be better implemented through the use of an A/C bypass solenoid (a second one, in my case).
The idle bypass channel can be set for 900 rpm at idle in N and the “transmission compensation” solenoid can be adjusted for 900 rpm with the transmission in gear, via the starter inhibitor switch with an inverted state (via a logic gate or just a simple relay). Then the idle speed would remain unconditionally stable.
In fact, this is what Volvo should have done in the first place! Now, where do we get a couple of extra A/C bypass solenoids of the adjustable type? It would take a certain amount of time until the solenoid opens the channel and more fuel/air reaches the cylinders, but it would also take a certain amount of time for the transmission to actually engage the epicyclic gearing, loading up the engine, so with a bit of luck, this could be very smooth!
This is something I’d gladly add to my 244! These are mounted remotely and are hooked up to the intake manifold and carb via fuel hoses (for vacuum hoses, but I prefer if they are rated to withstand fuel since it will be the fuel/air mix that they will be passing).
I actually thought that this was how it was meant to work when I first bought the car, and assumed that the solenoid may have given up, but after looking everywhere, I was unable to find such an arrangement for the transmission (confirmed by the manuals). It is only there for the idling and A/C.