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07/12/2004 15:01:30   Richard   Does anyone own a late 1980's Saab V4. Tom's car has two vac tubes that meet at a brass junction that is part of the water circuit. Then one pipe goes from this to the dizzy advance. I take it this is to do with emission controls, but I have little data on this. Tom is having problems with the running of the car. This vac advance system gives over 20+ deg advance at tickover at the moment. Basically you set the ignition to 6 deg, but as soon as you attach the vac advance pipes the revs increase and the advance goes above 20 deg. The car then runs with a too high tickover, so you adjust it and all seems well until you rev the engine. The advance dies back to 6deg as you rev it as there is little vacuum and with the now reduced revs the engine stalls.
Does anyone know what the brass water pipe connection is intended to do, does it make a difference which way round the incomming pipes goes into this?
I am going to have a look at the car possibly this weekend, I would like to be sure the system is operating as intended. I can see me converting it to the more conventional single vac pipe system.  
08/12/2004 16:24:58   Steve B   Hi Richard,
I know little about this but I thought I'd write a response anyway in case it helps.
I think you are correct that this is an emissions control device. The brass component is probably a temperature switch of some kind (bi-metallic strip or something). The idea is that vacuum advance is switched off until the engine has warmed up. Apparently this reduces the amount of unburnt hydro-carbons in the exhaust gasses. I think all this is only supposed to improve emisions at idle or during decceleration and this is acheived by having one of the vac tubes in a different area of the carburretor. Basically at idle the timing should be retarded.

I sounds like maybe Tom's temperature switch is stuck open so that there is too much advance or something.

Very vague I'm afraid.  
08/12/2004 16:26:17   Steve B   or try swapping the 2 pipes round maybe ?
Has Tom unplugged them recently ?  
08/12/2004 16:58:05   Richard   Yes that's what I think and second I dont know if they are in the right place on the thermal switch, but the bends look to go to the right take offs on the carb end (if you can understand that).
Toby is sending some info up on this system, my dealer. books are too early for this.

Thanks Steve.  
08/12/2004 22:19:36   Alistair   Could be worth asking the question on one of the US sites like Vsaab as they had the emissions kit from the early 70s, though it may not be quite the same.  
09/12/2004 07:35:34   Richard   There are some extra bits on the US cars from what I have been told.  
09/12/2004 10:28:47   Richard   Thanks, I think we will go to the older system.  

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