jerseyjoe

Can someone confirm on a 68 olds 350 a switch that is working properly should supply ported vacuum only to the vacuum advance unless in an overheating situation it would divert to manifold vacuum to increase timing. I have vacuum to the advance both cold and hot at idle. I believe this is incorrect and the valve is stuck open.

joe

hullinger

I believe your understanding is correct along with your diagnosis. For me, having the switch stuck open doesn't seem like a problem. On my '73, the switch was stuck closed so I just routed those vacuum hoses to other ports. Regardless, be sure to check your initial and total timing to make sure your getting as much as possible.

Chris

MDchanic

Yes, this, of course, brings us back around to the Ported / Manifold vacuum advance controversy.

My recommendation is to see which way your car seems to run best, and just leave it that way.
The only difference that the TVS makes is to apply full manifold vacuum at idle - the ported vacuum is equal to the manifold vacuum as soon as the throttle plates are cracked, so anywhere above idle, the TVS has no effect.

- Eric

drop top olds

Any difference in the TVS operation with three hose fittings on the stem verses two?

MDchanic

I thought they all had three: Distributor, Manifold, and Carburetor Port.

- Eric

jerseyjoe

Thanks guys. I know the later models run full advance but it is running just to rich at idle. Can't seem to get a great idle out of it and you can smell it is running rich. I will bypass for now and see if I can get it to idle better before buying a new switch.

If I recall the eighty's model years had two stems. Maybe to control EGR?

drop top olds

I thought so too, but the one on my engine has two plus the fitting at the top. My old one has three plus one on top.

jerseyjoe

Well being the dumb a$$ I am I should have checked the valve long before now! Put the new valve on today and it is a totally different car! Can anyone guess why? I cannot believe I did not realize this before, geez getting old