timming question

[fdbdw]

71 c10 350/points
I currently use a timing light and am set a 8 btdc, i was told by a guy at the parts store that because I live at high altitude that it is best to set timming with a vaccum guage. He said to connect to the vaccum port on the back of the intake manifold and adjust the timming until you get the highest vaccum reading possible and leave it there. He swears by this being the most accurtate way to set timming. Has anybody else use this method and does anyone have an oppinion on vac vs. timming light.

[67shortie]

Well, yes and no.

Usually one will adjust thier carb idle fuel mixture to the highest vacuum levels, but timing, there is a little more to it.

the problem here with adjusting timing this way will be if you set it with the guage it will most likely be way too advanced in regards to your total timing.

Example, lets say you whipped out the vacuum guage and advanced the timing at the highest reading/rpm and then put a timing light to it. It will most likely be around 25-35* initial (roughly), then you introduce mechanical advance and it will shoot up to over 50 which is way to much especially with your vacuum advance not in the picture yet. Most engines like about 34-38* total here, without vacuum advance in the mix which when hooked up could shoot this number up near the 70* mark under light loads=engine pinging and loss of power.

Look in the engine forums for the sticky at the top of the page 'timing 101' I believe.

High altitude I am not familiar with but this tends to involve carb setup more than timing, but someone may have more experience with it.