Join Date: Nov 2000
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Re: Need Better Gas Milage!! Holley Projection.
Is it a stock ignition system? Electronic or points? Sounds like an area to concentrate on from the get go if it's been causing you problems. Weak and intermittent spark could certainly cause the problems you describe. Wish I knew more about the 360's but I don't. Someone will pipe up I'm sure.
Regarding the vacuum source, if it's ported vacuum, and I'd suspect that's what you should be using, it will have no vacuum at all at idle, as the port from which vacuum is being drawn is above the throttle plates. It's only when you tip the throttle plates open a bit that they become subject to vacuum. Got a vacuum gauge? You can verify this. Should have no vacuum at idle and vacuum should blip upward as you give it throttle.
You need a good spark and properly timed to give you good power and economy. Is your timing set close to spec? That should be good enough until you sort out that problem. After that, you should find the maximum advance you can give it by road testing and backing off from the point at which you get ping.
If the projection is like other fuel injection systems, it too relies on the ignition system for a source of impulses to gauge rpm and meter the fuel. Is there an 02 sensor? A map sensor? If there is a map sensor, it should not go to the same port that you hooked the vacuum advance, as that sounds like ported vacuum. MAP goes to manifold source. IE high vacuum at idle.