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TurboBert TurboBert is offline
What freekin Oil Leak?
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Join Date: Oct 2002
Location: Oahu
Posts: 177
I also got the same indications as Wayne (insufficient advance at high rpm and apparent early advance at idle). My distributor was fine, springs were good it was another problem.

My car uses vacuum to retard ignition at idle (you leave the hose connected to the pot during timing). As soon as you press the gas pedal, you lose vacuum and this advances ignition by 15 degrees. As you accelerate, mechanical advance moves it another 18 degrees through 4000 rpm. For me, using the starter as Wayne suggested earlier (which is a great idea) to check early advance doesn't work because I need vacuum at idle.

My problem was that I was not getting sufficient vacuum to the pot at idle. Once I unblocked my vacuum port into the throttle body, I was OK (used copious amounts of carb cleaner).

This is probably something everyone knows (so feel free to correct me if I don't have this right), but it was a revelation to me: I realized when you look at the distributor vacuum advance curve for your car, you need to double the amount on the graph to get ignition advance. For example, for my car, the graph below tops out at 9 degrees total mechanical advance at the distributor. This is 18 degrees ignition advance.

[Every 1 degree of rotation at the distributor drives two degrees of ignition advance (distributor rotates once for every two turns of the crank.]

'79 930 US

Last edited by TurboBert; 12-31-2004 at 08:13 AM..
Old 12-31-2004, 08:11 AM
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