My "new" 75 convertible came with the original L48 that has been freshly rebuilt (about 2K miles) and speced out for substantially more performance than the original,(which still isn't saying much). It also came with a "DUI" HEI distrubutor which is also new. Engine has about 9.8:1 compression, hydraulic cam of unknown specs, Eldebrok manifold and AFB clone carb. Also has 2.5" ramshorn manifolds and pipes with regular mufflers; no cat. No pollution controls at all, basically a 60's type engine with HEI.
The PO had told me his engine builder recommended 35* advance and that he had set the engine to this value. He had also plugged off the vacuum advance for reasons he was unable to explain.
Now, the engine runs fine. No real complaint, other than poor fuel economy. Runs nicely, doesn't overheat, no pinging, so why am I even checking the advance? Well, inquiring minds want to know why the vac advance is plugged, and if I can get better gas mileage with it operating, which I should.
I hooked up a timing light(dial back), and found the initial timing set at about zero. Reving the engine to about 2500, I was still only seeing about 6*.
Attaching the vac can seemed to yield about another 6*. Checked the vac can with a vac pump and it starts at about 5" and is fully deployed at 10" of vac. The engine runs great now. It ran real well before, but something just ain't right here. I took the cap and rotor off and checked the springs and weights. They seemd ok, though the PO told me he had used the lightest springs in the kit and they seemed kinda stiff. I should mention that this is the first time I can remember even taking the cap off an HEI distributor, so maybe there is something I just don't understand.
The balancer has three marks on it and I ASSUMED that the middle mark was perhaps the one to check. I have ordered service manuals, but they haven't arrived yet and I have no references that are 75 specific.
The PO had told me his engine builder recommended 35* advance and that he had set the engine to this value. He had also plugged off the vacuum advance for reasons he was unable to explain.
Now, the engine runs fine. No real complaint, other than poor fuel economy. Runs nicely, doesn't overheat, no pinging, so why am I even checking the advance? Well, inquiring minds want to know why the vac advance is plugged, and if I can get better gas mileage with it operating, which I should.
I hooked up a timing light(dial back), and found the initial timing set at about zero. Reving the engine to about 2500, I was still only seeing about 6*.
Attaching the vac can seemed to yield about another 6*. Checked the vac can with a vac pump and it starts at about 5" and is fully deployed at 10" of vac. The engine runs great now. It ran real well before, but something just ain't right here. I took the cap and rotor off and checked the springs and weights. They seemd ok, though the PO told me he had used the lightest springs in the kit and they seemed kinda stiff. I should mention that this is the first time I can remember even taking the cap off an HEI distributor, so maybe there is something I just don't understand.
The balancer has three marks on it and I ASSUMED that the middle mark was perhaps the one to check. I have ordered service manuals, but they haven't arrived yet and I have no references that are 75 specific.
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