Old style points distributor with both vacume and mechanical advance. Timing light shows peak advance over 55 degrees free revving the engine to 4000 rpm. This happens with or without the vacume line attached. Makes me guess it the mechanical advance that's the problem. Is there a way to limit the total advance? Just telling me to buy a new HEI isn't the answer for an old school guy.
Chevy 302 ? recurve kits with springs, weights, and bushings (to limit max cent adv) are available all over the place. Mr GAsket seems to only offer springs for Fords. Some advocate using springs stiff enough to limit the total mech advance. That suggests some continued advance up thru max rpm (and beyond). I had a Volvo that as I recall that did that. Some claim that advance limited by the spring, not mechanical contact between weights and bushings is more stable at high rpm. Gotta subtract the "static" timing from the 55 '"total" to see what the dist cent adv is contributing. I'd map out the advance (with vac adv line removed from dist and engine side plugged). One of these days I'm going to calibrate my old craftsman "dial back" timing light against a damper with degree marks or with the correct 'timing tape". It has seemed to be close to correct in the 10-15 degree range, dialing back.
What is your initial timing set at? Are you running ported or manifold vacuum to the vacuum advance? There is a mechanical limit as to how much advance the distributor can provide using mechanical and/or vacuum advance, but that can be modified with aftermarket advance curve kits utilizing different weights, springs and bushings with various offsets drilled into them. Additionally, aftermarket vacuum advance units (as well as some OEM ones) are adjustable as far as total amount of advance is concerned, usually by use of an allen wrench through the housing. Most GM cars use manifold vacuum for the vacuum advance, providing full advance at high manifold vacuum throttle settings such as idle and cruise for smoother running and increased mileage. Fords tend to favor ported vacuum for the advance which assists the mechanical advance in quickening the curve as the engine is accelerated. Either way will work on any engine, but you must tune accordingly, with initial (static) timing settings and gasoline with the appropriate octane rating.
Assuming Ford, The advance slots are marked in distributor degrees. See attached picture. The crank timing advance is twice the distributor degrees. So the 15L slot adds 30° of mechanical advance. You need to pull the breaker plate and advance weights to see what you have. Some smog era distributors have an 18L slot, which is 36°, way too much for a performance tune. You generally want somewhere around 35° total for best performance. The factory often used the 15L slot for 30° mech with 5° initial. The "hotter" the engine build, the more initial and less mechanical you want. A good starting point for a high performance engine is to use the 10L slot for 20° mech advance and give it 15° initial. For a torquer, 10° with 26° mech might be a better choice. Use springs that bring it all in at around 3000 rpm. If you can't find a 10L rotor, you can weld the slot narrower, or add bushings to the limit pin to tune your advance curve. Here are some slot widths I stole from the reincarnation-automotive site. 8L slot = 16 degrees centrifugal advance = .358" 9L slot = 18 degrees centrifugal advance = .384" 10L slot = 20 degrees centrifugal advance = .410" 11L slot = 22 degrees centrifugal advance = .436 12L slot = 24 degrees centrifugal advance = .462" 13L slot = 26 degrees centrifugal advance = .488" 14L slot = 28 degrees centrifugal advance = .514
if chevy, check to see if the advance bushing is missing, I had one that was missing...this is the way ( different size bushings) you change the amount of mech advance...
The trouble with ASSUMING that everyone automatically knows what you are talking about is that only half the people are correct at any one time. This is a common thing on here and it always leads to guys throwing out answers that the OP wasn't looking for. 302 FORD OR Z28 302 Chevrolet? Each has it's own set of issues but the best way on either is to take it or send it to someone with a distributor machine who can set it up right from the get go. The guys gave good suggestions for either Ford or GM distributor in the posts above for you to pick from.
This is the answer I needed. My BAD, I should have said 302 Ford! Thanks for all the input. I'll pull the distributor today.
Updating: Relic Stew - Thanks so much. Pulled the distributor and found the "slots" marked 13 and 18. It was in the 13 slot. I followed your advice and tacked a small piece of metal to the slot making it about equal to 10. Put it all back together, points to apx 18 thou, set dwell to 28, initial timing to 14. ran it up to 4500 rpm, Maxed the advance out at 35 degrees. PERFECT for my application. Thanks again - Tom
Digging up an old post. Does anyone know if anyone makes these old ford distributor limiter plates anymore? I've searched around and have not had any luck. 8L slot = 16 degrees centrifugal advance = .358" 9L slot = 18 degrees centrifugal advance = .384" 10L slot = 20 degrees centrifugal advance = .410" 11L slot = 22 degrees centrifugal advance = .436 12L slot = 24 degrees centrifugal advance = .462" 13L slot = 26 degrees centrifugal advance = .488" 14L slot = 28 degrees centrifugal advance = .514
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