I have 350 sbc. Stock as far as I know. Vacuum advance disconnected and plugged both ends. I set the initial timing at idle to 10 btdc. Revved the engine to 2200 where the timing stopped increasing and set to 32 btdc. When I let it go back to idle it's sitting at around 24. How do I get idle timing back down to an acceptable number?
Timing for the first time
spiked_gonzo
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68 Base Camaro, 355 Offy crossram, Richmond Street close ratio 5 spd, 92K SoCal car
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A few thoughts correct me if wrong;
Centifugal advance responds solely to rpm as noted in John Z article & the spring rpm chart posted.
With vac advance temporarily removed, (which you did correctly for purpose of this test), you have the 10 initial you set + the centifugal. You rev to 2800 measured total timing 32 btdc which is what manufacturer data Indyguy supplied, (helpful ), you should expect to see, 10+22. But it rose very quickly and full deployed by 2200. I don't believe the medium springs should ever bring full centifugal in this early, good question for Proform tech line, Jegs probably won't have that answer but doesn't hurt to try unless someone has a spring rpm chart for your dizzy.
Second issue is back at idle centifugal should be out of equation, but appears still putting 14 degrees into total at idle along with your 10 for 24, which can mean it didn't full return to at rest position via springs. Agree with others to re-check the stuff that can throw your readings off, timing light, weights on dizzy hanging up or binding on posts or rough/poorly machined (may not hurt to try the new weights), make sure dizzy tightened securely, hasn't moved. Had you ever timed the engine with same light prior to dizzy change? That would eliminate pre-existing other issues you weren't aware of prior to dizzy install. If not start looking at things that may have pre-existed. Correct timing tab for your model year on front cover, check balancer is installed properly/securely torqued with keyways holding it in to crank. I once found upon teardown an engine assembled without keyway in crank snout to retain balancer in proper clocking. Hope this helps.
Centifugal advance responds solely to rpm as noted in John Z article & the spring rpm chart posted.
With vac advance temporarily removed, (which you did correctly for purpose of this test), you have the 10 initial you set + the centifugal. You rev to 2800 measured total timing 32 btdc which is what manufacturer data Indyguy supplied, (helpful ), you should expect to see, 10+22. But it rose very quickly and full deployed by 2200. I don't believe the medium springs should ever bring full centifugal in this early, good question for Proform tech line, Jegs probably won't have that answer but doesn't hurt to try unless someone has a spring rpm chart for your dizzy.
Second issue is back at idle centifugal should be out of equation, but appears still putting 14 degrees into total at idle along with your 10 for 24, which can mean it didn't full return to at rest position via springs. Agree with others to re-check the stuff that can throw your readings off, timing light, weights on dizzy hanging up or binding on posts or rough/poorly machined (may not hurt to try the new weights), make sure dizzy tightened securely, hasn't moved. Had you ever timed the engine with same light prior to dizzy change? That would eliminate pre-existing other issues you weren't aware of prior to dizzy install. If not start looking at things that may have pre-existed. Correct timing tab for your model year on front cover, check balancer is installed properly/securely torqued with keyways holding it in to crank. I once found upon teardown an engine assembled without keyway in crank snout to retain balancer in proper clocking. Hope this helps.
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The way I read it, he set the total to 32 at 2200 and the initial was 24 showing 8 mechanical in the dist. He also said he set the initial to 10 and rev'd it to 2200 where the timing stopped climbing. Reading what SY1 posted, I and others may have misunderstood the OP.
Does this mean he set it at 10, rev'd it to 2200 and the total was 32? that is the built in 22... If so then the question is what changed when he saw 24 inital? Are the weights sticking? Was the vacuum advance hooked back up?
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Just my thoughts on the OP issues.
1) Initial timing was set to 10 degrees and then rev'd to get the total timing at 32 or 34 degrees. Did the weights in the distributor get stuck and didn't return back causing the higher timing? Check for burs on the weights, and I have seen weights put on wrong and without enough spring tension to return to base timing.
2) Could the distributor have slightly turned when rev'd during that timing adjustment?
3) Does the timing go back to 10 degrees after you shut off and restart the engine? That would lead me to weak springs as being possibly the problem.
For me and the Chevy vehicles I have, my base timing is 12 degrees and have total of 36 degrees in by 2800 to 3000 rpm, That my starting area and I tend to be close to those numbers when finished tuning.
Hope this helps, and please update us on what you find.
Brent
1) Initial timing was set to 10 degrees and then rev'd to get the total timing at 32 or 34 degrees. Did the weights in the distributor get stuck and didn't return back causing the higher timing? Check for burs on the weights, and I have seen weights put on wrong and without enough spring tension to return to base timing.
2) Could the distributor have slightly turned when rev'd during that timing adjustment?
3) Does the timing go back to 10 degrees after you shut off and restart the engine? That would lead me to weak springs as being possibly the problem.
For me and the Chevy vehicles I have, my base timing is 12 degrees and have total of 36 degrees in by 2800 to 3000 rpm, That my starting area and I tend to be close to those numbers when finished tuning.
Hope this helps, and please update us on what you find.
Brent
68 Base Camaro, 355 Offy crossram, Richmond Street close ratio 5 spd, 92K SoCal car
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4,697 Posts
Dennis and Brent I agree. I had to go back to his original post to see what he first had which looked pretty good comparef to where he is now. Something changed. Brent exactly, a burr dragging, interfering, like the stamped weight wasn't cleaned up on edges at manufacture.
I also got digging and found the copper (weakest) springs can have 24 degrees in by 2000rpm (at least on the Petronix, so may Proform too?). So my comment as to being in 24 that quick could be with the weak springs).
Now if I can figure out why my Petronix has 1 silver (medium) and 1 light blue (non-existent according to Petronix). They shipped it that way. Now I got a project🤦‍♂️
I also got digging and found the copper (weakest) springs can have 24 degrees in by 2000rpm (at least on the Petronix, so may Proform too?). So my comment as to being in 24 that quick could be with the weak springs).
Now if I can figure out why my Petronix has 1 silver (medium) and 1 light blue (non-existent according to Petronix). They shipped it that way. Now I got a project🤦‍♂️
68 Base Camaro, 355 Offy crossram, Richmond Street close ratio 5 spd, 92K SoCal car
Joined
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4,697 Posts
Interesting mechanical centifugal advance chart for Petronix. Values may be similar for Proform or mat not be. But visuals always help me. At least you can get an idea what's going on without just a bunch of numbers. Sorry in advance about the sharpness.
![Image]()
Lighter springs give u the advanced timing earlier.(lower rpm)
the springs won’t give u more or less timing. The shims inside the weights do.(sone dist have none, they just have weights. If that’s the case u can’t adjust amounts of timing, just when it comes on.
Personally, I want the total advance I need to come in early as possible. I like locked times distributors. This can cause hard starts at times for some engines. Once running they like timing. All the vacuum, then springs etc. Try leaving vacuum unplugged, set timing at say 34 degrees for a sbc all in. Rev motor to 3k rpm, set timing at 34 or the total of ur desires and tighten down the dist. See how it runs, I bet fine. U don’t want way too much timing but all in early wont hurt. My 302 liked it set that way. My ls3 is locked (no dist) locked timing.
my big blocks ran 32 and my sb2 race engines 26.
the springs won’t give u more or less timing. The shims inside the weights do.(sone dist have none, they just have weights. If that’s the case u can’t adjust amounts of timing, just when it comes on.
Personally, I want the total advance I need to come in early as possible. I like locked times distributors. This can cause hard starts at times for some engines. Once running they like timing. All the vacuum, then springs etc. Try leaving vacuum unplugged, set timing at say 34 degrees for a sbc all in. Rev motor to 3k rpm, set timing at 34 or the total of ur desires and tighten down the dist. See how it runs, I bet fine. U don’t want way too much timing but all in early wont hurt. My 302 liked it set that way. My ls3 is locked (no dist) locked timing.
my big blocks ran 32 and my sb2 race engines 26.
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