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Discussion Starter #1
I'm tuning up my newly built 302 in my 65 Mustang. It has a Shelby Hi-rise intake, Carter 600 AFB, Comp XE256 (212 deg intake, 218 exhaust), 9.3 CR, stock distributor with 20 deg mechanical advance starting at 1000 RPM, all in by 2300, and a Pertronix.

I was hoping for an inital advance of 12-14 deg, but I'm right at the edge of detonation with only 6 deg initial. When I connect the vacuum advance, it pings at heavy throttle. The carb has it's original calibration. After 1500 miles, I pulled out one of the spark plugs and it looks brand new, except for small amount of fine white powdery deposits on the ground electrode.

I could use some advice as to what could be the problem: too much total advance, too aggressive advance rate, lean mixture? Something else???

Thanks!
 

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On 2002-02-24 00:17, Jerry wrote:
I'm tuning up my newly built 302 in my 65 Mustang. It has a Shelby Hi-rise intake, Carter 600 AFB, Comp XE256 (212 deg intake, 218 exhaust), 9.3 CR, stock distributor with 20 deg mechanical advance starting at 1000 RPM, all in by 2300, and a Pertronix.

I was hoping for an inital advance of 12-14 deg, but I'm right at the edge of detonation with only 6 deg initial. When I connect the vacuum advance, it pings at heavy throttle. The carb has it's original calibration. After 1500 miles, I pulled out one of the spark plugs and it looks brand new, except for small amount of fine white powdery deposits on the ground electrode.

I could use some advice as to what could be the problem: too much total advance, too aggressive advance rate, lean mixture? Something else???

Thanks!
When I ran my 302 we started with about 14-16 initial and 36 total. However we started the curve at a higher rpm. The curve sounds like its the culprit here. I would reset it to kick in over 1800-2000rpm with all of it by 3000-3500. You'll have to toy around though for your specific setup to get it just right. I'd fatten the carb up a little too. You might be leaning the mixture a little bit also.
 

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I had a mild 351W similar to your setup. It had a Performer intake and a 218-218 cam. I used the 10 degree limit plate in the stock distributor which gives 20 degrees on the crankshaft. I set the initial timing at 15 degrees and the total with the vacuum unplugged was 35 degrees. It didn't advance real fast however. The total timing was all in by 3500 RPM. It's quite similar to Pony's setup above. It worked well for me. Any more timing than that caused hard starting and some detonation with 92 octane pump premium.
 

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make sure you have the advance hooked up to manifold vacuum.
 

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On 2002-02-24 06:09, dragman64 wrote:
make sure you have the advance hooked up to manifold vacuum.
I don't think you want manifold vac. it should be ported from the carb. no vac at idle and you get vac when you start to accel.
 

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Discussion Starter #6
Your replies make sense. Pony1, could you explain what you mean when you say I "might be leaning the mixture also"? Is the fix for this different than fattening up the mixture by adjusting the jets/rods?
 

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That's quite an article Dragman64. It'll take me a bit to digest that...

Your setup is pretty similar to mine -- I also have a C4. I haven't tried the full-time port yet. My concern was that I would be running a lot of advance in park when I don't need it, and it would cause the engine to run on when I switch it off. When idling in drive the advance would drop off when I could probably use it.

What's your experience?
 

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stock distributor springs are very strong --- centrifugal advance will still be coming in at 5000 rpm -- check the total advance with the rpm up -- the centrifugal advance has a heavy spring and a light spring -- i take out the heavy one and leave the light one
 

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I'm having the same problem with my car. (see sig). Seems like no matter how much I dial the timing back and it still pings, even though the exhaust smells rich. Perhaps its just my dumps though. I'm trying to sort this out, since my engine isn't broke in yet.
 

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Carbon build-up can cause hot spots that lead to detonation.
 

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try using gas with higher octane too. I've been trying to fix this problem in my car too (i get some white smoke with mine though). I've heard many people say that it might be the springs inside the dist OR a leak on the manifold (broken gasket). Any truth to either of these?
 

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So, to cure detonation, advance needs to come in later and stop advancing later? I have a dist. spring set and adj vac. advance from crane, how do I need to set it up for it to work like this? Thanks.

<font size=-1>[ This Message was edited by: oldmustangjunkie on 2/27/02 10:21am ]</font>
 

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Sumary of the link that dragman gave, why you should run manifold vac advance instead of ported: dense fuel mixtures burn faster, compared to light ones, so you can have high advance at idle, because the cylinder charge isnt very dense, and burns slower, needing more advance. With ported advance, the more you are on the gas, the more vac is provided and the more advance you get, which is ending up too far advanced, with a dense fuel charge and causing pinging. With it on manifold vac, you have high advance at idle, which is ok since it is a light fuel mixture, that burns slower, and can take more advance. With manifold vac, when you get on the gas, manifold vac drops, and your advance would drop some as well, keeping you out of detonation when you are loaded heavy. Give it a try, see how it works.

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<font size=-1>[ This Message was edited by: Brian M on 2/27/02 5:24pm ]</font>
 

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On 2002-02-26 22:20, oldmustangjunkie wrote:
So, to cure detonation, advance needs to come in later and stop advancing later? I have a dist. spring set and adj vac. advance from crane, how do I need to set it up for it to work like this? Thanks
Anybody? Bueller? Bueller?
 

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The vac. advance pot uses something like a 3/32 allen wrench to adjust it. Read the instructions on it and check out the article in the arcives of this site "timing is everything". That will help you out a lot. If you're pinging and don't need your advance till later, don't use light springs and tighten up the vac. advance some. This will slow down your rate of vacuum advance and require higher rpms before you get full advance.
Read the tech article on this site. It will help you out way more than I can. Good luck.
Bozz
 

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On 2002-02-25 11:11, oldmustangjunkie wrote:
I'm having the same problem with my car. (see sig). Seems like no matter how much I dial the timing back and it still pings, even though the exhaust smells rich. Perhaps its just my dumps though. I'm trying to sort this out, since my engine isn't broke in yet.
Your problem is that your carb is way too lean. Lean air/fuel ratios cause detonation. Your exhaust smells rich but it's actually not. You have lean misfire which causes some of the air fuel mixture to pass through the engine unburned. I had a 70 4V Cleveland that seemed so rich at an idle that the exhaust felt like it would rot out my eyes. I drilled out the idle restrictions in the emissions carb I was using to richen it up and voila!.... it idles better, the idle screws actually made a difference and the smell was gone. Try raising the float level which will richen the entire fuel curve and see if the pinging and stinking exhaust gets any better. I'm pretty sure that it will.
 

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Would a lean misfire, cause backfiring through the exhaust on deceleration? I noticed it more with the full time vacuum on. I am still confused. If I am detonating, do I need to have the advance end at a higher rpm or a lower one than it does now. I know I need to slow how fast it advances, but what about the rpm it ends at?

<font size=-1>[ This Message was edited by: oldmustangjunkie on 3/7/02 11:02am ]</font>
 
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