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73-87 Chevy _ GMC Trucks => Performance => Topic started by: 83CHEVY on February 12, 2003, 03:56:00 pm
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A reputable shop last worked on my timing. I checked it yesterday and it was retarded somewhere around 10 degrees (not even on the scale). The wierd thing is there was a "scratch" on the balancer that appeared to line up with the 4 degree mark. I set it to 12 (using the real mark) and drove it - it pinged badly. I backed off to 10 - still pinged. Pinged at 8. It is set at 6 now and pings when cold, but not when warm - which I do not understand. Factory setting is 4, but I want to run as much advance as I can 'cause it runs better. I run 91 octane always and think I should be able to run 10 (at 4,400 ft elevation), but I can't.
So my question is...are there other things that could make it ping before it should? Could a rich or lean jetting cause it to ping at low advance???
Your expert advice is needed - and greatly appreciated.
Mike 
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ok a couple things. Are you checking with the vaccum advaance un hooked and pluged up? What compression, heads, and cam are you running? Lastly, do you use manifold or ported vaccum?
A stock motor should be able to take 10* without problems. Could that scrath in the balancer be because the cam timing or balancer mark is off?
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I checked the timing with the vacuum advance unhooked and plugged.
As for manifold or port, It comes from the stock location. I will check tonight and see if I can tell where the vacuum signal is coming from.
I have stock 305 heads, stock cam, and the compression ratio is 9.2:1.
I was wondering about that scratch myself. I had the distributor changed to a higher performance unit by Pro-Form. My mechanic put it in and timed it, cause I was too busy to do it that week. I don't know if getting the distributor on the "wrong tooth" would cause something like that or not. One other thing, I changed the timing chain and gears a few years ago, but I am sure I got the chain on the right teeth - but I did mess with it.
Hope this helps you help me 
Mike
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the old "put on the wrong tooth" is crazy. The distributor doesn't really care WHERE you stab it as long as you rotate the wires around accordingly to make #1 cyclinder fire when #1 piston needs it too. Point it any direction you want, it doesn't care as long as the fire goes where the fire is needed. As for advance, I've heard alot of 305's that have problems with rattling valves. I don't know if it's head design or running lean.... I guess it doesn't matter. The proform distributor you put in may have an extremely quick advance curve built into it and what you really may have to do is tailor the advance to your motor and driving habits. I always like to run a total of about 38 degrees and bring it in very quickly by changing springs. You may not want it to do the same. Usually bored and stroked has some good info on stuff like that too.
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If its in stock location on a stock carb, then its ported vaccum. I agree the proform might be giving too much advance. Does it ping at idle?
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It does not ping while idling, but when I plug the vacuum advance in, it bumps the idle up. It only pings under a load and only when not warmed up. Once it has warmed up, I can't get it to ping. I guess I will try setting it to the stock 4 degrees like the emissions sticker says, but it just seems strange that I can't run more than that. You think the ProForm advances too quickly? Since the carb is "out of the box" and has not been jetted specifically to my vehicle, do you think a rich or lean condition could be helping it ping? Plugs read normal (brown). I was going to take it down and have a shop run it on a dyno and give me the fuel/air readings, but I think I want to sort out my timing first.
Mike
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OK, since you say the idle "bumps up" when you plug in the advance it's definately a full time port. Take it off that port and find another port that only has vacumm when the throttle opens. You don't need advance when idling, you need it when you open the gas. With the proper line plugged in at the proper place, set your initial to about 4 before TDC. It's a good satarting point to start things off. You may be able to pull it a bit higher if the motor will take it but go for the ported vacuum port. It's just another possible way to fix the dreaded ping...... before the top of your rod bearings are gone!!!!
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Vacuum signal comes from the "B" port on the passenger side of the carb on the front up high. It is shared by other stuff, but that is the source. There is a disc looking thing that could be an orifice or a check valve between the carb and the distributor. Donno what it is. Does this splain why my idle "bumps up" when I plug in the vac advance???
Mike
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Some genius worked on a friend of mine's Chevy wagon and turned that one-way check valve around backwards. The only time that car didn't ping was when it was turned off!
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yeah if the engine idles up its for sure in a ported vacuum port. you need to get a timed port............once it has full advance down low it will ping like crazy.
Toys are my game
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I don't think it's ping.... I think your valve springs have reached the end of their life. Instead of ping you are hearing the rockers having a heart-attack.