miss after advancing timing

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I think Duster440 didn't read all the posts indicating that you installed MP lighter springs and that the "knock" was at idle.

Did you check if the exhaust was hitting the body/frame/trans/etc?
 
ramcharger said:
I think Duster440 didn't read all the posts indicating that you installed MP lighter springs and that the "knock" was at idle.

Did you check if the exhaust was hitting the body/frame/trans/etc?
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Everything appears to be clear from the exhaust. Defiently coming from the engine. It never did this until I changed the timing. So it must be too advance. I'll try to get a video tomorrow and post it. I'll also play around with it again and try retarding it down a few degress and see if it helped. There were a couple times when I was driving I noticed a odd sound. They say pinging sounds like marbles being dropped in an empty can. But what I heard was very quiet and sounded like it was coming from behind the guage cluster. Out of all the driving I did in the past couple days it only did this twice while crusing. It's very possible it was light pinging. But didn't quite sound like what I have read it's supposed to sound like. It was hard to hear. But maybe the timing is just a notch too advance. Or it could have been something in the dash.
 
It's so very hard to diagnose stuff over the internet. In my years as a professional mechanic I had to use all my senses. Sight, smell, feel, sound and taste (bad gas). Can't do that over the internet.

The more info we have the better. :)
 
ramcharger said:
It's so very hard to diagnose stuff over the internet. In my years as a professional mechanic I had to use all my senses. Sight, smell, feel, sound and taste (bad gas). Can't do that over the internet.

The more info we have the better. :)
Click to expand...


I'll try to describe the sound as best as I can. It's like a very rapid rattling sound, but it's almost a constant noise not a ping, ping, ping. And sort of high pitch. It's rather hard to hear and lasts for only a few seconds while driving. I always expected pinging to be just that, a ping. I know it's hard to describe over the computer. Hopefully tomorrow everything will be where it should be.
 
Could you have pulled (or partially pulled out) a spark plug wire out of it's socket on the distributor when you were tinkering with the timing?
 
I don't trust set back timing lights. Make a mark on your balancer at 36 degrees and use a non adjustable timing light. I've seen the set backs vary 5-89 degrees.
 
I fooled around with it again today. I drove up to where I work to visit a co-worker who used to build small block Mopars back in the day. Im usually off on the weekends. It's a auto parts warehouse but has a store in the front. So I went there to see what he thought was going on. I showed him the timing with the same light. Then he brought out a timing light from behind the back counter. This is just a basic timing light, no dial back. He said I had too much initial and total. My total was somewhere above 40* Bumped the distributor a little so it's in the low to mid 30's now. He thinks something is wrong with the dial back light. Seemed inaccurate. So now I don't seem to have any kind of knocking sound in idel or accelerating. And also no pinging type of sound. Everything is fine now. When I get the chance i'll try to do a burnout. But im not holding my breath lol

Thanks for everyones help. I guess what it comes down to is a defective timing light. I believe it was a craftsman unit. Glad it's not mine lol
 
34-36 total, with 12-14 initial should be well within the range of a 72-later 340 on pump premium. In fact, that should be about perfect.

So, just to cover the obvious stuff. Your plugs are new and a reasonable heat range (1-2 ranges colder than factory spec). Your plug wires are new, or nearly so, and of high quality (none of that carbon core crap). Your cap and rotor are new and of good quality (brass contacts, anti-arc ribs) and it is spotlessly clean inside. Spark plug wires are routed correctly and separated in factory clips or similar.

A vacuum gauge is good for setting idle mixture, but not absolutely needed. Here's my procedure: With engine off, run each mixture screw in all the way and count the number of turns, then back each screw out the average of the two plus 1/2 turn. This should be 1 1/2 to 2 1/2 turns out. Start engine and set idle speed to something reasonable, like 800 in neutral. Now counting the turns, tighten one screw until you can hear the idle just start to roughen and drop off, go back 1/4 turn. Repeat for other screw. Rev engine, allow idle to drop and do it again. This will get you a "lean best idle".

If you can either run the screw in all the way, or must open them more than 3 1/2 turns for the smoothest idle, something is wrong. You said you had 18-19 inches of vacuum? That's a lot for a 340 cam. If your cam has shorter duration than stock, you may be over advanced at low RPM. You could try backing it down a bit. Just make some sort of reference mark so you can put the dist back to where it is now if you should need to.
 
C130 Chief said:
34-36 total, with 12-14 initial should be well within the range of a 72-later 340 on pump premium. In fact, that should be about perfect.

So, just to cover the obvious stuff. Your plugs are new and a reasonable heat range (1-2 ranges colder than factory spec). Your plug wires are new, or nearly so, and of high quality (none of that carbon core crap). Your cap and rotor are new and of good quality (brass contacts, anti-arc ribs) and it is spotlessly clean inside. Spark plug wires are routed correctly and separated in factory clips or similar.

A vacuum gauge is good for setting idle mixture, but not absolutely needed. Here's my procedure: With engine off, run each mixture screw in all the way and count the number of turns, then back each screw out the average of the two plus 1/2 turn. This should be 1 1/2 to 2 1/2 turns out. Start engine and set idle speed to something reasonable, like 800 in neutral. Now counting the turns, tighten one screw until you can hear the idle just start to roughen and drop off, go back 1/4 turn. Repeat for other screw. Rev engine, allow idle to drop and do it again. This will get you a "lean best idle".

If you can either run the screw in all the way, or must open them more than 3 1/2 turns for the smoothest idle, something is wrong. You said you had 18-19 inches of vacuum? That's a lot for a 340 cam. If your cam has shorter duration than stock, you may be over advanced at low RPM. You could try backing it down a bit. Just make some sort of reference mark so you can put the dist back to where it is now if you should need to.
Click to expand...

The plugs and wires were installed last December. Plugs were autolite, I believe 65's. Wires are Taylor 8.2mm. I did the best I could to route them without touching eachother. Right now the idel mixture screws are turned out quite a bit. I tried turning them in but according to the vaccum gauge I was only reading around 14psi. The face of the guage shows around 17psi and above to be a normal running engine. You think I should re-adjust 1 1/2 to 2 1/2turns outs like you said and adjust the idel speed in conjunction to the mixture screws?

Thanks
 
I think that you should do what ever gets you the most vac, then turn them just a tad more. Mine are at 1 1/2 maybe 1/4 more were I got the best vac reading and I might have to re do it all after I mess with the timming
 
Both are right about carb screws. In a little from max vac is a lean idle but I think you want out a 1/4 to 1/2 past max vac for best throttle response. Next mark dampner at 0* tdc (ask how if you dont know) with that carb you are probably lean so I would suggest jetting up a bit 1 or two sizes to see if that helps. It wont run right being lean with too much (or the right amount) of timing If you want it to do a burnout unhook and plug the vac advance and try to lock out the mech advance in the dist (make the weights not move) and set the timing at 28* and if everthing else is right it will do a burnout and it will be alot crisper off idle post back with results good luck just my two cents
 
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