Timing question... pinging?

springer · 05-22-2003, 06:38 AM

Still working on finishing up with a rebuild on my 78 SC. I am setting the timing and am having a bit of difficulty. The engine was running rough, but running steadily and is now a bit better by changing from 40 degrees ATDC to around 15-20 degrees ATDC. The problem I am having is as soon as I twist the distributor closer to TDC it starts making a popping noise which doesn't seem to fit the description of pinging (although I haven't any experience with pinging). It is idling at 950. When set closer to TDC it sounded smoother but was popping consistently every couple seconds.

Any ideas?

MotoSook · 05-22-2003, 06:41 AM

You are on the wrong side of TDC. Stock is 5 deg. BTDC at idle and 26 deg. at 6000 RPM. Plus or minus a couple

I run mine w/o vacuum advance and set for total advance of ~31 degrees. That's about ~10-12 degrees at idle.

springer · 05-22-2003, 06:45 AM

Souk,

Thanks for the input. I know that I am on the wrong side. Problem is as soon as I turn the distributor to get the mark on the BTDC side it starts making this popping noise.

1fastredsc · 05-22-2003, 06:46 AM

I think with that much retard your actually hearing the combustion still taking place after your exhaust valves are opening in the cycle.

MotoSook · 05-22-2003, 06:51 AM

Where are you setting it on the BTDC side and are your plug wires correctly installed? I never assume I'm right when it comes to ignition (hate those damn electrons), so I always double and triple check.

If you can't get the static setting right, play with the gearing of the distributor. My static setting seems to be right when I install my dizzy, but for some reason, I have to rotate the thing on notch to get it right, then time with a light.

Good luck.

springer · 05-22-2003, 06:55 AM

That makes sense. I'll keep twisting it until it is BTDC and we'll see how that goes.

springer · 05-22-2003, 07:04 AM

Souk,

It almost seems like a may have to rotate it a notch on the gear to get it BTDC. On on end of the play in the adjustment on the dizzy it is at around 40 degrees ATDC. Didn't rotate it all the way to the other end because it started popping but I'll try that next and see if I can get past the popping to BTDC. I was just trying to get it set to 5 degrees BTDC.

I double check the wires and they are connected right but I'll check again just to be sure.

Thanks

MotoSook · 05-22-2003, 07:09 AM

Yep! Sounds like my problem..may be common for the 78SC motors. I thought at one point the builder had done sonthing wrong, but when I rotated the dizzy one notch the car runs so well I stopped fussing with it. I won't drive myself nuts with paranoia (frequent occurance).

Good luck!

springer · 05-27-2003, 08:03 AM

Quote:

Originally posted by 1fastredsc
I think with that much retard your actually hearing the combustion still taking place after your exhaust valves are opening in the cycle.

Okay, so I set it at 5 degrees BTDC but it is still making popping noises. If I twist it far enough BTDC to not make the noise it barely idles. If I twist it ATDC it runs and idles better. What am I doing wrong?

Rot 911 · 05-27-2003, 08:07 AM

What Souk and Springer are trying to tell you is that you might be off by one gear on the distributor drive gear.