Timing Question - Carb '02 with tii Mechanical Distributor

[72MetallicMalaga]

Quick timing question, i'm a little confused.

 

I have a:

 

• '73 M10 with dual DCOE 40s
• tii style mechanical distributor
• Pertronix II ignition
• E21 5speed (i can see the bb on the flywheel)
• I have an advanced timing light, where you can "dial back" digitally.

 

When I set the timing ball in the flywheel, do I set it with the carb'd 1500rpm rule or tii 2500rpm rule? Is it method of fuel delivery dependent or distributor style dependent?

['76mintgrün'02]

8 minutes ago, 72MetallicMalaga said:

I have an advanced timing light, where you can "dial back" digitally.

 

Yay!

 

9 minutes ago, 72MetallicMalaga said:

When I set the timing ball in the flywheel, do I set it with the carb'd 1500rpm rule or tii 2500rpm rule?

 

Nah.

 

9 minutes ago, 72MetallicMalaga said:

Is it method of fuel delivery dependent or distributor style dependent?

 

 

Yes.

 

 

The BB on the flywheel represents 25 degrees before top dead center.  TDC is marked on the flywheel as well with a little line marked OT.  I recommend painting the little line and the BB to make them easier to see.  The tip of a bamboo skewer dipped in paint works well as an applicator.

 

I'd ignore the BB at XXXX rpm process for now and set the timing based on the total advance you want and then see what that leaves at idle.  You can either use the BB or the OT line to set the total advance.  If you use the BB, you just add 25 degrees to the number you set the light to.  If you want 38 degrees total advance, you can set the light to 13 degrees and rev the engine beyond the all-in rpm and then rotate the distributor until the BB lines up with the driver's side edge of the oval hole.

 

Then you can reset the light to zero and let the engine idle and use the light to check the advance at idle, by adjusting the timing on the light until you see the OT mark aligned and that's your idle advance.

Make sense?

 

Tii engines require less advance than carbed cars because they do a better job of atomizing fuel.  Side drafts like a fair bit of advance at idle.  Hopefully, you'll have 12 degrees or more at idle with the advance set to 38, or so.

 

Tom

[72MetallicMalaga]

Ok that makes much more sense now, but now I have a few more questions:

 

• At the moment, I can see the BB with the Timing Light set at 18 degrees. Does that mean I have 43 degrees total advance? The car runs and idles fine with this setting, seems like a lot.
• How do I determine "all in rpm"? When the BB stops moving even if I rev the motor higher?
• Do you just use the idle speed screw to keep the RPMs consistent during measurement?

 

Thank you so much for your help here, things are starting to click.

Edited September 25, 2022 by 72MetallicMalaga

['76mintgrün'02]

1 minute ago, 72MetallicMalaga said:

At the moment, I can see the BB with the Timing Light set at 18 degrees. Does that mean I have 43 degrees total advance? The car runs and idles fine with this setting, seems like a lot.

 

At what rpm?

 

1 minute ago, 72MetallicMalaga said:

How do I determine "all in rpm"? When the BB stops moving even if I rev the motor higher?

 

Yes.  When the distributor has stopped advancing the timing it is all-in.  If that happens at 3k rpm, then you can set the total advance at any rpm above that.

 

3 minutes ago, 72MetallicMalaga said:

Do you just use the idle speed screw to keep the RPMs consistent during measurement?

 

Some people do.  I made a little wedge out of wood that I slipped in under that screw, so I did not have to change that setting, I could just push the shim in, or pull it out to set the speed.

 

I like to set the timing on the light and then rev the engine until the mark lines up and note the rpm; rather than doing it the opposite way, where you set the speed and then hunt with the dial on the light.  It is much quieter.

 

Tom

[72MetallicMalaga]

Oh sorry forgot to mention, at about 1500rpms I see the BB with the timing light set at 18 degrees.

 

Yes ok great, this makes sense now. I'm going to play around with the timing tomorrow morning and if I have more questions, i'll follow up in this thread.

 

Thank you again.

['76mintgrün'02]

6 minutes ago, 72MetallicMalaga said:

Oh sorry forgot to mention, at about 1500rpms I see the BB with the timing light set at 18 degrees.

 

18 minutes ago, 72MetallicMalaga said:

Does that mean I have 43 degrees

 

Yes, but you probably have more than that at higher rpms.

 

Do you know what pinging sounds like?  That is one indicator of too much advance.

 

38 total should be safe, but it might not leave as much as you want at idle... depending on how much advance the distributor offers.

 

Side question -- are your plugs gapped to spec. ?  (.024"-.028")  Bigger gaps can make for crappy idling.

[72MetallicMalaga]

Yeah there is no pinging at all, let me double check and ill post a pic tomorrow…maybe my memory is serving me incorrectly.

 

The plugs are gapped right around .025”

[Hans]

38 all in is a bit on the high side for a street motor, depending on CR and fuel quality. I use 33  all in at about 3000rpm. You could try increasing slightly from there listening for pinging (which is hard to hear with dual webers). YMMV

[cda951]

Because you have a digital timing light, you should paint a TDC mark either on the flywheel or the crank pulley and use that instead of the ball. This will make it much easier to determine the actual ignition timing without any math. My tii has a TDC pointer for the crank pulley on the timing cover, and your engine may also have one. This is more important on a tii because the flywheel window is partially obscured by the intake plenum. 

['76mintgrün'02]

 

 

 

Prescribing timing advance is beyond my pay grade.  I shouldn't have suggested a number.  I have 38 all-in (+ vacuum advance) on my engine now, it's a low(er) compression '76 engine with a 32-36 carb and stock #5 camshaft.  That leaves me around 10 degrees at idle.  I've shortened the curve in my distributor, to bring the idle advance up, without needing to go higher at the top end.  It's tempting to do that again.

 

It is a balancing act, between idle advance and all-in.  All-in rpm is dependent on weights and springs (only) and rotating the distributor won't affect that.

 

When distributors wear, they tend to give more advance and it comes in sooner, due to wear at the pivots, stopping/pushing surfaces and springs worn thin (on the old style), or stretched.

 

You can plot the curve with your adjustable light. 

 

 

 

 

[Mark92131]

Your car is setup like a Ti with those dual webers, but by using a "Tii Style" (aka IE?) mechanical distributor may not get you a Ti curve for your motor.  The factory Ti (026 & 033 Distributors) seemed to like a lot of advance early (25 degrees BTDC at 1500 or 2000 RPM respectively) and mostly all in by 2500 to 2700 RPM (39 and 30 degrees BTDC respectively.  Apparently, your motor seems like it can handle more advance (43 degress BTDC at 1500 RPM) without pinging.  I concur with the recommendations, use your adjustable digital timing light to plot the curve of your distributor and adjust your all in timing to 38-39 degrees BTDC and see where your Idle advance ends up.

 

Mark92131

 

 

[Hans]

Keep in mind that the ti advance of 39 was designed around fuel availability in 1970s Germany, i.e., leaded 98.

I have a ti motor with 40's and the tii style dizzy. 33 to 35 gets me about 10 at idle.

 

[72MetallicMalaga]

Alright, finally got around to setting timing today.

• I set the timing gun to 8 deg and found the pressed in BB in the flywheel hole at 2600 rpms (all in for my motor), totaling 33 deg advance btdc.
• At idle (around 980 rpm), I used the crank timing mark/pointer and ended up at 8 deg of advance tdc (picture).
• All in timing seems to be at 2500rpms, the BB doesn't move after that point when I move the distributor idle speed.
• My dwell is at 90 deg (picture). I have a Pertronix II, non adjustable plate.
  • Is this typical? Nothing you can do about the dwell on electronic ignitions, right?
• I posted a video of the motor running, other than typical valve chatter, everything seems OK?
  • I need to correct myself from earlier, I know what knocking sounds like, but I don't know what pinging sounds like. Do you guys hear anything from the video? There's a couple links below the images.
     

 

 

IMG_5090.MOV

IMG_5088.MOV

Edited September 29, 2022 by 72MetallicMalaga

[cda951]

Pinging or spark knock will never occur at idle, only during periods of heavy load/acceleration. It can be difficult to hear with DCOEs and/or loud exhaust, but sounds like a bunch of ball bearings rattling around in a coffee can, if that makes sense. 

 

Here is one of the better articles about the subject:

 

http://944enhancement.com/html/knock_ping.html

[Hans]

And in the extreme, it can damage your motor.