Computronix Ignition

[So Cal Mark]

here's a demo of how easily the twin cam starts when equipped with our Computronix ignition and an EMPI carb. The engine was stone cold after sitting overnight.
http://youtu.be/dH4BEAhliLs

[RRoller123]

Nice! Mine will be installed over the next few days, when the rain stops!

[70spider]

What size motor is that? I noticed your idle is extremely smooth and it looks like it is idlling @300 rmps, nice!
My 70 with a 1438 has a slightly rough idle and idles @850 rmps. It has an old school electronic igniton on it but the PO has got wires all over the the place, including one jumping straight of the fuse box to the balast resistor, see my post: http://www.fiatspider.com/f08/viewtopic.php?f=6&t=26598
I haven't finalized the timeing, only did it by ear, waiting for the good title from the PO so I can drive it to the shop.
I also like the exhuast note, sweet .
Pesto

[Holshot]

That's incredible Mark! Nice job... I just watched the whole video with the empi and weber shoutout on your website and was thoroughly impressed. If I had a carb car I would certainly be buying that entire setup, looks and sounds great!

[So Cal Mark]

it's an 1800 with a tach that isn't very accurate at low rpms. It idles about 800rpm

[aj81spider]

I have one on my 74 and love it. I do have one question though. The instructions say not to use a dial back timing light. Being a complete novice - how do you time it? If I run at say 3500 rpm I can see the timing is well off the 0 and 10 degree marks, but where it is exactly is a guess.

The engine is running well so it's not an urgent thing, but it would be useful to know.

[harmon30]

Mark, I noticed that your oil pressure gauge did not move when the engine was running. Is it connected?

[seabeelt]

I love mine as well. That coupled withthe gear reduction starter makes you think you have a new car.

[So Cal Mark]

you can check timing at idle, but using a light to check the advance won't work since it's a waste spark system. If you want to check your total timing it would be best to mark the pulley.
As for the oil pressure guage, that one had a defective sending unit. The warning light was working though

[phaetn]

I, too, have the CompuTronix and am about to check timing. I can see the indicators on the timing belt cover and the pulley.

Will it not work at higher RPM just because the strobe will be lightning so often that it doesn't help to make things look still and I will just seem almost always on? I just have a simple type light with no dial back option.

By marking the pulley do you mean putting white out or paint on the mark so it is easier to identify its location relative to the degree indicators? Then can one use the strobe at 3500RPM?

So what else to do to check advance? Would you suggest tuning by ear?

I guess first things first is that I should establish that TDC is, in fact, where the pulley mark indicates it is and, if not, make a new mark...

Are there any specific setting for timing with the CompuTronix, or do I just use the known settings for the engine (e.g. 0 degree from TDC at idle for a '74 1800)?

Thanks and cheers,
phaetn

[So Cal Mark]

set your initial timing at 12btdc. The unit will provide 20 degrees of advance. The light will flash double since it's a waste spark system. If you don't have a dial back light, mark the pulley at 34 degrees and you can check total timing with your light

[Daniel]

In case you dont understand what waste spark system means, the spark pulse sent to each plug fires 2 times this
happens because the coil packs are share between 2 spark plugs.

On the timing light i thought i read somewhere on the site it could be used by playing with dial back setting but
I've never installed one of these dizzys. I read up on it and like the simplicity, performance and size. Not sure
if I will use one on my motor or not I'll cross that road soon.

[phaetn]

In case you dont understand what waste spark system means, the spark pulse sent to each plug fires 2 times this happens because the coil packs are share between 2 spark plugs.

Yup, thanks. I understand that two sparks are firing at the same time, even though one won't be at the top of the compression/power stroke so on that cylinder it's just igniting nothing towards the top of the exhaust stroke.

set your initial timing at 12btdc. The unit will provide 20 degrees of advance. The light will flash double since it's a waste spark system. If you don't have a dial back light, mark the pulley at 34 degrees and you can check total timing with your light

Thanks, Mark. I'll do that. I wasn't sure if I was supposed to follow 0 btdc as per the original engine specs, but I guess that's all for the old distributor setup. I'll check TDC positioning, then mark the pulley for 12 and 34 advance.

Next step: Hunt for a printable degree wheel online...

Thanks and cheers,
phaetn

[Ptoneill]

Next step: Hunt for a printable degree wheel online...

Can't you just use a simple plastic protractor by putting the TDC Mark at zero?

[phaetn]

Possibly. I figure I can just expand this in a graphics app as needed, and then put it right on the pulley for maximum accuracy. Something like this.

See this related thread where DocGraphics has a very elegant solution where he even made his own new fixed pointer affixed where the belt cover used to mount:
http://www.fiatspider.com/f08/viewtopic ... el#p198670

Cheers,
phaetn