Help no spark!

[Eagle Keeper]

Well I just finished installing the engine after a top end rebuid. Engine cranks fine but it wont fire up! I'm getting fuel but no spark. I can hear the CD box humming away. Any ideas!?!?!?

[McDaniel]

Check timing, check correct wires on correct plugs. Check
coil wire to dist. Check that connectors are down and tight
on plugs.
I'd try one thing at a time...no point in doing more if the first
thing you try fixes it. Also give you an idea what to check
if it happens again.

[jmohn]

Also:
check connection at CD box
check connections to coil (properly connected?)
check "signal wire" to distributor (tends to break internally, I've been told)

Jerry M
'78 SC

[Eagle Keeper]

Thanks for the replys! I've tried everthing listed! Now I'm leaning to the coil because the CDI is humming away. I did all the voltage tests and everthing is good at the connector at the base of the CDI. But still no spark!!!

[Early_S_Man]

Jason,

All the CDI-unit whining signifies is that it has power and the DC-to-DC converter circuit is working ... it doesn't mean the unit is getting a trigger signal, or that the trigger signal is being processed!

Did you check for continuity through the 600 Ohm pickup coil at the CDI-unit connector? If it is good ... check for low-level AC signal [less than 1 Volt peak-to-peak] while cranking with DMM set on AC Volts, Hz scale, or oscilloscope ... at the CDI-unit connector terminals #7 & #31d ... as shown in the following diagram:

[Eagle Keeper]

I did that ck I was getting the correct readings. I'm leaning to the coil because it's cheaper!!! But it could be the CDI.

[boon-dawg]

hey bud, i have a 70t, had the same problem and it turned out to be the points.

[Early_S_Man]

Jason,

That was TWO tests:

1. 600 Ohms +/- 10 % at terminals #7 & #31d

2. 200 mV AC signal at terminals #7 & #31d during cranking or while turning removed distributor by hand

The only way to rule out the CDI-unit is to measure the 350 Volt to 460 Volt pulses at terminal 'A' of the coil ... with a scope, while cranking!

[Eagle Keeper]

Warren,

I didn't do the Ohms ck but I did do the mV ck on the distributor with the distributor removed and with it installed. I did get a slight drop when I was measuring it through the harness compared to when I was going straight off the distributer.

[jeff m]

You can use a 600v neon to test for output from CDI to coil
Get from Radio shack (called Tandy in UK)
and put a "clamp on" timing light on HT lead from coil to dizzy.
That'll prove it real quick.
Jeff