Toro CCR2000 Suzuki 2-cycle Ignition Problems Reposting

Reposting old forum thread, since still cannot fix.
I have a Toro CCR2000 2-cycle snowblower with a spark problem. I have tested for spark using a timing light with the plug grounded, outside the hole. Good spark observed. However, upon inserting the plug and rechecking for spark, there is no spark at all. I have repeated this process several times. With the plug just grounded to the frame, good spark. With the plug inserted, no spark at all.

I repeated testing as above again using a new NGK spark plug, cleaning coil mounting contact points, bypassing cutoff switch without the fuel tank installed. The results were the same.

Any ideas on what tests to do or procedure to use in isolating the problem would be much appreciated, as this is baffling to me.

 

The main thing that changes with the plug in or out is the speed you can turn the engine. Are you turning it at cranking speeds? If so, something else that changes is air density. If the spark is marginal, it may not be able to jump the denser air in the plug gap with the air under compression. Make sure the coil gap is correct, the coil is clean and well grounded at the mounting points, and unplug the kill wire from it and try again. If still no spark, I'd say it's the coil.

Edit to add... I believe this engine has a spark plug boot that unscrews from the plug wire. I think this has a resistor built in. Maybe try unscrewing this boot and touch the wire directly to the spark plug to eliminate the resistor in case it is bad, and test again. If it works, then you know the boot is bad.

 

I believe what Cheese is pointing out on the air density in/out of the combustion chamber is determining your spark/no spark. Air actually has mass, but no conductivity to it = resistance. Under compression the resistance increases so a spark that moves across the plug gap outside the engine can't make it across the same gap in the combustion chamber. Probably your coil is weak or the lead is bad.