View Single Post
Old 01-16-2013, 03:41 PM   #35
Cheesehead Klompen
Andyvh1959's Avatar
Joined: Feb 2012
Location: Da frozen tundra eh? 1.5 mile west of Lambeau
Oddometer: 735
Newest update on the CDI replacement on my GN400 ice racer/flat-tracker:

The combo CDI/COIL unit proved out to not produce enough spark energy to do anything more than just idle slowly, with the plug gapped at only 0.015". Generally speaking, a coil must produce about 1000 volts output per 0.001" of plug gap. So for the typical 0.025" spark plug gap the coil must output about 25,000 volts. Well, I proved the combo CDI/COIL unit I was testing could only produce maybe 15,000 volts. Enough to make it idle but it would not run on ANY addition throttle.

So I went back to the stock Suzuki coil, fired by a Honda CH250 scooter CDI, using the P1 pulser (red/green wire from the timing plate) signal for 10 degree BTDC static/idle timing. Plug gapped at 0.025", bike fired easily on one kick stone cold. Idled out steadily nice, right away, on the Mikuni VM36 round slide carb I mounted. I played a bit with the carb tuning, have the needle on the middle clip position. I did find out I was using the P2 trigger signal to the CDI previously. Doing that advanced the static timing to 25 degrees BTDC. NO WONDER the damn thing was kicking back SO hard!! Now with the P1 trigger to the CDI it kicks easy and starts right off.

I have heard from some tuners that using the CH250 (Elite scooter) CDI causes the bike to run hotter because of the internal advance curve in the digital CDI. Not sure I agree with that. The bike is using the P1 trigger signal for idle timing and the advance on the CH250 CDI doesn't start until about 2500 rpm. More to come one I get the bike on the ice to test it out. Sure looks cool for a lowly GN400 doesn't it?
When life throws you a curve,.....lean into it!
42+ year rider, 22+ year MSF Coach, Street, Dirt, Ice, ride em all!

Andyvh1959 screwed with this post 01-16-2013 at 04:10 PM
Andyvh1959 is offline   Reply With Quote