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Ignition interfering with dyno

Sportster Motorcycle Engine Conversions - The Sportster and Buell Motorcycle Forum - xlforum.net
I was going to title this thread "I Hammered my bike and it broke the dyno!" but I resisted the temptation.

Anyone have any tips for reducing ignition interference with a dyno's computer?

After a Hammer performance build and break-in miles, I connected with a friend at a small indy motorcycle shop where I used to work as a mechanic for some dyno time. I mostly wanted to check jetting, rather than beat on the engine to find out peak HP numbers. I was able to make one modest pull that resulted in a valid HP, TQ, and A/F curves. I made one carb adjustment (down to 165 from 170 main jet) and set up for a more aggressive pull. However, as soon as I got on the throttle hard, the computer locked up. Trying again a few times, the ignition signal would apparently drop out, and the RPM reading wouldn't increase, making me think the timing-gun style pickup attached to my spark plug wire wasn't working. My buddy said that this sometimes happens and he's not sure why. I am running resistor plugs, and added 5 ohm resister spark plug caps as well, but to no avail. I am running a TC88 with custom map from this site, and a stock coil and wires. My friend thinks that aftermarket ignitions send off so much interference that it screws with the computer.

Anyone ever run into this problem and come up with something that solves it? Moving the computer as far from the bike as possible? Shielding the plug wires or the pickup wire with a foil sleeve?


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