timing mark jumps around when using timing light

trying to adjust (and/check) timing on my tomos a35 with cdi....borrowed a timing light that is supposed to work fine, hooked up to car battery, lead on to spark plug wire, spark plug pulled and grounded, flywheel turned with a drill....mark i made to find when spark is firing jumps around all over the place....thought i had it once...stoppeddrill to get my sharpie, tried it again and the mark was jumping around again....any ideas, advice, what am i doing wrong?

Re: timing mark jumps around when using timing light

Have you tried it while running? The cdi will change the timing slightly based on the rpm. Not sure what the cdi will do when turning it at way less than running rpm (drill speed).

Re: timing mark jumps around when using timing light

That low rpm is likely your problem. The charge speed of the coil and cdi are slower and not consistent.

Re: timing mark jumps around when using timing light

Yeah, do it while its running.

Re: timing mark jumps around when using timing light

thank you for the insight...its a kick start....what do you recommend....for startinging it....or should i put it back together and start it and disassemble again....

Re: timing mark jumps around when using timing light

Start it with the drill

Re: timing mark jumps around when using timing light

ok cool....thought that would work....thnks

Re: timing mark jumps around when using timing light

you can take the spark plug out and just turn it over with a drill, too... most of the time that is easier.

got to get to about 500 rpm to get a consistent spark.

Re: timing mark jumps around when using timing light

You can start the engine without even having the whole transmission, just give the flywheel a kick.

Re: timing mark jumps around when using timing light

Make sure the spark plug body is grounded if you have it out while spinning the engine over.

Re: timing mark jumps around when using timing light

Great thank you for all the knowledge/advice....did it with motor running....worked great

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