If you're new to YS, I suggest you get a 175 cdi but run it with a glow plug to get used to the motor. I have been running the 170 cdi since 2009 & the 175 cdi before the end of last year, and here are my observations. The cdi does have the advantages of saving more fuel, better mid range transition & slightly better top end. However, you will be dealing with the following:-

1) Weight - about 100g

2) Spark plug - you need to check the gap about every 40 to 50 flights or once it started to misfire. I suggest using either a Rimfire VR-2 or a NGK ME-8, instead of the stock YS plug. If you're using the YS plug, be sure to file the tip of the electrode to a slightly pointed shape

3) Spark plug cap - can get loose, or the rubber insert inside the cap can get brittle causing it to misfire. Also, be sure to zip tie the cap wire so it will not be flopping around during throttle advancement

4) cdi box - can be an issue sometime

5) Runs hotter than the non cdi version - make sure you have good ventilation on your bellypan or nose pan with large enough entry & exit holes, plus gluing some foam on the nose section to force cold air directly at the pump, the valve cover & the crankcase fins

The reason why the cdi gives such good mileage & smooth transition is because the cdi unit keeps monitoring & changing the timing of the engine. Therefore, it almost always fire at the Top Dead Center, leading to more efficient run than the non cdi version. In addition, you can run the engine much leaner. Normally, my non cdi runs at 1-3/4 to 2 turns on the high needle, but with the cdi, you lean it down to about 1 turn. However, with the engine running so lean, it makes the cdi version runs hotter than the normal version. Also, the needle adjustment is much more sensitive, one to two clicks more can cause the engine to run lean. You need to get used to the power delivery, & recognize when the engine is running lean so you can richen the needle.

As mentioned earlier, you can run the cdi with a glow plug first, just open the needle more. After you've completely understands on how the needle & the pump operates, than you can add the cdi unit.

If you have any additional question, feel free to post or PM me.

Good luck,

Adrian