Motorcycle Repair: CV-40 MASTER KIT - REV 1 Yost Power Tube, yost power tube, slide spring

Question
Hi Mike, I’m respectful of your time but I haven’t seen this topic brought up in previous questions I’ve searched herein. I’m fitting a CV-40 in place of the original butterfly carb on my early production 84 FXR BT. (I already procured an a-mkt spigot manifold and a NOS SE air cleaner kit off eBay is on its way.) So in your opinion is the above subject CV-40 Yost kit worth the money and is it an effective performance enhancement when properly dialed in? I bought the kit for under $50 (returnable) but I’m sketchy about drilling the holes potentially ruining the slide. I also think that tuning may become complicated in achieving the best performing e-clip needle position and jetting? Would simply dropping in the tried & true Sportster needle and re-jetting for a basically stage 1 bike accomplish near or better performance at less time and cost? I also read that clipping 1 or 2 rounds off the stock slide spring improves throttle response similar to the SE CV-44 did back in the day? Any other tips and tricks you’d care to share? Thanks in advance for your reply. JR.

Answer
I have never used the Yost kit. I use the Dyna-jet kit. they are pretty much the same and do the same work. Yes, they really do help. they will give you more throttle responce and will richen the carb up where its suppose to be. I would not cut the spring, if you cut to much you will really hurt performance. Drilling the hole makes the slide move faster, thus a little more power.
Good luck and happy riding
Mike