I finally went and did it and it was a great decision. The increase in power is amazing and it noticeably improved throughout the range. My Predator Hemi has the usual billet rod, billet flywheel, governor delete, SS valves, 26 lb springs, milled & ported head, 10.5:1 static compression ratio, Black Mamba Jr cam, and pipe. I built it last year and ran a jetted stock carb (40.5 main & 18 pilot). It did well and had plenty of power. It also seemed to run out of steam at ~6600 rpm, just wouldn't pull much after that. This was sufficient to get my bike and 230 lb self up to 50 mph pretty quickly but I suspected there was more performance to be had. I recall looking at the stock carb while porting the head and thinking that the carb was going to hold the engine back from it's full potential. This certainly was the case.
I purchased the NR Racing "Chikuni" kit with short adapter. Jetting is 130 main and 15 pilot. Now it keeps pulling and I'm not sure where it tops out. It is so scary that I don't think I will ever find out what it's capable of. Going from part throttle at 30 mph to wide open pulls the front wheel off the ground. This occurs with me seated forward and leaning over the handlebars. It's terrifying.
One of the problems that plagued the stock carb has been corrected. It had less than 1/8 turn from idle to full throttle with my direct linkage. While I got used to that, it did make for a twitchy ride. The Mikuni throttle setup has 3/8 turn from idle to full throttle. It seems a lot calmer until you go WOT.
I had a year to think this through. Initially I wanted to go with a VM22-133 "real" Mikuni. After lots and lots of reading I concluded that I like the "Chikuni" more because of its popularity/availability, lower weight, smaller physical size, and readily available jets. I'm glad I made this decision. Upon opening the box, I was greeted with a beautiful part. The castings are of excellent quality. Fit and finish is spot-on. You read a lot about folks having trouble getting these setup. That was not my experience. I opened the bowl, verified the float level, and installed the 130 main jet. It came with the 15 pilot already installed. Based upon various readings I concluded that the 15 pilot was a good place to start with a modified engine. It seems a little rich at idle and I may install the 12.5 pilot when it warms up outside. Adjustments involved placing the bike up on wood blocks to get the rear wheel off the ground and alternating between the throttle screw and the air bleed screw. It was a brief iterative process that took less than five minutes. With the idle where I wanted it, I took it for a spin. Throttle response is great - no lag, no hesitations throughout the range. And of course, the power is outrageous. Not a little improvement, a huge improvement. Oddly enough, the engine has a sharper exhaust note and the cam chop is more pronounced. Sounds absolutely beastly now.
I regret not doing this sooner. If you were on the fence about the Mikuni, just do it. You will not be disappointed. When you have a little motorcycle, running a lawnmower carburetor does not make a whole lot of sense.
-Ray
I purchased the NR Racing "Chikuni" kit with short adapter. Jetting is 130 main and 15 pilot. Now it keeps pulling and I'm not sure where it tops out. It is so scary that I don't think I will ever find out what it's capable of. Going from part throttle at 30 mph to wide open pulls the front wheel off the ground. This occurs with me seated forward and leaning over the handlebars. It's terrifying.
One of the problems that plagued the stock carb has been corrected. It had less than 1/8 turn from idle to full throttle with my direct linkage. While I got used to that, it did make for a twitchy ride. The Mikuni throttle setup has 3/8 turn from idle to full throttle. It seems a lot calmer until you go WOT.
I had a year to think this through. Initially I wanted to go with a VM22-133 "real" Mikuni. After lots and lots of reading I concluded that I like the "Chikuni" more because of its popularity/availability, lower weight, smaller physical size, and readily available jets. I'm glad I made this decision. Upon opening the box, I was greeted with a beautiful part. The castings are of excellent quality. Fit and finish is spot-on. You read a lot about folks having trouble getting these setup. That was not my experience. I opened the bowl, verified the float level, and installed the 130 main jet. It came with the 15 pilot already installed. Based upon various readings I concluded that the 15 pilot was a good place to start with a modified engine. It seems a little rich at idle and I may install the 12.5 pilot when it warms up outside. Adjustments involved placing the bike up on wood blocks to get the rear wheel off the ground and alternating between the throttle screw and the air bleed screw. It was a brief iterative process that took less than five minutes. With the idle where I wanted it, I took it for a spin. Throttle response is great - no lag, no hesitations throughout the range. And of course, the power is outrageous. Not a little improvement, a huge improvement. Oddly enough, the engine has a sharper exhaust note and the cam chop is more pronounced. Sounds absolutely beastly now.
I regret not doing this sooner. If you were on the fence about the Mikuni, just do it. You will not be disappointed. When you have a little motorcycle, running a lawnmower carburetor does not make a whole lot of sense.
-Ray