After getting my Mikuni (Chikuni) carburetor sorted out last winter/spring I have been enjoying the new-found performance. It works really well with my build and rideability and throttle response is vastly improved over the stock re-jetted Predator carb. I used the air filter provided with the NR Racing Chikuni carb kit. The filter length (not including mounting flange) is 3-7/8" long by 2-7/8" in diameter. This provided plenty of filter surface area to feed my hungry engine. The problem was it stuck out far enough to be, well, a problem. Myself or others would invariably walk into it and cause the mounting flange to tear which would render the filter unusable:
The filter flange is foam core and not tolerant of the shear forces created by someone walking into it. They only cost 8 bucks but then there is shipping and the replacement is no better than the one it is replacing. After going through three of them I decided to try a different filter:
This conical pod filter looked promising until I took a close look at the mounting flange:
The flange reduces the diameter significantly and I suspected it would impose a restriction. During the test ride the engine would pull to ~4500 RPM and then start sputtering, falling on it's face. Further analysis revealed that the restrictive filter flange actually blocked some holes below the carb inlet whose function I do not recall, but I'm sure they cannot be blocked for proper carb function. This thing is essentially useless. I spent some time searching the internet for a suitable replacement but found the choices limited to cheap junk and expensive K&N filters. It took some time to accept the fact that I needed a $50 filter for my (initially) $100 engine, but considering that I have about $500 into the $100 engine, the pain was reduced. The present solution is the K&N RC-0330. This filter measures 4-1/2" OD by 1-1/2" tall (not including the mounting flange). It has an offset mounting flange that allows the filter to sit lower and it certainly does not stick out nearly as far as the original kit filter. The flange material is rubber and seems sturdier than the kit filter. Oh, and the chrome cover adds some bling:
While this filter has less filter surface area than the original kit filter, testing has proven that it does not impose a restriction. Almost seems like the bike has a bit more power however the butt dyno is not the most accurate. While swapping out the filter I took some time to eliminate the Mikuni fuel bowl vent and drain tubing. When draining the fuel bowl I always disconnected the tube and placed a cup beneath the fuel bowl drain outlet. That tube served no purpose so it was axed. The fuel bowl vent tube was cut down and a small filter was attached which seems much cleaner:
Anyway, that's all I got. Anyone else free to post your Mikuni air filter solutions. I'd love to see/hear about them.
-Ray
The filter flange is foam core and not tolerant of the shear forces created by someone walking into it. They only cost 8 bucks but then there is shipping and the replacement is no better than the one it is replacing. After going through three of them I decided to try a different filter:
This conical pod filter looked promising until I took a close look at the mounting flange:
The flange reduces the diameter significantly and I suspected it would impose a restriction. During the test ride the engine would pull to ~4500 RPM and then start sputtering, falling on it's face. Further analysis revealed that the restrictive filter flange actually blocked some holes below the carb inlet whose function I do not recall, but I'm sure they cannot be blocked for proper carb function. This thing is essentially useless. I spent some time searching the internet for a suitable replacement but found the choices limited to cheap junk and expensive K&N filters. It took some time to accept the fact that I needed a $50 filter for my (initially) $100 engine, but considering that I have about $500 into the $100 engine, the pain was reduced. The present solution is the K&N RC-0330. This filter measures 4-1/2" OD by 1-1/2" tall (not including the mounting flange). It has an offset mounting flange that allows the filter to sit lower and it certainly does not stick out nearly as far as the original kit filter. The flange material is rubber and seems sturdier than the kit filter. Oh, and the chrome cover adds some bling:
While this filter has less filter surface area than the original kit filter, testing has proven that it does not impose a restriction. Almost seems like the bike has a bit more power however the butt dyno is not the most accurate. While swapping out the filter I took some time to eliminate the Mikuni fuel bowl vent and drain tubing. When draining the fuel bowl I always disconnected the tube and placed a cup beneath the fuel bowl drain outlet. That tube served no purpose so it was axed. The fuel bowl vent tube was cut down and a small filter was attached which seems much cleaner:
Anyway, that's all I got. Anyone else free to post your Mikuni air filter solutions. I'd love to see/hear about them.
-Ray