125-200cc Keihin vs. Mikuni for 150

Well I am commited to the Mikuni as I just dropped $115 into it. I took it to RB Designs and got the divider plate, air screw, and he did some low speed circuit mods. I hope it works well.

IMS warrentied my tank. New Tank on the way. Looks like I will be using the MotoZ tires again for the Nat'l Enduro. Rocky and maybe wet (per extended forcast). So the slightly oversized rear tire won't be a major issue. Maybe a help. Only seems to be an issue in deep sand / loose loam, otherwise they work pretty good. I have a set of Pirelli on standby incase the conditions change . Probably will be installing some of Walts modified PVs this weekend. They may help the bike pull the oversized tire also.

Good move!

I hope it works well and more consistant than mine did. For just $100 more you could have gotten a 36mm PWK Airstriker. Why Mikuni can't design a carb that works as well , I don't understand. I never had any issues jetting a VM roundslide. Infact that is my prefered carb for my vintage bikes.

I say pick a carb and tune it to your preference, your riding style and what you want it to do.

A carb is $200 plus the slides, plus the needles, plus the jets and etc.... and next thing you know your up to $400. Sometimes your settings don't work for the next guy. He's running race gas, different oils, different ratios, different temps, different elevations etc.......

I have 2 carbon copy TMXX's that I am running between 40 degrees and mid 70's without touching an airscrew, pilot or main.

I have 2 PWK 38's that are pulling as strong as the 36 on bottom and I am close to getting them to run up top like the TMXX. My goal is to keep pushing them up top and not loose bottom/mid performance.

Some of it is in the powervalves, mass production engines, pipes, and ignitions.

If I put my stock 125 on the dyno with all the different carbs. You'd look a the graph and pick a carb for what you wanted it to do for your performance/riding range.

Hopefully, next winter I can take a stock Wr 125/Cr 125 and dyno all the carbs/ comparisons.

I did not want a 36mm PWK. I had one on my previouis Husky and have a 38 that I bought for my current one. It worked OK but is just much longer then then the stock carb and I don't like that.

I was considering buying a PWM like you have Vinduro but the Mikuni seems to work fine so I'm going to stick with it for now. My hope is that with the air screw and the low speed circuit mods it will be easy to keep the Mikuni working well.

i wish i had time for our bike to be down so i could send my Mikuni to RB.

It's a lot faster when RB is 2 miles from your house

Did you try the carb out yet?

I tried the carb out. The bike had some of Walts power valves in it also. I also put a fresh ring in.

Anyway, RB told me that I might have to lean the pilot jet one step. It was a bit lean with the 35 so I thought a 32.5 would be plenty lean. I was wrong as the bike is still real rich right off idle. At that point I was pissed because I had basically wasted a day of tuning since I did not have a leaner pilot. The divider plate and the power valves mainly change the very low end but I could not really tell much with it being rich.

The bike does have a very powerful yank from down low though. It will get going with zero hesitation. With the first 1/8 throttle too rich though the bike was a bit of a handfull on hills as I could not chug off the bottom smoothly.

I will get some leaner pilots and try again.

My Mikuni is off to RB Designs so I pulled the 38 Keihin PWK from my YZ-250. It has the TPS sensor and a solenoid enrichening valve on it. Can I use it anyway? The jetting is actually pretty close from what I've read.