People complain about how hard the FCR is to jet correctly

37mm Keihin FCR Carb - KLX/KLR 125/140/250/300 - ThumperTalk

But some have succeeded

http://www.thumpertalk.com/topic/948...d-fcr-klx-300/

 

Most of the pics I've seen looks like it's a nightmare to get it to fit because of the added height. I'd stick with the Mikuni pumper-it's much easier to get it to work.

 

And the FCR AP diaphragm ends up very close to the header

 

I found a nice fcr mx 37 on ebay it is on it's way
the fcr can be heavy on the time to get it right but that is what I do for a living.
I have installed many on other bikes and I know what it is all about
but I really like those carbs you can do a lot with them.
Here is some left over parts I had around the shop that I will use on
the klx fcr should be fun a nice adapter to go to the air box
and a scary fast power now

 

Great! It'll be interesting to see how it turns out for you.

Another mod option for KLX owners once you get it sorted out

 

Where are you at in southern Ohio? As you see, I'm in Delaware.

One other question, since you say you've done this stuff for a living.

For decades the round slide Mikuni has been used on Yamaha SR500s among other four strokes, no pump. Why is it that the flat slides like that are not used on bikes like the KLX? Fact is a lot of non-CV carbs have been on four strokes. I know the pumpers are the trick, but why not the common slide type for some boost in performance? Like I said, decades on the big single Yamaha with no accelerator pump.

 

Mark, on the round slide 36mm Mikuni, for example, how big would that carb be from the front of the intake manifold spigot to the rear of the intake boot bell? I've studied and read about some subtle fueling differences between the flat and round slide Mikunis, but one bigger issue mentioned is the alleged larger size of round slide carbs compared to equal bore flat slide versions. No, I have not confirmed that. In "our" olden days, we had a good amount of room behind the cylinder/head on most of our single cylinder bikes back then. Not so much the case with most of the more modern designs. Just a thought. Maybe some measurement comparisons would answer that.

 

Maybe you meant round slides? You could use round slide carbs on the KLX, but the AP/smooth bore combo offered these days is hard to resist.

Post #4 here in this 5yo thread suggest even then the round slides are old school and there are indeed better carbs these days

Post #5 says the pumper is way better than the round slide

Plus you lose throttle response with a big round slide as its inner volume sucks up engine vacuum (usually via the throttle cable slot in the floor of the slide) the same way a CV carb's slide does, instead of the vacuum being concentrated in the venturi and over the jetting orifices.

 

klx678 I am in south Dayton
as far as the round slide as long as you can make it fit and jet it right you can use
any carb you want here are some other tools I will use on the klx fcr if you want to see
more of what I do I have a little home made web site you can check out I am still working on it
www.113moto.com

 

What brand is that shift light on the bike in your website video? Can I add that to my KLX?