250-500cc WR300 jetting and tuning thread

BikeSDP,

Your line of questioning is a bit rhetorical,...you answered most of them correctly yourself.
The way I read it is that you just need a bit of confirmation.

You have correctly identified both the air screw and the idle screw.
Any air screw setting implies turns out from a seated screw as a starting point.
The air screw is a fine tuning adjustment on the pilot circuit. The more it's open the more air is pulled into the pilot circuit. That being said, at your altitude you're probably not going to be able to get that bike to carburet right with the air screw alone. You're almost certainly going to need a leaner pilot jet and a higher needle clip position.

You may find you'll need to back your idle speed down a bit when you get the pilot circuit right.

Yeah, you're correct in that observation. I wanted to be sure I had a basic understanding.
Thanks for the advice. I figured I wasn't going to be able to just ride this thing straight out of the gate without some tinkering.

So any recommendations on where to obtain some various jets?

Thanks guys for your answers. Yes there is a big difference between 250 -300 pipes.

250 have a bigger volume. I dont think 250 pipes will work. But i have one in stock, (Doma) so i will test one of my bikes.


/ Klas

Jeff @ Halls told me that one of their customers was going to put an FMF Gnarly off a WR250 on a 300 and try it last week. I will ask him how that went.

Kearney's been using a Pro Circuit on his 300 for months now. I called Pro Circuit in June and asked if they were close to marketing a commercial version. They told me I could special order one and they could copy Kearney's. I want to wait to see which "version" Kearney is happiest with before I order.

My problem with any PC is that they make you run their silencer with their pipes, which just adds to the cost.

I still bet that the 250 pipe works just fine on the 300. The 250/300 KTM and GGs both use the same pipe.

I didn't realize PC makes you use their silencer. Thanks for the info!

These are the "go-to" guys as far as I'm concerned:


http://www.halls-cycles.com/

http://upstatecycle.com/index.php


And this is from the Sudco website,...I think there's a link to
their main home page on there somewhere:

http://www.sudco.com/mikunijets.html

If not, www.sudco.com

So what does the 09 WR300 come with stock for main and pilot jets? I have seen 460 main here but 380 main in the manual (I wonder if the 250 and 300 are swapped in the manual). The pilot looks like 35 here but shows 17.5 in the manual (I assume pilot and idle jet are synonymous). I suppose I should pull the carb to be sure.

Yeah the manual is kinda goofed up. The US/Can bikes have a 460 main and a 35 pilot stock. The other info is for the Euro spec homologated street legal version. I think the owner's manual has the specs switched.

Thanks, Rusty 2. Just like Pedro's cousins, Jeff@Halls has all the sweet hookups.

He's sending me one of the "hang on tight" full power kits w/ some leaner main and pilot jets for elevation

That's what I'm talkin' about,....good deal!

OK, so I got the carb out and have gotten to the main and pilot jets. So far, so good, now one last question: How do I get the needle out here (see pic):

While holding onto the cap, compress the spring toward the cap enough to get some slack in the cable. Make sure you pull the white plastic piece at the bottom of the spring up with the spring. With the spring compressed, push slightly down on the cable and wiggle the cable back and forth a bit to make it pop out of the grove in the hex piece that srews into the top of the slide.

well, since you put it that way, it made sense and was easy to sort, thanks

Glad to help. I remember my first time trying to figure it out. It's not intuitively obvious, that's for sure.

Be extra careful while reinserting the cable back into the slide. Make sure it's positively locked in there.

Mine has released from the slide twice. Both times I was 20+ miles from camp.
I can reattach it in 7.6 minutes now

Good advice. I just finished buttoning everything back up just a moment ago and even ran it for a few minutes. I am pretty sure I got the cable in there, but I'd hate to find out I was wrong. So, anyway, I can become all OCD about that over the next 6 hours or so. So tomorrow, I shall go back out on the trail w/ the new jetting. The needle from the so called "full power kit" has the clip in second slot, main is down to 400, pilot down to 30, air screw out two turns. We'll roll the dice with that as the starting point for 7300-8500 feet, but what will be unusually high humidity for CO (it's been raining a lot lately). I have about 3 more gallons of 32:1 to burn as it has an hour on it.

Edit: 14-Sep-09
So after about 10 total hours of riding, I'll report the jetting I'm running in the Mikuni. I fattened up the pilot from 30 to 32.5 (stock is 35), I'm 1.5 turns out on the air screw and the main went from a 400 to a 410 (stock is 460). I'm still running the jet needle from the full power kit, with the clip in the same spot as mentioned above. I'm done obviously with the 32:1 mix and have been running 40:1 with Spectro SX2. I saw a post from Kelly suggesting that Spectro leads to less spooge and smoke. I decided to fatten up the pilot circuit up after an overheating issue about a month ago. This was on a trail that has about a 2 mile sustained climb that is rocky and the elevation is about 2K higher than my typical riding spots. I am quite glad I installed that computer and set up the temperature warnings. This is my first two stroke and I'm still learning to tinker with the carb, but it has been running great lately. I think I still might have some work to do to smooth out the transitions, but in time. I need to find a local guy with a 2-stroke that is well dialed in to see where I should be.

Damn that OCD..... I suffer from it too!

I've changed needles so many times on Keihin carbs, but this is the first Mikuni I've tinkered with except for my banshee, which has a completely different needle retainer. I guess I got too cocky and assumed it was seated properly from all my past Keihin successes

Last time it happened I expanded the spring a bit for extra tension. Guess it worked cause it hasn't happened again.

The first time it happened it didn't even happen to me. IT happened to NWetRider who was riding my bike and I was on his WR125. He made it 100 yards before it happened. I came back to him and my bike was trailside in pieces..... I was like WTF. Thought he was stripping my bike for parts

Good day all.
I am new to the forum, have posted an introduction on another thread.
If I hijack this post, I am sorry,

I need some advice please.............I own and race a 2006 WR 250 with a FMF Gnarly pipe on.
It is time to replace the piston and rings again. I was looking at somehow putting a big bore 300cc kit on.
A few questions
where will I find the big bore kit, everybody seems to only keep the 4T stuff?
Will the FMF still fit or will I have to replace the pipe as well?
Will the standard 250 Mikuni carburetor be good enough (I will play with the jetting to get it right)

The problem in South Africa is that there is only one dealer / importer so the availability and prices leaves a lot to wonder about.

Again, sorry for the hijack but I cauld not find the right place to start a new thread.

Johnnym