All 2st Jetting Chat - Need Help? Post Your Questions Here

I checked out R B designs and only saw the Keihin carb mods that they offered. Did I overlook their Mikuni section?

Rb does the same services to Mikuni as well . He has my Mikuni at his shop and is in the process of taking pictures of it with the carb mods to post on his website

I'm looking forward to your ride report when you get it back.

I dont know when I will get around to it . I just about have my 167 where I want it and I had to start fooling around with the NEDx / NECx series needles in my "perfectly jetted already" 300. Iam kind of burt out with jetting and just want to ride.

I have seen a Mikuni or two in his shop before. The Keihin is what most of his work is, so that is what is on his site.
You might also think about his divider plate and having him set your squish. I was playing with jetting off and on for 2 years till I had him do my squish, divider plate and metering mods. That and Jonny's jetting have me smiling.

Great link LD and should be be used as basic info for the way carbs operate.

Looking at the responses in this thread (and many others) it would seem a lot of trail riders are misled by a lot of carb tuning information out on the web as they seem to be main jet centric which really leave's the 'normal' rider scratching their heads when the pilot, slide and needle are the area's that are causing issues for the average 2t trailrider...keep the chat going

Here is another helpful link for the Mikuni carb

http://klx250s.suncup.net/Misc Docs/Tuning the Mikuni Carb.pdf

Hey PC...been meaning to ask you how did the jetting work for you in the Sierra's?

I dropped my stock needle to the first clip this weekend and was riding from 6000-7500 ft (09 WR250). My idle went up considerably and after lowering it, it ran awesome. Should changing the needle position change the idle that much? I was perplexed. And now I'm wondering if this will require a change in/or rechecking the main jet.

You might need a smaller/leaner pilot which would allow you to back off your idle screw. To answer your 2nd question the needle and the main jet are in play up to about 3/4 throttle so one does affect the other to a point. Read this link http://www.iwt.com.au/mikunicarb.htm and especially look at the chart fig.7 that shows the circuits and how they overlap.

Looking at that chart, the needle shouldn't have any effect on idle, that's what was confusing. By lowering it one clip, essentially the same diameter is in the needle jet so it shouldn't effect the flow at idle. I can see where I may need to adjust the main. Come to think of it after extended climbs where I was over half throttle I did sometimes notice a very slight delay in the revs coming down that wasn't there before. Acceleration was perfect and best ever though.

Another question: How does silencer packing affect jetting? If there is an effect, I may need to repack before doing anything (45hrs on bike). at 6000-7500ft with 30 Pilot, 1 3/4 AS, BFY needle in top clip, and 360 Main (40:1 mix with non-ethanol premium gas) I'm still getting alot of spooge - I mean like after cleaning it pre-ride it is running all the way down the silencer making a gooey mess in about an hour of riding. At the end of the ride I went down the road at high rpms to clean it out and thats when the fresh oil really came out and ran all over the place.

It doesn,t matter what people say. The needle affects the idle, but very slightly. It,s obvious when you change needle clip and nothing else. If the bike is "rolling" on idle or goes :bwwooaah on very light throttleopening after the needle is lowered, raise it again.

Johnny

After I got it warmed up and rode for a bit, I noticed the high idle and it did feel a little on the lean side. After I lowered the idle down, there was no bog or bwwooah or anything. Throttle response was great and after riding tight trails below about half throttle there was no hanging idle either.

My theory on this is that if you have to raise the slide by turning the idle screw in a long way to get enough air to idle it's probably pulling in a little fuel up by the needle. Mine was doing this so I went to a smaller pilot and could therefore use the air screw to give it enough air and not have to raise the slide so much.

09 WR250

I just edited my jetting data base (post #62). I have been playing with every circuit on my stock Mikuni and I don't think I can get it any closer. I found no need to change the stock needle since it responded well to clip changes and had no flat spots. The 1/2 step washer/spacer on the needle really did get it perfect as a full clip was too far either way.

Next I will see how many miles I can get on a tank of fuel and compare with others.

Hummmm...... Got a minor issue with my jetting, I think. I was at the Nat'l Enduro this past weekend and in the last section they had several very long steep hills. Of course I was on the smallest bike in the last section on my WR150. It would lose power and stall about 3/4 of the way up the spectator hill. I made 3 attempts and stalled it every time. If anyone tapes MAVTV and sees the show that I put on make a copy for me. I was told I was the star of the hill. I probably looked like a total spode but I entertained the spectators. I actually tumbled down the hill 3 times. I had to crawl and scratch my way back to the bike every time. You could NOT walk up the hill in any way. It was that steep. The bike has great power on top and runs clean everywhere BUT, I am beginning to wonder if I have a minor lean issue midrange. It just seems to be a bit flat under a severe load like this. I am running +2 teeth on rear sprocket too. Seemed to need lower gearing in first, still. I have a 36mm Air Stryker with a NOZH needle in the #2 position. 172 Main. 6 slide, 35 pilot. I am thinking of going to the #3 position on needle and if needed drop back to a 170 main. I had a 3/4 throttle bog with the 170 before but it seemed to be OK once it was on the main. What is your thoughts on this ?

PS: it was embaressing ! I lost 30 minutes more than the leaders in this section.

If your bike is running great every where else. You might want to check your float level. You might need just a little more going into the bowl.

At extreme angles, it won't let enough fuel in, then starves and develops an air lock.

It had a major bog before I lowered float level and it would overflow at anything more than a side stand angle. I was only getting 14mpg. Now I get 21mpg.

Is the actual fuel level supposed to be even with the bowl to carb body seam? The amount that the small spring on the needle is preloaded greatly affects the measurement however if the level was set by the actual fuel level there would be no margin for error.

Hello guys! I just bought a WR 125 2008 to my son and would like some advise on jetting. The bike has the standard TMX carb with #3 slide, 410 main, 35 pilot and 6DJ8-59 needle. It also has a very dented HGS exhaust system which i will fix. We live at sealevel and have around 60F. The bike starts fine, but i feel that it,s not pulling good in the middle. It also bludders and spooges quite much on light throttle. A thicker needle with more taper maybe? Any suggestions are welcome!

Johnny