Mikuni Tmx 38

[the Eel]

One or two quick ones here - Mikuni TMX 38 on a 1999 Husky WR125 ....

I opened up the bottom of the carb and screwed out the main jet, which appears to be a 430. The top end on this bike seems pretty flat but the throttle response seems OK. Can I improve the top end with a slightly larger or smaller main ? Which way ?

Next, after taking out the main, the next in line is another jet which is longer. Is this the Pilot ? (the main was screwed into the bottom of this longer jet) This seems to be a 60. The bike seems to bog when I roll on the throttle and then gets back to normal after the revs build a bit. I've read several articles on jetting but am still a little unclear as to whether this is the result of the pilot being too lean or too rich. My impression is that it is too lean, hence I ordered two larger jets - a 65 and a 70. Am I on the right track here ?

The mid seems fine. The only things on my wish list would be to get rid of the bog (or miss) down low and maybe get some more top end out of the bike.

Any thoughts ?

 

[David Trustrum]

Oh dear, oh well the main screws into the needle jet. The needle pokes into it right. These can’t have been cheap.

The pilot is the little biddy one down the hole to the side of the main. Remember jets are responsible for their relative THROTTLE position, not the revs. The pilot will affect from closed throttle -cracking it on. After that you are into the realms of the slide then the needle & needle jet. Full open is the main’s domain.

Chances are they set them up rich as too lean can fry your engine so try rich first then lean. Make one change at a time. Chant that bit about throttle position for a while & it will all make sense.

 

[Gyrros]

Eel, welcome to the 2stroke world. The long jet is the pilot and the short one is the main.

 

[Marcad]

Eel, welcome to the bad information world. The long jet you had removed was indeed the needle jet.

Go to Eric Gorr's site and read up on carb tuning. You seem a little lost.

 

[the Eel]

Thanks Gyrros - I confirmed this with a Husky dealer. They suggested a 390 main and a 30 pilot. I'm gonna try a 410 main and a 45 pilot and then go from there. By the way, when are we gonna do Gorman again ? That was a a fun day last time.

Marcad - are you sure ? I have studied a .gif file of this carb ... what I'm talking about is definitely not the jet needle / needle jet ... or is there a difference ? The Mikuni site I looked at leads me to believe it is indeed the pilot. There is no taper on this at all. FYI - Eric Gorr's site is great and very helpful. I had already scoured it for info but still had a few specific questions.

Here is the Mikuni link - I think it's a good one.
http://www.carbparts.com

 

[Marcad]

I didn't see a needle jet in that gif. The needle jet is what the needle slides into and main jet screws into from the bottom. That is pretty much what you desribed. The pilot (showed in the gif) is off to the side.

The last dealership I went to didn't even know what a needle jet is, where it is located or if it ever existed. I'll try to find a better link for you.

 

[Marcad]

Here you go.

http://216.37.204.203/Yamaha_OEM/YamahaDB.asp?Type=13&A=144&B=30

#21 is the pilot
#23 is the needle jet
#22 is the main which screws into the needle jet

 

[the Eel]

Marcad - you got it !!!! Thanks - that looks exactly like what I revmoved - the needle jet ! Now what carb is that - is it flat slide ? Barrel ? TMX ? What size ?

 

[Gyrros]

Hey Eel, I have this week end off. I was planning on going sat or sunday. if you want to hook up just let me know.

 

[the Eel]

Gyrros - check "Places to Ride / Organized Rides" .. look for "Phelon 9-1"

I'll be there Sat at 6 or 6:30 AM for the 7 AM start - it's Saturday morning. The directions are in the post. Hopefully I'll see you there !

 

[Marcad]

The carb in the pic is from a 98 YZ125, a TMX36. Many of the parts should interchange with yours. The Mikuni jets are cheaper than the OEM ones if you can find them.

 

[HiG4s]

Factory stock is 400/35 Which is what I'm still running on my 99 CR125, but I do have a PC pipe. I run 40 to 1 with Honda synthetic oil and it runs pretty well. 390/30 would be one step leaner than stock on both jets, mainly for hot temps at sea level like here in FL. Higher altitudes may need to be leaner. I have a 390 but the 30 is back ordered and I want to change that first as it seems to run good up top but hesatates a little down low. If you have a fax machine I can fax you the jetting chart and carb parts pics from my shop manual.

 

[the Eel]

Al - you want to go to 30 on the pilot - is that why the bike hesitates down low ? 'Cause the pilot is too rich ?

The reason I ask is because that is the only complaint I have - there is a hesitation when I roll on the throttle - not what I want when I'm trying to get over an obstacle on a 125 !!!! It also smokes quite a bit when I start it up. Is that another sign of the pilot being too rich ?

The specs you mention - 390 main, 30 pilot - were exactly what was suggested to me by a Husky dealer in Michigan. However, there was a 2001 125 test in DirtRider executed at tracks local to me here in CA. DirtRider kept the 35 pilot (stock), went to a 410 or 400 main, and varied between 2 or 3 notches down on the clip (stock is 2 per the article).

I changed the main to a 410 today and kept the pilot at 35. Unfortunately, since I've never fiddled with a carb before, I could not get to the needle. I couldn't get the darn throttle cable out of the slide housing !! Oh well. I also have a 390, a 400 and a 430 main. The 430 was in the bike when I bought it. It worked fine it seemed but I wanted to try something different to see what effect it had. I'm riding tomorrow - I'll report back on the results.

Will changing the main affect the top end in any way ? It seems pretty flat on top.

Also, is the choke off when it is all the way down ? Or all the way up ? I'm thinking all the way down is off. I hope that's right.

I'll email you regarding the fax.

Thanks !

 

[Marcad]

Holy cow!!!! You are lost aren't you?

I suggest you find someone with some experience dealing with carbs and ask for some help.

 

[HiG4s]

Yes, down is off on the choke. Main jet only affects from 1/2 to full throttle so if it runs good hard on the throttle the main is probably OK. from off to 1/4 throttle the things that affect it are the air screw and the pilot jet. Inbetween the two is the needle, the needle valve and the throttle slide cutaway. I personally don't mess with replacing the slide or the needle valve. For midrange I dropped my needle one clip position, and yes getting the throttle cable off, even if you have done it before, is a pain.

Husky's stock settings of 400 main and 35 pilot are suggested for 70 degree temperature at sea level. They suggest for about every 15 degrees hotter go down (leaner) one main size and for every 15 cooler go up one size. Pilot recommendations aren't as straight forward but still leaner for hotter and richer for colder. They never recommend leaner than a 30 pilot for any condition.

They also recommend for higher altitudes to go leaner, about one main jet size every 1200 feet. Remember running it too lean can damage the engine, too rich will not. Knowing that also realize most manufactures stock settings are a little rich to protect the engine. If you don't plan on changing jetting with the seasons you should jet for the coolest temp and lowest altitude you plan to ride at. I personally am running 400/35 with the needle on postion #2 This seems a little rich but still runs good on top but heasitates a little down low. Which is why I plan to try a 30 pilot jet. I may also change the main to see how it runs, but once it cools off here, I would change it back anyway.

Another thing to consider, most 125s don't have a lot of power down low to start with and if the power valves are gummed up and need cleaning it will have even less than normal. What oil ratio do you run and what type of oil. I run 40:1 with Honda HP2 full synthetic. I tried a synthetic blend and my bike would foul plugs and drip spooge and hesitate even more. With a full synthetic it is much better even with out changing the jetting.

 

[the Eel]

Al - I rode Saturday at between 2000 to 4000 feet elevation. Temps around 80 to 85. The 410 was OK but the 390 main was much better. Excellent in fact. I may try the 400 just to be safe (don't want to stress the bike too much).

I climbed some big hills and the little Husky did pretty well. Do you run a 110 or 100 size tire on the back ? I run 110 but am wondering if the 100 might be better.

I am going to try the 30 pilot as the low end bog is just plain annoying. The 35 is in there now.

On another note - the shock settings are really hard to nail down. The back end pogos pretty bad at hi speed through whoops. I got thrown off the bike because of this. It freaked me out. I now have the rebound full soft, the HSC full soft, and the LSC full hard. Seems OK but I will need more time to sort it out for sure. I have read that the Sachs shock has very, very slow rebound characteristics overall. It was recommended to go almost full soft on rebound to keep the bike from kicking like a rabid mule. Those comments seem to be on target, as I learned first hand, and rather painfully.

I have varied my mix ratios quite a bit as this is my first 2-stroke. In other words I haven't paid much attention but it is usually 40:1 or 32:1. I will look into your recommendation on full synthetic. If I can get rid of the low end bog and sort out the shock, I will be very happy with this bike.

Thanks for the all the help.

 

[HiG4s]

I went through and set it back to factory on the suspension when I first got it and have since set HSC midrandge 3 clicks harder than factory and LSC sortal hard 4 clicks harder than factory. Damping I'm not sure what you mean soft, I have the rebound set at 3 clicks more damping than factory. not enough rebound is makes the back end bouncy. You turn the adjuster at the bottom of the shock clockwise for more damping (slower return). Until I added rebound damping it would kick the back end up on jumps. I don't have my manual handy right now, I'm at work, and will have to get back to you on what factory settings are. You do have your shock preload race sag set (so the back end sags from 95 to 100mm with you on it)?

I had a 100 Pirelli on it but just this morning switched to a 110 Michellin S12 haven't had a chance to ride yet, won't until Thursday.

 

[tentbound]

Eel, make sure your front and rear sag are in the ballpark before you adjust the clickers. You will have a difficult time getting the suspension right if the springs are preloaded too much or too little.
Also, don't be afraid of trying race gas if you are having problems with jetting. The gas is more consistant so you won't have to deal with that variable- just compensate for elevation and temperature. Remember, 2 strokes are more sensitive to jetting than 4 strokes.
One of the nice things about Huskys and KTMs is that the dealers know the bikes! I really miss that since turning Japanese.
I don't know where you live in LA, but Eric's Motorcycles in Pasadena, and Bill Saltzman in Baldwin Park are two great dealers. Bill has been with Husky since the earth cooled- and always has a good story to tell!

 

[the Eel]

My rear-end kicking problem seemed to only improve when I rolled the rebound to full soft (full counter-clockwise).

I also have the HSC at full soft and the LSC at full stiff. I still haven't tried it fast through big whoops yet because last time it spit me off hard (before I made the changes) !!!!

Any thoughts ? I was wondering if soft rebound and soft HSC might not add up to an awful lot of force loaded up to kick that back wheel down - and then back up - and then me off ! Maybe I should add back some more HSC to counteract this? I really need to solve this problem - the bad rear end pogoing 'caused me to suffer the worst crash I've ever had. It's got me spooked a bit.

I read somewhere that the Sachs shock has very slow rebound characteristics and therefore needs to be very soft to return the wheel to the ground quickly enough.

By the way, the rear sag is set OK but I don't know how to set the front - and I finally found the air screw !!!!

 

[tentbound]

Eel,

Is the bike pogoing from poor rebound, or from the compression damping too hard? For off road, I would try to completely back off the compression damping then add more and more until it stops bottoming. If the rear end is pogoing from lack of rebound with the clickers, then back off the spring preload for more sag. This will keep the spring from overpowering the rebound damping.

A good starting point for sag for off road riding is 3 inch front and 4 inch rear. But again this needs to be fine tuned for your style and terrain.

I might be wrong, but the way I set up the suspension for offroad is to adjust the sag to get the ride height and "balance" right. Then adjust the compression damping to minimize bottoming and enough rebound to prevent "packing down" or kicking in the whoops. This is a starting point. Call Scott's or RG3 as they may have some good setup info.

Sometimes the hassle of setting up a new bike outweighs the joy of the new ride!

 

[placelast]

Eel-er: we hope to be @ Jawbone on the 22nd, say noon to 1pm. Bring yo bag-o-brass & screwdrivers - there will be plenty of time for us to tweek.

We should also set the sag & clickers. Sounds like U need mo rebound (damping). Why? Pogo (quick rebound) & packing (slow reabound) are @ opposite ends of adjustments, so lets take some time & do it, then take short runs to check - there's some good terrain for checking setting there.

Do you have a manual? If not, give Eric's a call to get some idea of which way the clickers go (write it down) - some euro brands (few 'Zokes) are opposite, even in different locations vs. asian brands.

 

[HiG4s]

I have a manual and will e-mail you the placement, adjustment direction, and stock setting if you send me an e-mail to remind me. I'm at work right and don't have access to the manual.

Also a NOTE. the OEM TMX on a Husqvarna is not quite the same as the across the counter TMX or the one on most Japanese bikes. It uses different pilot jets.