I am at the end of my needle!

[bclapham]

OK, i am having a lot of fun getting this 02rm144 really dialed on the jettting and it seems like everytime i ride it, it just gets faster and runs better!

However, i still feel there is room for improvment, and i think i need to go leaner still from 0-1/2 throttle positions- it might be the v-force and the bigger bore making it run rich.

so i have two areas to work on, 1. pilot+slide and 2. needle+nozzle.

1. pilot- i have the smallest pilot (25) and have cut the slide ~0.75mm, the bike is still rich and the idle/peakrev method with the airscrew is peaking around 3 turns so i know i am still rich here- Can i cut the slide a bit more (~0.5mm) to get this circuit back on track or are there any pitfalls to going to far? it ran loads better with this mod btw.

2. I started the day at the 3rd clip of the stock needle and it was loading up a bit. i went to the leanest posn and it was loads better. then i went to the next leanest needle (0.02mm wider) (infact the leanest suzuki needle you can get) in the 3rd clip and it was not as good(rich)- then moved the clip to the top and it was even better.

so here is my predicament, i am at the leanest needle setting i can put in there, will a smaller nozzle be in order here, or can i find a differenent needle series to help both the 0-1/4 and 1/4-1/2 throttle positions?

btw- i am now much happier with the main, no more detonation since i think compression and too close a squish clearance was hot helping there.

sorry for the long questions, thanks, BC. :thumb:

just to add a bit more info, i opened up the carb tonight and took out the nozzle, however, it has no markings on it so i cant identify it- i wonder if it is the S-9 though similar to the yz's??

also, i noticed from the manual that the needle OD only really effects 0-1/4 throttle, so this again send me in the direction of a different nozzle but which one, LOL!

 

[motometal]

I think changing the nozzle has the same effect as moving the clip, plus the diameter.  In other words, it should change the mixture over a broad range.

It's easier to change jets than it is to try and glue the metal particles back on to the slide :confused:

 

[nephron]

Bruce, just park it and wait 'til winter, man. That'll do the trick. ;)

 

[G. Gearloose]

Originally posted by bclapham
or can i find a differenent needle series to help both the 0-1/4 and 1/4-1/2 throttle positions?

Very Likely..
What carb? What needle? throw us a bone! ;)

A needle with a different diameter straight section sounds in order...

What throttle settings are acceptable? Where do you want it richer/leaner?

 

[bclapham]

Originally posted by nephron
Bruce, just park it and wait 'til winter, man. That'll do the trick. ;)

Nephron: as you well know, the only difference between winter and summer is being able to run 5 laps instead of 3 before passing out from the heat! :thumb:

gearloose: its a stock TMX38S carb

the stock needle is 6BGY27-77, i am running the leanest 6BGY27-79 which is 0.02mm wider, that said i dont know where to start with the needles.

i want to lean the bike from 0-1/2 throttle since i am only my leanest pilot and leanest clip, if it goes too far, then ive got plenty of jets and clip posisitons to play with.

thanks

 

[G. Gearloose]

Well, I have no business talking about a Mukini,
Browze something like Sudco.com and you'll see there are lots more Mukini needles out there besides the Suzuki ones. Now you need to hook up with someone who can translate the OEM code to the closest Mukini then its time to play...good needles are cheap power..good luck!

 

[motometal]

Thinking a bit more about it, the nozzle diameter would make more difference at lower throttle settings (than it would at higher settings) because the needle is blocking off most of the flow.  As the needle comes into the tapered section, a nozzle diam. difference would make less progressively less % diff. in the overal mixture, this is controlled mostly by the clip position.

 

[john stu]

bclapham 25 the smallest pilot jet?they sell pilot jets down to size 15 for the tmx carb i should know i have one in my hand right now, i just went into my box of jets and looked at what i had and the smallest size was 15 you can order them from parts unlimited.thats where i got mine and they fit your carb the mikuni tmx hers a quote from the parts unlimited catalog "genuine mikuni pilot jets here are geniune mikuni pilot jets that will fit any rs,hs,or tmx carbs such as the ones that come on late model suzuki rm125/250 available in sizes 15-30 in increments of 2.5 and from 30-60 in increments of 5 now available in 4-packs.i hope this helps you out i would try smaller pilot before cutting the slide that way you can always go back unlike after cutting the slide.the nozzle is also a very good idea i did this on my cr and it helped bigtime, if you take your nozzle out the size is stamped right on the side so then you can orde the next size smaller.to remove the nozzle just put a socket on it and unscrew it you don't even have to remove the main jet from the nozzle you can just slide the socket right over the main and take them both out as one piece.

 

[bclapham]

john: ive got a 20 and a 22.5 pilot that will fit, however, i dont think it is the right jet! The correct jet has a small band machined in the bottom of the thickest part and the turret with the holes in is much wider than the other jets that dont have the band. i wonder if that turret width is crutial?????

 

[john stu]

as motometal said the nozzle afects closed to 1/2 the most when i changed mine on the cr it didn't seem to afect the main jet if it did it wasn't much the plug looked the same after full throttle runs as it did before

 

[bclapham]

yep, that is why i want to try a different nozzle since everytime i have leaned the neddle the bike ran better but ive leaned it as far as i can- i want to take it too far so i can get a good enough idea to back it off to the best setting- i could be there, but without a leaner setting i will never know! (does that make any sense?) my hoping was that the nozzle would also help the rich pilot and enable me to run the "proper" pilot jet.

the only problem i have is that i dont know what the stock nozzle size is.

 

[john stu]

like i said before unscrew you nozzle and the size is stamped right on the side.and as far as the pilot jets i have seen the differance you are refering too and i tryed two pilot jets that looked like you said slighty differant but they had the same number stamped on the side and one had the machined ridge and one did not and the bike ran excactly the same with both (they were the same size)i would have no fear run the one without the machined grove i know it looks different but the diamater on the inside must be the same because like i said the bike ran the same with both.but if you need to got that small on the pilot i would definatly try the smaller nozzle.

 

[jmics19067]

Bruce there are plenty different sizes available. watch out though an 88 rm250 tms is different than a 94 yamaha yz tms carb. both are the "d" shaped throttle slides without a replaceable nozzle. the suzuki has a different top<where the cable mounts> a different needle<shorter length then yz> and a different pilot style<short jet that sets in a well like the old round slide mikuni compared to yz no well long style pilot jet>

You should be able to get the short pilot jet down to a 15 and the long style down to a 10<1999 white bros catalog has them listed that way>

the stock yz jet needle is 6ej33-61 where acoording to my manual says that the e is the angle of the first taper the j the angle of the 2nd taper and the 61 atthe end is the root diameter of the straigh portion,<higher number is thicker .....leaner>

the rm needle is a 6 ej12-55 now I suspect that the 12 is the actual lenght of the needle since it is shorter than the yz according to my catalog here a flatside 35mm carb takes a say a 6 en 11- XX while a 38 would take say a 6 ej 12-xx but I would have no clue where the yamaha numbers fit in

Your different pilot jets you have is it possible that the band you are talking about is only a difference between geniune Mikuni and somebody else making it?

I am not sure how this would affect you being a newer carb with different requirements but I hope it can help decipher some of the coding.

 

[jmics19067]

ooh and make sure you do have a removable nozzle some mikunis don't you will have to mess with the slide cutway for that 1/4 throttle responce..... but atleast the slides are a bit cheaper than the Keihins.

 

[bclapham]

if you look at the pilot jet with the band in, these jets have a wider tube with the holes in the side- i think i will try a smaller one anyway again

the reason i wanted to try the nozzle is that i didnt want to get into the needle thing, LOL- it looks tricky. Yes the nozzle is removable since i took it out last night- i will take it out again tonight, just to convince myself there wasnt any markings on it!

 

[jmics19067]

I suspect the difference between your pilot jets are whether or not they are genuine Mikuni. Look at your different jets genuine mikuni will have something like @ before the number. and maybe the band helps the quality control of the flow. Although I am sure they will work the actual flow rating maybe questionable and certainly won't make your jetting issues any easier.



heh Like I know what I am talking about with jetting compared to most of the people on this site.

 

[bclapham]

here is a pic of the two types of jets, the one with the badn has the wider tube with the holes in.

the nozzle had no marks on, FWIW it had an ID of 3.93mm with my calipers but i expect that is nowhere near precise enough.

 

[jmics19067]

thepilot jet on the right is genuine Mikuni I can just see the little funky mikuni symbol in the picture don't know about the other one and those type of jets should go all the way down to 10. If you need smaller pilots<sounds like it with the air screwout 3 turns>. If you go to the dealer have them breakout a rocker tucky or white bros. book to order it for you.
I can't help with the nozzle since I don't have a removable one but a leaner slide should help in that 1/4 throttle area also.

another thought is too use a more oil in you mix or oxegenated fuel , but I am sure you know that your wide open settings could be dangerously lean if clean up the bottom that way.

 

[bclapham]

back to square one, the brass tube on the right in the photo is is the main jet holder- the nozzle is pressed into this carb and wont come out.

so any slide experts out there, is it worth taking another 0.5mm off the slide and what happens if i go too far???

or any needle experts, i have no clue here either.

 

[jmics19067]

If you go to far my guess would be that you will be lean in the 1/4 throttle setting.

not to be a wise guy but at this point I would double check reeds, engine condition ,timing, silencer etc..... just to double check. if you look over it enough you might find something you overlooked :confused:

can you guestimate what your slide is now? say stock 4.5 with .75mm extra cut so it act like "5.25" My opinion would be to buy a 5.5 if available, try it out, if you think that progress can still be made, cut your modified to 5.75. when you think you are getting close put a richer needle in and cut try cut etc. if you go to far hopefully the last lean needle will pick up the difference if not you have the new 5.5 to put in to ride and a better idea on what you have to do <just a thought>

there just might be some strange phenomenom<sp?> happening in between the air filter and silencer preventing it from feeling as crisp as your 250.
Hey dont laugh suzuki thinks there is some wierd vibration thing going on to warrant designing a 20 $ plug right?

 

[Luft]

Have you considered testing a different main jet. There's an interesting jetting article in the August MXA.

 

[Studboy]

Judging by bclapham's posts, yes, he has tryed SIGNIFICANTLY MORE than a different main jet. :)

 

[bclapham]

OK guys, here we go.

the engine just got rebuilt new seals, and a v-force- this is where i think my problem lies since the v-force is known to often want up to 3 sizes smaller on the pilot. Then figure in ive got a big bore, that "should" warrant leaner jetting also. then figure i am running C12 (although a bit spiced up!:)) which often warrants leaner jets, then figure i am riding in near 100F heat at anywhere from 2000-4000 ft which............... get the story!;) so, all in all, i am not that far off, and i think i will just cut the slide a tad more and suck it up elsewhere, and maybe slosh in a bit more MTBE. unfortunately, Carlsbad raceway is closed costal temps and sea level would bring me ball park!

as for the main jet, i have to look into this again- theory dictates that on this bore, i "should" need a leaner main, however, up until last week no matter how big a jet i put in, the spark plug would vibrate loose from detonation and come out white.:eek: since then ive raised the cylinder a bit since my squish was just a bit tight, so i will have to look into the main adjustment again.

in comparison to the 250, this thing runs so much better- in the last few weeks, ive learnt so much about jetting i actually cant wait to get back on the 250 since i now think i get that running much better too, the only problem is that the yz is such a PIA to get the plug and needle access on that bike.

i really enjoy riding this RM and i jsut want to get it "dialled" soon so i can stick some numbers on and start racing, i am sure when people hear me talk about all this technical stuff they might think i am half fast, but i am a real slow rider, LOL, but i am having so much fun with this bike and feel so much more confident on it and thats what its all about.:thumb:

 

[James]

Those are both genuine Mikuni jets. They have two different versions and I am not sure why. From what I remember, the wider tubed pilot is in the newer Honda, Suzuki, and Yamaha carbs and the smaller tubed jet came in recent but not the latest model Suzukis.

 

[G. Gearloose]

BTW what plug are you running?