Home Forums Tech Talk TM Carburetor Tuning, Where to Start?!

This topic contains 9 replies, has 2 voices, and was last updated by  Glenn L Riggs 1 year, 6 months ago.

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  • #87751

    Hey Gang,

    Blew my TM K9b up again this past weekend.  After talking with some folks at the track, I have a plan of attack to hopefully cure my issue, but one thing I can’t seem to find any solid advise on is where to start with a base tune for the carb.  It’s the VHSH 30 Dellorto carb.  After searching for a few hours, I came up with 3 “proven” settings that are all different.  Here are what I had found from Italian Motors, Tom Barth, and Swedetech…

    From: Italian Motors

    Needle: K22

    Clip Position: Not Listed
    Atomizer: DQ 268
    Inner Idle Jet: 45
    Outer Idle Jet: 50
    Main Jet: 162 – 172
    Idle Screw Adjustment:  Not Listed

    From: Tom Barth Posted on EKN December 19 2011 – Supposedly from Tec Sav

    Needle: K93
    Clip Position:  Not Listed
    Atomizer: DQ 264
    Inner Idle Jet: CD1 – .75mm
    Outer Idle Jet: 60
    Main Jet: 130
    Idle Screw Adjustment: 2 Turns

    From: Swedetech Racing

    Needle: K22
    Clip Position: 1st – 2nd position from top
    Atomizer: DQ 266-268
    Inner Idle Jet: B45
    Outer Idle Jet: 60
    Main Jet: 135 – 155
    Idle Screw Adjustment: Not Listed
    The settings seem to range drastically and I’m wondering if any of you out there are anywhere near these settings, and what you guys run.  I have a lot of work to do on my end to figure out what keeps happening, and I need to take the carb apart to see what is in fact in it, as I don’t currently know.  But any input on what seems to make the most sense would help me out with a base tune to work from.


    Thank you


    2008 GP 8 Honda 125 / TM K9B
    Building F125 Enduro

  • #87755

    Glenn L Riggs

    I use a similar set up as tom barths how ever the 130 main can be lean a 135 will handle everything up to a cooler road course. If warm an humid where you are the 132 to 130 will do but the above is bullet proof. There are more things to consider when jetting also how tight is the piston clearance. Hope this helps

  • #87790

    Thanks Glenn for your reply.  Now as far as jetting to piston clearance, would I be correct in assuming I would want more fuel to keep a tighter piston better lubricated?

    Also, I edited my original post to make it easier to read.  Sorry something happened when I copied all of that from my text document.

    2008 GP 8 Honda 125 / TM K9B
    Building F125 Enduro

  • #87791

    Also, what gas mix ratio do you recommend?  I’ve been running 20:1 using 110 race gas and Klotz Super Techniplate.  Some guys at the track suggest I switch to the more castor based R50.

    Then, I’ve also read these engines are meant to run on pump gas, 93 octane.  Guess I figured the higher octane wouldn’t hurt, especially getting rid of the alcohol content.  Would running the race gas hurt me at all?


    2008 GP 8 Honda 125 / TM K9B
    Building F125 Enduro

  • #87795

    Glenn L Riggs

    You are correct in assuming the tighter the clearance the more fuel you have to run. Yes they are meant to run on pump  gas but purity an consistancy are a problem plus the lead in the race gas acts as a lube. So by using race gas you know where you are everytime. Myself we use amsoil dominator when that isn`t allowed I use some sort of castor and I use alot compaired to others 8 0z  a gallon, does smoke alot after warm up but that keeps the rod happy and on a 20 mm bearing basically the same as a kt100 it is a weak point.

  • #87829

    So Glenn if I am reading this correctly, your running a 16:1 mix ratio.  That’s the heaviest I have heard of yet, but if it works, it works.  Most all of the info I have been able to find claim 20:1 for break in, about 6oz to the gallon, and thinning oil out a bit for racing.  I guess as long as you jet accordingly, there shouldn’t be much issue.  Do you have any problems with fouling plugs being that rich with oil?

    I have a friend that does well, with a ICC engine and the Delorto carb, and he was running a 140 main to be safe on our day.  Temp was mid to upper 40’s.  I haven’t asked him yet, but rumor is he runs 40:1 mix ratio, which is less than 1/2 of what you’re doing.  I’ll try to see if I can get a little info out of him and find out his actual gas mix.

    Talk about variables lol.

    2008 GP 8 Honda 125 / TM K9B
    Building F125 Enduro

  • #87832

    Glenn L Riggs

    No i never foul a plug. you have to be carefull when compairing jets as there are many places to richen an lean out on this carb you can go goofy trying to make a best setup for the day. way to many variables.  we could talk slides an nozzels an really get you confused.  lol. also icc engines are not the same a pavesi uses less fuel than a tm, an a modena use a tad more fuel than the tm so best to do your homework.

  • #87920

    Thanks Glenn for all your input.  I have been doing some homework, starting to compile data.  Both from the interwebs and from a couple friends that run TM’s pretty successfully.  Hope I can get a decent base tune, and be able to put some hours in, take notes, and learn what I need to adjust.

    Thanks again, and if I have any more questions I’ll be sure to reach out.

    2008 GP 8 Honda 125 / TM K9B
    Building F125 Enduro

  • #88138

    So, if any are wondering, here is what was in my carb…

    Needle: K22, clip position 2

    Atomizer: DQ 268

    Inner Pilot: B45

    Outer Pilot: 50

    Main Jet: 150

    Air Screw: 2 turns


    Also, I found my floats were sitting way too low in the bowl.  I’m guessing that was my main issue, even with the pilot circuit being a little lean.  I have the B2 float system currently, and their guide states the lowest point of the float should be 11mm from the mounting face of the float bowl.  It was more like 15mm.  I think that was the major cause of the lean engine and the stuck piston.

    I noticed no one talks much about the float needle and seat, or the slide profile.  My needle and seat are a 300 and the slide is a 50.  Is that pretty standard, or should I look into others?


    2008 GP 8 Honda 125 / TM K9B
    Building F125 Enduro

  • #88142

    Glenn L Riggs

    Well those are pretty much stock from the factory and are fine what you will be learning with. most use a 60 outer idle. Now for your answer some people use a smaller needle an seat to reduce the amount of fuel it can flow therefor you can get away with not running a return line. I dont use this. Others do. Slide is like the accelerator pump in a carb it controls the air flow over the carb nozzle a 40 as used in a rotax pulls more fuel when throttle is opened. under certain condittions hot an humid I may use a 55 slide on a tm but rarely a 60 reason being as there are different nozzels that also effect fuel flow. I believe 9mm is stock down to 5mm the shorter the leaner that is why I stated to go with a simple setup and work with that as you can get in over your head an it gets expensive. Hope this answered some of your questions.

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