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Thread: tf125 help needed

  1. #1
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    tf125 help needed

    So after riding a rmx250 the last few series of vinduro , I've decided to step up the challenge and ride a mud bug.
    After a couple of rides and one race I have adapted to the suspension and brakes, and lack of ground clearance but even a modest increase in power would make the world of difference. The bike is a reasonably new one (white one) with 1500km on speedo, I've removed all the farm stuff, 15w fork oil and pre load spacer, doubled the intake snorkel size , halved the size of the muffler baffle and gone from a 100 to a 110 main.
    Have a month until next race and really looking for advice on gaining a couple of hp, struggling on gnarly hills where can't carry enough momentum/speed in 1st yet not enough power to pull second.
    Are there restrictions in the stock expansion chamber?
    Any guidelines for inlet/exhaust porting for modest gains?

    Thanks Paul

  2. #2
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    You need help. Sicko.

    But if you must I'd try find an old 125mx chamber and adapt it to fit.

    Read my thread about Petes TF. Some tips there but you won't go so extreme.

    You want to bring it up to PE175 port timings. Find a copy of Graham Bells 2 stroke tuning, he uses one as an example. Copies have emerged online. Std they are made for peak power at a very pedestrian rpm. Even the TS is sportier.

    Likely the suspension will be too soft. A preload spacer just increases ride height not spring rate. To do that you can cut a few coils off the tightly wound end and rebend the top coil with heat then grind it flat as std. YouTube should help here. Make up the removed length.

    You can also often sneak another cm or two by lengthening the damper rods. You will have to check there is reasonable overlap .

    I'd invest in better rear shocks for your backs sake.
    Don't you look at my accountant.
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  3. #3
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    OK so the tf has has slowly evolved and has proven to be pretty competitive in its classs.
    Removing the two washer shaped restrictions in the expansion chamber coupled with a rm80 muffler made a big difference to power. The oil pump was removed and running 30:1. Mild porting with Ex at 176 and inlet at 140 degrees. Had to go up to a 170 size main jet .
    I fitted ts185er forks and triples and Hagon shocks, it now handles much better with better ground clearance. ts185 tank and early rm125 seat give it a slimmer profile.
    The start of the vinduro season is coming up and the cylinder looks like it will need a rebore or at least a hone, will get it measured up.
    Is it worth skimming a little off the head for a bump in compression and slightly better squish? Squish is currently 3.0mm. Ive scoured a lot of the older posts but they're pushing engine development beyond what I need, I don't need to rev to the moon, and don't really want to get involved with changing the ignition.
    Would taking 0.75mm off the head be beneficial?
    Thanks

  4. #4
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    You need to measure the compression ratio. Cutting numbers off here and there are pointless if you don't know the important details. You should be able to safely run 12:1 if you run 98. 3mm squish is throwing power and cooling away. 0.8 will be better and parallel to piston crown. But just skimming to this will take the compression dangerously too high I'd bet. That's why you have to measure and take a bit out. Central sparkplug head makes this much easier and brings its ow8n benefits. Might have to make room for it in frame.

    The std pipe will be biggest restriction. An old RM one or similar will take you to proper mx type revs. You dont need roadrace revs sure. Some emulators in the forks will help a lot.
    Don't you look at my accountant.
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  5. #5
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    Make a pipe, specific to your engine, from the Bell book. You're be better off. Infact, get the book.
    Horrible little TF's respond well to a hot up, done properly.

  6. #6
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    Thanks guys will look at the pipe but the standard one is strong and tucked in nicely. One of the guys on this site took 1.1mm off the head and used a thinner head gasket, he went from 17.5cc to 13.7cc and 8.1 to 10.7cr with 1.8 mm squish.

  7. #7
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    These books
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  8. #8
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    Quote Originally Posted by Flettner View Post
    These books
    They look well used.

  9. #9
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    Stock pipe will restrict peak power to about 7000 RPM or less. Hard to make any power there. Std ignition are a bit shite. Grafting on a 125mx one of any type will get you in the ballpark for what you are trying to make which is a mx125 with a slightly heavier flywheel to make it a bit easy and say a 28mm pwk carb instead of a 32mm roundslide like an old RM will have if rules allow.
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  10. #10
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    Haha, he is going to need every bit he can squeeze out of that thing.

  11. #11
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    Quote Originally Posted by F5 Dave View Post
    Stock pipe will restrict peak power to about 7000 RPM or less. Hard to make any power there. Std ignition are a bit shite. Grafting on a 125mx one of any type will get you in the ballpark for what you are trying to make which is a mx125 with a slightly heavier flywheel to make it a bit easy and say a 28mm pwk carb instead of a 32mm roundslide like an old RM will have if rules allow.
    Ok thanks, plenty to work on I need to read up.
    No restrictions on engine just needs to be 125cc max and air cooled. I looked at carbs and thought a vm26 might be worthwhile, not a lot of room before it will hit cases and current carb bolts on with a flange so will need some kind of adapter.

  12. #12
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    Quote Originally Posted by Flettner View Post
    Haha, he is going to need every bit he can squeeze out of that thing.
    To be fair the power is in harmony with the handling.

  13. #13
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    Quote Originally Posted by gwynfryn View Post
    To be fair the power is in harmony with the handling.
    Yes, although there is also limited rules around supension. 36mm forks but can be leading axle, good scope. Twin rear shocks but can be anything and at any angle / travel, plenty of scope also. Brakes, drum.

    You could build a monster, you dont have to use the TF frame.

    Clearly Im thinking about the speed sections. The road to glory, is power, everyone knows that. Haha.
    Id use an LOL emoji but my phone wont let me.

  14. #14
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    Quote Originally Posted by gwynfryn View Post
    Ok thanks, plenty to work on I need to read up.
    No restrictions on engine just needs to be 125cc max and air cooled. I looked at carbs and thought a vm26 might be worthwhile, not a lot of room before it will hit cases and current carb bolts on with a flange so will need some kind of adapter.
    Flange sucks as vibration.

    PWK28 will flow enough and be far superior throttle response to shitty old mikruddi. Also small. Look at my Pete's TF thread for how I did it without overly long adapter. I'm keener on genuine keihin, but some have luck with copy cheapos.

    If I was building it, it would be a 35mm PWK, rev to 13,000 and generally be slower around the track until you got to a long flat straight.
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  15. #15
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    Quote Originally Posted by gwynfryn View Post
    To be fair the power is in harmony with the handling.
    there's no such thing as Harmony when you're talking TF125

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