tf125 help needed

[gwynfryn]

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

[F5 Dave]

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.

[gwynfryn]

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

[F5 Dave]

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.

[Flettner]

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.

[gwynfryn]

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.

[Flettner]

These books

[gwynfryn]

These books

They look well used.

[F5 Dave]

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.

[Flettner]

Haha, he is going to need every bit he can squeeze out of that thing.

[gwynfryn]

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.

[gwynfryn]

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.

[Flettner]

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.

[F5 Dave]

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.:banana:

[jellywrestler]

To be fair the power is in harmony with the handling.

there's no such thing as Harmony when you're talking TF125

[F5 Dave]

Debbie, Baabra, Harmony. They've all enjoyed a ride on a mud-bug to the top paddock for a romantic interlude with the friendly farmer.
What goes in the the top paddock. . .

[Flettner]

In the real world stick to Dave's advice, if you want to finish and do well. TF will respond well to even a mild hot up.
What I have in mind likely wont even finish an event. By the time it spreads hot burning bits all over the place, won't be invited back I bet.

TF, the sensible choice actually.

[F5 Dave]

Well the sensible choice would be a DT125 if you can find one. Full reed barrel and better crank parts, better piston. Probably better handling .

[Flettner]

Better handling? Really.

[F5 Dave]

I've ridden neither as dirtbikes (I did say 'probably') but applying my bias;) the Yamaha was designed as a trailbike, the TF as a farmbike. Like an AG vs DT. But single shock can probably be built up ok.

Full reed is always nice for throttle response.

I mean, look at what we are talking about. Like the two drunk guys at 2am.. "you take the ugly one. I'll take the really ugly one.":crazy:

[Flettner]

But single shock can probably be built up ok.

Against the rules, and rest assured, I will be that guy, the rule monitor.

[gwynfryn]

Against the rules, and rest assured, I will be that guy, the rule monitor.

Non linkage monoshock is all good in Hustler class.

[F5 Dave]

So this with a DT engine.

https://www.trademe.co.nz/a/motors/motorbikes/motorbikes/dirt-bikes/yamaha/listing/3694087805?bof=zvbUhTny


Or . . . A late model YZ with the best but legal front end grafted on with a drum. Then remove the shock linkage and buy the best twin shocks you can afford with new brackets.

And fit a DT engine.

Or. . And I've done a short search for rules and only found a Facebook waste of time, but I think Flet knows where I'm going with this. . .

Either mill the YZ barrel and add cooling fins, or cast an aircooled barrel.

[gwynfryn]

So this with a DT engine.

https://www.trademe.co.nz/a/motors/motorbikes/motorbikes/dirt-bikes/yamaha/listing/3694087805?bof=zvbUhTny


Or . . . A late model YZ with the best but legal front end grafted on with a drum. Then remove the shock linkage and buy the best twin shocks you can afford with new brackets.

And fit a DT engine.

Or. . And I've done a short search for rules and only found a Facebook waste of time, but I think Flet knows where I'm going with this. . .

Either mill the YZ barrel and add cooling fins, or cast an aircooled barrel.

Yep lots of options.
From my experience of riding vinduro over the last couple of years hp doesn't count for that much. Sharp tyres, reliability and a little talent does.

[F5 Dave]

Bah!

Technology and one upmanship for the win. :first:

And Flet hasn't even started to talk about Hooky fuel that helps cool air-cooled bikes disproportionately.

[F5 Dave]

Against the rules, and rest assured, I will be that guy, the rule monitor.

Yeah, well I see you 40hp and match you 32 and 20 less kg.


This really is the best thread currently.

When do we start smack talking?

[Flettner]

Non linkage monoshock is all good in Hustler class.

Is it? Right change of plans then on the frame.

[Flettner]

Yep lots of options.
From my experience of riding vinduro over the last couple of years hp doesn't count for that much. Sharp tyres, reliability and a little talent does.

You are completely correct.

But thats not the point, I want something just a little different, I like the engineering challenge, and I'd like 40HP thankyou.

Im thinking ahead for when VMX follows this wonderful class template. Haha, they won't know what hit them.

[Flettner]

Non linkage monoshock is all good in Hustler class.

You work that TF properly, you could have an excess of 20HP, that would surely help, on the hills.

[Flettner]

Yeah, well I see you 40hp and match you 32 and 20 less kg.


This really is the best thread currently.

When do we start smack talking?

Reckon you would get 32HP from a TF? Im not so sure.

[F5 Dave]

The 2005 YZ125 with fins welded to a dejacket barrel. ie if rules were aircooled but not limited by age or competition origin. 32hp seems good there in a modern bike with suspension downgrades.

I have since read some more rules that seem a little less open, but not hustler ones. Bah.

[husaberg]

So this with a DT engine.

https://www.trademe.co.nz/a/motors/motorbikes/motorbikes/dirt-bikes/yamaha/listing/3694087805?bof=zvbUhTny


Or . . . A late model YZ with the best but legal front end grafted on with a drum. Then remove the shock linkage and buy the best twin shocks you can afford with new brackets.

And fit a DT engine.

Or. . And I've done a short search for rules and only found a Facebook waste of time, but I think Flet knows where I'm going with this. . .

Either mill the YZ barrel and add cooling fins, or cast an aircooled barrel.

https://www.vmx.co.nz/enzed-vmx/classes

[F5 Dave]

That's vmx not vinduro. Although they do have an amusing typo in their enduro class.

[Flettner]

Vinduro, see, Hussler, a fun class with minimal rules. Made for tinkerers, could bring out alsorts.

[F5 Dave]

http://www.vinduronz.com/vinduro-nz-regs.html

Didn't see it here.

[george formby]

"Not intended as serious competition"!

:killingme A bloke took huge umbrage at me getting ahead of him in the last Vinduro I did, most miffed he was until I had the chance to get a word in and fully admitted to getting lost and missing a bit of the course.

[Flettner]

http://www.vinduronz.com/vinduro-nz-regs.html

Didn't see it here.

Too new, they clearly havent updated yet.

Its on their facebook somewhere.

[Flettner]

"Not intended as serious competition"!

:killingme A bloke took huge umbrage at me getting ahead of him in the last Vinduro I did, most miffed he was until I had the chance to get a word in and fully admitted to getting lost and missing a bit of the course.

Last one I went to, arrived late, missed half the event, only enteted trail bike class anyway.
Came home with a first place trophy, not even sure what class it was for. Serious competition, sure. But loads of fun.

[Flettner]

Further, the year the F9 won its class, at prize giving they were handing out medals to the winners. At the end as the prize giving was about to finish the speaker said " we have a few medals left over, if anyone else wants one just help yourself from this box"
Haha completely ripped the shine of the win.
I like that easy going nature of Vinduro.

[husaberg]

Vinduro, see, Hussler, a fun class with minimal rules. Made for tinkerers, could bring out alsorts.

okay i only heard what you had said in passing, golly they are wide open
with the rules . If it’s not explicitly in the rules then it’s not cheating....

[Flettner]

okay i only heard what you had said in passing, golly they are wide open
with the rules . If it’s not explicitly in the rules then it’s not cheating....

I know, aye.
I don't want to use this XS but I can't find anything else suitable. Best I order it up on monday I think.

[husaberg]

I know, aye.
I don't want to use this XS but I can't find anything else suitable. Best I order it up on monday I think.

do you want me to send pics of the 350/f stuff
there is a few engines in pieces
but i still think the honda 230- or 125T is a better bet
did you try this guy?
https://nzbikeparts.com/
He had a cmx250 listed.

i found you a poked cd175 maybe?
did you try Pete Sales?

[Flettner]

do you want me to send pics of the 350/f stuff
there is a few engines in pieces
but i still think the honda 230- or 125T is a better bet
did you try this guy?
https://nzbikeparts.com/
He had a cmx250 listed.

i found you a poked cd175 maybe?
did you try Pete Sales?

I googled a CD175, too old.
CB350, Grumph frightened me off those heads.
But thankyou anyway. Ill contact Good Parts on monday, see what hes got.

[husaberg]

I googled a CD175, too old.
CB350, Grumph frightened me off those heads.
But thankyou anyway. Ill contact Good Parts on monday, see what hes got.


The cb250 cmx250 is based on the CB125T they are basically 125 sized.

the CD is 4 speed too i think.

[Flettner]

I'll sort a fourstroke twin base engine on monday, after all Ive got two weeks.... plenty of time.

In the mean time I do have a completly stock AG100. Perhaps I might have to give it a tickle up for the first round or two. Borrrrring. Where did I put that Jennings book. I hate AG100 engines.
Pipe, carb, cast a new barrel, bugger, here we go again.

Yes CD is four speed I see.

[husaberg]

I'll sort a fourstroke twin base engine on monday, after all Ive got two weeks.... plenty of time.

In the mean time I do have a completly stock AG100. Perhaps I might have to give it a tickle up for the first round or two. Borrrrring. Where did I put that Jennings book. I hate AG100 engines.
Pipe, carb, cast a new barrel, bugger, here we go again.

Yes CD is four speed I see.

this will get you started with the AG i mght have a RD250 reed valve somewhere.
https://www.kiwibiker.co.nz/forums/showthread.php/180353-Making-an-ag100-keep-up-with-an-xr250?p=1130983825#post1130983825

351503351504

[Flettner]

this will get you started with the AG i mght have a RD250 reed valve somewhere.
https://www.kiwibiker.co.nz/forums/showthread.php/180353-Making-an-ag100-keep-up-with-an-xr250?p=1130983825#post1130983825

351503351504

Did I write that shit? A bit optimistic I think.

[husaberg]

Did I write that shit? A bit optimistic I think.
Well I did my part and found the old school hop up diagrams:2thumbsup
I likely have a rd250 cylinder and head somewhere that would be a better start?
I can even loan a you 350 one?

[Flettner]

Here is an AG100 engine but unfortunately I cant use it as the head is water cooled.
https://youtu.be/TOHKls3Cxjs

[Flettner]

I likely have a rd250 cylinder and head somewhere?

That might be a good start. :yes:

[husaberg]

That might be a good start. :yes:

it will be rusty but the price is right.
if you are allowed 175 why not the 350. i can loan that only as its for a complete bike.

oh shit i just figured out that ag is under square that isn't going to work, you need the bigger ag

[Flettner]

I do have a 52mm stroke AG100 crank. To go out to 54 Id have to spin up another one. Depends on just how serious I want to get.

125cc twostroke, 150cc fourstroke. No limit on induction pressure.

[husaberg]

I do have a 52mm stroke AG100 crank. To go out to 54 Id have to spin up another one. Depends on just how serious I want to get.

125cc twostroke, 150cc fourstroke. No limit on induction pressure.

okay i will start an excavation at dads.

[Flettner]

Drill down to 1973:laugh:

[husaberg]

Drill down to 1973:laugh:
its was subterranean looks like it was drug out of a swamp
Yes its pretty manky, but it will clean up it has a reed and manifold attached.
Its also unmolested with the porting which is pretty unusual.
No 250 head but i have a 350 one here you can mod.
if you want them they should be there by Tuesday.
351506351507351508

The offset fining will give room for a large pipe
A dt or ag175 head had radial head fining

[Flettner]

its was subterranean looks like it was drug out of a swamp
Yes its pretty manky, but it will clean up it has a reed and manifold attached.
Its also unmolested with the porting which is pretty unusual.
No 250 head but i have a 350 one here you can mod.
if you want them they should be there by Tuesday.
351506351507351508

The offset fining will give room for a large pipe
A dt or ag175 head had radial head fining

Thankyou, yes. What bore size? 56?
I might leave it like that on the outside, in keeping with the rest of the bike.

[Flettner]

I shall name the new fourstroke the,
SC150T
Its most important it gets a proper name. :niceone:

[husaberg]

Thankyou, yes. What bore size? 56?
I might leave it like that on the outside, in keeping with the rest of the bike.

its i think 54 maybe plus .5.
it def going to need a hone :laugh:

[Flettner]

Yamaha used to like 56 x 50.
I can change the crank to 50.0 stroke if need be....

[husaberg]

Yamaha used to like 56 x 50.
I can change the crank to 50.0 stroke if need be....

Yes, especially with the singles but the RD were 54mm. They went to it around the yds3 and back to 50.6 for the TZR.
oddly looking at the head the early 350s it seems had smaller fins than the late 250's.
I will have a decent dig foe the 250 head
Pretty sure you can make it work Flet.
either that or i know a guy a few km's from here that might have a DT125 cylinders maybe something even flasher.
They were 50mm stroke std

[Flettner]

Yes, especially with the singles but the RD were 54mm. They went to it around the yds3 and back to 50.6 for the TZR.
oddly looking at the head the early 350s it seems had smaller fins than the late 250's.
I will have a decent dig foe the 250 head
Pretty sure you can make it work Flet.
either that or i know a guy a few km's from here that might have a DT125 cylinders maybe something even flasher.
They were 50mm stroke std

No no, that cylinder will be fine, I can make it work. Even if you can't find a head, Ill make something I have here fit. The 52 stroke crank I have will work fine, Ill make it all work together. A filthy old AG, with bite, nice. I have a spare Ignitech.

[husaberg]

No no, that cylinder will be fine, I can make it work. Even if you can't find a head, Ill make something I have here fit. The 52 stroke crank I have will work fine, Ill make it all work together. A filthy old AG, with bite, nice. I have a spare Ignitech.

The hot ticket for reeds valves for them is a late YZ85.
What frame are you going to use?

[Flettner]

The hot ticket for reeds valves for them is a late YZ85.
What frame are you going to use?

Its got a frame, you know, AG100. It will be fine for now, I've only got a couple of weeks to prepare it.

SC150T , Ill build somthing using the engine as part of the frame. Motor is solid and save weight by missing out not needed frame parts.

[husaberg]

Its got a frame, you know, AG100. It will be fine for now, I've only got a couple of weeks to prepare it.

SC150T , Ill build somthing using the engine as part of the frame. Motor is solid and save weight by missing out not needed frame parts.

okay like an early xr200
https://i.ebayimg.com/images/g/wwwAAOSwBLNfF3Lh/s-l1600.jpg

Or an Ag200
https://s3.amazonaws.com/advrider-photobucket-images/images/T/Tony_T12_2P6C9891.jpg

[F5 Dave]

Or a TM250
https://motocrossactionmag.com/mxa-race-test-the-real-test-of-the-2021-tm-250x-two-stroke/#:~:text=A%3A%20The%20TM%20250X%20is,fuel%20inject ion%20or%20a%20carburetor.

Sorry. I got all excited.

[Flettner]

Or a TM250
https://motocrossactionmag.com/mxa-race-test-the-real-test-of-the-2021-tm-250x-two-stroke/#:~:text=A%3A%20The%20TM%20250X%20is,fuel%20inject ion%20or%20a%20carburetor.

Sorry. I got all excited.

Me too. Perhaps Ill use the TM I was sent.
Lying Barstards.

[husaberg]

Me too. Perhaps Ill use the TM I was sent.
Lying Barstards.
Your head and cylinder should have been there today?
i used the address google had for you.

[Flettner]

Your head and cylinder should have been there today?
i used the address google had for you.

Perhaps tomorrow? RD always takes longer.
Actually I had a little trouble tracking down the AG. Loaned to a guy who loaned to a guy, you know how it goes.
Found, in Rotorua, be back by the end of the week. Apparently it makes for a good hunting bike. Wont be good for that by the time Im finished with it, Deer will be long gone.
Thankyou.

[husaberg]

Perhaps tomorrow? RD always takes longer.
Actually I had a little trouble tracking down the AG. Loaned to a guy who loaned to a guy, you know how it goes.
Found, in Rotorua, be back by the end of the week. Apparently it makes for a good hunting bike. Wont be good for that by the time Im finished with it, Deer will be long gone.
Thankyou.
its nz couriers it should be 24 hours?


i think the address was wrong ? pm sent.
the tracking sticker is at work.

[Flettner]

Doubt it? More like 24 days.

[husaberg]

Doubt it? More like 24 days.

So if i have a 250 villers starmaker powered Kx250
the chassis is essentially same as pre 70 so it can run vintage with its 250 four speed. Interesting.


intake rubber

https://www.trademe.co.nz/a/motors/motorbikes/parts-for-sale/engine-components/listing/3709597560

rip off v force reed valve
https://www.trademe.co.nz/a/motors/motorbikes/parts-for-sale/fuel-oil-tanks/listing/3701507704

[Flettner]

Mk 3, or 4? Can't remember exactly now. Its still there under the bench, somewhere. Cut down Wade supercharger off a Commer Diesel, TS3.

[Kickaha]

While we're on the subject of the legendary Tf125 how much fork oil do they hold of what grade and if keeping the oil pump on it how do you bleed and set it up ?

[F5 Dave]

6 inches from the top and add some if not enough is a rule of thumb, (that I've heard and never tried).

Check my thread Pete's TF. Too long ago to remember but the left main could, or should have a hole from the transfer to main. Right could have seal so bearing is on gearbox side . But can't remember accurately. If there wasn't you need to make a hole to match one on the left. The T125 had all sorts of other shielding and feed holes, the RG was simple and fukd if I can remember which was which. Poxy Suzukis. You'd think I'd be a fan.

Otherwise open the bleed screw on the pump till it runs easily. It should then progress up to the barrel feed. Run it on premix until you are sure it is getting there with no bubbles. If there are two lines, one will be to barrel and one to a main and there will be check valves.

[husaberg]

okay here is the updated rules
351515

[F5 Dave]

Thinner forks in this with drum front brake. Find a 125 barrel.

https://www.trademe.co.nz/a/motors/motorbikes/motorbikes/dirt-bikes/yamaha/listing/3709392123

Sorry, 200 is linkage. So was going to suggest a steel round swingarm with a brace and the 175 or 125 shock. Or graft twin yss shocks .

Could even dress it up with a steel tank and shorter plain seat and generic non it guards, sidecovers.

[gwynfryn]

6 inches from the top and add some if not enough is a rule of thumb, (that I've heard and never tried).

Check my thread Pete's TF. Too long ago to remember but the left main could, or should have a hole from the transfer to main. Right could have seal so bearing is on gearbox side . But can't remember accurately. If there wasn't you need to make a hole to match one on the left. The T125 had all sorts of other shielding and feed holes, the RG was simple and fukd if I can remember which was which. Poxy Suzukis. You'd think I'd be a fan.

Otherwise open the bleed screw on the pump till it runs easily. It should then progress up to the barrel feed. Run it on premix until you are sure it is getting there with no bubbles. If there are two lines, one will be to barrel and one to a main and there will be check valves.

The oil pump only supplies oil to the inlet tract on the tf125. I've deleted it on mine and run 30:1.

[F5 Dave]

Cool. I wanted to be careful in my response as it has been 5 years since inside one and other motors get stored in the same memory cashe.