Basket Cases

[David Lahey]

I recently saw online a 123 Cota modified to fit a XL125 engine with a TLR200 barrel which brings the capacity out to 167CC.

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Has anyone completed the 4 stroke dream for some of the other manufacturers?
Yamaha could have had the TXTY by fitting a TY250 with an XT250 engine.

Think I have seen a photo of Mick Andrews riding an XT500 modified to trials spec.

A friend in the UK fitted a Serow motor in a TY175 frame many years ago because he wanted an electric start 4 stroke trials bike. The Serow was also called an XT225. I think it was a 2 valve motor a lot like the earlier 2 valve TT/XT250 motor.
Jon Cull if you see this can you post a photo of it?

[Greg Harding]

Hi Everyone,

I recently saw online a 123 Cota modified to fit a XL125 engine with a TLR200 barrel which brings the capacity out to167CC

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That is an interesting combination Kurt, it would have to be easier to start than the awkward kickstart! Do you or anyone else know which bike that kickstart is off? Maybe CRF? For some time I have wanted to fit an aloooominium kickstart to the TLAhhhhh.

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My first attempt did not work out so well as I had secured one of these in the hope of making it work:

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It is off a TLR 250R:

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Many years ago I got to ride one of these and I was impressed with the low starting height and the length for a smooth follow through easy start. So I was hoping it would be a good modification but the bend was not right for the older model. Making a custom kickstart knuckle is something I have done a few times but reworking a heat treated aloooominium arm is not something I want to get into. Now that I look at the comparison photos I realize there is a fair bit of height difference in the kickstart splines.

The hunt continues..........

[Kurt]

Not sure what the kickstart is from Greg but by comparison with my CRF250 it looks very similar.

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[Greg Harding]

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[Greg Harding]

Happy New Year Everyone,

A friend in the UK fitted a Serow motor in a TY175 frame many years ago because he wanted an electric start 4 stroke trials bike. The Serow was also called an XT225. I think it was a 2 valve motor a lot like the earlier 2 valve TT/XT250 motor.
Jon Cull if you see this can you post a photo of it?

David, I have been riding my TL 250 lately as it had been sitting in the back of my shed for a long time now. The reason I am bringing it up is that I think the XT 225 (2 valve) motor might be a better choice for a Trials motor? 2 valves might mean less engine braking? That along with the overall weight is most likely why I parked it?

An old school friend contacted me chasing a TL 250 flywheel to try on his XL 250 Motosport. He said they are lighter and he is chasing more revs racing VMX. My first thoughts were that can't be right as pretty much all Trail bike engines converted to Trials have a heavier flywheel, DT 250 and TY 250 for example. So it turns out I was wr wro wr wro, not correct!

TL 250 flywheet:

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XL 250 Motosport flywheel:

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Yes they do fit and work as the bore is the same.
TL 250 flywheel weights:

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XL 250 flywheel weights:

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So 2 kilos for TL 250 and 2.6 kilos for 12.5 mm bigger diameter Motosport flywheel.

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Obviously curiosity got the better of me so I had to try the Motosport flywheel on the TL for myself. My other concern that I did not mention is the TL250 can fire early when kick-starting and steal the kickstart leaving you with an air swing and over extending your knee!

All fitted up easily and I had a test ride this afternoon and I am very happy so far. The heavier flywheel smoothes out the transition from idle to mains and back to idle so that is a positive! There is minimal difference accelerating and lightly less engine braking so another positive! I can't feel any difference in power as they are quite a torquey motor.

As for my theory that a heavier flywheel might cure the air swing kickstart, well the jury is still out???? Time will tell.

[David Lahey]

Well that's amazing Greg. It is so counter-intuitive that I'm not really convinced yet that you are not just playing another trick.
When I was a youngster and riding my enduro-ised SP370 in serious terrain up in the mountains, I thought many times that it would benefit from a heavier flywheel in the slow, steep stuff. What stopped me doing it was the thought of the ridicule my mates would dish out for slowing down further an already fairly mild-performing bike. I even measured up the space available inside the casing for a ring of steel on the OD of the flywheel.

[Greg Harding]

Hi Everyone,

Well that's amazing Greg. It is so counter-intuitive that I'm not really convinced yet that you are not just playing another trick.

Yes David, I can get things backwards.......
So now for an update as I got to have a good ride on the TL 250 on Sunday.
This is an old post of George's referring to differences between TL 250 and XL 250 Motosport:

About the only thing that is the same is the basic motor, everthing else is totaly different.
Even the motor is a bit different. From memory the TL head has a centre inlet port(same as the later XL250), TL cam is a softer grind , the ingnition flywheel is the same as an XL350, the TL has different gear ratios , TL has the later style crankcases with ball bearing mains although the cranks are the same as are pistons, cylinders, valves and all the cam drive bits.

They are quite popular with the Pre75 MX guy's being the only pre75 Jap four stroke that is anything like usable in MX.

When I read this, my thoughts were that the flywheel was heavier because it was off the XL 350 but I now realise that was wr wro wr well you get the point. Still do not know how much an XL 350 flywheel weighs but my guess is 2 kilos.

Back to the riding and I think the heavier flywheel is the single best modification that I have done to the TL 250 as it makes it smoother. Even going up and down through the gears is more enjoyable plus the power is more linear. With multiple restarts stopping to clear some vines and lantana, there was no stealing of the kickstart so I am happy about that. One negative that has come to light is the Variable Idle Speed is more noticeable like the TLR 250 with Keihin carby. They are basically the same carby on both models so not surprising really. A Mikuni would fix that I am sure!

So my TL 250 theory has now changed, I used to think that when made the TL 250, they panicked about the weight so they made the tank out of aloooominium....... The stated 99 Kilograms was a bit optimistic but I understand why they were worried about tripple digits!!!! Now that I have weighed the seat (goes on after the tank):

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My new theory is they chose a 600 gram lighter flywheel and hoped for the best!

This is not about a Twinshock but it is relevant here, Donna's bike Shirley 125 was a little racey for her so I tried to source a flywheel weight and no such animal anywhere! There was an old truck axle that held my door open, it had a nice sizeable flange for mounting the wheel on. So we machined a ring out of it and heat-shrunk it on. The outside diameter was what was left after machining the stud holes off and the width was worked out to clear the pick up and cover but I did not weigh it.

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It has been on there for years now and certainly made it more rideable.

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[Greg Harding]

Hi Everyone,

Just sharing what I have been up to with the TL 250, so I have had a few rides now I am really enjoying it. There is a bit more of a balancing act (to keep neutral balance) than other bikes and you need to hang off the side a bit more in some situations. If you are not ready for a change of terrain and the Heavy Old Non Directional Appendage wants to lay down for a while, it is quite hard to recover if you know what I mean.....

So between each ride I have been doing some maintenance and refining some things to make riding more enjoyable. The clutch and front brake cables have had length changes. Another thing that has been annoying me is I seem to drop the bike in a puddle each ride, not deep enough to drown it but wetting the grips and then have them slip seems to be my latest trick. Most of my bikes have a knurled section under the grip but not this one. The bars are old school high and wide, they suit me on this bike because of the extra leverage. Pretty sure bars like these are no longer available so I have decided to work with what I have and knurl under the grip with the handlebars still fitted to the .

Before

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After

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[David Lahey]

That's pretty cool Greg. I haven't seen a hand knurling tool before. We used to knurl things in lathes when I was an apprentice but those knurling tools didn't have the wheel at the back to provide the reaction force.
Apart from knurling TL250 handlebars, what would be the usual use for that tool?
By the look of the grippy knurled finish, you might not even need to fit handlebar grips to get a good hold of the bars.
If you've got enough water lying around to get your grips slipping, it sounds like you have been getting lots more rain down there than we have up here.
By the way, that's a nice-looking weight band you fitted to Donna's . Exactly what I had in mind for the SP370.

[Greg Harding]

Hi Everyone,

That's pretty cool Greg. I haven't seen a hand knurling tool before. We used to knurl things in lathes when I was an apprentice but those knurling tools didn't have the wheel at the back to provide the reaction force.
Apart from knurling TL250 handlebars, what would be the usual use for that tool? Hopefully this explains it's normal use? Pretty sure there is no such thing as a hand knurling tool.

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By the look of the grippy knurled finish, you might not even need to fit handlebar grips to get a good hold of the bars.
If you've got enough water lying around to get your grips slipping, it sounds like you have been getting lots more rain down there than we have up here. OK so I now think that we got your share as we have been riding with wet tyres every weekend this year.....
By the way, that's a nice-looking weight band you fitted to Donna's Exactly what I had in mind for the SP370.
Thankyou, in other news I had previously upgraded levers and perches from a 1980s model so I decided to upgrade the throttle assembly as well. Hopefully this will reduce the vines controlling my speed and me dropping the again?

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