DT1 250 pre 70 legal BArrel

[Tim754]

My head hurts................................

[Freakshow]

What's the go with PRe 70 mods then, like are there restriction on a round slide carby etc ?

Obviously you have to use a flange set up or do you ? can you just then make up a flange to rubber and run a 34mm mukuni or somthing, or does it have to be an original 30mm style Flanged carby ?

Anything else im missing that has to be Dt1 etc to be legal or is everything else free ( not era specific - ie 74 mdl Dt forks etc )

[vandy010]

got your PM Freaky and we'll work it out.
my RT1 carby is a 34mm unit and jetted to the RT1 specs straight from the manual and runs fine.
i needed to get a rubber boot from T.D. Hatricks {mikuni guys} to make it work and they're pre~70 legal no probs.
any yammie 34mm forks with straight leg bottoms and the correct travel amount will do the job for pre~70 but the earlier type with the mudguard mount brackets "look" the part for that era {my opinion only}.
bascically, any DT/RT 1,2,3 as long as they're converted back to a piston port barrel, will be fine for pre~70.

[Freakshow]

Do you have a part number for that flange boot ? IS it like the TM suzi one.

SO a set of 74 Dt250 forks are ok then ?

any thing else im missing ?

[L.Ron.Pursang]

What's the go with Pee 70 mods then, like are there restriction on a round slide carby etc ?
Obviously you have to use a flange set up or do you

No Freaky you aren't limited to the flange mount carby. I used a rubber boot and a 34mm Amal off a Weslake speedway bike on my DT1 which worked great. I'm initially using a 34mm flange mount Mikuni on the Cheney RT1 to simplify things but will probably go over to a 34mm in a similar setup as Vandy.

I used 35mm Betor forks from an OSSA on my DT1 but to simplify the job I'd be using 34mm Yamaha forks with alloy sliders from a later model and fitting PDF valves which overcomes the lack of adequate performance of the Yammy forks . I don't think the conical style Yammy front wheel is legal for pre '70 so I'd be use fork sliders that easily accept the old DT1 full width hub.

[Freakshow]

kewl thanx firko, ill try to get a heads up from vandy on the rubber bit, 34 muks i got and boxes of jets so iid like to stick to what i know.

i got a set of betor here somewhere i might have a look at them , but from what your saying a full width front drum is the go ? i have a 75 TS 250 front end which is full width and might be an easy bolt on F/end ? thoughts, it looks way old school particulaly with the big drum andi thik it also has a brake stay too not a tab.

what trees can i use then  that are legit to take the 34mm forks or do i get the 32mm reemmned ?

[Nathan S]

I don't think the conical style Yammy front wheel is legal for pre '70 so I'd be use fork sliders that easily accept the old DT1 full width hub.

Mmmmm... Interesting point... According to the on-line parts catalogues, the conical hub was first fitted to the 1972 RT2MX, which was reed valved.
However, the wording of the rules says that 'any' RT1 with a non-reed barrel is legal for pre-70.
The obvious debate then centres on whether an RT2 is really an RT1 (they've all got RT1 stamped into the frame and engine).

Meh - I'm running the full-width DT1 type hub on both my DT1 and RT1, because there's no argument over legality and because the brakes are awesome.


Firko, all of the 34mm in-line forks have the same brake lug - so you'll have no drama fitting the early brake/hub to later 34mm forks, or visa-versa.

[Freakshow]

so nat what did you do to the triples to take the 34mm forks .

If im reading it right your saying the 34mm forks are OK and there also is no need to modify the DT1 axle or shim to slot later DT 34mm forks, the axles etc the same.

[Freakshow]

Found this bit of info on the DT1mx when i was going through some stuff on the GYT mods etc for my next project.

Any ow remebered this debate and not sure if it relates to it, anyhow it mentions a differant hieght and window on that piston spec, which maybe where all that sizing crossed over, also noticed they head volume changed and on the other pages it also mentions window and timing changes for the 1 mx version ?

[Nathan S]

so nat what did you do to the triples to take the 34mm forks .

If im reading it right your saying the 34mm forks are OK and there also is no need to modify the DT1 axle or shim to slot later DT 34mm forks, the axles etc the same.

Sorry, I missed this when you first posted it.

All DT1 forks are 34mm, so there's no need to do anything to the triple clamps or brakes or anything - what changes is the lower legs. Early models are chrome plated steel, while later ones are alloy. The alloy-leg forks apparently have better internals, as well as the improvement in weight and stiffness.

[Freakshow]

Any advance on whatr the flange rubber mount is for the 34/36mm Carb ?

[Freakshow]

Come accross a PP with a deck barrell, what am i lookng for piston wise to make this work.  > bottoms i have are 214 rods, any idea what the piston was that used the decked barrell ? before i go making up a spacer ?

[Freakshow]

bump