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anyone ever have any porting done on an old dt250 monoshock ?

i happen to have 3 spare barrells and heads for my old dt,and thought it might be interesting to get a bit of tuning done on one of them,

not looking to turn it into a rocket,just a sort of bit more all round sort of tune,if there is such a thing,

i know the it's and yz's of the same era used basically the same engine,so theres obviously room for improvement,

anyone an opinion on a more modern , flatslide carb,or maybe a slightly larger mikuni vm,the stock 28mm does seem quite small for a 250 ?

as i said not looking for a rocket,just a bit livelier and torquier,

thanks for any opinions/advice

nick

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Have you checked to confirm the HEAD is the same between DT and IT? On my DT, It seems to kick over too easily, as if it is designed with low compression. Maybe use a YZ head or compare head cc's with a YZ and shave it to match. Also compare port location and size with a YZ.

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anyone ever have any porting done on an old dt250 monoshock ?

i happen to have 3 spare barrells and heads for my old dt,and thought it might be interesting to get a bit of tuning done on one of them,

not looking to turn it into a rocket,just a sort of bit more all round sort of tune,if there is such a thing,

i know the it's and yz's of the same era used basically the same engine,so theres obviously room for improvement,

anyone an opinion on a more modern , flatslide carb,or maybe a slightly larger mikuni vm,the stock 28mm does seem quite small for a 250 ?

as i said not looking for a rocket,just a bit livelier and torquier,

thanks for any opinions/advice

nick

Which year? If you have an engine that is similar to the TY 250 model of the 70's there is a cure for your demands, even additional cc up to 320cc is then possible.

A pic and engine number would be cool too.

Edit:

Here an article about modded TY from 1979, some of the Majesty kits are still available:

Majesty Yamaha 320 250 200 and 175cc

Edited by P-Schrauber
Adding some information / Link:

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Which year? If you have an engine that is similar to the TY 250 model of the 70's there is a cure for your demands, even additional cc up to 320cc is then possible.

A pic and engine number would be cool too.

as far as i can tell its a '79 model,it has cdi instead of points,which i dont think we got before '79,

a few more cubes sounds interesting,theres no substitute,

you dont want a picture,its no show winner ,but imagine a scruffy old dt with a pe250 front end,and the back end jacked up,it all works fine,but a strip down and repaint wouldn't hurt,

i'll find the engine numbers out in the morning,its bed time here now

see you added a link whilst i was writeing my reply,will have a proper read tomorrow,thanks

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If it is a 1979 model the performance can be improved by putting a 77-78 top end on it.

The 79 was the last year for the "Big" DT and it had some mods that were intended to

improve emmisions, they robbed power too natch! The head has an "Off Center" combustion

chamber. There is also an Air injection thingy on it, so the early cylinder helps get rid of that

cleanly it will save a couple pounds getting rid of that stuff too.

Not sure if the ignition timing was messed with too, but I would check and set it to the earlier setting

while you are at it. The exhaust has a very restictive "Swirl type" spark arrestor that should be checked,

you may want to remove it and put on a more modern silencer with an approved spark arrestor.

The port timing is very mild, even on the earlier cylinders. There is more to be had with porting, but I

would leave that to a guy like Eric Gorr, and follow his recomendation on carb, etc.

That 320cc mod listed in the article on the TY involves resleeving and using a 80mm piston from a 360

There was a company here that made a kit for the early DT's, it will give more low end, good for trials

not sure if it's what you want. I think a few of the TY specialty companies in England and France have

parts to do that now.

Keep us posted with what you end up doing.

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i think all that emissions stuff was just for the u.s market,we didn't get it this side of the pond,

had a good trawl around the net , and haven't turned up anyone selling piston and liner kits,but did find the pistons for the 320 kits,after a bit more searching found a company making custom sleeves,any size you want,and they're only 20 miles from where i live,could well be an option if i decide to go the big bore route,although i hadn't really considered it until yesterday,was just thinking a bit of porting and maybe upgrading the carb,but the more i think about 320cc,and a bit of porting,hmmmm got some thinking to do

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A pic and engine number would be cool too.

ok heres a picture,like i said its not pretty,but it all works,when ive finished doing all the mechanical stuff ,then i'll do something about the way it looks,

the engine number is 1r7-201814,so what does that tell you?

http://i1117.photobucket.com/albums/k599/nickxjr/076.jpg[/img]"]http://076.jpg

sorry its such a rubbish picture from my phone,you may just spot my dads old 500 triumph trying to get in the shot,been sorting the gearbox and clutch for him

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Sorry about the info above Nick, didn't see that you were on the other side of the Pond!

The photo shows the 1979 style tank and sidepanels, slightly different that he 77/78 parts.

And the leading axle forks that were new in '79. The VIN doesn't have the same prefix as the US

models, so not sure what that means, didn't Europe get the DT's for a couple years more? Til 81 or 82?

US Vin's for 1979 DT250F . Competition Yellow . 2N6-000101 to 004320

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ok heres a picture,like i said its not pretty,but it all works,when ive finished doing all the mechanical stuff ,then i'll do something about the way it looks,

the engine number is 1r7-201814,so what does that tell you?

http://i1117.photobucket.com/albums/k599/nickxjr/076.jpg[/img]"]http://076.jpg

sorry its such a rubbish picture from my phone,you may just spot my dads old 500 triumph trying to get in the shot,been sorting the gearbox and clutch for him

What it tells me, you find here: ForumTY

The first three numbes "1R7" of you engine number is the model or type number of your bike, which is actually a DTMX model. (see in the link of the French Forum above, nice pic of the same bike too). You might use it for rebuild, ... contact the French rider of the bike, ...

And of course, thank's for the posted picture the forum lives from pic's.

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dont let that front end fool you,forks , yokes and wheel are off a pe250 of about the same age,

yea,your right about us getting the dt into the '80's ,'81-''82 would be about right,a change in new rider laws pretty much killed off demand for 250's,used to be able to ride a 250 at 17 , without passing a test,but they changed it to 125,i turned 17 in '83 so just missed out,i had a dt175 with 125 stickers on the panels,

no need to apologise for not spotting im in the uk,your trying to offer some useful advice,thats what counts :lol:

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Simple power for this bike... raise and widen the exhaust port 1-2mm. Run a modern carb off almost any 250 race type bike,rm,kx,yz. 96 or newer. The manifold (and reeds)are smaller than than the yz,mx bikes of that era so it will be a tight fit,and might need an adapter built..

There is a mod you can do to the intake.Make a hole,or a "port" from the reed area to the bottom transfer area,it really helps. I have pictures on how it's done...

Here's the thread and pictures,...http://www.thumpertalk.com/forum/showthread.php?t=973265&highlight=boost+port

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thanks scalejockey,thats really good info :lol:

the boost port sounds easy enough,and a mod that should be carried out even if i do nothing else,

with the exhaust port diagram for thr tri-z it looks like the port is only raised in the middle,reducing to nothing at the edges,would this be the way to do the dt too ?

i presume the widening of the port is from top to bottom,not just wider in the center,reducing to nothing at the corners,unlike the pic of the raised port,

this all looks like stuff i can do myself with a drill and dremel,is it as simple as it seems ?

you say a carb off a modern mx 250,dont they use something like 38mm carbs,seems like a huge leap from 28mm,i was thinking more like 32mm,you reckon big is the way to go

thanks again nick

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I use a 38mm carb off a 2000 RM on my 75mx250. (But it came with a 38mm round slide stock.) My cylinder is very much like yours, But the reeds and intake are somewhat smaller on yours. So you might do a carb off a 125,a 36mm or so. Mainly the 'modern' style carbs simply work SO MUCH better.

The boost port is really easy,Honda had the patent way back when,,(like in the 80s')so no one else used that design. I did a lot of 83-87 yamahas'.

I do believe a mx or yz style piston will fit too. ...(I think.) It will have a large "U" cut on the intake comparred to your two holes in the piston intake side.(even more power) If you measure yours i can measure a spare one of mine to be sure.

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the big end let go today,thought it was running a bit rough the last time i rode it,but couldn't put my finger on the problem,happen to have 3 spare crankshafts,and none of them are too good :lol:,so whist ive got it apart for a bottom end rebuild i can have a play with boyeson ports and a touch of exhaust port raising,

actually found another barrell today,whilst looking through my spares for a decent crank assembly,so that makes 5 in total,no idea how i acquired that many,will experiment on a couple and the one that turns out best will get a rebore and new piston,

i used to run a wiseco piston ,that had the crescent cut out,instead of the holes through the piston,sure it was advertised as for dt,it,and yz, but it snagged a ring a couple of years back,which ended up making a bit of a mess of it and the bore,replaced it with a cheaper piston , same as original dt piston,cant say i noticed any difference in performance,

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had a practice at drilling the boyeson ports,ive drilled them at 10mm and opened the mouth of them to 13mm,dont think its safe to go any bigger than 10mm,not a lot of clearance between the stud hole and the liner,the barrell i used was in the poorest condition of the 5 barrells ive got,for a practice i dont think they came out too bad,

http://i1117.photobucket.com/albums/k599/nickxjr/010.jpg[/img]"]http://010.jpg

http://i1117.photobucket.com/albums/k599/nickxjr/009.jpg[/img]"]http://009.jpg

Edited by nick cresswell
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thanks,made a nice job of the boost ports on the barrell that i'll be using too,which has now been dropped off for a rebore,

i've decided to do things a step at a time,will reassemble without doing the port raising,just to see how much each mod changes things,

these old aircooled 2 strokes are so easy to work on , its no problem to take the barrell off again at a later stage,

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thanks,made a nice job of the boost ports on the barrell that i'll be using too,which has now been dropped off for a rebore,

i've decided to do things a step at a time,will reassemble without doing the port raising,just to see how much each mod changes things,

these old aircooled 2 strokes are so easy to work on , its no problem to take the barrell off again at a later stage,

The old bikes ARE great to work on!! I did a clutch rebuild,, trail-side once.

Even had piston skirt break,removed the cylinder,cleaned out some piston bits a rode it a little longer that weekend.:lol:

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Simple power for this bike... raise and widen the exhaust port 1-2mm. Run a modern carb off almost any 250 race type bike,rm,kx,yz. 96 or newer. The manifold (and reeds)are smaller than than the yz,mx bikes of that era so it will be a tight fit,and might need an adapter built..

There is a mod you can do to the intake.Make a hole,or a "port" from the reed area to the bottom transfer area,it really helps. I have pictures on how it's done...

Here's the thread and pictures,...http://www.thumpertalk.com/forum/showthread.php?t=973265&highlight=boost+port

Have any tuning tips for a dt 400? I have a spare engine so I wouldn't mind experimenting.

I think I'm gonna try drilling the hole like you said.

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Have any tuning tips for a dt 400? I have a spare engine so I wouldn't mind experimenting.

I think I'm gonna try drilling the hole like you said.

That 400 is basically the same motor. Well... the cylinder won't fit on the 250 lower end but the design is the same.(yes i tried):lol:

So the same mods will work.

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