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Tuning a Yamaha DT 400

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Hello everyone, and happy new year! :banana::busted::smirk:

My name's Filippo and I'm from Perugia, just in the center of Italy.

I'm a newcomer in this forum and I need a lot of help from you. :bonk:

Just a couple of days ago, I bought a Yamaha DT 400, a bike pretty uncommon in my country, but for sure not in the U.S.A.!

DT400b.jpg

DT400a.jpg

I'm afraid you would laugh when you'll read why I bought it: because I would like to race with it in Italian Vintage Enduro Championship.

I know: you would ask why the hell buying a DT instead than an IT, simple: ITs in Italy were never imported, and more: are pratically unknown if not in magazines.

As logical I should work pretty a lot on my bike, and I need advices and suggestions from you, just because here no one knows this kind of Yamahas.

So please read what I write and correct/confirm and tell me everything do you think of it.

I think the first thing is to replace the carburator with the one of the IT 400 (and the carburator boot, logically): I already found it on the web and I think it shouldn't be a problem.

Next step could be the exhaust: do you think is possible to find an IT 400 pot? Does it fit on the DT?

And how much would it worth?

Maybe another good tuning could be changing the rotor with the lighter one from the IT: is it easy to do or it'll be a problem?

Another thing could be the body parts: seat, tank, fenders and so: as far as you know, do they fit on the DT without problems?

Does the IT front fork works better than the DT stock one?

How different it is?

Longer, bigger?

Do you think I have to replace even the clamps?

Does the swing arm of the IT fit on the DT?

Is it different (I heard is longer) and better?

And How's about the rear shock absorber?

Well, I think that for a first wiew I gave you a lot to "work" about! :awww:

Thank you very much in advance to everyone that could help me in every way! :bonk:

Ciao,

Filippo

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i'm in the process of trying to improve the suspension on my dt250,using it250 shock,

done some research and it looks like the it from 79-80 had a swinging arm of same dimensions,although slightly different style to dt,so should be able to use it shock,may require some spacers ,and will require a new mounting hole in frame,for top of shock,should give 10" -250mm of travel,my it shock is still in uk customs,as like you we have very few it's in uk,so had to order from usa,will let you know how it works when ive got it on,

have just fitted a xr250 front end on my dt,before that i had a pe250 front end fitted,but wanted longer forks and a disc brake,

a friend of mine has a late model 83? it250 front end on his dt250,it didnt just bolt on,required some spacers and bearing changes,suppose you could make anything fit really,

good luck with your project,looks like a nice example,mines a scruffy old dog,so dont mind messing with it too much

nick

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Strange....The front of that bike has a leading axle,the ones in the States don't.

Your idea of simply changing the carb from an IT might not fit at all,the DT carb are REALLY small and the mainifolds are way different from the DT to the IT. If i recall the IT is more like the MX or YZ,it's a lot bigger with a different bolt pattern too.

But that is the bike from the states..what size is your carb?

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Well, thank you for these first interest! :bonk:

Yesterday my flu finally left me and I could try a little the bike.

It's amousing and smooth, incredibly smooth...

I'm not used to old two strokes, if not for the Rotax 250 I have on my Kramer and Kram It, but this Yamaha seems to be sleeping...

It seems quite as powerful as a Vespa 200, but Vespa is much easier for wheeling...

Ok, I didn't expected to rip off asphalt from the road, but neither this placid laxity...

In the time the engine keeps to gain revs you could kill a donkey throving at him moldy figs...

I'm afraid that if I would race with it as it is, timekeepers would fall asleep waiting for me to get out of the special tests...

Ok, seriously: the former owner wasn't the quickest person on the planet, but he's a terrible fusspot, and told me the bike was restored completely a couple of months ago: tires (on the rear ther is a brand new Pirelli TRIAL!!!), oils ("oilS"?!?), braking shoes, chain, candles ("candleS"?!?) and so on.

In effect the bike seems really well kept, carburator seems clean, air filter is not the problem (there is NOT air filter now...), the candle is in good brownish colour, for sure exhaust isn't clean, but doesn't sound as it is completely stuffed.

So probably the reason of this placidity I figured out it could come from reeds and the decompressor, that maybe doesn't work properly...

Anyway, for sure I want to tune my bike as much as is reasonably possible, so I'm thinking of buying a few things from the USA:

- piston

- cylinder

- head

- carburetor

all from old IT 400s

An important question: are there differences between the various IT 400 MY (model year) for this stuff?

I think the carburetor is essential, I don't know how is mine, but it seems something ridiculous, 24 or 26 mm maximum!

DT400g.jpg

DT400f.jpg

Somewhere I read that people used to change three things on DT 400 for tuning them: carburetor (ok), pot (I can't change it, I will work it internally) and "the head"...

I don't get this last one: what difference could a head do in a 2 stroke, if not for compression?

Wouldn't be more important to change the cylinder?

Ok, last question:

Do you think could be worthable to change the rotor with the IT one?

Well, don't worry: I'll be back soon...

Ciao,

Filippo

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Strange....The front of that bike has a leading axle,the ones in the States don't.

Your idea of simply changing the carb from an IT might not fit at all,the DT carb are REALLY small and the mainifolds are way different from the DT to the IT. If i recall the IT is more like the MX or YZ,it's a lot bigger with a different bolt pattern too.

But that is the bike from the states..what size is your carb?

 

This bike is a DT400F (82-83) ...... It uses 35mm diameter forks and the axel setup is off an XT250/500 of the same age.

Plastic panels look great ..... if ever you want to sell them??

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Super old post .. ( circa ) 2012

This bike is a DT400F (82-83) ...... It uses 35mm diameter forks and the axel setup is off an XT250/500 of the same age.

Plastic panels look great ..... if ever you want to sell them??

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Super old post .. ( circa ) 2012

It SURE IS old!  II wonder what ole' Filippo did with it. He hasn't logged on to TT for 5 years.  These kind of posts bug me just a little because people offer suggestions, tell their own experiences and you never even find out if the whole ideal was sh!t-canned or not.

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I would like to see how it turned out, nice to see running bikes some what similar to mine. I know that his carb is a lot smaller than what my YZ 400 has. He says that things got a 28mm?! No wonder its slow. My 350 has got two 28mm carbs. Why would Yamaha put such a small carb on a big motor like that?

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I would like to see how it turned out, nice to see running bikes some what similar to mine. I know that his carb is a lot smaller than what my YZ 400 has. He says that things got a 28mm?! No wonder its slow. My 350 has got two 28mm carbs. Why would Yamaha put such a small carb on a big motor like that?

IT  was almost strictly street OR maybe a dirt road.  The next step in performance was the IT line.

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I see.

Having said what I said, a couple of friends had various DT models. They moved along pretty good.  Kind of like some Toyota's - Image was more important than substance.

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