Does anyone have a port layout diagram for the 1975 DT250B? Or just as good has anyone modified ports for a positive improvement?
Thanks
Tom

I changed my 78 dt250 Reed valve engine to mx250 (30hp) porting also added an extra 17mm hole in the piston and cut the skirt so it has 360 degree inlet opening and also cut the sides of the piston to help flow up the transfers which I also opened up at the base gasket and matched to the cases. I followed some pictures out of a yamaha piston port manual I found online also fitted a pwk35 carb off a kx125 k4. It's night an day much gruntier than a stock dt250 and I don't even have a decent chamber on it yet haha

I also split the chamber down the middle and took out the other 2 layers inside it consisting of fibreglass packing and perforated inner mesh layer which changed the resonance inside it we used to do it to Kdx200 chambers and it made them work like an fmf fatty haha

Has a rex's speed shop dual power cdi setup with a spark curve for my porting and a chamber

Bit of a cruise through the Bush gets thrashed every weekend

You can also just raise the cylinder a couple of mm or 3 with a spacer between 2 base gaskets and drop the intake floor as far as you can go without going through the bottom of the cylinder. Widen the exhaust top half blend to bottom sort of like an upside down trapezoid. A larger carb and a pipe will take the porting much further as stated above.

www.3wheelerworld.com/showthread.php/125151-yamaha-porting-book

I dont know if you want to do your own porting , But If you want tomgive me a call we can go over what I could do for you . I have concepts that surpass old school mods .

Rich

That is fascinating with cutting the crown.

Excellent replies. Thanks Rich. I live in Melbourne Australia, currently under curfew and lock-down :(
I am preparing an almost wrecked 1975 DT250 for dirt bike riding. The bike sat outside for about 19 years. The motor has been stripped. Looks good inside but for the mains and rod bearings which rusted out.