MX vs DT cylinders

[evo550]

Going through some DT/MX stuff I have and I'm trying to work out what cylinder goes with what.

One cylinder has what looks like an oil injection port into side of reed block, one doesn't, everything else looks identical. Any ideas 

[vandy010]

i've had a DT250C barrel fitted onto MX250A cases but it was just a bolt up and not on a running motor.
it all looked good to me with the only real notable difference being the fins on the DT barrel were smaller in size thus making the MXA head look big.
a die grinder should bring the ports up to spec

[Nathan S]

DT-A barrel also has more fins than MX.
Not so sure about DT monoshock.

[evo550]

Cheers guys,
Just counted the fins and the cylinder with the oil injection port has 8 fins against the other one with 7. Just wanting to keep the MX cylinder with the MX bottom end....turns out it's only on it's first oversize as well....rums all round
Are rod kits/pistons still avaliable for these rockets in Aus ?
Any hot up tips ?

[vandy010]

Are rod kits/pistons still avaliable for these rockets in Aus ?
Any hot up tips ?

i'm guessing you're talking about the "A" model.
i had a bit of trouble finding a rod kit for mine but ebay came to the rescue.
pistons are easy enough to find.
mine runs a DT piston and the heavier DT flywheel/cdi ignition with stock pipe, carby, jetting etc and i quite like the tourqey feel the motor has.
while it's apart, be thorough in the gearbox as a few of them like to jump out of gear from time to time

[Freakshow]

Rods are easy enough as are piston. prox makes a kit as well.

The inlets and ports also should be slightly differant.  IF you stick them side by side they do stand out as differant

[mx250]

Any hot up tips ?

How much money have you got?

My mods were 34mm carb, Webco head and the back of the piston cut away - it boogied . And was reliable - MX, Enduro, DT and Road Raced (just inspect/replace pistons on a regular basis - should be done on all racing 2t's ). The biggest improvement was the 34mm carb (against all advice and expectation .

I can't remember the Webco been an obvious 'kick in the pants' mod and I'm not certain it is a necessary mod (but sure looked trick ). But It probably did have a better squish band something which could be done to the standard head I'm sure.

The cutaway piston was an big improvement adding HP and response everywhere (Yamaha later copied this mod - I should have patented it . The later piston might fit. They have the reinforced 'ears' protruding down which in theory should be better than 'no rear skirt' as mine were. The ears stop the rocking motion.) I used DT [pistons checked and replaced regularly (and cheaply).



But I'm sure more could be done with time, money and technology. There is a lot of metal around the ports to doing porting. The basis for mods are there; good transfer ports and room to improve. Ask Lozza, I'm sure he would salivate and enthuse at the prospects.

Lozza will probably enthuse about newer better ignition and a new pipe as well.

If I was to complete my wish list I would investigate an aluminum liner and electroplating to get better heat transfer and more consistent performance and less HP drop due to heat build up (and save 1 kg off the beast ). 

The Webco Big Head (or was the trade name 'Cool Head') was 'sold' on the promise of better heat transfer and more consistent performance. It is feasible but I can't vouch for it. A trial using one of those flash laser temp gauges at the end of a race would be an interesting experiment. In fact it would be an interesting tuning tool methinks.

[Freakshow]

34mm is the standard MXA carby so why would you run anything else ?
i wouldnt waste mytime doing a special lining thing cost vs result on that bike wouldnt return outlay.

Loos weight off the bike would give you more results.  Maybe new pipe.  YOu can drop boost ports in from the intakes, Squish the head a little, and tweek the port but more so tidy up the inlets in side the barrell and all pathway. Reeds can be modded as can the piston. other than that dont fork about with the motor.  PVL ign bolt straight on and they will be reliable for years.  Then id spend time shedding and also tidying up other things.   Even stop eating pies and loose 5kg yourself would be a wiser investment than screwing a good motor up with radical pie in the sky port jobs.

Id have both the Dt twin ring, the mX single and probally the later 79 yz pistons here to suit.  Much of a muchness really , but it depends on what your racing the bike in as to which to use as a preference.

[firko]

Back in the day I screwed up the bore on my MX250 prior to a club round at Nepean dirt track. Not having the ready cash for a rebore and new piston kit, I borrowed the top end off a mates ride to work DT250 just to get some track time and score enough points to stay involved in the club championship. The big surprises to me were 1: the lack of major jetting changes needed and 2: I was expecting a major drop off in speed but I was pleasantly surprised to find that there wasn't much difference at all. It wouldn't take a porting genius to get the DT running as quickly as an MX.

[mx250]

34mm is the standard MXA carby so why would you run anything else ?

30mm was standard .

[firko]

It's been a long time but I thought the DT had a 30mm, MX-32mm and the MX360-34mm. I could go and look it up but it's too hot to go out to the shed to check my manual.

[mx250]

It's been a long time but I thought the DT had a 30mm, MX-32mm and the MX360-34mm. I could go and look it up but it's too hot to go out to the shed to check my manual.

MX250 30mm, MXA250 either 32 or 34mm. Mine was the MX250, silver grey.

[firko]

Mine was the silver model as well but the previous owner had fiddled with it a bit and may just have fitted a 32mm. I later skimmed a few thou off the head, fitted a 34mm from a TM400, a Torque Engineering pipe and put her on methanol. It was a fairly ordinary motocrosser but bejesus it was a good dirt tracker. Unfortunately I only had it a year and sold it to buy a 250 Maico which, despite my love of the Maico marque, never went as well as that Yamaha or the CZ that had preceded it.

[evo550]

There seem to be a few anomolies with the MX 250 A's one being the carb size, mine is a 34mm, can't vouch thats standard, but it's painted black so I'm assuming it came with it from the factory, the other being points/electronic ignition. Going back through the files there was a bit of a discussion on this a while back, mine again is fitted with points, but some others claim they come standard with elec ignition. Maybe Freaky's and mine are brothers from the same mother. 

[Nathan S]

MX250 (pre-A) = 30mm(?) carb.
MX250A = 34mm carb.
DT250A = 26mm carb.

DT360 was 30mm and MX360 was 34mm, IIRC.

I've never seen anything suggesting that MX250s ever came with points - and after 35+ years, its highly likely that some were converted back to DT ignitions.

DT250 twinshock = all points.
DT250 monoshock = f#$ked if I know - never figured out any rhyme or reason to what's fitted to what.
DT360/400 = all CDI.