My MX250A project.

[Nathan S]

Ah yes, those shocks... For a while I owned three of them, and I'd swap the third one between two bikes. Somehow I kept one silver and one orange one, rather than a pair!? So now they're a mis-matched pair, which adds to the "no expense spared" look of the whole project! 

I got it running this morning. Was difficult to start from stone cold - sometimes it would fire, other times it would ignore you.
Once warmed up, the mixture screw makes no difference across the normal range of adjustment - just before it bottoms out and just before it falls out will have it faltering, but anywhere in the middle is exactly the same.
Any suggestions on what I should be trying?

Still, once warm it starts easily, idles happily (perhaps a bit fast) and free revs fine. Test ride this arvo.

[mx250]

I got it running this morning. Was difficult to start from stone cold - sometimes it would fire, other times it would ignore you.
Once warmed up, the mixture screw makes no difference across the normal range of adjustment - just before it bottoms out and just before it falls out will have it faltering, but anywhere in the middle is exactly the same.
Any suggestions on what I should be trying?

Are you running a DT barrel and head with an MX chamber? If you are I would think it is a mismatch of chamber to porting (lacking back pressure at low RPM). You might be able to achieve something with jetting but I think you are pushing shit uphill with a pointy stick .

The 'bees knees' is MX barrel and head, carby and chamber with DT ign. I think you have it arse about.

[Nathan S]

There's lots of things that are 'non-ideal' at the moment - no time, no money!

I've sourced another MX barrel, but it won't be fitted until after the Nationals. FWIW, the bolt-on MX pipe spigot lines up beautifully with the DT exhaust port (ie: Its 'port matched' without being touched) - far better than most of the YZs do from the factory... The MX pipe is still 'milder' than the aftermarket DT pipe I've got here, so I don't think that's an issue.
I'm also running the MX head - mostly because I don't think a DT head fits under an MX pipe.

Yes, the heavier ignition is almost certainly a good thing - but I don't own a spare functional external rotor ignition.


And for all of that, it goes a LOT harder than I expected - admittedly everything feels fast in the backyard, but it still impressed me that it lifted the front wheel in second gear on moderate throttle application alone (not threatening to loop out or anything, but still better than I expected).

My shoulders are about three inches higher than they've been all week - the weight has been lifted!

[JC]

FWIW, In terms of timing the DT barrels are quite advanced (esp for a trail bike) & not far behind the MX & YZC.  eg DT Exh duration is 180deg.  However the MX/YZ ports are considerably wider.

I'd have tho't yr combination would have been quite decent Nathan, tho it'll proably run out of breath a bit on the top end esp up against the gun machines of the class. But don't be psyched out by using a DT barrel.

Probably 'tailor made' for short-shifting.