Hi. I've just got myself a 1979 registered DT250MX. I'm in the uk and it's a uk bike. The carburation felt messed up when i rode it. It was stuttering at part throttle but seemed to clear at full throttle although the bike feels gutless. I've stripped the carb and ultrasonically cleaned it. The needle jet was an absolute pig to get out and i mangled it. So i've got a new one coming. According to the manual it says the pilot jet should be size 50. There was a size 30 in there. Main jet should be 140 which it was but not a genuine mikuni jet. Needle set at the 3rd notch.
The vin starts with 1R7 and the carb has 1R7-00 printed on the body. The air jet is clear but i noticed there is no brass ball in the hole like my rd350lc has. Is this normal for these carbs?

 from near Salisbury.

You're on the RD forum as well?

Anyway, you clearly know the dangers of using pattern carb parts.

Others will comment on the brass ball scenario, but I think I've seen carbs without them.

I am yes. I've not seen a carb with floats like this before so that confused me but i've worked that out now.
The airjet is 2.5mm too which seemed big to me but thats right in the manual. I was just expecting to see a brass ball there. Every days a school day

First thing for gutless is exhaust restriction in my books. but blubbering on part throttle sounds needle.
To get the needle jet out [too laste now i know] i use a 5mm long screw turned in & nipped tight as thread is a bit different but works good to just tap it out.
Pull it back in the same way using the long screw. It will reach to meet the nedle jet before it starts down the hole.
Remember the guide pin at the bottom from the side. Once jet is out you can whiz it up & down a few times using the screw & it'll slide in easy after that.
They get crudded around & grown in there a bit. If a new jet is on the way it'd be best to get a needle as well. Start on the middle notch & should be close.
But wait there's more--Just a thought that slightly possible the flywheel has been off & sheared of the crank key if fitted Not Tight enough on the nut.
That's clutching at straws but is a common thing to happen on the older 250/360's. If it moved it'd likely move so far it wouldn't run or backfire or kick back hard & not run.
I'd definitely go looking at the exhaust although in theory it shouldn't rev past where it blubbers. So guessing a bit.
Good way to get a hint of if it's 'that', is pull the complete end muffler out of the chamber main exhaust. Appologies to the neighbours in advance & give it a rev Trev. Might have to hold it on full song to clear for a bit. All a guess--but!!.
Oh & maybe try it minus the carb air boot incase something weird is going on. Have seen rags left under the seat blocking inlet to the airbox.
Air boot i guess its a bugger to remove with everything in place but heat it with something like a paint stripper gun on low setting [ i use].

Has the carb got the two separate black floats on pins. If so, just be sure to have the side pins of those floats at the lower end or they'll hit the float arm & have zero fuel entering. I'm sure ya onto it & i'm woffling about nothing.
Also, Welcome from NZ downunder [umm & with the same King] Tough job for him to live up to his mum. I remember waving a flag to her in a 1953 trip down here i think it was, & in my school shorts lol.

Hi. Thanks for all that so far. so it has a Dep silencer on it. The floats are the sperate ones that slide up and down the 2 pins.Never seen that before and it threw me for a while until i worked it out. I'm going to take the exhaust off and see if it's coked up and also take the top end off to check the bore ect. I noticed it seemed to top out around 6k revs and not want to pull further. I'll check the flywheel too while i'm about it. This bike is new to me and i do like to take things apart to learn how they work.
The needle jet had the numbers 169 and 0.6 on it s othats what i orded. I'm having trouble working out which manual is correct for this bike but as far as i can see the manual is saying it should be a 0.4??

Another thing i noticed was the rubber seal on the end of the choke plunger was not flush with the end like my rd400 was. It was pushed in or worn by around 2mm. So thats been sent off to have a viton seal fitted too