White Brothers DR400T

[cloggy]

 I thought the SP400 was pretty hideous offroad. It's no match for the DR, and requires expensive time consuming surgery to get it even close. There's a lot of back in the day tests saying the same thing.

[oldfart]

Cloggy .... re-read the first sentence and then have a close  look at all the bikes posted in this subject and tell me time and surgery have not taken place.


 

[cloggy]

 Yes but it hasn't been done much since the DR400 came out. DirtBike stated very clearly that it was not straightforward and that the DR400 was a further step change
 The french DRM had GN frame rails grafted to a RM. I don't doubt that's better than a DR. When racing in the USA 4 stroke championship and the veterans 4 stroke championship the DR mod seemed to be tightening up the head angle a degree. Much more or there'd be no clearance.   
 I had a SP400 as my sole transport for 8 years and I've got several DRs now, 2 actually run!

[aehunger]

Hi All,
My '80 DR400 has a unusual carby fault somewhere....The bike starts easy with the choke and decomp but once running its terrible in the mid range. Idles o.k and top end seems ok. Then if I operate the choke a few times while giving it some revs it seems to come right and run fine from then on. Would like to know if anyone else has experienced this with a 36mm Mikuni carb or could suggest what is the problem. If it ran like it does, once ive fiddled with the choke, i would be over the moon.

Alex
Paeroa
NZ 

[maxvmx]

Back in the day before 4 strokes came to the fore front of MX I had a freind racing XR 400's with 2 stroke 36mm carbs. His comment was always that he had snappy response but doing away with the pumper carby did leave some lag in certain situations.

[oldfart]

Alex ....Do you have the cam operated type, if so they work well with that motor . The diaphram type are shit
Turn the  air mixture ( RHS ) so it's about 2 turns out.....   
check the float level..... 24mm.... gasket surface to top of float carb inverted 
Check to see if neddle clip is secound slot from bottom .
Have you put compressed  air to the the rear air ports ( back of carb ) to see if air comes out of the needle jet  and air mixture holes .... as they  block up with grit.
check to see if piolt jet is not blocked ... and again blow air thru this hole.

Paeroa  Eh ...   know the place very well 

[SON]

Can of Carb Cleaner with the extension tube,
Don,t forget safety glasses, eyes don,t grow back.

[aehunger]

Thanks for the good advice all,
Its a cam style carb and ive dropped the needle clip to the bottom because when i first fitted the carb it had this very problem and i figured it may have been starving but didnt know to fiddle with the choke for better performance. It goes like hell when it I do get it to stop the miss-firing. Really hoped to avoid stripping the carb again though so any ideas how I can achieve your points without breaking it down again?

Alex

[oldfart]

From your orignal  discription it's a blockage .... so unless you find the problem   it won't clear it's self......sorry but it looks like you will have to pull it apart again.
Or as "Son" has suggest give it a quick squirt of carb cleaner.
 

[GT43]

I have a DR500 which has the diaphragm type carb.

Just wandering, could I run my spare IT490 38mm Mikuni on it ?

[cloggy]

 If you have the original carb it will not work at mid throttle if you've junked the airbox or opened up the inlet trumpet. Believe me I've tried. The problem is due to the the engine needing a dual taper needle in that carb once additional air is supplied. The 370 carb works great as it has a dual taper needle, however top end isn't so good as it's 1mm smaller. The bodies are different sizes and lengths so I doubt the 370 needle will fit in the bigger carb, but I haven't tried it so don't know for sure.
Er this is only relevent for the DR400!

[GT43]

Ok, thanks Cloggy.

I'll put the original carb back on for now.
Currently a little worried about a heap of metal shavings in the gearbox, just as I read that DR500's have weak 3rd or 4th gears.

Do you know what Carb would work well on a DR500 ?
I know somebody in UK runs a DRZ400 pumper, - but very expensive.

[mick25]

I ran a 38mm flat slide mikuni on my DR500 went great, better than the 40mm org diaphragm job...

The 38mm flat slide comes in two diffrent sizes where it mounts in the rubber manifold out side dia of the carb , so check that if you get one brand new ones out that is.
I had to cut about 4mm off the front of my org diaphragm carby and place in the manifold first then place flat slide in.
with out the 4mm ring in the manifold first ,the flat slide moved up and down to much, because the recess part on the flat slide is located in a diffrent spot to the org carby. To suit the inside rubber ridge in the manifold.
I hope you under stand my instructions.

[DR500]

I use a flat slide pumper carby off a DR600. works great on the DR500 and no flat spots.

[TT5 Matt]

what size is the dr600 pumper DR500