White Brothers DR400T

[TT5 Matt]

ive sold a few std 34mm tt500 carbs to sp370 owners as there a bolt replacement and everyone loved the extra go,a sr500 pumper might work well aswell

[mick25]

The DR500 1983 I had, (usa model alloy swing arm etc)
It had a 40mm standard carb butterfly job, I changed it to 38mm flat slide went heaps better,
but I did try one of my  TT500 carbs on it before I got the flat slide it went well.
I got a stainless header pipe made for mine ,larger than standard I think it was 1 and half inch or 1 and three quarter.
I would post some pics up but dont know how.

[oldfart]

Evo ...Pic is deceiving, as there is 25mm clearance

[aehunger]

Hi there,
Carb is a VM for sure and will have to take a look if its possible but lifting the needle a notch would be worth a try as bike idles o.k and has low range power but mid range is rubbish. Under hard engine braking and then throttle im getting a puff of blue smoke also the head is wet with oil around the exhaust port where the header attaches, after hard riding. Obvious answer is it flogged but wanted to know if it could be a attributed to the restricted muffler im currently running as on inlet side it steps down to 30mm where as the header is 40mm could this back pressure force be enough to make the engine burn oil?

[oldfart]

Valve guide seals may need replacing also .

[cloggy]

 I'd agree with oldfart, new seals might well solve the problem.
 What may be happening is that oil is being sucked  by the vacuum in the exhaust caused by a shutting throttle. If it doesn't burn oil all the time that's the likely cause. I found the rings to be pretty good on the engines. Generally they lasted till it was time for a rebore. The rings on the 400 are the same part number as the 500. The bore and oversizes are identical; that goes for SP and GN variants too.  Midrange was rubbish using my standard oval bore and the modded airbox. VM doesn't mean a lot, there's so many variations.

[aehunger]

Cheers for the advice folks,
Valve guide seals is that a head off job right down to the the block or the tappit cover only and are you aware of the parts being available new at what cost?

[TT5 Matt]

if your going to all the trouble of taking off the head you may as well replace the rings as well and give the valves/seat a valve grind or at least lap the valves if its not too bad

[oldfart]

Generaly these motors are pretty well built and can take a good floggin all day long when well set up.
The best way to tell if your motor is in good nick is to pull the top end off down to the block and check piston to bore clearances- condition of piston and blow by.
Ring kits - file fit  ( 350 4XC = 89mm    $60 ? )  can be procured from serco if the ring landings are OK.
 
Now to the head ... you have valve stems that can be replaced if badly worn ( still available   $4 each ) of which are a press in fit with a small oil ring... ( still available)
be carefull if you are pulling the vavles off yourself as they can break real easy and end up in tears  $$$$.
Your Valve's go up and down inside these stems and have a unbrella seal ( vavle stem seal  $10 each) they  go hard and brittle over time and let oil pass into the  cylinder ...Ie old holden red motors were bad for it.
hope this helps
 

[cloggy]

 Get a manual if you can. Generally these motors are simpler to work on than old brit singles. The Clymer one is ok, and the suzuki SP400 manual is very good and has sections for DR and GN, though the motors are pretty much identical anyway. They turn up on ebay regularly
There's a DR400 specific manual available from New Zealand right now, turned up on ebay.com

[SON]

Cloggy have you spoken to Mark Cutler about these engines?

[cloggy]

 No
 I don't know who he is, unless he's the guy that roadraces, and then my knowledge is secondhand. I did get a modded piston off someone I met at Farleigh, but I don't remember his name.

[Marc.com]

as stew said drill some holes in the air box to get it to breath. When i built the dr in VMX mag i fluked the pipe and muffler kit on evil bay for about $60 US they had 2 of them and only 2 people put a  bid on them

Think I got the other one 

[Marc.com]

This one is worth a look, DR/GN lower cradle and engine slipped on to RM top half with bunch of goodies, why didn't Suzuki do this in the first place?

[cloggy]

  That's Jean-Francois Helaine's bike. He intended to stroke it hence the 470, but when I last saw him he hadn't yet done it. He managed to bend both wheel axles at Farleigh about 2 or 3 years ago. He told me the following year. The craftsmanship was stunning. He'd grafted a set of GN bottom rails onto an RM chassis. The motor was pretty standard apart from a 38mm Mikuni, despite that it seemed to have no trouble running with the 5 to 600s He managed to mash the tank on the first day of racing. I think he's a lecturer/teacher in a french technical college. I got talking to him as I was trying to work out just exactly what it was.