2 stroke expansion chamber mods – OLD Bull Trailriders

This topic contains 10 replies, has 0 voices, and was last updated by Alex 14 years, 11 months ago.

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May 3, 2010 at 1:03 pm #98397

greg williams
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hi i have a 94 mod dt 200 yamaha. the expansion chamber feels realy heavy and sounds dull when i hit it. i have drilled 2 10 mm holes in to it at its largest diam. and there seems to be a seconond skin in side the chamber that is lined whith insullation and perforated steel. what i want to ask is would there be any bennifit in me cutting the chamber open say were the chamber is joined to the engine pipe and remove the lining to get the gasses flowing. i do have a mig and are confident i can weld it back to gether. would i have to play around whith the jetting after. the auto lube has been disconected and i am pree mixing it at 40 to 1. it has a pro circuit silencer fitted as well.cheers greg :laugh:

May 3, 2010 at 1:25 pm #177627

Dean
Member

Gyday Greg and welcome to the site.

Your pipe is a twin wall job made that way to pass our ADR’s. You can cut the outer skin away using a cutting wheel on a 4 inch grinder then as you say weld it back up.Not sure if its the outer or the inner that you need to keep, there should not be any hassle with the jetting but play it by ear and seat of the pants for the first ride. Premix is the only way to go with your two stroke,I dont trust the autolube after an incident I had with an old TS250x

ollie

May 4, 2010 at 12:43 am #177630

Trent
Member

Is there some sort of solvent treatment that could clean it out without opening her up?? My single wall pipe may as well be made of paper its that soft but it does sound great.

May 4, 2010 at 6:14 am #177690

Scott
Member

Austblue wrote:

Quote:

Is there some sort of solvent treatment that could clean it out without opening her up?? My single wall pipe may as well be made of paper its that soft but it does sound great.

On old trials bikes that are renowned for coking up the exhausts, you could either take it to an engine rebuilder and put it in his acid bath. Or
Put some petrol in it and light it up, the roar is like a 747 taking off and there is heaps of smoke but it works.

May 4, 2010 at 6:16 am #177785

Steve Wyeth
Member

Acid dip.

May 4, 2010 at 11:21 am #177786

Anonymous

Another way of de-coking / cleaning out the crud is to us an oxy/acetaline set and stick in the end of your pipe.

Same job as the petrol as it burns the muck out but probably not as dangerous.

Both of my DT’s had that treatment, can’t really remember the result though???

Its got to make some difference though, getting rid of the built up crud

May 4, 2010 at 2:00 pm #177837

Dean
Member

The problem he has is that the pipe is a double walled pipe ie outside skin mesh then inside skin.and the only performance gain will be from weight loss. I agree with the previous guys views on giving it a good cleanout though oxy/acetylene works a treat. The DT200 was a great little bike in its day,but a bit long in the tooth now, I reckon you should take the bike for what it is and just ride her as is,if and when you get the desire for something newer and more capable then trade up. Just my opinion.

cheers

Ollie

May 4, 2010 at 11:29 pm #177846

Bruce Curtis
Member

The WR200 pipe is a good mod for the ole DT200R.

Good 2400w heat gun will clean the pipe out, just be prepared to take a while to get whole pipe hot on the inside, then WOOSHCA, it will look and sound like an F1-11 with after burners on.

May 5, 2010 at 12:41 am #177628

KTM05
Member

Hi Quiting

I did exactly what you are proposing to my KDX200 that I was racing in the early 90’s. You should notice a huge increase in responsiveness and power at the top, with a little loss of “lugging” power at the bottom. I needed to go 2 or 3 sizes up on the main jet and adjusted the needle after the mod, as it was breathing so much better.

Heres how I did it …
Inspect the external of the expansion chamber, looking for the little round spot welds (about 5-8mm dia.) This will give you an idea of where the internal skin is located. Choose a point were the expansion chamber has the largest diameter and scribe a straight line around the circumference. Also scribe a few lines crossways to allow you to position the two halves correctly when you are ready to weld it all up again.

Cut the pipe in half along the scribed line – hacksaw, jigsaw or other tool that will give you the narrowest cut. Then drill out all the spot weld marks using a small drill bit and then increasing the drill size until the spot welds are broken to allow the inner skin to be removed.

Scrape out any excess carbon build ups that are visible inside the two halves. Position the two halves together on the scribe marks and weld together ….. and weld up the spot weld holes.

Now you will have a pipe that will perform as it was intended before ADR restrictions were added. Now for the real important part – jetting. Do not try and ride the bike without increasing the jetting …. if you do the bike will be running extremely lean and will destroy the motor. It is better to run the bike too rich initially and then lean it up in small increments at a time. Or a full dyno tune if you have access to one.

Remember the bike is already quite old so take care …….. enjoy the “new” ride.

Hope that helps …. :cheer:

May 5, 2010 at 1:54 am #177866

Alex
Member

As per KTM05’s response. I would burn the carbon out first then cut it up and de-restrict. You would be amazed what’s in the chamber. Some have reinforced ribs, some even have steel mesh or wire in there.I have a WR200 and probably wouldn’t bother adapting that to a DT. The WR pipe is quite heavy. Get an ebay search going for DT/WR pipes. Sometimes you can score an AM unit to adapt.

May 5, 2010 at 8:48 am #177629

greg williams
Member

thanks heaps guys for your replies. i have burnt it out whith a gas torch and the od squirt of degreaser to get the f1 11 efect :woohoo: :woohoo: I all so poked a length of mullti strand stainless steel wire in to it connected to a drill. the wire when turned worked great i collected a margerine con tainer of crud out of it.i welded up the two holes and disconected the hot water from the carbie then took her for a spin. it has made a huge differance . i am keen to cut and remove the guts out of it in the future. but i am going riding now :laugh: thanks to all. first post and very impressed whith the replys cheers greg
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