JDMCRX
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JDMCRX
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RJH
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Well…the newer engines are just fine stock – but that baby could use some help.
What you have done so far probably won’t do too much, but it looks good. You need to hack all that material out of the intake track. The only concern is that the cylinder wall doesn’t collapse or the piston gets stuck in a hole. Take an equal amount from the piston skirt face as well – so it matches the holes in the reed block.
Your best bet is to saw that stock reed block off and buy a junk 125 cylinder on eBay. Cut that reed case off the 125 and weld it to your cylinder. Then – you can put in some 6 petal reeds. Doesn’t need to be hi-tech – just make sure there are no air leaks. The late Jim Adema once made a reed block from OAK and won everything in his class.
You don’t want to grind above and below where the reed block sits as that only adds to crankcase volume. If you did – get some liquid metal or good epoxy and fill in the gap. The reed block should be tight to the ceiling and floor.
Next – you need to find a Can-Am 250 pipe and bolt that on with a 34 or 36 mm carb.
Make that edge a tight round entry - gas don't like sharp edges.
What you have done so far probably won’t do too much, but it looks good. You need to hack all that material out of the intake track. The only concern is that the cylinder wall doesn’t collapse or the piston gets stuck in a hole. Take an equal amount from the piston skirt face as well – so it matches the holes in the reed block.
Your best bet is to saw that stock reed block off and buy a junk 125 cylinder on eBay. Cut that reed case off the 125 and weld it to your cylinder. Then – you can put in some 6 petal reeds. Doesn’t need to be hi-tech – just make sure there are no air leaks. The late Jim Adema once made a reed block from OAK and won everything in his class.
You don’t want to grind above and below where the reed block sits as that only adds to crankcase volume. If you did – get some liquid metal or good epoxy and fill in the gap. The reed block should be tight to the ceiling and floor.
Next – you need to find a Can-Am 250 pipe and bolt that on with a 34 or 36 mm carb.
Make that edge a tight round entry - gas don't like sharp edges.
JDMCRX
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Ok so basicly the intake track around the cylder wall the one around the pistons area looking from the bottom is were i should do alot of work?
The Reeds im gonna stay with what i got for now. AS for the side of the piston has the intake ports on it ill post a pic
The Reeds im gonna stay with what i got for now. AS for the side of the piston has the intake ports on it ill post a pic
JDMCRX
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You can narrow up that bridge in the intake considerably, make the throttle response better, the intake isn't really the place to make alot of HP though, in fact if you cut out too much it just slows the velocity of the incoming charge which can counteract the gains you made.
You want it too scream raise the height of the exhaust port a little bit and widen her out some, that'll make some power, tends to make them run like a light switch though.
Make sure if you do any serious cutting to chamfer the edges of the ports when you're done.
You want it too scream raise the height of the exhaust port a little bit and widen her out some, that'll make some power, tends to make them run like a light switch though.
Make sure if you do any serious cutting to chamfer the edges of the ports when you're done.
JDMCRX
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Well i did the exhaust port widened it a bit raised the rough roughly 1mm.
So on the Reed case the divider sharpen it a bit?
Now about the piston should i port match the piston and reed case??
So on the Reed case the divider sharpen it a bit?
Now about the piston should i port match the piston and reed case??
Junior
New member
don't cut the piston, cut the skirts on the cylinder infront of the reed cage.
to clarify, you don't want to take alot of material out of the countoured parts of the intake ports, the tunnel is shaped like it is because that's a shape that encourages flow. You just want to de-burr it to encourage that flow. A mirror finish on the transfer ports isn't really necessary, most guys swear by satin intake for abit of turbulance in the intake charge to encourage atomization.
We can help you out if you get us some measurements, I don't know that motor off the top of my head, so I need some numbers to work with. if you can get me port heights, bore/stroke, and chord widths (the straight across distance) for the port I can help you abit more. It would also help us out if we knew what kind of powerband you're looking for, a higher, peakier, MX type? or are we talking fat and loose enduro type?
to clarify, you don't want to take alot of material out of the countoured parts of the intake ports, the tunnel is shaped like it is because that's a shape that encourages flow. You just want to de-burr it to encourage that flow. A mirror finish on the transfer ports isn't really necessary, most guys swear by satin intake for abit of turbulance in the intake charge to encourage atomization.
We can help you out if you get us some measurements, I don't know that motor off the top of my head, so I need some numbers to work with. if you can get me port heights, bore/stroke, and chord widths (the straight across distance) for the port I can help you abit more. It would also help us out if we knew what kind of powerband you're looking for, a higher, peakier, MX type? or are we talking fat and loose enduro type?
JDMCRX
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OK coo thanks alot tomorrow ill measure it all up.
Motor is a 87 DT200
66mm bore 57mm stroke
Im gonna bore it .50 over and im looking for just trail power.
Ill get all the measurements of all the ports tomorrow
Thanks alot guys
Josh
Motor is a 87 DT200
66mm bore 57mm stroke
Im gonna bore it .50 over and im looking for just trail power.
Ill get all the measurements of all the ports tomorrow
Thanks alot guys
Josh
JDMCRX
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RJH
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JDMCRX
Ok just to get an a direction here – this engine no matter what is not going to be any kind of crotch rocket and you don’t want to spend big bucks. You just want to have the satisfaction of doing a good job, having some fun and hopefully get a little more speed out of the old thing. Right?
For HP you’re going to need a better pipe – but we don’t want to spend the money on pipe – good. So…you need to be careful fooling with the exhaust height. The timing from the spark to when the exhaust opens is further dependent on what the pipe can do for you. If you change that much and keep the stock pipe – you will go slower – possibly.
Go wide and make sure with the piston down, it’s flush with the bottom. Go wide on a taper so the rings don’t get stuck. Check where the gap is as well.
An easy way is to cut a long bevel on top of the piston exhaust side – say take about ¾” of the aluminum away between the top and the ring. Some pistons have no room. Ding this is a cheap way to test to se if you go faster before hacking the exhaust port.
Transfers – they look OK – make the bottom nice like one of the other pictures I saw.
The intake – you see it’s not a piston port so you can have as big a hole as you want. When you finish then cut the piston face to match the holes in the cylinder. You don’t need to cut too on the piston as you don’t want it to fall apart.
On that old engine – you need to make the reed tight. Buy new petals for it – very important on the vintage. All around the sides of the reed block should have no gap so to speak. You can fist that with epoxy. Having a gap increases the crank volume – which you don’t want on that engine.
Attached would be an ultimate lower end. This is a 6 speed 125cc. It can’t make the HP of a sled engine as it needs some rpm to shift. Each shift on a bike drops a 1000 rpm +/- per shift.
So this engine makes 42HP at 12500 rpm. (new YZ dirt bike is about 33HP stock). It had a 30 mm carb.
Again, fresh reed petals – good rings, chamfer the ports, fix the intake and you will be good. Notice on my engine how the reeds have been tuned with the slit. Notice my engine how tight the intake is to the reed block.
Notice how the transfers have been cut up. What you did may work on an old engine – I’m sure but this one, at 12500 needs some form of long path to get the fuel settled down. Notice the 3 port exhaust. The top of the exhaust is about 4 mm lower than a stock YZ125. Again at 12500 – it needs time to work. Notice the wide squish.
This would be the ultimate in engines at this time.
Ok just to get an a direction here – this engine no matter what is not going to be any kind of crotch rocket and you don’t want to spend big bucks. You just want to have the satisfaction of doing a good job, having some fun and hopefully get a little more speed out of the old thing. Right?
For HP you’re going to need a better pipe – but we don’t want to spend the money on pipe – good. So…you need to be careful fooling with the exhaust height. The timing from the spark to when the exhaust opens is further dependent on what the pipe can do for you. If you change that much and keep the stock pipe – you will go slower – possibly.
Go wide and make sure with the piston down, it’s flush with the bottom. Go wide on a taper so the rings don’t get stuck. Check where the gap is as well.
An easy way is to cut a long bevel on top of the piston exhaust side – say take about ¾” of the aluminum away between the top and the ring. Some pistons have no room. Ding this is a cheap way to test to se if you go faster before hacking the exhaust port.
Transfers – they look OK – make the bottom nice like one of the other pictures I saw.
The intake – you see it’s not a piston port so you can have as big a hole as you want. When you finish then cut the piston face to match the holes in the cylinder. You don’t need to cut too on the piston as you don’t want it to fall apart.
On that old engine – you need to make the reed tight. Buy new petals for it – very important on the vintage. All around the sides of the reed block should have no gap so to speak. You can fist that with epoxy. Having a gap increases the crank volume – which you don’t want on that engine.
Attached would be an ultimate lower end. This is a 6 speed 125cc. It can’t make the HP of a sled engine as it needs some rpm to shift. Each shift on a bike drops a 1000 rpm +/- per shift.
So this engine makes 42HP at 12500 rpm. (new YZ dirt bike is about 33HP stock). It had a 30 mm carb.
Again, fresh reed petals – good rings, chamfer the ports, fix the intake and you will be good. Notice on my engine how the reeds have been tuned with the slit. Notice my engine how tight the intake is to the reed block.
Notice how the transfers have been cut up. What you did may work on an old engine – I’m sure but this one, at 12500 needs some form of long path to get the fuel settled down. Notice the 3 port exhaust. The top of the exhaust is about 4 mm lower than a stock YZ125. Again at 12500 – it needs time to work. Notice the wide squish.
This would be the ultimate in engines at this time.
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RJH
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RJH
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porting
QUOTE=Junior]don't cut the piston, cut the skirts on the cylinder infront of the reed cage.
Incorrect Junior!!, this is a cylinder reed engine, not a case reed engine. You do shorten the rear skirt, relieve the bottom piston skirt in a recess and add a boost hole in a cylinder reed engine, the cylinder skirts have nothing to do with the reed area and case filling on this engine!
RJH is giving the correct information and exactly the path this guy needs to follow with his engine.
QUOTE=Junior]don't cut the piston, cut the skirts on the cylinder infront of the reed cage.
Incorrect Junior!!, this is a cylinder reed engine, not a case reed engine. You do shorten the rear skirt, relieve the bottom piston skirt in a recess and add a boost hole in a cylinder reed engine, the cylinder skirts have nothing to do with the reed area and case filling on this engine!
RJH is giving the correct information and exactly the path this guy needs to follow with his engine.
Last edited:
JDMCRX
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Cause the piston is not feed from the lower case .
Ive seen like YZ were the reeds are in the case this one is on the head but the rigns stop right ontop of the reed port holes.
Ive seen like YZ were the reeds are in the case this one is on the head but the rigns stop right ontop of the reed port holes.
montynormand
Member
RJH and mrviper700 are fun to listen to. I've been reading rjh's comments and trying to invision what my little 292 porting job looks like!!! LOL
someday I hope to have a better handle on this stuff
someday I hope to have a better handle on this stuff
JDMCRX
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Ive done ton of 4 stroke motors lol from 200whp NA to 400whp turbo 4 cyl lol
But this is were i am learning lol
But this is were i am learning lol
JDMCRX
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The carb is a 28mm i wanna get it bored out to 30mm anyone do this???
ModMMax
New member
Hat's off to you guys who will take the time to teach. Great thread.
RJH
New member
ModMMax said:
Ya but we need to keep throwing in the "snowmobile" word or this thread will be deleted.
I’m not a fan of boring carbs. You lose the design factor that the engineers designed into the carbs. I think you have a round slide VM Mikuni??? There is a ton of 34’s or 32’s on eBay – probably cheaper than having yours bored. Bigger hole means slower air speed so jet smaller.
Hey…the DT200 is the blaster engine – isn’t it – I have one of those – a 2000 stock.
Check on line – you will find lots of stuff on mods. I think the only difference is the gear ratio but even mounting bolt holes are the same….all this talk. Check it out….lots of stuff. That’s a rock solid engine. A pipe alone would give you a ton more HP.