DT250 pipe

[50gary]

Help, I need a plan for a expansion chamber for a Yamaha DT250, it's a 1975.  I've converted it to a road bike and need a down pipe.  I'm sure I can make it if I can get the specs?  I have the routing worked out fine.  I took two old pipes cut them up and welded them into the pipe that will fit and look the way I want.  Motor is stock for now.  Dry build is done except for this pipe thing.  Thanks for any help.
  Cheers, 50gary

[paul1478]

I did not recall what a DT250 looked like so I did a quick Google search.
found this:
https://www.dimecitycycles.com/blog/giancarlo-sulmontes-1973-yamaha-dt250

it has the guys contact info and looks like something you may like. he may have the details of the pipe.

[bracket maker]

Help, I need a plan for a expansion chamber for a Yamaha DT250, it's a 1975.  I've converted it to a road bike and need a down pipe.  I'm sure I can make it if I can get the specs?  I have the routing worked out fine.  I took two old pipes cut them up and welded them into the pipe that will fit and look the way I want.  Motor is stock for now.  Dry build is done except for this pipe thing.  Thanks for any help.
  Cheers, 50gary

my stock dt did 55 wot at max rpm. was worthless as a road bike. 38t rear sprockets are what they ride in Europe. found this mod more important than pipes. good luck. I'm a fan. at least get the 17t front sprocket. jt sprockets are available. this bike has the following problems, heavy steel antique rim locks. low compression dykes rings. heavy antique pistons. antique porting. fixed ignition timing. 6v lighting. if I pipe mine I'll take one from a modern 250 dirt bike and modify to fit. may happen when I change the engine. the only thing stopping me is the cool chrome heat shield and the American style '70's scrambler stock pipe.

[teazer]

There's at least one DT1 or 2 racing in AHRMA and they fly.  SOmeone probably has a set of pipe dimensions and if not try MOTA or the Wizard software. I prefer Bimotion for pipe design because it gives me more variables to play with to tweak the design before it's necessary to start cutting tin plate up and rolling cones.

[pdxjim]

A buddy of mine had a '69 DT1 setup for roadracing with a GYTR MX250 cylinder and Webco head.  I believe it was running a pipe off a modern YZ250 and he also had a few pipes made by a local guy from GYTR specs.

It ripped.  Very, fast for a 50 year old dirtbike.

Last I heard the bike is now in Germany after a few years doing the Motogiro d'Italia.

[bracket maker]

here is an old pic. very fast, not without major engine mods. eventually I'll get to the engine swap. I felt like I was riding the biggest moped in town. sorry the pic is not from the pipe side but it is a thing of beauty.

[50gary]

First off I want to thank everyone for the replies.  It's not as easy to find information on 2t bike if their not RD based.  I just got off the phone with Jemco (they actually returned my call which is cool.)  He will make a pipe for me to my needs and his specs so that's excellent IMO.  $370.00 shipped TX to MI. so that is not too bad.
   Yeah, the stock DT is porky and not a world beater but I've used the DT/RT frame as a platform twice before.  The other two are linked mono-shock & 24 degree rake.  I strip everything, for this one I've got RD 400 forks re-sprung and emulators, FZR single brake with R6 caliper, EBC pads.  New 18" (FRT & RR) from Buchanan, RD 350 frt hub modded, rear hub is stock with new arc-ed EBC shoes. RZ front fender Avon Road Riders.  I've also done some minor frame bracing.  I have a RT360 (351 actual) motor that will get a rebuild over the next winter to bump up the performance some.  If you run a single cylinder against twins in the 250 class they give you a 100 cc bonus so that's something to think about.
   Cheers, 50gary

[bracket maker]

First off I want to thank everyone for the replies.  It's not as easy to find information on 2t bike if their not RD based.  I just got off the phone with Jemco (they actually returned my call which is cool.)  He will make a pipe for me to my needs and his specs so that's excellent IMO.  $370.00 shipped TX to MI. so that is not too bad.
   Yeah, the stock DT is porky and not a world beater but I've used the DT/RT frame as a platform twice before.  The other two are linked mono-shock & 24 degree rake.  I strip everything, for this one I've got RD 400 forks re-sprung and emulators, FZR single brake with R6 caliper, EBC pads.  New 18" (FRT & RR) from Buchanan, RD 350 frt hub modded, rear hub is stock with new arc-ed EBC shoes. RZ front fender Avon Road Riders.  I've also done some minor frame bracing.  I have a RT360 (351 actual) motor that will get a rebuild over the next winter to bump up the performance some.  If you run a single cylinder against twins in the 250 class they give you a 100 cc bonus so that's something to think about.
   Cheers, 50gary

that's my feeling, the frame is a platform with an untraceable vin #. it is a pig stock. the engine alone is 50lbs extra weight with a lame 5 speed wr tranny.


the 6v to 12v conversion is really easy. I know almost as much electronics as sonreir. happy to guide you if you want to upgrade. I've done this same stator twice and like you said there is not much info. I have the missing pages from your manual. happy to share.


cheers,

[50gary]

Motor weight 50# more than what?  I'll be in touch about the 6v to 12v conversion when I get to that point (No pun intended) . I've wondered about adding a 6th gears to this.  Yamaha has an aversion to 6th on their off road bikes.
  Cheers, 50gary

[bracket maker]

50# more than 80's air cooled 250 2t. when I get around to the engine swap I will have fixed the following problems. heavy low compression engine with antique porting. 5 speed wr tranny that does not allow kick starting without being in neutral. fixed ignition timing.

no pun made. points ignition works independently from lighting on that bike. it's ac stock works well with its dedicated stator coil and does not need to be messed with. ignition is already 12v+. lighting is 6v. 4v at idle without a battery. the stock sealed beam headlight is lame.

[nojoke2stroke]

I am building a DT250 (1973 DT3).  Here is the latest from a photo today.  I have added 14.5" shocks and a modded KX100 front end to raise the height of the bike.  I also fabbed up some pannier mounts for the saddle bags.  I am going to run the RD400 tank for larger fuel capacity, which I think will work well.  The down pipe is from Jemco and comes in 2 pieces.  I will finish up the welding on the silencer soon.

[bracket maker]

that's not an dt its an rt3. the rt360 has 31 hp with a top speed of 80. the dt2 has 17 hp stock.

https://www.bike-urious.com/legend-born-1972-yamaha-360-enduro/

bought my dt250 after being inspired by jay leno. I wanted the first enduro. you dont need his money to buy it. they basically are unchanged from 1968-75. paid $300 after an unsuccesfully bid on an rt3. although more powerful it still is a turd because the 80 mm piston with its 70 mm stroke is a paint shaker in the power band. the physics of the piston are all wrong.

the earliest rt is 1970 making it more modern than my 1974 dt2 that was designed in '68

50gary, why ask sonreir honda twins electrical questions. the answer is buy sprackmoto. he is less than straight foward. this is the forum trust me they read here too.  been putting care free miles on my batteryless cb. yes I know it can't be done I've been told and banned. you need a part that costs 1$ to run the kohler regulator on a honda twin. should be blazingly obvious 3 ac stator wires won't work on a regulator with only 2 ac terminals without a tweak. feel bad for you, I understand your question, sonreir should have answered it long ago. go back and read my honda post in the 4t section. I may be a lot of things, I may make mistakes often, but I am honest about it. those pics at idle without a battery are real. I may strike out from time to time but this time I hit a home run.

read method #1. order the 1$ part. when it is in your hand how to wire it will be obvious.

[50gary]

Nojoke two stroke, good to see the Jemco pipe I just ordered one the other day.  Fingers crossed.  A different combo you've got going there?
Bracket Maker, I'm not sure what you mean about electrical questions to some Honda guy?  Cross that bridge when I come to it.
  Cheers, 50gary

[bracket maker]

06-27-2019, 04:05 AM
#503
gazzweld
Junior Member

Join Date
Feb 2019
Location
South Grafton Australia
Posts
22

replaced all the old wires between engine plug and r/r and decided to delete the old rectifier plug that i was using because the r/r connections are removable anyway, and reduces any possible bad connections. i spliced the yellow and white AC wires together close to the plug, so ended up with two wires direct to the r/r AC connectors, red wire from battery positive to B+ connector, green wire from battery negative to mounting bolt, then to frame. battery still sparked when leads were connected.
disconnected r/r and bench tested with my multi meter and found no resistance between one of the AC and the B+ terminals.
faulty unit out of the box, but i guess that happens with electronic components. waiting now to hear what my options are from the supplier. cheers, Gary.

sorry dude read this post, this gary talks just like you. didn't notice he is aussie. basically spent a lot of time figuring out what this gary did wrong. saw cheers, gary and assumed wrong. I apologize.

without flaming another board what I see voodoo mantra. yellow and white in the handle bar gets connected so lets connect yellow and white. the mistake is its ok to connect yellow and white after it rectified through the stock 3 phase rectifier. connecting yellow and white b4 rectifying won't work. if anyone is a member at honda twins, please pm gazzweld and Kungfutoast send them both the link below. kungfutoast has a cb77 and wants to run without a battery. simple enough.

http://www.2strokeworld.net/forum/index.php?topic=418.0

50gary is problably about to throw up so lets try to make it up to him. add this page to your manual. in order to run a modern scoot rec/reg you need to do a simple mod but you have to remove the flywheel to rewire the lighting stator coil. once the flywheel is off you will see 3 coils at 7 o'clock 12 o'clock and 5 o'clock. the lighting coil is at 12pm and is the only one that needs to be modded. carefully remove and unground this coil. you have to remove the stator plate to do this. make a couple of score marks so you can replace it with the same timing. the brass o terminal will come right off with a touch of a soldering iron. the insulation on the wire is varnish. you prep with sharp knife unless it comes off tinned with solder at the tip. solder a wire to the tinned end and insulate the repair with 2 layers of shrink wrap. this wire is fragile. take care. zip tie the repair to the stator plate then route this wire out. you can even be slick and use the 5 o'clock wire. cut and attach it to the tinned end then use the stock plug. use the stock insulator if you can save it from the 5 o'clock wire. its fiberglass and is better than shrink wrap. the tail light stator is unused in this conversion.

written a lot but done little. recap, unground the lighting coil and routed this wire out of the engine using the stock plugs and wires if they are in good shape.

why do all this. because floating ground is a rabbit hole you don't want to go down.

at this point you have a 2 phase full wave ac current from two headlight stator wires. the gy6 r/r runs 2 phase ac full wave. if you tired to use this part without the stator conversion the thing will burn. other two terminals go to + and frame ground. the whole reason to unground the stator is so you can ground the regulator to the frame making the frame 0 volts.

at this point you can use an 4.5 or 5 ah 12v alarm battery or better yet a battery eliminator. its enough juice to run the stock headlight, led tail and signals, horn, 12v led flasher. if you skip the battery you need to change the headlight to led. well worth the effort, the $1.40 h4 led is just as bright at idle as full speed and will not dim.

the ac igniton coil is a different story. leave it alone and run it with the stock wiring because it works well. ac circuit diagram can be found in my post in the tech section. draw it from memory and you will be an expert


ps: you only need a four of wires and two poles out from that crazy igniton switch. that many wires and positions were needed with the antique electrics. + into the switch then out to lights. ac on another pole from the ignition to the coil. I make the run position where the key comes out if I can. I like the key in my pocket when I ride.

this info can only be found here at 2sw. I have not seen any info on the net anywhere. gary sorry the yamaha enduro site is closed to new members. those guys know how to change tranny gears and other stuff I don't know. did that same stator twice. once down the rabbit hole. even blew up a scoot r/r. they do advertize half wave scoot r/r on ebay. have no idea if they work. full wave is twice the output. thats why mark likes ac. so do I but for ignitions only. an ac wave is full wave. the clipper regulator is fine but ac blows dc componants. full wave will alow for a stupid loud horn at idle without the lights dimming from just the headlight stator coil. keep the stock horn. if you are like me you hardly use the horn. the pipe you ordered along with your middle finger should be enough. cheers,

[2strokesforever]

Ive piped the DT 250s and the 400s aswell. GYT spec pipes in both cases that Ive built myself. For 370$ id go for it.
The only other mod you might want to do to take full advantage of the pipe to its fullest is a bigger carb. I run the 38mm Mikuni roundslide, which delivers very, very good results with some pretty straight forward tuning.
My opinion is if you do the pipe, do the carb aswell.

You dont need to swap an aircooled engine for another aircooled, you just need to learn as much about the one you have and go from there.

If your going to swap out engines you should just go for a 2004+ Yz250 and have 50hp out of the box and be done.....