AndyDtr08

Ok cheers. I just cut open a pre 99 exhaust I had in the shed that is damaged. No restrictor in the expansion chamber. Although could that been have removed previously? I'm hoping not otherwise i'll not know whether to cut open the other one! So by the looks of it, pre 1999 exhaust have the restrictor in the exhaust/engine manifold end in the form of the cone and 99-04 have the plate welded inside the expansion. A Pre 99 zorst will fit on a later bike but the mount by the rear brake resevoir doesnt match up.

Ah no sweat just didn't want you thinking I'd been deceptive. Why on earth you they ground those lugs off I've no idea. I like the disc cover personally. It's nice and subtle compared to some of the big heft Kawasaki full disc guards. Just cut open one of the early exhuasts to check for restricting plate. None found. Photos to follow!

Hmm. Yeah I see your point but surely the valve won't pertrude past the barrel lining? Yamaha would have thought of that when they designed it. Otherwise they wouldnt have had oversized pistons. The shop I use is Boretech engineering who are a motorcycle engineers based at a motocross track. They arnt just an engineering shop. Well the one that's built at the moment will stay as is I think but I'll consider that with the next one. Cheers Nev.

When was that? That must have been years ago? I cleared all my DT bits since then and got the RD350 and havnt dealt with them again for a while. You must have skipped a few chapters of my novel then, i said at the start that I bought loads of parts off ebay at the start of this project. That disc guard came from the front end in the photo below that I got off ebay for 30 quid all up i think.

Hmm some interesting things to think about there. My current build has had the barrel re bored and an oversized piston gone in. I didnt skim the powervalve, head or anything like that and never did on the 2002 DT i re built ages ago. I can't believe that Yamaha would design it so that the powervalve would hit the piston after a re bore it just seems mad. Have you read this up anywhere or is it common knowledge or what? Just wondering where it's come from as I've never heard anything about that before.

Good Job! The exhaust is marked 3MB? I have one in the shed which has holes in. I'll go cut it open and see what is inside. Andy

Nice introduction...

It's an interesting one there airhead. I'm still confused by the "Y codes". I have a 3mb that's y-1 but another that is y-3. I also have 3bn y-3 y-4 and y-2. My 3mb barrels appear to be y-1. I have a 3bn barrel but can't remember what y code it was.

Cheers guys. Yeah he does know what he's doing and would probably be embarrassed by me asking advice on here but I thought if try and get sizes etc in case it was any use to him. I'll look into those places though. Those prices are what I worked out including vat. They are 45 + vat for the bore and 55 + vat for the piston kit. If my guy can do it then I'll get him to do all the ones I have as he'll have it all set up and then I can just buy the piston kits as and when I need them. He just txt me saying his work has a boring bar big enough and he can hone them aswell. I'm helping him renovate an import tzr 4dl so he will do me a good price I'm just settling down to a night shift so will probably end up scrolling eBay for Dt parts all night. When you say clearances, that's what I'm after. I'm sure he will probably "bore" me with the details at some point but if any one could enlighten me it would be useful to make me look clever. The bore pun wasn't homo erotic before anyone makes that connection!

So I have accumalated a number of DT125R barrels all of which would need a re bore before use. I have used a local engineering shop called Boretech Engineering who do a stunning job. However they are expensive. They charge 54 for the bore, 66 for a mitaka piston kit and somewhere just short of a tenner for a small end bearing. All up it comes in at 130. I can get a mitake piston kit through ebay for 45 quid delivered and small end bearing is about 5 quid so I'm thinking about going elsewhere for a rebore. I have a friend who works at an engineering place and says he should be able to do the re bore so I have a few questions. If the piston size is 56.00mm then OS is +0.5 +0.1 +1.5 +2.0 what should the re bore be done to? Should be it bored to this exact size or is there a clearance that the rings take up? Or is this worked out and the piston is infact slighlty smaller and the "56.50" size is the size the barrel is bored to? Honing... has anyone honed their own DT125 barrel? I have a draper flexi hone that i used on my 50cc barrel but the blocks appear too small and would get stuck in the ports. Any help would be much appreciated! Andy

I don't.....emissions. They we're struggling against the regulations since around the milenium. Thats why they redesigned it in 2004 and brought out the electric start. It has an exhaust full of CAT to meet the regulations. Then in around 2008 the regs were changes again and they couldnt do it anymore so jacked it in, in favour of the more eco WR125 four stroke.

welcome back weimieman! I have a few suggestions. I'm guessing with the DT125lc 86 you never got to experience th YPVS so how about 3 other 2 stroke options all of which utilise the power valve servo motor. A bit too samey maybe but a later DT125R? A move across to the sports side of things with a TZR125 or a step up to a Yamaha RD350LC YPVS with your experience of Yamahas and the 2 stroke engines im sure they would feel nice a familiar.

Wow i bet that was a scary moment! You say you couldnt hear the exhuast? The silencer end couldnt have been under?

Great news! That sounds effective then. The red line will be, as you say, caused by the wire in the back of the speed as it is a rev limiter. Has it increased top speed or just power? Andy

Progress update... Re sprayed the fork legs. I have to admit I didnt do a fantastic job as can be seen up close but it'll do the job from a distance. I have finished re building the Rear caliper with genuine new yamaha seals and piston. Am still waiting on the aftermarket kit for the front from ebay. It got lost in the post... I abondoned the nitromoors and went to town with a wire brush attachment on a drill and it proved far more effective. Thanks Nev I was viewing your thread! The seat was tired and tatty so I had ordered a replacement seat cover from Portugal with my plastics. Stripped the seat back and cleaned the base and dried out the foam in the sun ( water had got in through the tears). Then I glued the foam back onto the base and began an attempt at stapling the cover in place. I found that it needed a lot of stretching. I messed it up the first time as i lined the Yamahas up first and worked from there. I have found the best way is to line the front up, staple that in place and start working down the sides, stretching as you go. I then stretched and smooth it all the way to the back and put one staple in place at the back. Then I worked my back to the back putting "marker" staples in place and working in between them. Sucess came eventually but I have a couple of small holes now where I didnt line it up right the first time. Dissapointing but I will leave as is for now and if it causes issues I will order another for 20 quid and have learnt from my mistakes. Overall im pleased with the result. A few creases as to be expected which may settle. I resprayed the disc guard I had from spares. I cleaned it up with soapy water and then used panel wipe (alcohol) to prep it. Then i Primed it and wiped again with panel wipe and sprayed with Satin Black paint. I wasnt too bothered about the finish as long as it looked black. I also sprayed the side panel in the same way. The R/H side rear panel should have the front black but the ones from portugal are all blue so I sprayed it to match. Both this and the disc guard are awaiting laquer at present. Forks need to be rebuilt now and fitted onto the bike replacing the ones that are on there at the moment. I'll do this and the wheels at the same point. Hopefully the caliper will be ready by then and all can go on. Looking to get a blue covered braided front hose but am tempted to just go silver goodridge. I will take the advice and put 15 weight oil in the forks when they are re built. Enjoying every minute and can't wait to build one from the ground up with everything being clean! This one will be sold to pay for that next one. Have had 2 cheques cashed by the DVLA for the 2 logbook applications on the frames I bought so they should be here soon! Thats all for now guys.

You're over complicating things. I cant picture what little balls there are in the carb but I would personaly.. have the carb off and give it a full clean, all jets etc cleaned with carb cleaner. Replace the carb to airbox connector and the hose clip that holds it tight against the carb. If this is loose, thats where water is getting in so make it water tight. Yamaha designed the airbox very well so I wouldnt go messing and trying to do better just repair and replace to get back to how those clever Japanese fellows had planned it to run.

Different Hangers and pegs on the TDR but may still fit. Generous offer there! The hangers and pegs come up on ebay a fair bit. I saw some not sell for 5 quid the other day. Search completed listings for "Yamaha dt125 rear" and you'll find them eventually. If i see them come up ill let you know. The carb on a lanza is a TM30 if im not mistaken. Is it you I'm txting about bits?

Yeah that will be the restrictor. Wait for a few more confirmations but I'm pretty sure that will be restricting it quite alot. According to some who have done it, you get better power from the Yamaha original exhaust once this plate it knocked out compared to fitting a DEP downpipe which costs £150. I think that ring would be disrupting the back pressure of the expansion chamber. I think it was DeeTeeMX who posted about the exhausts. Up until 1999 the exhaust was only restricted by the cone insert that you looked for in the end of the exhaust. After 1999 the exhausts had 3RM stamped. Their fittings were slighlty different and the restriction was moved to the expansion chamber ( like yours). I presume this was to make it harder to removed or maybe more effective at restricting. You'll need to be very careful at lining it up when you weld it back together. Might be worth lining it back up now and putting some lines to match up when your ready. I'm on the look out for an earlier exhaust for my 1998 bike so hopefully will only have to remove the cone in the end. Keep us updated with photos and results.

Nice one airhead. I'm on my phone at work using the IPB mobile app and could t work out how to get back to the first post. Worked it out now and see you have some nice clearer photos there. As you say it's the same as yours after the removal so no restriction there.

Well I guess you'll want to check the hose clip that holds the air box to carb hose in place. Anything getting in the air ox side should be stopped by the air filter. Is it getting in the float bowl or the bore of the carb? Check your fuel filter. In the tank. The later flats life carbs also had a fuel filter built into the fuel pipe where it connects to the carb. I found this the other day, unless it had been jammed in there by a previous owner, but I think I checked a spare and found the same. The air box is built in 2 halves and there is a rubber seal that fits between the 2 halves in a recess all the way around. Might be worth a check there too. Water in your carb is a dangerous situation though. Don't want that H20 stuff in your engine!

There is a "small pipe" that is a restriction in that part of the exhaust but I don't remember if it looks like that. It's welded at 3 points into place and can be removed by disc cutting the weld points and it should slide out. If that's not what you are talking about don't start cutting. There is a site that is something like Dtr. Net that shows photos of it in place and removed. I removed one from my brothers 1989 model but have not seen one since.

Congratz! You'll have heaps of fun on that. I don't remember mine having that guard around the rear brake master cylinder. Did you fit that? Is that a DEP pipe but sprayed black?

Yeah I think the flat slide carb was on the 1997 onwards bikes. So the first 4bl. My 1998 has a flat slide but an old style pump cover and 4bl engine numbers. The clocks were kph so mine may well be an import.

Welcome to the forum! We all friendly to anyone who introduces themselves. I keep walking passed one of these half covered by a tatty motorbibike cover in someones front drive near my work and keep having to hold back the temptation to buy it. I've even knocked on the door and left my number as the owner wasnt in. It hasnt moved in months. I'll resist though! Will see keep an eye on your project though and hope it doesnt become too much!

Welcome to the forum! Get some photos up!