Apart from oil leaking from engine block, the engine runs good when it runs.

Oh is it? I did wonder as it has a tread can’t remember was awhile since I took it out. I was thinking it could be blank cheers mate.

Moral of the story from this I can see is More horse power = power maintenance worm with pustion changes probably more regularly Keeping the dep exhaust carbon reeds and sprocket changes seems like the best for performance with out risking blowing pistons more frequently I did see a video on YouTube on how to make two stroked more powerful but with this there was a risk of blowing the engine maybe if you want a fast bike just get a bigger one? I wanted a yz road legal but for daily use I can imagine these get warm and aren't really good for road bikes sure for the track for a couple hours it's all good The dtr is a true work horse in my opinion

Done. Thanks guys

Morning guys I just popped of rad cap went for a ride and she's now staying cool cheers guys

@mbmO8 This explains the YEIS box between the carb and reed valve better than I can: https://global.yamaha-motor.com/stories/history/stories/0019.html When working around that area it's not that difficult to remove as long as you have a decent pair of pliers to squeeze the clip on top of the reed block, just stuff a rag in the hole until you refit it. The one behind the carb on later bikes, I've never owned a DTR with one of these fitted so maybe someone else can help out explaining this? I see a lot of people blank these off with the lid off a Coke bottle.

@dominik22 I'd start by refitting the airbox snorkel and the stock silencer if you have one. My French '93 4BL ran very well running the jet sizes you mentioned (i.e 240 main) with either a full stock exhaust system or a Tecno expansion/DEP silencer combo but it didn't like the stock expansion/aftermarket silencer combination. Sometimes the tailpipe can affect performance as the stock expansion chamber and silencer are designed to work together; if you change one it can alter back pressure and mess with the pressure waves going backwards and forwards. These evacuate exhaust gases from the cylinder, assist in drawing fresh mixture up through the transfer ports and act to keep the fresh charge from escaping straight out the exhaust port. I never thought the tailpipe alone would affect this but once I tried a brand new DEP silencer on my otherwise stock French '93 4BL with 3NC CDI; it immediately refused to rev beyond 9k. I rode it around for about an hour to eliminate wind direction etc., came home and refitted the stock silencer and straight away it revved to 10k+ again. This is only personal experience, I don't have access to a dyno or anything but it made a big impression on me. A Tecno expansion chamber would probably work well with that Athena silencer. Tecno expansion is identical to the Athena apart from the clearcoat and under half the price. Only downside is the clearcoat melts around the header pipe and is difficult to sand off making your bike look like a Crème Brûlée. If I bought another one now I'd paintstripper it and paint it heatproof black before fitting it. Very good quality pipe for the money, gives a more usable mid-range hit than the DEP which delivers peak HP revs about 600rpm later. https://www.ebay.co.uk/itm/253780922884?gclid=Cj0KCQjwurS3BhCGARIsADdUH5215jUowscJtBepB7NQYPYfR4AeBV1Gu63S4cHFVVEN8aPRotYawA4aAoc7EALw_wcB&_ul=GB&mkevt=1&mkcid=1&mkrid=710-53481-19255-0&campid=5339059258&toolid=10044&customid=Cj0KCQjwurS3BhCGARIsADdUH5215jUowscJtBepB7NQYPYfR4AeBV1Gu63S4cHFVVEN8aPRotYawA4aAoc7EALw_wcB

I hoon around town on an unrestricted DTR and it uses less than 5 L/100 km.

Good that you've confirmed that it's not the powervalve, that's one thing we can rule out.

First things first, bin off that coil. Get yourself a genuine 3RM one. https://www.fowlersparts.co.uk/parts/view/4RP8231026 I had a horrendous issue that took me months to diagnose, since it would run absolutely fine from cold-warm. But after a short while it just refused to rev. It took me literally forever to figure out, I swapped loads of bits out and considering my bike was a "fresh" rebuild I didn't think it would be the "Racing Coil" I bought. It hit me when my brother was having problems with his RD I noticed he had the same type of coil and the tuner said bin that immediately and all his problems went away! So first things first, get yourself a genuine coil. Later coils are a different part number: https://www.fowlersparts.co.uk/parts/view/3KJ8231013 So it might be that your coil isn't right for your bike/year. So just source the correct year/model coil for your bike and make sure it's a genuine one (Denso I believe makes them). Secondly, I've seen this before whereby the exhaust got full of water after a DTR was stood outside for a long period of time and this had very similar behaviour. Running rich and lacking the ability to rev/pull hard. So whip that exhaust off and give it a good clean, it was very odd and not something I had considered. Later model DTs were fitted 210 main jet, but again this all depends on your carb that you're running and whether or not you're fitting genuine Mikuni Jets. Ideally you want to be fitting the right jet for the year/ignition etc.

@dominik22 Well you're doing better than me, once I was rebuilding a TDR250, thought I'd finished and then rode to my friend's house without connecting one of the carb warmer hoses! As you can imagine the temp gauge skyrocketed, luckily it wasn't far and we were able to top it up so I could get home.

Nice one, thanks for that suggestion! I’ll give that a go. Ps. Nice name!

They are fuel overflow hoses. Attach a hose like shown on the other side and feed it underneath the bike away from any hot areas. They're designed to flow gas away from the bike and hot areas should the bike fall over and the tap not be shut off.

@eric74 Fair play for getting on and replacing the tacho drive O-ring. Looking at your pics I'd say the oil is definitely coming from where the cable joins the tacho drive so I'd order the oil seal for this (item 7): https://www.fowlersparts.co.uk/parts/4083282/dt125r-3py3-1991-999-a/tachometer-gear Looking at the 4th image you posted up, the plastic breather stub should be right behind the tacho drive about where the old O-ring you mentioned is so it looks like your breather is missing (items 14 and 15): https://www.fowlersparts.co.uk/parts/4083277/dt125r-3py3-1991-999-a/crankcase Not sure whether oil would be visibly leaking out of here if it simply wasn't fitted (you never see any oil in the clear tube IIRC) so it may be that someone had the bright idea of plugging the hole with silicone sealant or something similar. Have a poke around here but be careful, if that's what's been done it would be too easy to end up with it disappearing into the crankcase, but if you're patient with the needle nose pliers/tweezers etc. you can remove a wodge of sealant like that from the outside.

It's doable. I've taken parts from 3 Mikuni 28s.One from my DT,one of a TDR250,one that has oil feed tube don't know what bike and made my current carb. The one with broken is off,the bent tube is overflow if memory serves. Chokes are the same.

@dominik22 I take it your pump is not the plunger type? https://www.youtube.com/watch?v=WwFUzgr2xnA This is how I set my pump many many years ago. I did not align the lines intentionally just to run a fraction more oil due to the porting work I was running at the time.