Stevie’s French '98, Mid-90's WR/YZ/DT (An idiotproof guide to building your own DTR)
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@Stevie-Wonder Looking good, USD front end with a speedo cable reminds me of the KDX125SR or RMX250. Nice spot to take some pics as well
Definitely keep an eye on the oil drain bolt. These are very soft and visibly stretch when overtightened, it was Yamaha's intention to spec the bolt like this IMO as it means if it's done up too tight, it will always snap the bolt rather than wreck the thread in the crankcase whereupon you can just pop the clutch cover off and wind out the broken part with pliers etc. I must admit I speak from experience here as I repeatedly overtightened the drain bolt on my 1990 I owned as a teenager and then sold it to a mate, and the very 1st time he changed the oil it snapped! So I felt duty bound to go over and help him repair it, we removed the engine assuming we'd have to split the crankcases to get the thread repaired, and then fortunately it just unwound so we could just put it back together. The genuine drain bolt is like £2 from Fowlers so again, well worth buying genuine (including a few copper washers) because if you go and get a really strong bolt and then overtighten it by mistake this could make the difference between an easy repair and a complete engine rebuild. Torque setting is 15Nm IIRC (check this) so another job for your 1/4" drive torque wrench.
I know I always say this but a DTR fourstroking at medium engine speed is almost always a blocked emulsion tube (the brass tube the main jet screws into) so I'd look here first. Tap it out and make sure all the holes are clear as these get blocked with moisture/crud and it just starts fourstroking one day. HT lead breaking down is also possible but when this happened to me it started at very high rpm like 9000+. Definitely do a carb clean even though it's a PITA I know. Also check the air supply for the emulsion tube, it's the brass tube on the right rear of the carb body just in front of the carb-to-airbox rubber. You should be able to blow through this, but only just.
Autolube leaking I would just do an oil pump recon as the Yambits kit contains all the seals and gaskets you need to completely recondition the pump, including the gasket where the pump body joins the crankcase. Do this and replace the ball and spring kit where the delivery hose attaches, clear delivery hose and a new supply hose from the tank (retain and re-use the spring-like sleeve this passes through) and you're golden. One thing about the Yambits clear oil delivery hose is, it's slightly thicker walled than the OEM hose and quite a tight fit through the rubber grommet where it comes out of the oil pump housing so 5 minutes with a Dremel and you can make this a nice snug fit which still doesn't allow water ingress.
The gearchange shaft seal can be replaced without removing the shaft if you're careful to avoid marking the shaft. First give the entire area a good toothbrush/Jizer clean to remove all chain lube/road grime from the exposed part of the shaft, and clean this up with wet and dry to remove any rust/sharp edges which might rip the new seal during installation. Then what you have to do is go to a model shop and get some 1mm Lexan offcuts from RC car bodyshells, cut off a small section and jam this between the old oil seal and the shaft to protect the sealing surface as you lever the old seal out. Lexan is flexible yet tough and it's not uncommon for a bodyshell to still look good after a season of crashing at scale speeds of 400mph+ so it's ideal for this, this also works on crank seals.
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I also forgot to mention whilst checking the powervalve I found that the whole valve had play in it.
Whilst the top end was other I give the valve area a proper good clean out of all the gunk carbon and oil that’d built up over time and replaced all the seals
Also thanks @HOTSHOT-III for the tips. I will report back my progress etc when I’ve got the parts.
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Side to side is ok. It’s up and down play that you don’t want…
I’m
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Didn’t someone else have the exact same problem with the emulsion tube a couple weeks ago? Hard to start and bogged out at open throttle?…
My memory isn’t like it used to be 🤪
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Update,
I’ve checked the air filter and as suspected it’s still like new.
I’ve removed the carb which is still also like new, before the bike went bang and stopped getting used I had Jim Bailey drill out the AFR screw as it’d seized and also refurb the carb. I checked the emulsion tube too, not a single bit of dirt.
I also did a few compression test’s and I’ve got really good compression.
3-4 tests and every single one coming a touch under 120psi with the engine stone cold. Pretty impressive.Also sidenote does anyone find it a right asshole getting the compression tester into the spark plug hole? I was having a right mare
The coolant and trans fluid/oil leaks seemed to have stopped too. The only fluid I could find was blue. None the less I’ve bought a couple OEM copper washers. Even if I don’t end up needing them they’ll get used eventually.
I had noticed some fluid around left side crankcase gasket but that was blue as well (same colour as putoline mx5 two stroke)
There wasn’t any trail showing how it got there though? Odd… Had me wondering if the trans oil could get dyed blue from the gasket?? Then I realised that’s just silly.
I also made a job of trying to fix the OEM fuel tap.
EBay replacements do the job and are nice and shiny but the material quality is sub par by comparison. Just look at the erosion on the copper.
My other gripe is your reserve leaves you with about 5-10 minutes worth of riding to get to a petrol station or you’re fucked.Unfortunately things didn’t go to plan.
I found out the hard way the petrol cap isn’t watertight.
Between the tank being upside down whilst I repeatedly fit and took off the pet cock and it sitting upside down I ended up losing 3/4 of a tank of fuel. By the time I’d realised it was too late. You can’t help but laugh.To make matters worse no matter what I tried with the original petcock I just couldn’t get it to seal.
Where it screwed into the tank was fine but petrol would piss out with the Cock left on Off position. Further inspection showed the tiny little metal washer that goes between the two rubber pieces was all bent in multiple directions I assume this was stopping it seal properly.
Unfortunately you cannot buy this washer anymore, I’m kicking myself now though as I should’ve tried to see if the repro one had a washer identical or similar I could’ve used
Either way it still doesn’t make sense to me as it didn’t just leak a little bit fuel pissed out like the tap was on.
Im also missing the filters, pretty handy if you don’t fancy having the carb off every 5 minutes.
The more I type the more it sounds like buying a new OEM replacement sounds like a good idea. Unfortunately they’re £75-85. A lot of money I don’t currently have
Long story short what was meant to be a 5 minute fix ended up being a ball ache. If anyone finds a good condition OEM replacement petcock / fuel tap or has one laying around I could buy I’d be forever grateful.
Now that the bikes on the road I really want to get the miles in and enjoy her once again only issue is I used to run out fuel often enough with the old petcock which gave you a fair warning so I don’t fancy my chances with the repro one
.Gear shaft seal is still leaking but barely enough to form drips. It needs fixing for sure but I can get away with neglecting it for a little while until I can order a new OEM seal.
The gear shaft also has some play side to side, I’m guessing this indicates a worn bearing? I’m not surprised being honest as my gear lever took quite a bit of the impact. Still though it’s not doing any harm or causing any problems.
I also had couple spare plugs laying around, I took the old one out which was blacker then the midnight sky and put a new one in.
This seemed to have made a difference as I noticed the bike fired up first kick.
Even better I could start her without choke, my old method of a few priming kicks, one more to get TDC then one big kick holding the throttle wide open done the trick and she comes to life.
Unfortunately I didn’t get a chance to go for a test ride. I thought I was done but some silly twat (aka me) forgot to remove the carb warmer hoses and didn’t realise until they’d got the carb half way out of the bike. Not fancying wrestling with it to get it bike I removed them in situ. This led to coolant running down the manifold and into the reed cage so that all had to come out and get cleaned as best as I could before reassembly.
Said silly twat then puts it all together goes to ride off only for the bike to begin revving its tits off from idle. At one point I’d even hit the kill switch only for nothing to happen.
Having spent 6-7 hours working on the bike at this point, I shit myself and let out the biggest sigh you could imagine. I wasn’t happy. Was my engine running away or had my kill switch gone faulty?
Luckily my brain went “did you tighten both sides of the manifold?” I reached down and you could feel the force of air being sucked from underneath the manifold into the reeds.
As annoyed as I was, I was just as relieved as the last time this happened it was time for new crank seals
.I also have no idea why when I hit the kill switch she kept running, I turned her off using the keys kicked her over and tried again and the kill switch worked. Very odd behaviour… especially with the kill switch being magnetic, there’s nothing to really go wrong.
Anyway I go to tight the bolts for the manifold and you wouldn’t believe it? My 10mm is missing. Yes. You heard it right. It’s not a meme, it genuinely happened. For fucks sake, you couldn’t make it up.
It wouldn’t even be an issue if it wasn’t for the fact I’d put everything together so there was absolutely no chance of getting a socket in there, I managed to use an adjustable wrench to do up the top left bolt furthest from the carb which fixed the air leak and settled the idle and ordered a new 10mm spanner.
Just as I thought I was done I noticed a puddle of coolant forming underneath the bike. “FOR FUCKS SAKE WHAT NOW” silly twat muttered under his breathe. Dripping from the bottom of the carb was green and clear droplets. I knew for a fact all the bolts on the carb were tight, then I noticed the lower carb warmer hose leaking. I don’t know why because the hose was pushed back on to the nipple far enough and the clip over the nipple with it.
I can’t lie it sent me over the edge because the coolant is bright green yet there where also clear droplets mixing / forming with the green. I really don’t fancy taking the carb off again assuming it’s petrol leaking however a quick whiff and there’s no petrol smells.
Ya know when you’re really tired and ready to call it a day but you just can’t give up? I’m at this point. Luckily after a bunch of faffing around and head scratching the coolant leak stopped. It was the carb warmer hose not sealing the whole time.
As to why or even how the bright green putoline coolant decided to turn clear I don’t know. It probably did it just to fuck with me. Who knows?
By this point I’d run out daylight and with what was a full tank of petrol mostly on the floor I thought it’s time I call it quits
With that being said silly twat returned to cave he arose from to return another day with more energy and enthusiasm.
Silly bike things aside I took 3 different calls for new jobs! Overall making today a pretty good productive day
All that’s left to do is actually go take the bike out for a ride and see how things go.
I’m also going to have a day where I ACF50 the bike and give her a deep clean and detail. She deserves it and as mentioned it’s been too long. It’s just hard to keep on top off when she’s always getting dirty!
If things haven’t worked themselves out then the only thing that leaves me to check is HT lead / coil !
Outside of getting to Rev out that just leaves using @HOTSHOT-III tips and advice to sort out the oil pump and gear shaft seal.
Anyway’s good evening chaps. Hope you got a good laugh out of some of the mishaps I was having. Sorry about the “wall of text” I was so busy I completely forgot to take photo’s. Alll
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@SpookDog Yes I think it was someone with a TDR125?
@Stevie-Wonder Sounds like you're moving forward with this, those pattern fuel taps are a bit of a mixed bag but I've bought good ones before. Next time you have to disturb the carb warmer hoses, just bypass the carb altogether and run a single hose from the banjo on the head directly to the one on the thermostat housing. You still get the benefit of the cooling system being self-bleeding when refilling, but it makes the carb a lot easier to remove and UK winters aren't really cold enough to worry about carb icing.
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So back again with an update. Bike still starts on the button, maybe with a couple extra kicks when she’s been sat but most of the time that’s just because I haven’t primed her.
I’m still having issues with the bike revving out. I took her on the bypass a few weeks back and held the throttle wide open to de-coke her which worked well. It actually fixed her she coughed spluttered then shot off like rocket up to 9-10k. I was ecstatic.
However this was short lived as I then went to the jet wash to clean her up ready for bike night where afterwards she then refused to Rev past 6-7k.
I put a fresh spark plug in, no difference. I did notice the plug I pulled was wet and smelled of petrol so can only assume that’s just fuel that isn’t getting burned from where I’ve got the throttle open past where it’s revving too.
I put an old plug in that was gapped to spec (i don't have a gap tool to do my plugs and had never bothered doing it or realised why it might be of importance).
To my surprise the bike ran worse, refusing to rev past 6k maybe 7k in second if I was lucky.
This could be something to do with the fact the plug that went in it was about 5-6 years old and could’ve got removed due being fouled. I did give a good clean before installing though.I checked my carb over again and everything’s in very good condition. Emulsion tube looks brand new. Main and pilot jet clean as can be with no blockages. Float height was set to around 16-18mm. I changed this to 20-21mm as per the Hayne’s manual however @HOTSHOT-III was quick to point out this is an error and only applies to the 26mm round slide carb. The DT125RE with the tm28ss states the float height should be between 15.5-16.5mm.
I then corrected my previous adjustment to what it originally was.To adjust the float height would have seemed illogical anyway as I’ve never messed with the carb settings since I’ve owned her however it was always worth checking as I could’ve accidentally adjusted something in the process of me learning my way around the carb.
The YPVS is set up and functioning properly, I’ve checked this a couple times once with the exhaust off and following the standard process of chucking a 4-5mm Allen key in the slot and tightening the cables by a turn and a half.
The only suspicious thing I noticed is how on one side I’d nearly run out of thread getting the cable tight, if it wasn’t for the nut screwing back then and locking it into place it wouldn’t have set firmly in place.I think I’m going to check the YPVS one more time though just to be sure. I had a similar issue a while ago which was caused just because of the powervalve pulley being put on the diamond out of the powervalve 45 degree’s out. I still get paranoid it’s happened again no matter how many times I check.
Referring back to my what I said about the carb, I figure given that everything seems okay in the fuelling department maybes it’s electrical?
So I checked my battery as it’s quite old and often sits for a while and was a cheap replacement. My first time using a multimeter, I realise now why they’re a vital piece of equipment. I was pleasantly surprised that the battery reading is 12.74/12.5v whilst not running. Whilst running at idle 1.5k/2,000rpm reading is 14.25-14.35v and 14.45/14.5v at 3,000rpm. All within spec.
Next up was to check the coil resistances. Earth and low tension/where cdi connects Primary resistance 0.7 to 1.00ohms. Secondary resistance/Earth and HT lead is 7.50-7.52ohms. Once again all within spec. A visual inspection shows nothing concerning too. Whilst I was there I used a little wet and dry to clean up the contact points.
@HOTSHOT-III recommends replacing the HT lead so this will be my next move. Yambits do a NGK Racing red HT lead that looks pretty cool. Red + “Racing” means gains right guys? May as well kill two birds with one stone.
In regards to things to check to fix the issue this only really leaves me with the pulse and source coil resistances and stator.
I’m happy that I’m slowly but surely eliminating potential problems one by one and learning in the process however I’d be a lier if said the closer I get to having tried everything the more I feel defeated. I just want to ride my bike! @SpookDog I’m starting to get how you might’ve felt with yours!
Here’s some links to the video’s I watched that helped me
Float height measuring and adjustment.
Testing a battery / using multimeter.
Battery, stator and coil.
Coil testing
HT Lead (I know this one is meant for cars but the principles applied are the same)
Gapping a spark plug / How to gap a spark plug.
https://youtu.be/IuW3svdqKZM?si=YwFvBwoAFYtx0ozyAll very useful. I find visual aids and how to’s very helpful as I sometimes struggle to learn or understand unless I see it or do myself. Big thanks to @HOTSHOT-III for his help too.
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Make sure that the air waves are cleared on your bike, you don't seemed to have mentioned this.
So there is nothing nasty blocking your intake solution. A quick, dirty, way to confirm this is to just remove the airbox to carb joiner and take it for a quick run. Sounds like it's running rich, so doing this should cause the bike to lean out. If it's only for a short time it shouldn't hurt. You just want to know if it's getting air.
So check the airbox and renew the filter if you find that removing the boot fixes the issue.
The other common problem is water getting into the exhaust expansion chamber. So cleaning the exhaust is really vital for a two stroke. I've seen this before where a bike was sat for a long time and the exhaust was full of fluid. The bike would refuse to run if this was the case.
