So Close!...
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Bud! I call it ‘dirt ball’
it’s a fucking nightmare. It’s on the list to reupholster a new seat. I brought a spare especially. It’s just not a priority atm. You can get silicon seat pads, but I haven’t spotted a good fit yet...I’m 5,11 and can’t fold my legs up anymore and still work the gears...
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Re cleaned the carb out last night, paying special attention to the pilot jet. Also I sealed up the hole in the bottom of the casings as well as the seam/join with silicon RTV sealant.
Took the bike out for a 70 mile ride and it has been very good! Really good ‘resolution’ throughout the Rev range, especially the ‘throttle just cracked’ problem area. I’m not sure if it’s the sealant that has fixed this or the carb. All I know is that I’ve cleaned the carb a lot of times with no results. Even on the jetting I’m on now...
Looks like a bottom end airleak was causing problems since day one.🥴 ...Only thing is it’s taken over 600 miles (of knocking & misfires)to figure this out, and the head gasket has been failing at about 700 miles before! Whatever tho! As long as I fix this eventually I don’t care anymore
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744 miles and still running. Bike is running @ 95%+ still. Descaling the .25 pilot jet that came with the 2nd carb seems to of done the trick, there was a lot of hard deposit inside that wasn’t obvious to (my) naked eye until it was gone. Still think there’s an airleak (small) when hot (bottom end. Not top). That or the mixture screw wants tuning...
Well happy with results for now. Just worried that 600+ miles of missing &knocking have already taken the toll on the head gasket.
Right fork seal fixed...
Edit: I forgot to memo that I stripped & cleaned carb when I bodge tested the rotor side seal. The pilot jet definitely seems to of been the biggest culprit. Can’t believe how long it’s taken to suss out
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@SpookDog really mate sealing up the hole under the engine won't help anything.as for your carb, have you removed and cleaned the emulsion tube? There's so much more to cleaning a carb than the jets. What part of the country are you in? Someone on this forum may be able to help you out.
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I sealed up the whole underside seam, including the hole. What I know is a casting feature but still has area inside that has access to the crankcase seam. I’m a fool but I’m not that stupid. If you’ve read this thread you’ll see I’ve tried everything to suss this problem and I’m basically crossing t’s & dotting i’s for any possible cause...
Yeah I removed and cleaned the emulsion tube as well as making sure the plastic breather pipe and air access to it was unimpeded...
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@SpookDog I just thought that if it was leaking then you'd surely see evidence of fuel/oil leaking or be able to feel the air by running your hand over it? I have been keeping up with this entire thread and I understand you're trying to eliminate everything. Obviously something somewhere that you're missing and the most annoying part of it, it's probably a stupid little £10 part and 20 minutes work. These type of problems are surely the most frustrating of all.
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Sorry bud, I’ve been pulling my hair out for over a year, I do get really frustrated with it sometimes. It’d be a lot easier if it had been running properly at the start, but I haven’t been able to get it properly 100%, Close sometimes, but no cigar
worst thing is I’m usually pretty good at fault diagnosis. Believe it or not! -
@880 miles. Slightly worried cause the radiator level has been down slightly the last couple checks, only 5mm but it’s how it starts. And about the right mileage...
Still running the same, slight ‘splurble’ at coasting with throttle just cracked. None of the knocking & lurching misfires like before though...
Looking like it was a too small pilot jet causing a lean spot misfire has been my problem all along...
Can’t believe my luck that I couldn’t find a genuine Mikuni .25 jet for sale outside of the USA! Or that the one in my second (immaculately clean carb I brought recently) carb would be half blocked with hard deposits that I couldn’t see without a magnifying glass! OMFD’s! You have to try and laugh!
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932miles & counting...
Adjusted the air screw and the bike has been running the best ever. Cooling is good...
It did spit out a big old cloud of smoke when I went above 7000rpm @ nearing 70mph which speed I never usually do because of the ‘imperfection’ of the motor (it seems to want to run @ the mo’ Like a dog straining at the leash!). I don’t know if it was ‘flushing’ the build up of 2 stroke oil in the bottom of the crank case or something else through the clutch side seal at high speed & revs? Will see with more testing...
I really need to find the right way to set up the airscrew & tickover screw from scratch...
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972 miles and all is well! Coolant is excellent and holding up to the top top of the radiator, bike is running tip top too
no misfiring at low throttle...I’m wondering about the cloud of smoke at ‘highish’ revs at highish speed. I’m wondering about the seal. It can only be unproperly/unburnt fuel, burning 2stroke or burning gearbox oil...
I’m gonna replace (with new original parts) both crank seals as soon as the flywheel side one comes in the post from PJME it’s been a couple weeks which is unusual for them... -
@markus-w said in So Close!...:
@SpookDog https://www.allensperformance.co.uk/
Birmingham company for all your carb parts.Excellent shout @markus-w , I was going to suggest Mikunioz.com but had no idea a UK equivalent exists!
Considering the price and scarcity of OEM DTR TM28SS carbs, a great project for someone with a seized air screw would be to purchase a bog stock TM28SS and powerjet kit from Allens and see if it's possible to get the bike to run as well as (or better than) one with the original carb.
Could open up a whole new chapter in the DTR story!
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There are at least 3 different Dtr tm28 carbs that I know of ( not including TZR tm28’s) all have different jetting & needle, emulsion tube variations. Also the power jet size is cast into the intake ‘plate’ for each different year/model...
RamAir sponge filters used to come with a ‘jet adjustment kit’ which was a screw in power jet that allowed for the difference in ‘suction’(?) that ‘wide open throttle’ creates to draw the fuel up from the bowl to the jet. You had to drill it out and tap it yourself. (Kudos to Hairy Steve for this info!
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@SpookDog Yes, depending upon year DTR carbs are marked 3MB, 3RM etc so there will be variations. Also if you look on Yamaha France parts lookup they tell you the jet sizes which vary between years even among the DT125R.
https://www.yamaha-motor.eu/fr/fr/service-maintenance/parts-catalogue/#/
The TM28 from Mikunioz.com looks fairly generic so the crucial parts are the same (cable fits into the slide the same way etc.) and it's then up to the end user to jet it correctly, so potentially it's possible to buy one of these and a powerjet kit (which itself requires jetting to suit the bike/use), invest in some dyno time and achieve the same or better performance than the OEM TM28 carb.
Had a nose around the site and their explanation of how to jet differently for a powerjet upgrade is pretty good, I suggested it because OEM carbs are so scarce and expensive now it's getting harder and harder to find a good one.
https://mikunioz.com/shop/tm28-418-28mm-mikuni-tm-carburetor/?v=13b249c5dfa9
https://mikunioz.com/product-category/power-jet-kit/?v=13b249c5dfa9
https://mikunioz.com/shop/tm28-vm28-8001-tuner-kits-for-2-4-stroke-engines/?v=13b249c5dfa9
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I haven’t found a carb with any markings yet! I wish, it would of saved me a year of fucking around with the wrong jetting! I found out about my carb from the back of the Haynes manual. It says that 2004 onwards carbs have a unique plastic insert that sits over the main & pilot jets. That and a unique plastic throttle spring seat. That (my) particular carb has a 240 main & .25 pilot jet. At first I was trying to jet my carb according to the year! (1988, 210 main & 22.5 pilot) it had a 180 main jet in when I first got it! The manual even said it was a 26 mm carb to confuse things!
You live and learn!The main, important difference is that generic Mikuni carbs don’t have the 15-20degree slant that the Yamaha ordered Mikuni’s have. That allows the float bowl to be level...
There are carbs out there, but sheeple look at the asking price on fleabay like sites and copy unrealistic high prices. I’ve found reasonable people selling for £50 for a usable carb, but they are few and far between
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