So Close!...
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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!
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@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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@SpookDog I appreciate you are going for that OEM style, but I run a VHSA carb on my DT and it runs great. So it doesn't have to be the real deal for it to run well.
That said I had a similar issue when I bought my VHSA I didn't realise there were variants of it in a similar fashion and the one I was jetting to was different to the one I was interested in!
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I’m not for or against anything that works! I just don’t want other people to have to go through the same kinda shit I have. To be aware of the differences. Also Mikuni are good carbs but I’d rather run a Delorto 30mm flatslide if I was going to change to a ‘parallel’ carb
I used them before in ‘days gone by’ with nothing but a bellmouth on them and never had a problem, also old 30mm Amal carbs...I’ve never had so much trouble with a bike as I have with this Dtr. Then it just makes it more rewarding when you finally do suss out what was bitching with you in the end!
I’m @ 1300 miles and the head is still holding (& the cooling is great!)
Really does look like a good unblocked .25 pilot jet was all that was needed to stop it missing/knocking!@marcus
Was it marked near the choke? I read somewhere that it’s the place?... -
@Calum
I did not know that! I’ve been waiting for a realistic break in the nightmare so I can get a barrel done by PJME. I have a good condition (studs &threads!) 3mb that I’m gonna get a rebore done to. I’m also going to find out more about the o-ring conversion to the barrel. I really just want to know if it’s 1 o-ring (for the bore pressure only) or 2 (1 for the coolants outer as well). My current barrel is a bit worn & ‘slappy’ at low revs, which didn’t help my diagnosing at all!!I’ve also got a couple of 4fu barrels. I wouldn’t mind getting one resleeved with a cast iron liner. It works out the same price as plating but with ‘future proofing’ rebore options
it’s just whether the FU porting makes it really financially worthwhile, HP wise? (If it doesn’t suit the Dtr I have a TZR (hw) chassis to put it in) I know the exhaust port is wider, ect, but don’t know how much difference it makes, Powerwise? Or if the inlet porting is different?... -
@SpookDog said in So Close!...:
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
...I wouldn't take too much notice of Haynes if I were you when it comes to DTR/TZR carbs, they've never quite got their heads around the difference between the TZR 2RK/'88 DTR VM26SS and the TM28SS fitted to the '89 onwards DTR. As far as I know all TM28SS carbs have the plastic insert which pushes into the pilot jet and fits around the main jet as my 1990 from my youth had it, and my '93 I bought in 2020. Likewise the plastic throttle spring seat; it's more of a retainer for the cable nipple in the slide really.
But regarding the angled venturi in the stock carb body, well admitting this isn't exactly going to make me look like a 2-stroke tuning guru but I didn't even notice it when I was on the site! Trying to imagine how that would affect the jetting; for a given float height it would have the effect of making the pilot jet and choke tubes more deeply submerged in the fuel but not sure it would affect the main jet too much as it's pretty much in the centre of the bowl.
Anyway I've asked the question on a couple of FB tuning pages so we'll see what everyone thinks:
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