I'd start by just pinning the valve and disconnecting it to just eliminate this as a source of problems.

Sounds like a short to me but haven't got a lot to go on.

I'd do a compression check and get an idea of the state of the health of the engine before diving in too deep.

Obviously your description is rather vague so it could literally be anything.

Do a compression check, this is invaluable and will give us a good insight into the bike before checking things.

Basic stuff will be:

• Head Gasket
• Spark Plug
• Fuel/Air
• Exhaust
• Electrics

Would be how I'd approach this.

I've had similar problems myself with regards to an aftermarket ignition barrel that disintegrated on me and was causing gremlins.

@HOTSHOT-III I was waiting to get home to grab my Haynes, so thanks for chiming in.

The Mikuni TMX28 is a very good carburetor, I wouldn't swap it for an inferior Chinese part. You'll risk an assortment of fueling issues which can lead to detonation and engine destruction.

Carbon fibre reeds are your cheapest option for a "Performance" upgrade. I didn't notice any difference with them but that's your entry level upgrade. The Zeeltronic is plug and play and comes with several maps to choose from. As I say, single biggest upgrade from me, but the UK ignition system was restricted and I don't know about any other regions.

Hi @Nerin_BMX ,

Oh just Google'd that carb, I wouldn't touch that with a barge pole I'm afraid. Looks like a cheap Chinesium part.

Getting the fueling right is absolutely critical to your engine, you do not want to be scrimping here.

If you're after a decent carb in the 32mm range then Mikuni/Dellorto have some great options here. The Dellorto VHSA is a 32mm flat slide carb that was found on the TZR 125 RR Belgarda (It's the setup I run) and I either run premix at 2% or pump at factory settings.

The nice thing about the VHSA, or rather the TZR 125RR Belgarda, is that the bottom end is near identical to the DT125RE, so it's a great place to start when you come to jetting.

Out of interest, why are you looking at swapping the carb? What's the matter with the Mikuni? Bigger is not always better, as demonstrated in Graham Bell's excelled Two Stroke Performance Tuning. I've always maintained that if you're just starting out on the DTR and only have money for one item, make it the CDI. Grab yourself a Zeeltronic ignition system and you'll gain a lovely bump in midrange and top end. This is followed by a DEP pipe. Those two items alone made the biggest difference. After that it was all very...meh.

Can't go wrong with: Zeeltronic, DEP Pipe & Carbon reeds and then leave the rest as is. As I've aged, I've also come to appreciate the Athena 170 kit. Just gives the DT a bit more welly to boot my fat arse about. Didn't feel necessary when I was 17...all those years ago.

@Harvey It's just blank isn't it?

Useful bearing part numbers for the N1 Cagiva Mito/Raptor/Planet Bottom End:

Name	Dimensions (mm)	Part Number	OEM Part Number	Notes
Left Hand Main	25x62x17	6305C3	800098349	Can obtain C4 for looser clearances. C4 bearings have additional internal radial clearances to allow expansion in high speed / temperature environments.
Right Hand Main	25x62x17	6305C3	800098349	Can obtain C4 for looser clearances. C4 bearings have additional internal radial clearances to allow expansion in high speed / temperature environments.
Left Hand Balancer Shaft	15x42x13	6302	800053248
Right Hand Balancer Shaft	15x42x13	6302	800053248
Left Hand Gearbox Output Shaft	20x52x15	6304	800024947
Right Hand Gearbox Output Shaft	20x28x13	RNA-4902	800036440
Right Hand Gearbox Input Shaft	17x47x14	6303	800043382
Left Hand Gearbox Input Shaft	16x24x13	RNA-NA4901	800037198
Left Hand Water Pump Shaft	8x12x8	HK0808	800047678
Right Hand Water Pump Shaft	12x16x10	HK1210AA	800033718
Oil Pump Shaft	8x12x8	HK0808	800047678
Output Gear Pump Shaft	13x19x12	HK1312	800049016
Selector Drum Shaft	24x30x7.5	HK24X30X7.5-TN	800062200	This will need to be salvaged due to replacement parts not being easily accessible. Shares parts with KTM/Husqvarna but very expensive and not load bearing so not worth replacing IMO.

To completely overhaul the engines bearings you'll need a total of 13 bearings for the crank cases.

I have spent all day on this and I THINK it's correct. I've checked and cross referenced the part numbers and my existing cases and have tried to marry up the numbers to real-world buys. If there is a mistake please let me know and I'll update the table.

The links are not affiliated, they're just a reference to what's around.

Pretty sure that bike is the TDR to the DTR. Looks to me like the same frame as my ETX, albeit Rotax 127 equipped.

That's fine, I actually bought this because it was tatty to batter off road and maybe drop. But I've yet to actually take it off road

It's almost getting to the point in that I think it's time to abandon this project....

On July 16th 2024, the bike was collected from me to be repainted again. This time under instruction that they could weld the frame up if there was a problem.

I got a phone call yesterday afternoon. Prognosis...not good.

The bikes been stripped to the bare metal but the fabricators are refusing to weld it up. Scrap I believe is what they turned around to me and said.

And this afternoon they dropped the bike off to me £120 lighter with a frame that I am told I need to scrap.

You gotta laugh sometimes

The truth is, I've ridden the bike say 5 times back in 2021 and that's that. I'm now knee deep in my RD project and I am not sure I want to spend more money on it.

The joke is, I've spent so much money restoring all the other bits and bobs, all that's really left is the frame and slapping it back together.

Even gone to the extent of designing bits you simply cannot get anymore.

It's only got to last till the MOT and back
My Dad's offered to sort the frame and paint it and I'll see what happens after that.

For now the project will go on hiatus (although I may order the end can system for this bike as I am confident they won't be around for much longer).

I've not used aftermarket cranks on the DTR. Ultimately the bottom end isn't designed to last forever so it does depend on how it's been treated and used. PJME typically stock quality items, just make sure it's correct for your year of bike.

Looking at the price of them, I can't imagine they're being as good as the OEM ones, but should be fine to use. The DTR is pretty woefully powered so you should be fine.

Maybe others have had better experience than I though.

I typically would get someone to rebuild it for you, my local garage charges £30 and then spend the extra money getting a quality connecting rod.

Cheers @HOTSHOT-III. No me neither, but there seems to be some sort of cult following for this specific bike.

https://www.ebay.co.uk/itm/266746773795?_skw=inbred+saddle&itmmeta=01JCWRW4QB5SS11ZFX8KDWMB3R&hash=item3e1b58c123:g:Og4AAOSwmM1mCeqw&itmprp=enc%3AAQAJAAAA8HoV3kP08IDx%2BKZ9MfhVJKkWfuy4MxoMsoGrwb2giF5IuJ4JUgTU2sobSDUxWJJ10sEFzFekpJiuBA1RUgJDZT3BcLltngaRYdfZlWDBqDIuW8h9xlCDdZALoSOtQpSRe47adfMUnpkk4H3DUZflKOtKOl5JTDqNYsBWEdR5bIxefoBgwy%2FLiXqQufFVlWCCANyJRs7zFvxjx2zPVnY7u%2B9hsGIU1B4%2FLq50EP1J8SvaEFKXz1tRRTWqsH3KpAGG0hoN90GwbF2wAxLDkeRjx9jvJeGw3RRbpPDX99jeRTS9o51KFaqCLJzIXxSkvkyUSA%3D%3D|tkp%3ABk9SR-TL8JjnZA

That's the saddle and they want £110 USED.

And the single speed frames seem to command decent money on the used market.

https://www.ebay.co.uk/itm/166940463387?_skw=inbred+on+one&itmmeta=01JCWRXAMN8GW0M7WRC1W1C62H&hash=item26de6d511b:g:rHcAAOSwovlmzdPf&itmprp=enc%3AAQAJAAAA8HoV3kP08IDx%2BKZ9MfhVJKnglou7JHksNfzbpds5ZHq%2B6K7Gg%2F8jKo0lS%2Fw88V3fscSTfcW71enskrh3LBLi%2FwqWsYjd0DSrWYVJnI3eSjESH7fphYY5BP%2BwSOliuVCeNdYzzxbH%2BwIelzDEqelFESKo70TdnrFQVMNUQjPIAS%2BGS0WWHxT%2FLKFyVJkF03R%2F6BM28TTet1e%2BQxKxgJN4gCWorRud3Ul8VMfLlCiQhEUi53Elq2oB9S38mlf711AYvdhswdZFCKWjWM2VinoRx7TNmVm5I2TAd8Qnn0ojSc09dZisy9qNF6iw7ReEjNA%2F3g%3D%3D|tkp%3ABk9SR7Sq9ZjnZA

This one here is for £600!

Few teething issues just snagging the bike yesterday morning and then went to go ride the bike and came back to a flat tyre. Not sure if it was a defective inner tube as the puncture repair kit just melted the inner tube.

So I've ordered some more inner tubes and if I can be bothered could cycle over to Halfrauds and buy one so I can use it today.

The floating parts of the disc were fouling the bike/caliper so some minor adjustments needed and setting the chain tension etc. But it's basically there. Went around the block and I probably need to drop a few teeth on the front chain ring as I won't be doing any uphill cycling with it as it is. Fast on the flat though

Asclepius Project (On-One Ti29er Inbred Lynskey)

Merely documenting this for my own sakes for when I need to replace something

This is a small project for something I have been looking for for about three years and randomly popped up on eBay back in September, which I immediately hit the "Buy It Now" button and worried about how I'd pay for it later

The Beginning

Five years ago I moved 15 or so miles from my place of work, where I'd used to run to work, I'd now have to cycle. What I found was that given enough time, something would let me down and my commute to work would be hindered.

One day on my way to work both of my bikes failed on me, if it wasn't an inner tube Blow Out, then it was the derailleur. My Dad had this original Single Speed On One Inbred hung up in his garage for the past ~15 years. He generously donated me the bike and it's so simple that it can be relied upon due to the minimal amount of things that can go wrong. It's a cracking bike, but not content with leaving anything alone, I decided to dismantle it and throw some money at it.

Having it in a damp garage done it no favours and the frame suffered some minor surface corrosion and was generally a bit tatty.

Once I started using the bike, I became absolute enamoured with it and there began the hunt for the perfect Single Speed bike.

The problem with this base came in four folds:

• It was a medium frame and I'm 1.81 metres
• It was an old school 26er setup
• It utilised rim brakes
• It suffered from some minor visual blemishes due to being steel

I was therefore on the hunt for a Titanium Large 29er Single Speed Frame. After 6 months of scouring the web, all I could find were either Mediums/Geared/26er/Cracked. It seems that in recent times, dedicated single speed frames have dropped out of favour and instead people now just convert geared bikes and use a chain tensioner. I wasn't content with this as I wanted that elusiveness of the single speed frame.

Keen to get out and cycling, I abandoned this idea as a short-term solution and then I uhhmmed and arred about getting it resprayed. Unfortunately Covid happened, my car was taken off the road and a series of other projects got in the way.

I reassembled the Inbred bike, threw a set of rigid carbon fibre forks and SRAM hydraulic brake and Magura rear hydraulic rim brake and did countless miles on it.

On-One Ti29er Inbred Lynskey

A couple of months ago I was explaining this dilemma to Dad and on a whim quickly searched eBay for the thing I have been searching for, lo and behold there it was, the bike that ticked all the boxes.

An 18 year old 29er Titanium Single Speed Large Frame in Scotland was for sale, it was more than I wanted to pay, but after wanting one for 3 years I decided I just had to have it and after a quick message on eBay I hit the Buy It Now button.

And then it arrived, light enough a baby could lift it, rigid enough it won't fold when my fat arse sits on it.

And there began the part search.

Parts List

Below are a list of parts that I scoured for the build. I already have a titanium road/gravel bike that is my pride and joy daily commuter. The idea for this bike is the occasional 30+ mile round trip to work, but more to hit the trails near me on the weekend.

I may have overspent on the frame, but I won't be going all out on the parts list (or so I hoped). Some items are gems, and others are run of the mill intentionally. The frame is complemented with all bolts being titanium.

• On-One Ti29er Inbred Lynskey Frame
• eXotic Rigid Carbon 29er Mountain Bike Fork, Post Mount PM Disc Brake, 49.0cm 29
• eXotic Full Carbon Ti Seatpost 27.2x250 with Titanium Bolts 0 Offset MTB/Road
• Halo T2 29er Rims (36H)
• Halo 40 x 288mm Rear Double Butted Rear Stainless Spokes
• Halo 20x288mm + 20x 286mm Front Double Button Front Stainless Spokes
• Halo 29er Rim Tape
• DMR Revolver Single Speed Rear Hub
• DMR Front Hub
• DMR - BRENDOG DeathGrip - Flange - Thick - MTB Grips
• DMR 10mm Chain Tugs for BMX Track Fixie Dirt Jump Single Speed Bike
• DMR V6 Plastic Pedals (PAIR) Mountain Bike BMX (9/16") Flat Platform (NEW) BLACK
• FSA Orbit UF 1-1/8 Threadless Sealed Bearing Headset , Black
• FSA Headset Carbon Spacer 1 1/8"
• KMC S1 BMX Wide Single Speed Chain For Internal Gear Hub 1/2" X 1/8" - 112 Links
• SRAM Truvativ Powerspline MTB Bottom Bracket - 118 x 68mm
• SRAM SX Eagle Crankset - Boost - Powerspline - 170mm - 32t
• SRAM Guide G2 R Hydraulic Disc Brakeset ( Front + Rear) + Clamp + Rotors
• Hope 2 x Floating Disc Rotor 203mm 6 Bolt Cycling Bike Ride Performance
• Maxxis Grifter 29 x 2.50 60 TPI Wire Single Compound tyre
• Salvaged Original On One Inbred Seat from Steel Bike
• Salvaged Original On One Handlebars/Stem from Steel Bike

Assembly

It would turn out, finding a rear single speed hub proved to be a little challenging so I just decided to build the wheels myself and that way I can have matching hubs/rims/spokes and build it exactly to specification.

With the parts arriving thick and fast, I began first by building the wheel.

£20 for this little wheel truing stand off of eBay I was ready to build the wheel. Probably took around 3 hours per wheel as I like to take my time and fully lubricate things.

I could place the forks in situe but not ready to cut the stem.

I've been running a set of these forks on my steel frame and they've held up to the tasks that I'm going to put them through. I dislike suspension as I'm relying on this for commuting in emergencies and it's annoying having the energy zapped out of you!

I could lightly place the other components on and get a feel for how it's going to hang together.

I'm building this a bit of a joke on myself really, so a set of 203mm Hope floating discs (pretty sure these are better spec than ones fitted to my motorbikes).

Start throwing the setup together now.

Stem cut and awaiting seat post.

Seat height adjusted and saddle fitted.

The saddle is well worn, but turns out people want like £100 for these used on eBay

SRAM Glide2 brakes arrived this morning so I've slapped these on.

Not silly expensive brake setup, I shouldn't be going fast enough to even need them. The steel frame was rear rim and that was fine.

And throw on some of the original On One Inbred parts for good measure.

Concluded

Which brings the project to a finish.

Only a 3 month project, which has siphoned money from my RD project, but the reality is the RD project IS the fun, whereas this is something where using it is where the enjoyment comes from.

I'd listen to @HOTSHOT-III as he's on the money here.

The mixture has been leaned out. That's detonation.

https://www.reddit.com/r/Dirtbikes/comments/wnl4gt/does_anyone_know_what_could_be_the_cause_of_this/

You'll need to check the fueling as something has gone wrong here.

@ZKJE101 Sorry bud, a move was necessitated and access to the lathe has gone

I can send you the CAD files and you can get someone to knock them up for you if that helps?

I use a chap called Quantum Solutions who seem to fit the bill nicely.

Hell, they're not structural I could just 3D print you up a set if it helps.

Hi Kieran,

Yes the waterpump is beneath the oil pump.

It is driven by nylon gears from the crankshaft so you'll need to remove the clutch cover to get access to it in its entirety.

Naturally I would inspect the simple things first but I suppose it could be that the gear is broken. I have not heard of this being a problem in all my years, but they are nylon so it's possible.

Cheers @HOTSHOT-III

That's more like it.

The problem is, the bottom end is labelled 3BN, but the cylinder will have something stamped on the side. Very early DTRs ran a different cylinder to the rest of the models (3BN) and the later ones 3MB00.

So just "ordered every part for this engine code" is misleading as the engine code is used to reference to distinct part numbers.

The fact it's now making 10-11 Bar is a good sign that you haven't accidentally ordered the wrong size piston, as I said before, the 3BN runs a bigger bore.

The stock Mikuni TM28S runs something called a "Power Jet". This alters the mixture at wide open throttle.

You might want to ensure that this is not blocked, this could be causing the hesitance at the higher RPMs/Load/Throttle.

@Davidae5 Cool, so what compression is the engine making now then?

What about my other question?

It shouldn't misfire anywhere.

The main points I am thinking is if you've not followed the steps I described above is that you're leaking coolant into the combustion chamber, which at high RPMs is causing problems.

Similarly, it could also be something simple like the coil, HT Lead, or even just the spark plug.

But I want to eliminate the questions I set out above before throwing a million and one ideas around.

Is that 3 Bar? As that is really low and I'd be very surprised if the engine ran at such low compression.