DT125R FORUM

Yeah that looks like the head gasket.

Did you dip your fingers into the neck?

A compression test would tell you for sure as it'll be down on compression. But this is an indicator.

A compression tester is like £20.

https://www.ebay.co.uk/itm/167499985920?_skw=gunson+compression+tester&itmmeta=01JTP74TSF0N5BEDMP9VBQ7WCM&hash=item26ffc6f400:g:BXwAAOSwlhpoG3Cl&itmprp=enc%3AAQAKAAAA0FkggFvd1GGDu0w3yXCmi1fRWRe%2BDCnd%2Fv8ASPfYcwl4Qwe6G9UQ%2FUi8k0py2nze%2BaGESUbULwGf1He2oKCL4P8mfShHgcCAe7A1bXkgaijR5TEPPfOrSIvrYmzQb3dM8BDgU8JU5FDDAdAElgJH%2Fakz8RdSeFQARHDfao8VgDAERcjm9Z5MdcFSwi%2B6DHnh%2FdqVr4uDakoIcpV%2FQ5HjmuEEjfgpDcOQSxz7isQI7MNl1c%2FWpDDQSvpDTxjmFclGOKUCTbPqjBKAKGnqb6VjXBg%3D|tkp%3ABk9SR4Ctk8fVZQ

Well worth getting one.

@Calum said in Bike no longer starts help:

What's the mileage on the engine? What's the health of the engine? Have you got a compression tester to check?

Has the head gasket blown and you're leaking coolant into the engine. Stick your fingers into the radiator cap and check for the presence of any oil residue.

oil

What's the mileage on the engine? What's the health of the engine? Have you got a compression tester to check?

Has the head gasket blown and you're leaking coolant into the engine. Stick your fingers into the radiator cap and check for the presence of any oil residue.

This symptom sounds like the reed switch, but I've never had to derestrict one myself.

Have you got a compression tester to check the engine's health?

The easiest way to derestrict these bikes is to simply get an aftermarket CDI and then you don't have to worry about the reed switch.

Managed to source OEM indicators/mirrors (although not my taste personally).

A fair chunk of change was dropped on renewing brand new OEM NOS throttle, clutch, choke, Odometer cables.

I also decided to paint the mild steel arrow pipe. Just make it look like a factory pipe and nothing fancy.

I must have bought this pipe brand new 3 years ago and it's been in storage since and even then it's rusting....

It's no TYGA pipe for sure!

Buzzing to get this bike complete though.

Normally, they just add a throttle stop to restrict the bike, so you can only open it 3/4s of the way.

This is what a lot of the test centers do as it's easy then to unlock the bike to full power afterwards.

@glynn6500 oohh, yeah very hard to source.

@scrimsmustang is a bit of a legend for finding things as well as @oldman IIRC.

Your best bet is CMSNL from what others have said they are Wizards!

Finally!

Actually found some time to go out on this thing!

The original gearing I bought for this was a no-go and I ended up chucking it in the bin.

Instead, I found a Trail Tech crankset made for an E-bike, had to swap out the bottom bracket, but the result is something which gives me the ability to go up a few teeth on the front (currently rocking 24t), blitzes up moderate inclines, but lacks real top end.

I managed my usual route easier than the 26er, both up and down hill. It just felt like it handled the rocky sections better than the 26er, the lower gearing made it easier to climb some of the hills I had to get off and push, overall I'm very pleased about how this one has turned out, hopefully get a lot of use out of this over the coming years.

@fishy-fish I'll put money it's that then.

Piecing it together bit by bit.

Got some Ferodo brake pads for the rear caliper.

Wiring loom gently fitted, I think this is where it goes.

The original ignition barrel was ropey as f. Clearly non-genuine and been replaced before. This gem came up new old stock genuine, so snapped at the chance to get it.

Just focusing on the front end at the moment. Got some genuine wing mirrors from Italy winging their way to me.

Hi there,

It will be very unlikely to be the magneto as the bike runs off the battery and the output from the stator is rectified to 12V.

Based off of your very basic description, some of the common pinch points are:

• Faulty battery
• Faulty wiring
  • Check ignition barrel leads to loom
  • Side Stand Switch
  • Kill Switch
• Poor/Aftermarket Ignition Coil
  • I've had this problem myself with a Chinese Ignition Coil which basically resulted in the bike running great from cold, then once it warmed up the ignition would die above anything from 5k onwards
  • Replace with genuine 3RM Ignition Coil

I am sure there are lots of reasons, but since you've only given a sentence to go by the above should do for now.

Don't forget the Search function as others have experience similar issues and the common faults are well documented on here.

Can't remember if the side stand is NC or NO. Looping stuff might night work if that's the case.

Have you got a wiring diagram handy? There is one in the Haynes for your model.

My advice would be to put it back to stock and not just randomly looping stuff.

Check the side stand switch circuit.

Here are the differences in the 3BN Cylinder head

It'll be marked on the cylinder head.

The 3BN head is interoparable with the 3MB head, but has a combustion ring which is said to adversely affect performance.

Here is a video of the difference between a 4FU cylinder and a Belgarda 3MB00P cylinder.
https://www.youtube.com/watch?v=P8okvTxe-Bs

Here is a 3MB cylinder.

You'll see the crankcases are stamped 3BN

For the most part you don't need to worry about it, it'll be rare that you'll find a DTR with a 3BN crank/cylinder and most of them will be 3MB cylinders. But it's just worth bearing in mind.

There are variations in CDIs and Exhausts which affect the performance, but these are less important as there are aftermarket support that recitfies any loss in performance

It's only bikes where the cylinder is 3BN. You'll see that the crankcases will have this marking on all years, but it's the cylinder you're interested in.

You'll also see this marking on the cylinder head where the cylinder will still say 3MB. My understanding was that this was only fitted to really early models.

From 1989-2007 all models designated 3MB are compatible.

There are various revisions across the years to stator and flywheel, but the internals are compatible

The last few years added a starter motor and therefore the crank, stator and flywheel are not interchangeable, the rest of the engine is the same.

Yeah, I hear that the bargains at Lidl get great reviews.

@HOTSHOT-III Would definitely like to see that. Would make for an interesting build for sure.

I was surprised to see cast pistons in this kit, but apparently I have to junk them anyway to go with the stroker kit I bought as the wrist pin offset is different.

So I've got a few more things to buy before this is called done.

Been saving for months to purchase this!

With Christmas and what not it was a difficult item to purchase.

Athena 392cc big bore, with the hot rods kit this will take this up to 421ccs.

Brand new gearbox layshaft and a 1st gear tall conversion to duot.