lemur

Manual for the 2020 ST250 shows a drain hole plus an inspection or fill plug they tell you to remove to drain the oil. Odds are the plug is at the same height an oil level window would be if it had one. First check would be to measure the quality of oil you drain out and go with roughly the same volume and then see where that fills to relative to the inspection/fill plug hole. Search for "Oil comparative viscosity chart" and you will find a chart that details the relationship between ISO, AGMA, SAE auto and SAE Gear oil viscosity. Personally I use ISO 46 hydraulic oil in all my 2T and 4T wet clutch/transmissions and never have a problem, same oil they recommend for all season excavator and farm tractor applications which use virtually the same type of gears, seals, shift forks and friction plates. ISO 46 viscosity equates to AGMA 1, SAE 20W auto oil, or SAE 75W gear oil. ISO 46 can be purchased from any heavy equipment store in quantity and costs about half the price or less, so you can change it out twice as often. Too much oil in the case can cause clutch slippage problems and robs power, the oil level is relative to the clutch basket, the clutch should never be completely submerged or the plates will not compress because of hydraulic pressure on the inside of the clutch plate friction pack. Your transmission and clutch do not require a multigrade engine oil which is formulated to accommodate cold startups and a much hotter internal operating temperatures.

It's a permanent magnet is it not? There are a lot of iron filings stuck to the magnet in the photo, that might cause shorts and indicates a wear problem, I would clean it all up, test the coils and try again.

The 4RT is a superior all around trail bike, they have a broad powerband, start easy, cheaper on fuel, tough to break and hold resale value better than most. Easier to ride at non-competitive level trail riding, if you can still ride a motorcycle I would think 4RT is the one. I ride TRS now but would go back to Montesa 4RT in a heartbeat if sales and parts dealerships still existed where I reside, I rode 4RT' for 16 years. Montesa/Honda fuel injection makes the 4RT far superior to other 4-stroke trials bike models imo it would be the only 4-stroke trials bike to consider. As for servicing the 4RT, you will need to be able to adjust valve clearances accurately after 4 or 5 years of riding and it becomes harder to start, otherwise they are not much different compared to a 2-stroke to service. Replacement spark plugs are way more expensive but you will rarely need to replace one. Air filter is way better compared to some and the plastics are expensive but durable. 4RT works great in winter as long as you don't let the oil get thick in sub zero temps, sub freezing temps makes it near impossible to start unless you build a fire under it. 4RT Header pipe runs very hot and needs a shield upgrade or you will melt your riding pants on it regularly.

"Stator looks OK, noting obvious." Are you testing the stator coils with test equipment or by eye 🤔 looking at coils tells you nothing unless they are burnt to a crisp, you can meter test coils for resistance or you can oscilloscope test the AC output and confirm it is fully functional. Sparkplug cap and wire has been changed? They don't last forever. "Plug is gapped ok, looks ok, not fouled. " Sometimes the insulation is cracked and the defective plugs will spark way up inside the plug body and not at the electrode gap. Try another new plug. If you can't narrow it down to being either a carburetor or ignition issue there is not much anyone here can help you with. Do you have access to another GasGas TXT you can swap parts with, that is what a dealer would do to eliminate the carburetor as being your problem. Parts swap is also the only way you can reasonably test the ignition module.

Holy that looks expensive, I hope I can own one 😎

You act like a thermostat switch is a totally non-required 20$ part that every manufacturer puts on their machines without reason. What's the big deal with just fixing it! If he leaves the fan run 100% and fries a 90$ rectifier he can thank you for the recommendation to ignore it.

Wait a minute, so if you never had a thermostat switch fail either 🤔 the only thing self induced is if he doesn't fix it after he bought a broken bike.

That's why you still have a thermostat switch on there, the bypass switch is wired in parallel to the thermostat switch not in series. op Diodes can't take heat, it's the rectifier/regulator that will fry first, followed by the coils, followed by the fan motor that makes its own cooling

Must be why I never had to replace a fan, I clean most parts like that with a toothbrush and some spray cleaner 😎 op. When you run a generator and plug in a toaster you can hear the engine work way harder to make more electricity, bike alternator is identical, making electric power takes energy, making more power all the time needs more energy and making energy produces heat which is damaging to electrics. It's not fuel injected so the Fan motor is the highest power draw on your bike, it would be normal for it to draw down on the idle speed some when the fan kicks in, I added a toggle on my 315 Cota to deal with that exact issue, idle dropped noticeably when the fan kicked on.

Can't understand why anyone would permanently bypass a thermostat switch with anything other then a switch 🤔 they saved a whole 4 bucks on a switch and I imagine those same dealers have no problem selling additional replacement stator coils, rectifier/regulators and replacement fan motors as a result of that downgrade.

Can only think of two reasons to do that, they didn't want the engine idle speed to change when the fan kicks on or the thermostat went faulty. The better way to fix it is to install a working thermostat and put a bypass toggle switch on it to manually control the fan. I guess the question is does your engine speed change if the fan is connected and disconnected, if idle speed does change significantly that relates to the power load increase on the alternator.

Carburetor can't work great if the bottom end seals are not great. I'd be inspecting the bottom end seals for signs of leakage on any 2-stroke engine that has constantly changing carburetor type issues. ... when it runs does it fire with a nice clear compression pop-pop-pop or does it have a ring-ying-ying engine sound ?

Once you rule out everything else, it will end up being the need to adjust the valve clearances very carefully and accurately. Same thing happened with four out of four 4RT's that I rode from 2005 to 2020 they just didn't want to start one day and a valve clearance adjustment fixed every one of them. Owned two of them at a time which made trouble-shooting simple.

Better watch out it makes me feel invincible 😆

👍 Vest arrived, first impressions are it comes very lightly padded and some spots are not protected at all but it is Way more comfortable to wear compared to the flat board back protector I wore before. I like it 👍 Might add a tensor bandage for the 2-day trial this weekend but I think I'm good to go, if it gets too serious I can just drop down a line and ride as clubman.

Did that about 50 years ago but it was to prevent additional damage to the engine covers in the event of another fall.

I'm just coming off yet another episode of busted ribs and finally ordered a chest protector that has yet to arrive, recommend you consider the same, ribs hurt more then most things and most of my bad get offs has been bar ends or foot peg into the chest and mid abdomen 😐 your crash damage may vary.

Easy bike to work on, no real surprises, rear suspension linkage is vulnerable to damage and once water gets to the needle bearings they rust quickly. If you don't know the history of the wheel bearings I would replace them, bearings can be had from almost any bearing supply store and good wheel bearings make a huge difference in the efficiency of your brakes. If performance is not great check the reed valves very carefully to make sure they close light tight. The exhaust packing is prone to clog with oil if you use some oil brands at their recommended ratio. Service the front forks lots, keep good slide bushings in them and change the oil frequently and ride it lots 👍

I had one of them, loved it. Sturdy frame, good performer, tough plastics, some current model parts will fit right onto it, they respond well to race fuel. Can't say I would want to be sourcing new parts if it needs anything significant, but that really depends on what part of the world you live in 😎

Super easy, search for "TRS motorcycle wiring diagram" and it will be the first image that shows. ... if the headlight is having low power issues the fan should be having problems as well.

That's because your roughly 1000$ to replace fuel pump did not burn out.

That's a strange one, I looked at the wiring diagrams and can't see anything that would account for that unless the tail light wires are shorting out or you have a bad ground back to the engine.

Is it a Light Emitting Diode or incandescent lamp and guessing it has no battery? If it's LED what does your bike have for rectifying the AC produced by the alternator to DC required by a LED? ... + does the fan work as expected? (the fan also operates on DC)

Oil in the coolant means you would also see coolant in the oil and that would almost certainly be the water pump seal. Just a hunch the part number also relates to the dimensions 12.30.7 oil seal

FWIW Montesa from 315R on uses 2 different types of friction materials in their friction plates, a mix of paper and cork apparently alter the friction point. I bought a full set of new plates in 2001 and they are still in the spares box, never managed to kill a clutch. My understanding was that the paper material grabs faster because it takes on less oil then the cork.