section swept

Ah...now then where’s that screwdriver thingy.

What’s a screwdriver?

The detent plunger holds the selected gear in place, this component can sometimes make gear selection feel very stiff. With the detent removed you could possibly have selected one gear and caught another which would lock the gearbox. I am assume here that the piston in the cylinder is free and not seized. Alternatively you could try a role reversal and let your wife with her logical thinking take over the restoration. This would leave you to do the cooking, dusting and hoovering, but you would be able to use your 4rt for the shopping??

Yes and if you should happen to fall off with the bike on top of you, the slope of the bank can make extracting yourself dammed difficult. Some railway banks can be very interesting and challenging, what with overgrown bushes, tree stumps, railway detritus and of course rubbish. ??

Toni Bou could probably win on a rigid framed Bantam! As for your bike, you obviously love it! What about some top end engine work; polishing and porting with some appropriate mods to enhance low end torque and throttle response. What fuel are you using, pump gas or other? You don’t mention tyres, which to some riders is most important. Have you had the suspension (current) set up by someone who knows what they are doing, you may have already done this yourself perfectly well, what suits one does not always suit another??I know of one rider who spent most of his time just getting the wheel bearings as friction free as possible, alignment in the hubs, selective bearings etc, worth at least 3-4 hp he would say.

You’ll hate this, CDI sends a much faster and powerful charge to the ignition coil. The CDI unit is triggered by the Hall effect sensor or trigger as some call it (little black or grey unit close to crankshaft where the points would have been on older engines) this is the component that electronically sees the timing/ignition point. The Hall sender/sensor can work quite well even when its starting to break down in performance. Did you send the Hall sender to be checked at the same time as the stator. I’ve replaced no end of these senders, they can perform just like a human with toothache, it’s hurting like hell but there’s no sign of pain when the dentists approaches??I bet the previous owner went through the same checks you are now involved with. Hall senders can become unstable in that one moment they work and then the next nothing. Many ignition systems get pruned down in design so that the coil sits directly on top of the spark plug and there is no HT lead just a cap to connect to the plug, again one coil per plug produces more efficient ignition. What was wrong with the stator? Hope you sort the problem out, please keep us posted?Your CDI unit may contain the Ignition coil, on some systems it’s a separate item. Testing the ignition coil is the same procedure as for seperate coil, but you need to know the electrical specs for your particular unit.

Just another thought, you aren’t confusing the drive chain rattling against the frame etc. ??

I used to practice on a disused railway line, the track was gone but the banking and the fact it was right out in the country meant that no one could see me or hear me. Make sure if you go ahead that no planning consent is needed to use the land.

Original bikes one day will be acknowledged as such. Bring it on, just look how much value they command in totally original condition! That may be a bad or a good thing but either way they have character, history and presence; bit like a film star or Royalty.

Was this noise evident before changing base gasket? Have you had bike long? What oil/fuel mix ratio are you using? Its best on a two stroke to not close the throttle fully on ‘run down’ as this could cause the piston to nip up due to lack of oil, momentarily is ok but on downhill you should keep the throttle slightly open. What you may be hearing is the piston slapping the cylinder bore as there is no stabilising power stroke, so rather than the piston doing work it is being driven by the transmission. All this is fine and dandy but without hearing the engine my advise is purely based on conjecture. ??

Ditch the pump and the oil tank, that’s two less things to go wrong. Throttle cable only pulling on the carb slide means easier action and less effort from rider. Don’t forget to remove oil pipes and unions, plug oil in holes otherwise you have an air leak. Space now freed up by oil tank removal allows for better access to air box etc.

Ignition coil may have a defective primary or secondary winding, in other words a broken wire. Hence your stated ‘power to ht lead but no spark’. The engine running for a while and then stopping is indicative of the coil wire being broken internally. Double check the coil earthing to frame before removing. Also easily missed, but have you changed/checked the spark plug cap? The CDI unit as the name states contains the capacitor which may have gone open circuit. Can you borrow (rather than buy) from another bike the suspect parts to eliminate before spending out? Are you using a multi meter to check electrical items etc. Ignition coil should have a range of between 0.5 to 3 ohms between wiring connector tabs on coil body. From neg terminal to ht lead 7+ thousand ohms, you will need exact specs from w/shop manual. £130 for a CDI unit sounds a lot, most are not repairable unless you burn out the resinous sealing and can get at the pcb and find the faulty component. The time and frustration in doing this plus possible health issue due to burning the resinous sealant out needs to be taken into account. Maybe another CDI unit from a breakers might be worth considering. Bet after this little lot you find it to be something simple and obvious, but then we have all been there at some stage or other, good luck. Oh, I don’t recommend sticking your CDI unit in the oven either, not good for other half relations or the CDI unit. You might try a hot air gun to warm the body of the unit but I doubt it will have any effect. If moisture has got in the unit the damage will have been done.??

Could be a supply error, sounds like you have received 4-stroke piston rings (XT 250) and the expander(50 pence shape-ish) ring is supposed to go behind oil control ring. I could well be wrong ?. GDT and TY OE rings must butt up against the ring locator pegs in the grooves.

And it’ll be even longer than ‘in a while’ after having performed that little lot. Maybe just ensure it’s safe to start the engine, then work out from oni nous extensive list what you need to do. Cotton buds...cotton buds for reaching all those little places that need cleaning?Like the list and especially the energy drink ?

Kawasaki, Suzuki, Honda and Yamaha have all used similar types to the ones you show in your first picture. It was a novel way of getting more suspension travel without raising the height of the bike at the front end. The design was first seen on MX bikes and then migrated to Enduro and Trail bikes. You might find that the extended lower part of the leg may foul on rocks and other trials type going, which would be a disadvantage. They probably weigh a bit more than the normal forks.

If the engine has been allowed to overheat then the thermostat will suffer. Usually the high heat causes the wax in the stat capsule to escape and then the stat will no longer open causing overheating. My advice is to 1) lift the head and inspect the cylinder bore for excess scoring and signs of seizure. 2) check the temp sensor switch for the cooling fan. Do this with a multi meter set to continuity, meter lead on each terminal of the sensor. Hot air gun played onto sensor tip. Continuity should be made when temp hot. No continuity then sensor shot! 3)The cooling fan housing may be distorting with heat and jamming the blade, or the motor is worn. 4) The coolant should have anti freeze in it. Anti freeze raises the boiling point of water as well as protecting from freezing, if the mix is too weak or non existent then this will not help with the cooling. 5) Water pump impeller may be slipping on the drive spindle. 6) Thermostat needs changing, you would have already looked at this, to test it use a piece of wire and lower into a pan of water that is warm and turn up the heat. When the water reaches approx. 75 degreesC you see the thermostat start to open and be fully open by 86degrees C. Hope you don’t find anything nasty wrong with bike? With the clutch drag, put that on the back boiler and sort the engine out first. Most trials bikes have clutch drag and owners have different ways and means of reducing or eliminating it! Start with the external operating mechanism parts clutch lever pivot first then adjustment check. Lube all items that you can, find out what oil the previous owner used, it may be wrong spec. You might end up striping the clutch down to do the job properly, cleaning burrs off of plate edges and clutch drum. I’m fairly certain there is a good amount of info in the GasGas section on this forum.

If the ignition timing has altered you need to find the reason why. If the stator plate has not moved, and the woodruff key is good and there is no excess play in the key way...you don’t say if the key way is good. Why did the engine run away, was the throttle slide stuck? Not sure if your electronic ignition unit has an advance map or not, still if it was faulty I doubt it would retard the ignition enough to cause reverse running.?

Hope you get to the route cause of the problem. Lube the oil crankshaft seal lips with either two stroke oil or a smear of silicon grease. Good luck, let us know how you get on??

You can experiment with richening and weakening the mixture by adjusting the carb needle. This may also be very worn as will the main jet allowing too much fuel in and hence the engine trying use up the excess fuel. This would also cause the engine 4- stroke and try to bog down. Are you using a manual? I ask as it appears to me that by asking how to alter the mixture you are not that experienced. Please take that comment with the good intentions meant by it, we all learn something new each day and this forum and it’s members have a wealth of experience to share and to learn from???

It’s not the air before the carb that influences engine run down from acceleration, its the air that can be drawn in from other areas including the throttle slide. So as suggested by others, crankshaft oil seals, crankcase drain bungs, cylinder base gasket, carb air leak after throttle slide( engine side), breather pipes blocked, kinked and incorrectly routed. Popping at the exhaust could be ignition incorrectly set, possibly crankcase containing excess fuel residue, the list goes on.?

Sorry that wasn’t helpful?

Suppose really it depends on how far round you twist it?

Assuming no fire extinguisher was played directly onto the wheel rims e.g. sudden cooling by water, then the rims may well still be serviceable. Make sure the hub bearing seals haven’t been scorched. Get some Astonish plastic window frame cream cleaner to gently remove heat marks if anodised rims, otherwise normal cleaning polish for alloy finish. If you have steel rims the heat will not have done much apart from discolouring the chrome which can usually be got back again with normal cleaning methods. Be very careful as some rubber when heated can produce a nasty substance that will eat your skin, bone and the only way to get it off is cutting the skin off. Burned out cars are a nightmare for the fire service and others such as recovery etc. It’s the door seals and the like so you might just want to wear gloves and dispose of the tyres with thought.??‍♂️

I hope you have the other bits for the bike, not showing in photo! Otherwise either way it’s going to be an expensive project. Someone is looking for a road bike project so it should sell well. As others have said buy a C15 already converted or if you can a genuine C15T ?? converted road bikes can be very nicely done with all the right parts and then there are the conversions done purely because a trials 4 stroke attracts far more money??? just compare the price of a few such as AJS and Matchless road and trials variants, you get more bike for less as a road variant and a lot less bike for the Trials version! I’m still trying to get my head around this price differential as I too would love to have any one of the afformentioned bikes. I had a genuine C15T as a schoolboy, bought for £15 in bits. I took the forks to Valu Motorcycles in Luton for them to rebuild £12. I then sold the C15T on for £35 still in bits. I sold it to a mechanic who had it built up and running within the week and was riding it at Oughton Head Common Hitchin. He then junked his very old BSA 250 with gas pipe home made swing arm and swinging footrests for wheelieing. That bike had external oil pump with adjuster but I can’t remember what Beezar it was but it was old but had knobblies and chrome petrol tank, so some conversions can be quite interesting??? Pick your bike with care.

New trials wet weather one piece suit. Available from Double Breasted. Co. Uk