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Thanks, if the "stator" is broken I think I'll simply abort the project and will try to cut my losses... found a guy here in Italy who's breaking an Ossa MAR 350 but don't know the production year... was the MAR still around when they changed the teeth of the levers on the engine block?

If anyone has one that they'd like to sell at a reasonable price, please reach out. Thank you. Tbone.

Howdy everyone! I have been reading this forum for many many years. I am 60 years old and started riding motorcycles when I was five. I've owned just about everything you can think of. About 10 years ago my boys and I all had Gas Gas TXT 300s. At the time we lived in rural Kansas in the Kansas River Valley that had heavy woods and Rocky bluffs and lots of creeks etc. Those bikes were powerful and athletic, but I found them a bit too much at times. Fast forward to today, and I now live in Steamboat Springs Colorado with access to a lot of beautiful single track Mountain trails. I recently purchased a 1974 Yamaha TY250 which is much more my riding style at this point in my life. I am looking forward to getting back into some great trials riding.

Triad, below is a link to a US company that specializes in electrical components for older bikes. Not sure if it will have the right one for you, and if not, it’s still a very good source to bookmark. I believe they make everything in-house so it may be possible to get what you need built. They also have a CDI, ECU Repair Unit also. Good luck! https://www.regulatorrectifier.com/

Today I was away so couldn't check the gear lever and the exhaust compatibility... will try to do it in the weekend. Hopefully I'll find a solution for both

Same for all models, they changed the gear and kickstart shaft sizes around late 1973

Uh, forgot to ask: the bigger shaft on the kickstart lever is on the enduro models only or it was also on other models and depends from the production year? I mean, the Gripper/Yellow etc. have this same bigger lever shaft?

Uhm... I think I'll invest the money for the coil, as I'd need it anyway. But the rest is definitely more expensive and harder to find. I'll check the exhaust later today and will report back... thanks a lot for the advice, I've been toying with this project for a year now and taking a short ride in my yard would already mean a lot to me LOL

You can take stator resistance reading as woody suggested. Although that does not guarantee functionality, you can find some definitely-bad components that way. A peak-reading voltmeter is better, but again will not guarantee proper function. https://www.thumpertalk.com/forums/topic/1034259-build-your-own-peak-voltage-adapter/ I have used a drill motor and socket on the flywheel nut (or primary gear nut) to spin the motor for stator testing. This is best done with the head removed for easiest cranking, but just removing the spark plug may be adequate.

The carb was fitted on a rubber manifold, no bolts... but yeah, it's smaller. Didn't check the exact diameter but I'd say it's something like a 24-26mm maybe? The biggest problem is that I'm missing the kickstarter lever and the coil... I could at least know if/how the engine runs if I had them. Is there anything that will fit when it comes to kickstart lever? Maybe from a newer bike from another brand? It's clear I'll have to gamble and buy a Motoplat coil without knowing if the engine runs, but for those old lever sellers tend to ask pretty unreasonable money and they're not easy to find. Even a borrowed one would be ok, I'd gladly pour more money into the project if I knew for sure the engine runs OK.

Yes, you'll need another kickstart and gear lever with the correct number of splines, the earlier engine shafts have more splines than post 1973 engines The exhaust won't be a straight fit, yours has a flange held in the cylinder by the threaded screw in collar. The exhaust on the enduro engine is a push fit held with springs. To get yours to fit you have to cut off the flange so it pushes into the cylinder and weld two hoops on it to locate the springs - as long as it is the right diameter to fit. But how the enduro motor will run with the trials exhaust I wouldn't know You also need a carburettor, yours won't fit as it is bolt on and probably also too small for the porting, whereas the enduro cylinder is a stub fitting

Trunk monkey theft retrieval system 👍

I didn't pay enough attention before buying the new engine, the owner didn't know much about it but... even the gear pedal is different? About the exhaust, I see they have a similar flange... maybe the Explorer one will fit? If I have to buy all these parts with the risk of the engine non even being completely fine I'm screwed big time.

The stator can be checked, you'll need the workshop manual which will give the expected readings, I've no idea, electrics are a mystery to me. In the UK we can get them repaired. The motoplat coil for the Ossa is a combined coil / cdi so you need the two connector type. New replacements are available (at least here in the UK they are) When I saw the picture of your replacement engine I assumed it was the same year as yours but someone had changed the cylinder head for a later one. It seems the chassis number list I have incorrectly lists the engine as a 1972 but it's actually a 1976 enduro version, so, the kickstart and gear shafts have a different number of splines from your explorer engine. I think that the exhaust fitting on the later enduro motor is push fit with springs, not threaded collar, so your exhaust header isn't a straightforward fit To be honest you're probably better off fixing your explorer engine, all parts are available.

Uh, so the coil integrates parts of the CDI? Damn, in this case won't work. Can I test the rotor/stator without a working coil? Today I finally managed to literally kick the engine in place, only to find out my kickstarter lever won't work... different shaft. 😭

I think all those red Motoplat "ignition coils" contain other CDI components too. Best source of Motoplat information I have found: https://motelek.net/motoplat/

Uh, forgot to ask a very important question: with the Explorer I received a Motoplat coil but it's the single pin version. I also bought on amazon a 2 pins "universal" coil... will the engine work with it or it absolutely requires the red 2pins Motoplat unit to work?

an airtag hidden somewere in bike is a good thing when everything else fail...

Thanks a lot! Yeah, I tried to "open" the mounting brackets a bit by hammering a round piece in but still won't go in freely. I think I'll remove some material from the casing as the frame side brackets aren't exactly ultra-thick... So I'll need a different intake manifold? Might probably find a silicone one on Amazon, maybe... but my priority is to see if it has spark and runs. If it works I'll gladly put some work into it, but due to my previous bad luck I'm a bit skeptical

The centre cases are all the same casting so are interchangeable. The reason the ignition cover might look different is because the rear most part sometimes gets cut off or modified, either to stop a build up of mud or they simply get broken by derailed chains The replacement engine is an enduro engine, the Explorer is a trials engine. The enduro motor will have a different state of tune/porting and different gear ratios. They also use an expansion chamber motocross type exhaust although your Exporer exhaust should still fit into the cylinder. They use a 32mm carb as they're basically a race engine It's not an uncommon problem to find a different engine won't slide into the rear frame mounts. You might find that the mounting brackets have been squashed inwards slightly with repeated tightening over the years. You can try puting a piece of solid bar against the inside face of one and putting a solid bar through the hole in the other and tapping outwards, then repeat on the other side to try and open them out a bit. Or just take a bit off the engine to enable it to slide in

Well, the original Explorer engine turns but it takes a lot of force... probably a seized bearing on the bottom? Also not sure the Motoplat works, as it requires 500rpm to make a spark and there's no way to make it turn that fast as is. It's been outside for years, I think, so rust might be the issue... and the reason for being there might have been a broken Motoplat unit (no spark)? No way to know for sure. The "new" engine was stored on a shelf with the inlet taped, and the guy told me it was bought from a reputable seller, so IN THEORY it should run. I plan to make the engine brackets slightly thinner as they're massive, while the frame brackets are already thin. I'll have to measure them, but as I said I'm now worried other parts might be different and I might find out the hard way.

What is "semi-seized" on your old engine? Can you make one good engine out of old and new parts?

Yeah, I plan to measure the old engine "brackets" with a caliper and compare them to the ones of the "new" engine. I didn't pay attention to it before buying, silly me, but from the shape of the right side cover I'd say it comes from the enduro version... who knows what other differences there are. The carb inlet is bigger, can only hope the exhaust flange is the same.