konrad

"Hello World." Obviously a computer geek. 🙂 (It takes one to know one.) Glad you are here! If my count is correct, in the year ossa-efi.com has been active its brought 5 new members to TC.

Thanks. That's a very good answer. It also explains why I have seen rapid degradation of the nitrile O-rings I use to measure fork travel. Did not realize they cannot tolerate UV exposure. Glad I asked.

I thought EM Connect only was introduced on the 2024 models. Have a look at this page of my website: https://www.electricmotiontech.com/home/em-epure-race/controller/em-connect Does you bike have the module shown in the photo adjacent to the verbiage about the TCU?

As long as we are picking nits here, I'd like to respectfully discuss this. Where does the UV light come from? The head to cylinder joint is pretty tight, so not from the sun. I can imagine IR light coming from the combustion side, but UV? I always use nitrile for the outer o-ring and typically silicone for the inner o-ring (because Yamaha did on the TZ roadracers).

Cool! Please do start a rebuild topic here. I'll look forward to reading it.

Hello Matteo, welcome to the forum. I am happy to see there is still interest in the EFI OSSAs. I have a website devoted to them here: https://www.ossa-efi.com/home Maybe you will find some information that is of use? Best of luck with the rebuild!

While the information posted above is correct for nearly all motorcycles, I have never had it work for any of the 9 trials bikes bikes I've owned. The closest it ever came to working was a Honda/Montesa 4RT. Many years ago, I wrote a computer program to verify a VIN's check digit when I got suspicious about a used dirt bike I was buying. Nowadays, I just use an on-line VIN checker: https://vpic.nhtsa.dot.gov/decoder/Decoder

My experience has been that you can get the newer GasGas trials parts in the US via KTM dealers (often at a discount). But you may have to come up with the part number on your own.

To borrow a British expression, they are as different as chalk and cheese. A trials bicycle will be much less expensive than a trials motorcycle, but more expensive than a "similar" bicycle. I searched "trials bicycle near Singapore" and this was the first hit: https://www.carousell.sg/p/trial-bike-1264009023 Search "danny macaskill" to see the very pinnacle of street trials ability. Trials Central has a forum devoted to trials bicycles: https://www.trialscentral.com/forums/forum/19-bike-trials/ Good luck. That's about all I can help.

I spent quite a lot of time in Singapore and have fond memories! How about a trials bicycle? Younger is better for that sport, and the skills will transfer.

An inexpensive thing to try is replacing the spark plug cap (which do go bad). My favorite 2T spark plug cap is the NGK TB05EMA. It is a nice waterproof cap with a 5K-ohm resistance. Although your spark plug has an internal resistor, I think it's a good idea to use a resistor cap as well. Resistance in the high-tension circuit lengthens the rise-time of the spark event which helps minimize radiated electromagnetic interference that can upset the workings of the CDI.

Hmmm, I think mcman makes a good point about gearing the bike shorter that I had not considered. I'd say gear the bike taller so it has less driving force, but gearing it shorter means a slower ground speed before running out of revs. Use whatever works for you. My opinion is that learning to use the clutch proficiently is always your best protection against a "too much" mishap. The best advice I got when starting out in trials was, "One finger, and one finger only, always, always, always on the clutch lever."

If you are looking for an inexpensive option to a low-compression head, consider installing a thicker base gasket. This decreases the compression ratio by increasing the clearance volume, however it also changes the port timing. But in your case that may help achieve your goal by moving the torque up the rpm range slightly. Increasing the thickness of the base gasket by 0.5mm will have a very noticeable effect. Ideally, you would measure your current base gasket first, but a lazy person might just order a 1mm gasket and test the result. See: https://www.thehellteam.com/products/gas-gas-genuine-parts/gaskets/ I've written some basic information about heads here: https://www.ossa-efi.com/home/engine/heads If you have access to a lathe, a zero-cost option would be to increase the combustion chamber's blend radius. This will slow the rate of combustion and thereby make a less aggressive power delivery.

Welcome to the board. I don't know anything about your bike specifically, but decreasing the compression ratio will both help starting and reduce the motor's torque. Other things to try would be retarding the ignition timing and making the low-speed jetting richer. Both of those things will likely make it easier to start too. Also, try riding in a higher gear (or gear the bike taller). A flywheel weight will decrease the motor's rate of acceleration, but only if you have excellent clutch skills. Otherwise, that mod may just get you into more trouble.

The older EMs (5.7 / sport) require that the battery switch be on during charging. The BMS detects voltage at the charge port and enables the charge relay instead of the discharge relay.

That's strange behavior. The LED display is an autonomous voltmeter that is not being controlled by the BMS. There are two relevant pages on my EM website. This one describes the 5.7's battery in some detail: https://www.electricmotiontech.com/home/em-5-7/5-7-battery This one shows two inexpensive power meters (one for the DC side, and one for the AC side of the charger) that have helped me understand the charger's progress: https://www.electricmotiontech.com/home/em-5-7/10-amp-charger

Re-plating the cylinder may be less costly than replacing it. If it's a light seizure, it's possible a diamond hone and new piston may be all that's needed. It's not typical for the head to be damaged due to a seizure, and even then it may be repairable. You don't say where you are located but if in North America, try https://millennium-technologies.com/

After one year of owning an EM Race, I agree. Yesterday I rode my EM and my OSSA in the same areas. The EM is a fabulous trail bike, but the OSSA is a better trials bike (for me). The EM's complete lack of vibration and minimal noise coupled with no need to start it make for a much less fatiguing riding experience. The bike's forte seems to be climbing. But I'm unwilling to attempt my most difficult obstacles with it. I find it really difficult to generate lift without velocity.

From what I've observed over the years, not all trials bike manufacturers follow the convention of encoding the model year in the 10th character of the VIN. If I'm not mistaken, 2002 was the first year for the Pro model. 40mm forks started about 2005.

If the bike in question supports EM Connect, it will have an additional electrical module near the rear master cylinder reservoir. The module has a QR code that uniquely identifies the bike.

Try this company in The Netherlands: https://nonstopmotoren.com/?s=ossa&post_type=product At one time they rebuilt OSSA gearboxes. They will only deal with EU countries.

Wow, this is only the second TR125i I have heard about! Do you mind telling us where you live (country)? Please don't throw the bike in the trash! The OSSA TRi gearbox is unique and gears from other manufacturers won't fit. In fact, it's much more difficult to disassemble than a typical geqrbox. Some information may be found here: https://www.ossa-efi.com/home/engine/gearbox All the EFI OSSAs use the same gearbox. Some spare parts were available, but it may be easier to find a complete gearbox.

Some engines have required me to make an extension for my dial indicator. All timing specifications assume that you "zero" the dial indicator when the piston reaches TDC.

I've not investigated the fuel level sensor but have been told it's a thermistor -- which seems really, really weird to me. If it is, you can construct a table of resistance versus temperature and compare that to commercially available thermistors. Of course, you may also have to manufacture a housing too. That's what I had to do for a failed coolant temperature sensor.

K-Scan works for me under Windows 10 (Pro x64 is the only version I've tried). My new favorite USB to RS-232 converter is made by Okiwan. It uses the FTDI chip. Here is an example: https://www.amazon.com/Serial-Adapter-Chipset-Supports-Windows/dp/B08B5M1KBZ P.S. K-Scan can only see COM1 through COM10 (I think). So you may have to reassign your serial ports using Device Manager. P.P.S. Just noticed that I had initially linked an Okiwan converter with a female DB-9 connector. You need a male DB-9 to mate with the Kokusan Communications Unit. Link is now correct.