thats_a_five

The engine was basically the same from 1994 to 1998. There were different capacities 125, 250, 270, 321 over the years.

Wow, what a gorgeous bike. It reminds me of when I had a '94 and my riding buddy had a '95. Probably the best trail (trail, not trial) riding bike I ever owned. Also a good trials bike. Jordi Tarrres won some world championships on them. 50:1 is too much oil but OK for break-in use. After 1 or 2 tanks, switch to 80:1. Keep your eye on the transmission fluid. Those motors had common water pump seal failures that leaked coolant into the trans. If the fluid gets milky, there is coolant leaking. The wire you mentioned is the signal wire for the small electronic readout located just behind the fuel fill cap. I have never seen one that actually worked. I have a parts manual and electrical diagram I will try to attach. Parts manual is about 8 megs. I have to agree with Oni Nou. That bike is too nice to actually ride. Know that being new to trials, you WILL drop the bike, scratching the paint, denting parts, etc. The bike will never look that new again if you ride it. I strongly recommend you see about trading,or selling, it to someone who wants a museum piece. Then go get a newer bike that already has been ridden. Don't misunderstand, I DO want you to ride trials. It is a blast! I just would hate to see such a perfect piece get damaged. Take it to the local GasGas dealer, the local club events, post it on CL. You might be surprised at what you get offered. 1995_Trial_JT25_Parts_Manual.pdf

I am not exactly clear what you mean by " feels like it needs a good clean " but there are only a few moving parts so here is a rundown of what is possible: 1) remove the lever,clean all pivot points, lube and reassemble. 2) Bleed the hydraulic system as suggested by Maxwell Smart. 3) Clean the friction plates inside the clutch. Remove the side cover, remove the 6 screws and take out the pressure plate, steel plates and the discs with friction material. Clean thoroughly, lube with transmission oil and reassemble in the same sequence of disassembly. Probably a good idea to change the transmission fluid while you are in there. Make sure you know what fluid you plan to use before taking things apart. Montesa recommends a special oil.

I removed the metal heat guard, then wrapped my pipe with header wrap. Stainless steel wire wrap to hold in place. Reinstalled the sheet metal guard. Haven't melted any pants since.

Hey Dan, that’s not fat, it is “traction enhancing body mass.” For all you youngsters posting, here is a link to video of one of our club members, Bill Thompson, who not only competes at the USA National level, but wins in his “over 80” class. He has been an inspiration to me and I hope he will inspire others. Truly a great man.

How does your spark plug look when the bike acts up? I have been noticing my plug getting sooty, black more and more. Cleaning the plug or changing the plug fixes the running problem. First I noticed that when the air filter got dirty, the plug would foul as described. New filter, very lightly oiled helped. Recently it has been getting harder to start and the plug is fouling when letting the bike warm up at idle. I have heard that this could indicate the valves need adjustment. I have not had time to do so. Once the bike gets warm and with a clean plug, it runs great.

As far as I know, USA GG's did not have turn signals. Therefor, no need for a flasher. I do recall recently seeing an add for a flasher with adjustable flash rate that is intended for using LED lights in vehicles that originally came with incandescent bulbs. I think it was on eBay. Perhaps they will meet your needs. Good luck.

That plug looks pretty good, maybe a tad lean as mentioned by Scot_Taco. The carb has 2 screws. One is idle speed, other is idle mixture. Idle speed screw is central to the slide bore, mixture screw is offset and usually smaller head size. Adjusting the mixture screw out and it will richen the mixture but mostly at idle - minor effect at higher speeds. Other ways to richen the mixture are to adjust the little needle in the slide up (put the clip one groove lower - beware those little 'C" clips are tiny and always try to fly off into the nether regions of your shop). It is counter-intuitive but reducing the oil percent will richen the mixture but I wouldn't go less that 50:1. Regarding upgrades versus original, I have to ask about how aggressively you ride. Reason is, many of those original parts (Tank, headlight rim and bucket, switches) which look really pristine on your bike are worth big money as spares. Ride aggressively you are likely to drop the bike, damaging those and reducing their value significantly. So you might want to consider looking around for some used parts or upgrades, so you can take the pretty parts off and keep them pristine. If the shocks are OEM, they might be sacked out and upgrades might be worth it. You might want to take a look at Bob Ginder's site B&J Racing. He has some cool info and stuff for TY's. Enjoy!

1-2-3-4 While you have the tires off, may I suggest a couple things? Check the wheel bearings. If your current rear tire holds air well, do not remove the rim strip. They can be a P.I.T.A. to reseal. If you do remove the rim strip, put a drop of oil in each of the spoke nipples and see if you can loosen and retighten them. Better to keep them working then have them corrode to the point they are seized. If you replace the rim strip on the rear, the ones with the molded in nipple are easier to seal. Also, the new tubeless rear tire can be very difficult to mount and get the beads to set. A lot of guys use soapy water to help the rubber to slip on the metal rim. I do not recommend that because soap is alkaline. Alkaline loves to eat (corrode) aluminum. I use a real tire mounting lube but a little vegetable oil can help. Also, a warm tire mounts easier than cold (set them out in the sun for a couple hours first.

JonV8, true that many people have switched to pre-mix. Like you, I can't tell from the pic if the cable is still in place but I think I can see the hose from the pump to the cylinder which is why I brought it up. Between us, hopefully JohnnyJazz learned more about his bike and can make good decisions. FYI, my '74 TY250A still runs the oil injection pump. That way I only have one fuel can for all the bikes. Cheers!

I had a similar situation with a previous bike. This may help you diagnose your bike. After doing a water pump change and some other maintenance I went riding and after a while and noticed steam coming from the radiator overflow tube. Rechecked my work – all looked OK. Topped up radiator and next time riding, same steam. To learn how much was escaping, I zip-tied a small plastic bottle to the frame and ran the radiator overflow tube into the bottle. Rode the bike and it spit 5 – 10 cc’s into the bottle once hot. If I topped up the radiator, it would spit the same amount. If I didn’t top up it would not spit any. Conclusion: The cooling system needs a little air space in the radiator to allow for normal heat expansion of the coolant. Bike never overheated but if I overfilled, the bike would spit the excess. Removed the bottle and relaxed, knowing there was no real problem. I hope this helps you.

One more comment. FeetUpFun is correct that screaming the bike for long road runs will cause the top end to get hotter than desired. Increasing the main jet will allow more fuel which will help cool it. On the other hand, adding more fuel will reduce the relative amount of oil being injected (assuming you are still using the automatic oiling system) which will affect the lubrication of the bottom end. So it is a trade-off depending on how you will be riding the bike. A way to check: After riding on the roads back home, shut the bike off, let it cool a bit (so you don’t have to deal with hot pipes and plugs) remove the plug and inspect the ceramic insulator by the spark tip. Bright white = too lean. Would benefit from bigger jet for more fuel and cooling Black and oily = too rich. Would benefit from smaller jet. Light tan = Perfect. Do yourself a favor and always carry a spare plug and wrench to change it. Even well jetted bikes will foul plugs from time to time (usually at a very inconvenient time). Spare plug and you are back riding in 5 minutes. No spare plug and you are pushing the bike 20 to 45 minutes for 2-3 miles. Not fun.

Hi JohnnyJazz. That is a very pretty bike. If you did the restore, great job! A couple thoughts, facts, and questions. Words in italics below are from your posts. August 8. I only want to potter around the back streets of Brooklyn where the average street speed is 25-35 mph getting to some off road places I know to practice trials. Sept 8 . . . have found with the current gearing of 12/53 I really am struggling to keep up with traffic even on slower roads. let me state that I am well aware this isn't a road bike and isn't geared as such and I am not a speed freak at all, I’d just like to not be a hazard to others! I’m only riding 2-3 miles to get to a few industrial construction sites where I can practice trials. . . . . . I find with the 12/53 I am lucky to get maybe 35 mph tops and if my sums are correct the difference between a 12 and a 14 front is 16.9% so that's nowhere near 60! The bike seems to be running very well, a lot of torque and smooth but just as slow as a steam roller. . . According to the Yamaha ad material for the 1974 TY250, it has a top speed of 100 kph (62 mph) with 14/53 final gearing. Going to 12/53 is 14% reduction (14-12, divided by 14) which should net you a top speed of 51.6 mph at redline (Yamaha did not post how many rpm that is but max torque is 15.2 Ft# at 5500 RPM so it should turn at least 5500). First question: Are you getting into 5th gear? Fifth gear is a 0.656 overdrive, where 4th gear is 1.0. Fifth to 4th is about a 48% reduction which would net you top speed of about 32 mph. Second question: Are you getting full opening of the slide in the carb? If not, you will not get max power or rpm from the engine resulting in lower top speed. Solution could be a simple as a throttle cable adjustment. Meanwhile: Learn to use that rear view mirror and move right to let faster vehicles pass. At most it will delay your arrival to your riding location by a couple minutes. Riding in and around Manhattan, you are probably spending more time than that sitting at stoplights. Learn to pull away from lights in second or even third gear. That will get you up to speed faster so less bothersome to cars behind you. Observations: It looks like your levers are located fully out toward the ends of the bars. You might try moving them further in toward the center of the bike. This will increase the leverage you have on the clutch and brake, while also reducing the chance of breakage if/when the bike falls over. Is that a bulb horn I see in the picture just above the fuel cap? It brings back decades old memories since I had one on my bike. I suggest relocating it so you can honk it with your thumb without having to take your hand off the grips. If you need to honk, you will probably also need to work the clutch, brake and or throttle at the same time while hanging onto the bars with both hands. Have fun!

Check to see if your throttle cable has moved down and is being hit by the radiator fan.

That is great to hear it just needed a good cleaning of the carb. A five hour ride is always a good day. And certainly a good test that all is well with the bike. Have fun!