thats_a_five

Electrics Most of the electrics are right above the radiator, jammed into a small space under the fuel tank cover. Before you start disconnecting things, take pictures and good notes so you can get it back together correctly. I often use painters tape and make small flags for each wire, writing numbers on the tape and making a drawing showing which number wire goes where - before and while I am taking it apart. Testing I was not able to view the video of your spark plug. I would remove the plug, reattach the high voltage lead, hold the body of the plug against the head and kick the bike over. Look for a good strong spark. You could also, bend the electrode to increase the gap to about .085” or 2mm and try again. A strong spark should jump that gap as well. Or it may jump through your body and light up your life! You may want to hold the plug with insulated pliers – especially if you wear a pace-maker. I think the videos referenced by others above show you how to test resistance of the stator with an ohm meter. Cleaning connections FYI, my reference is my ’94 JT25 so it may not be exactly like yours. What I know is, mine has a jumble of wires in a small space. There is wiring for the spark, for lights and for the fan all in there. There are 2 small boxes; silver one is voltage regulator for lights and fan, black one is spark box. Be gentle as you dig in so that you only disconnect one thing at a time. Clean any metal parts with emery cloth or a fingernail file until the metal is shiny. You might even want to replace any old screws, nuts and washers with new. Clean the frame where the parts mount to ensure good ground (earths). I like to gently squeeze any slip-on connectors before installing to ensure a tight connection. Check the kill switch to be sure it is working correctly and the wires are not pinched or shorted to ground somewhere. Check the connection at the rubber cap that clips on the top of the plug. I have seen those badly corroded and even with most of the wires broken right at the cap if people pull the wire, not the cap. If in doubt, replace it. The stator (windings that generate the voltage) is located on the left side of the engine. To access that, you need to remove the shift lever, stator cover and flywheel. The flywheel requires a special puller. You can easily remove the plastic cover to look for signs of water – rust on the flywheel, etc. If it is clean inside, OK, if there is rust, you will probably want to remove the flywheel so you can access the stator to clean all the connections and ground screws. With a good hot spark and gas, the bike should at least start. 2 strokes are pretty simple design. Let us know how it works out.

Starting fluids I would be cautious about using too much starting ether or brake cleaner. Remember, a 2 stroke engine is lubricated by the oil in the premix. Solvents will remove the oil from the moving parts and bad things can happen. Better to simply dribble a little premix into the spark plug hole and try to start it. Questions: 1.You are using new, fresh fuel, right? 2. When you turned the bike over and liquid came from the spark plug hole, are you sure it was gas? Could it have been water? From your pics, the rear fender was off when you picked it up. Is it possible that rain water had collected and gone into the airbox, carb and into the crankcase? You said you drained all the fluids 7 years ago but yet there was “goo” in the carb. Normally carbs left dry get a white powder inside, if they get wet, they grow “goo.” If there is water in the crankcase, it will kill any spark and the bike will not fire. I would remove the spark plug and carb (leave the reed block and intake boot attached to the engine) and kick it as I previously described. Then, with the carb still removed, install the plug, kick it over a few times and look at the plug again. It should be dry. If it is wet, smell it to see if it is gas or water. With the carb removed, you are basically moving air through an air pump. There should be no way for liquid to get to the plug. If the plug is dry, dribble a little premix in the spark plug hole, install the plug and wire (with the carb still removed) and kick it a few times. If you get no start or popping like it is trying to start, you can be 99% sure it is an electrical problem. More later on electrics.

You say you turned the bike upside down and "a fair bit of fuel came out." Just to be clear, there will be fuel that comes from the carb bowl. That is not a problem, it is just the bowl draining. If the fuel poured out of the sparkplug hole, it came from the crankcase and will give a very rich air-fuel mixture that will not burn (flooded). This usually happpens when the float in the carb sticks and excess fuel flows through the carb, down past the reeds into the crankcase. Simply pouring the fuel out is not enough - there is still a very over-rich condition that will just make your plug wet so it will not fire. You need to clear out the excess fuel Here is what i would do. 1) Turn off the gas at the fuel tank. 2) Remove the sparkplug 3) Put a rag over the spark plug hole I usually tie it in place because any liquid fuel still in the case will shoot up in your face with the next 2 steps. 4) Hold the throttle wide open to get max airflow. 5) Do this outdoors. Kick the bike over and over to clear out the fuel and excess vapors. 20 or so good kicks should clear it. 6) Remove the rag and kick is some more. If you are seeing visible vapor, it is still clearing the excess gas. If you hold your hand above the spark plug hole and kick 2 or 3 times, your hand should NOT be getting wet with fuel. 7) Install the plug and connector. Hold the throttle wide open and kick it a few times. It should pop and run poorly until the remaining excess fuel burns off. It will gradually clear out. Once it is running, turn the fuel back on at the tank. If it does not start, pull the plug. If it is wet, there is still too much fuel or a really weak spark. Repeat the above process until the bike starts or the plug comes up dry. Good luck and keep us updated.

Brake bleeding Since your bike has been sitting a while I strongly suggest you dissaemnble and clean the clutch and brake master cylinders before trying to bleed them. My '94 JT25 was giving me fits to bleed the clutch. then i removed the lever and small bellows on the plunger. The snapring was all rusted and there was a lot of crud that was preventing the piston from coming all the way back to the snapring when the lever was released. This prevented the fluid from returning to the reservoir. Once I cleaned the crud, sanded off the rust, and applied some oil to it, they bled perfectly. Gearbox When you drain the box, see if the oil is milky. The water pump seals go bad and let coolant leak into the box. Not a good lubricant. I use ATF in the gearbox. Works great, and is cheap so i can change it fairly frequently. It is amazing how much difference in clutch drag there is with dirty versus clean oil. Ride on!

On the older TXT models, there are three springs associated with the shift claw and the detent rollers. These items can all be accessed by removing the clutch cover and clutch. If they are not installed correctly, you may not be able to select any gears, or they may not stay engaged. When my shift claw broke, I replaced the claw, the rivet and all three springs. It made a huge difference in selecting gears and those gears staying engaged. I don't know about the Pro models, but I think they are similar in how they work. Good luck and let us know how it works out.

Yup, sounds like you found the problem. A bad gasket will do that. If you can't find a new gasket, you should be able to buy plain gasket paper and cut your own.

I had a similar problem with the clutch sticking on a '95 I just bought and sold. Fired up fine, pulled the clutch, shifted down and off it went! Fortunately I held on got control. Rode around the yard pulling the clutch lever on and off while twisting the throttle and after a couple minutes the clutch worked normal. Just stuck from sitting. I would suggest changing the tranny oil because it sat for 3-4 years and try again riding again before tearing into it.

Most of the riders I know who have the pre "Pro" bikes use ATF. I run ATF in my '94 and it works great. It has not caused any swelling or de-bonding of the clutch material from the plates. I did have a problem when I bought the bike with the clutch material de-bonding but that was because the water pump seal had failed and the ATF had been contaminated with anti-freeze. I still use ATF and will continue to. Nice thing is it is cheap and readily available so I can change it frequently.

Go to the Trials Training web site. They have many really good training videos you can watch then go practice. Learn the basics really well, balance, throttle control, tight turning, etc. Only then should you start working on the tough stuff. Most important - have fun!

Your description does sound like vacuum leam but.... At the risk of sounding silly, you did check for smooth operation of the throttle cable and throttle tube on the bars, right?

Maybe I am not understanding the issue. Is this a competion eligibilIty question in the UK, or just a question of what tires will work? I run modern tires on my '74 TY250. I have used both tube and tubeless type on the old rims - I still use a tube and rim locks. I did the same thing when I had a TY175 in the past.

Yesterday - rode, rode and rode. Cleared out a new section and rode some more. Came how, washed off the bike and put it away. One of the benefits of living in Seattle where it reains a lot but rarely snows - ride all year as long as you don't mind getting wet and muddy. Woohoo!

I know many will say this is not a right fix; however, I know some people who have used a metal filled epoxy (JB weld in USA) to repair cracked cases. Many of those repairs have lasted for years and years. This type epoxy is hard enoough that you can machine it, drill and even tap holes in it. As with any adhesive, the key is a super clean surface, possibly made a little rough for the epoxy to bite better and plently of time to dry and cure fully. Keep in mind that if the original case was 5 mm thick, you will need at least 5 mm of epoxy thickness. Good luck.

Did you look inside the side cover where the points are? I had a TY175 that ran great in the dry. When it got wet it would not run. It turned out to be a bad seal aroiund the side cover. When I pulled the cover there was a lot of white powdery substance for water and oxidation of the aluminum. A good cleaning of the residue and points, good sealing of the cover with new gasket and silicone seal and it worked great after that.

I assume you have tried a new sparkplug. I have seen some plugs that showed spark but woiuld not fire when installed in the engine. Did you remove the reed cage and intake when you changed carbs? Perhpoas a vacuum leak from missing or bad gasket?

Glad to hear that. Ride on!

I have a '94 JT25 and my buddy has a '95 JTR250. The triple clamps are different as are the forks. His has sagged way more than mine and it makes the front end feel very heavy as you have described. I do see replacement springs on ebay sometimes for your series bikes. About US$80 for the set. Spacers may work for you, just be careful about making them too long becasue that could cause the coil spring to completely bottom out which could damage things. Good luck.

This is exactly why I alwys try to run my locking cable through the frame rather than the wheel. I hope you get your bikes back.

Like others, I suspect it is the pivot shaft binding in the brake plate. A good cleaning and new grease would fix that. Here are a couple more ideas. When the brake lever pivots, the flats on the shaft act on the shoes to spread them. 1) If the shaft rotates excessively the end of the shoes will not be on the flats but on the major OD of the shaft. They will not release. 2) If a spring has broken or come off during assembly, there may not be enough tension to pull the shoes back together. 3) If the shoe has come out of position at either end, it might allow the shaft to rotate past the flats. 4) If the lever is not on the correct position on the spline, it may allow the cable to bottom in the end fitting and bind inside the cable. A good strip, clean, lube and careful reassembly should solve the problem. Good luck and let us know what you find.

Just checking - your post says TY250 Mono yet the pics with the piston pics show TY250 Twinshock. If you have to do that much machining to fit a piston, maybe it would be easier to sleeve the cylinder and get back to a piston that is more readily available? Have you tried B&J racing in Tennesee? They are pretty well known for TY work.

Here is info from a couple more bikes from my collection. I hope I don't add another level of compexity to the discussio but I noted one other significant difference when I was measuring - swingarm length - so I am adding that also. '74 Yamaha TY250 51" 29% Swingarm 15" '85 Honda TLR200 52" 29% Swingarm 18" '94 Gas Gas JT25 53" 33% Swingarm 20.7" I am not a suspension engineer but I think I see a trend here. Related to this is the location of the swingarm pivot. The TY250 pivot is only slightly in front of the pegs. The TLR and the JT swingarms pivot 3 to 4" in front of the pegs. Can't change that because of the length of the engine. For those who lengthened their TY175's how did it change the riding characteristics?

Sting you are right in desribing the high pressure pulsing that comes with each compression stroke. It is waaayyyyy more pressure than you will get from heat expansion. I do not know the exact numbers for a trials engine but consider these general numbers. Radiator cap release pressure 11-13 pounds per square inch (PSI) Compression for worn engine 110 to 115 PSI High compression engine 155 to 165 PSI. Not many rubber seals can handle 150 PSI. If they could, reeds and valves woud more likely be rubber than metal.

I appreciate the discussion so far. Let me get back to my original post. Here is some background. I normally ride a ’94 Gas Gas. I picked up the TY250 mostly as a buddy bike that would be easy for new riders or friends who had not ridden in a long time to ride. My Gasser was out of service and I was helping set up a trial so used the TY250. I was able to keep up with my buddies on the trails and was really impressed with how well the old girl worked. The main thing I noticed was the back end seemed “skittish.” By that I mean the back end wanted to go sideways almost as much as forward. FYI, I am using modern competition tires. In reading one of the forums here (maybe Yamaha, maybe Twin shock) I saw a post comparing TY250 and Honda TLR200 rear suspensions and the feeling was the TLR is better. I also happen to own a TLR200. I lined up the Gasser, the TLR and the TY and it became immediately obvious that the TY swingarm was much shorter. I don’t remember the measurements but I think it was 1.5” shorter than the other bikes. Then I saw a listing on eBay for some swingarm extensions for the TY250 built in the UK that add about 1.5 inches in length. My ball bearing sized brain said “Aha!” then went back to sleep. Hence my post. I do like to tinker so may give them a try but didn’t want to waste my time if everyone told me it makes the TY turn like some Harley chopper or drag bike with wheelie bars. So, I am still open for input. To Old Trials Fanatic – The TY is actually a little more front end happy (which I like) than my Gasser. I agree completely on your comments about body position. Now if I could just get my old, fat body to stop flopping around like a cork in a bathtub. . . Cheers mate.

Nice clean looking TY175 Goudrons. I do expect I will need to extend the brake rod and chain if I do this. And we get plenty of mud here in the US Pacific Northwest - climate similar to the UK. Matty - not sure I want to move the pegs back. The bike is already pretty front end light, in fact I was thinking the longer swing arm might take it down a little for steep uphills.

It sounds like the threads may have gotten crossed by the plug being threaded in at an angle. Be very careful here. You may still be able to recover the original threads if they are not too badly damaged. Do not try to force the plug in with lots of torque. This will make the threads even worse. Also be very careful if you go with the tap. If you get the tap crooked you could end up taking out much of the remaining threads. I do not know your mechanic skills but here is what I would try. Remove the plug and drain any oil. Remove the skidplate so you can see the threaded hole well. If you have a way to hang the bike up almost vertical will make this much easier. Inspect the threads closely. If the threads are not badly damaged, you may be able to clean them up with a small scraper. If you use a tap, it is critical that it is aligned with the original threads, not the crossed threads. Be careful to avoid pushing any metal chips inside the gearbox. A small vacuum hose can help suck the chips while tapping. If the threads are really badly buggered, it may be necessary to have the hole machined out and a helicoil inserted or tapped to a larger size plug. When I change my oil I always thread the plug in by hand and be sure it makes several revolutions before it starts to snug up. Only then do I put put any real torque on it. If it only turns less than 1 revolution, it is probably not straight and should be removed and reinstalled straight. I have seen some expanding rubber plugs that can be used if the hole is badly stripped. Check with your local quick-oil-change place. I am not a fan of them but it may be a viable alternative in a pinch. Good luck!