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Hi there, I think you might be over thinking it! Generally it doesn't stand for anything! Naming conventions are just part of the manufactures plans and future plans. We'll call the first one A then B and the next C and so on. Occasionally some bright spark comes up with a gimmick and says let's call something MX which could be for Moto Cross "M X" but this is not common by any means! The very first Ford car was the Model T, However, after its success Ford launched the Model A and then the B and so on but it never stood for anything. it's not like an Android OS naming convention!! On the otherhand the manufactures rarely call something a "Mark1" or "Mark 2" of their product. It normally starts off just as a name and then when the next version comes out it gets dubbed by the media/public "the Mark2" when it comes to differentiate it. Then, by default, the first model becomes the "Mark1". I can assure you Ford never launched the Ford Cortina in the early 60s as a Mark 1. It was just a Ford Cortina! In fact when the replacement got launched, that too was a Ford Cortina. it was not badged as a Mark 2 on it's bodyshell. Advertising and Marketing coined the Mark names thereafter to help identify it. (I guess some of you reading this might wonder what a Ford Cortina is!......) Hope this helps, PS if you're going to stick around, pop over to the new members section and post a little introduction about yourself and you'll meet a few other members.

Have you ruled out the throttle cable? Disconnect it at the carb and manually operate the throttle at the carb. Does it still have trouble returning to idle? At least that way it would rule out the cable completely. It doesn't rule out the throttle slide , just the cable.

It's not something simple like the throttle slide sticking and not returning to its idle position is it? or the cable binding at a 'hot spot'? just a thought!

Very frustrating for you indeed. Bear in mind the bottom line is it's likely to be either fuel/air or timing. That's all it can be. Afterall it's only a collection of moving parts which do nothing until they are moving! Effort is required to get them going and fuel/air and timing keep them going until you turn it off by stopping. Simplistic view yes but in essence that's all it is!! Having said that my ramblings here might help guide you ......or not! Fuel/air mixture: making it lean or rich effects speed and whilst the carb is set up to deliver that correct mixture leaks on the induction side can screw it up too. When things get hot they expand so what's air tight when cold can get exposed when hot!, and conversely the same happens when cold. Leaks occur when cold making it difficult to start until hot when the expansion swells and everything closes! Which is why it becomes difficult to trace any faults! You test when cold only to reveal the problem when hot OR you test when hot and miss it when it was cold.The same Tests need to be done both hot and cold. Checking for air leaks is tricky, you can't hear them like an air leak on a punctured tyre. Mix up some washing up liquid in warm water making it as bubbly as possible (cold water doesnt make bubbles so well) then with a 1/2 inch paint brush paint it quickly around any joints of the induction side, paying attention to any rubber connector, they can leak at the interface or anywhere along its rubber length. Paint it on around the head gasket and on two strokes, especially around the base gaskets of the engine. Work quickly because the heat of the engine will rapidly evaporate it all even more so when hot. Listen out for changes in the engine speed not so much for the sound of air leaks although you get a nice reaction in the bubbles when you stumble across the leak. And before anyone says don't spread soapy water around it could get in the engine, it's likely to be a pin hole not a bloody great crack! Timing: A collection of bits which controls the high voltage to ignite the aforementioned fuel air mixture! Opening contacts too big or too small effects the timing and a few thousands of an inch can change it dramatically as many of you old dinosaurs like me will know. Equally wear and tear can also play it's part and have the same effect. Points should be checked when cold because when hot everything expands and the reading might not be so accurate. Equally when hot, things can stick! and also stop things working efficiently, don't spread it all in grease thinking you're making things better; it could have the opposite effect. Minimal oil works best here. One area often neglected is any spring loaded advance and retard mechanism found behind the contact sets. The goveners (weights on springs) move with the engine speed and advance the ignition automatically and can stick when hot, especially when covered in grease and crap over time. Pay particular attention to keeping these clean and maintained especially the pivot points. If it all sticks here it may take a little time for the springs to pull everything back and return the timing to normal. Replace the springs for example if they are suspected to be worn (springs do wear out!) Some vehicles have a vacuum mechanism attached to the goveners( I'm talking old classic cars here)but these are connected to the carb which influences the fuel/air mixture. Leaks and blockages here will also effect the performance. You might already know a lot of this but there again it might help others who stumble on this thread in the distant future! Hopefully of some help.

I've seen this once before when a mate put on a different wheel from another bike, whilst it fitted, the gearing for the speedo drive was on the opposite side and ran in a different direction.

Just a thought but where abouts are you? (i dont mean publish your address) just the general area. Sometimes members are willing to come over and help.

Hi Lee, Wemoto is a good place to start, i just typed in YZ80 and a load of parts came up:- seals,bearings,sprokets,tyres,tubes etc. ie parts to keep the bike up and running. If you're looking for replacement yamaha parts/OEM like engine/gearbox parts frame wheels instruments etc then it becomes more challenging. After all its 42 years old if its made in 1976. I have a Honda 400/4 from the same year, and there is quite a following for them. Dave Silver spares over the years bought up closing down Honda spares and has also remanufactured a lot of obsolete parts. Whereas I'm not so sure the same can be said for the YZ80. A quick search on google doesn't yeald the same results. You can get parts cleaned up, restored and polished, rechroming etc etc You can strip it all down , powedercoat the frame , repaint the tank, ....but it all costs money and you can literally throw a few thousand at it to get it into a very nice example or even showroom condition. Don't get me wrong it may be worth it.....to YOU, it was for me and my 400/4, but you'll not get you're money back, it can quickly become a bottomless pit.! But if it's a hobby it may well be worth it afterall its now a classic.! It really depends on where you want to go with it. if its a keeper then you've got to decide If it's a full restoration/hobby be prepared for a lot of hard graft and fruitless searches seeking the parts you need. If it's just get it working with the minimum expense then wemoto and the like should suffice. If its time to sell it, then only you know how much you want to spend to move it on...... On the plus side....it's now TAX and MOT exempt! ....................However, that doesn't mean you can just take it on the road! MOT exempt means you're taking FULL responsibility for it being roadworthy!!!! Hope some of this may help you..

Hi welcome to the club, We're not allowed to post links to copyrighted material or service manuals, its part of the rules of being in the club. In fact theres a pinned post above yours stating that, worth a read, even if I've said the same here! Having said that, I went to google and typed in TT250 service manual and found several links. ranging from a post on ebay for a laminated copy to a pdf for a TTR250 on a website. I also found the complete parts list on the cmsnl website. Various other posts on other forums looking for the same manual give links to tt350 and another for 1986 tt250. There doesn't appear to be a clymer book or haynes manual covering the actual bike according to those posts. Unless someone else knows any different.....

I found this on our website....post no 8 states... ,when it is warm it still tends to be slow returning to idle. https://yamahaclub.com/forums/topic/26876-xs-250-running-issues/ may be of some help.

Hi there, The trouble is with many DIY ultra sonic cleaners is their small size. You can get bigger ones but You'll need one to fit at least one carb if you want the internals cleaned properly so you would be looking at at least a 1 litre one. Having said that you might want to consider looking up ultrasonic cleaning services for motorbike carbs (often seen on ebay as a service). These guys can strip it down and reset them etc,I appreciate it won't be cheap but an industrial one will beat any home purchase one hands down. As drewpy says it's likely the internals which are blocked and often no amount of blowing with an airline will clear them. Petrol if left standing evaporates leaving behind a shelac like varnish which is unbelivably rock hard!!

Good to hear you're up and running Brett, Nice one. As regards to the output at the headlamp, Here's a little tip for you especially if you don't understand electronics etc. Batteries produce DC wheres a Generator will produce AC. (I know some bright spark may pipe up and say about Invertors and Commutators, which are generally expensive devices to get AC from a Battery and DC from a generator BUT you wont find these on a little DT motorbike!!!) As you're working in the headlamp shell you will find both AC and DC. However, only the headlamp bulb is fed from the generator so it's the only one which is AC. All the other wires will supply DC from the Battery. And to supply the headlamp with AC the generator needs to be running. Turn off the engine and the AC stops....the headlamp goes out! Hope it helps, Well Done mate!

And here's the same circuit with the modification. Note nothing else has been touched.

Brett it may be useful for you to locate a DT175MX 1978~1982 wiring diagram and compare the layout to yours. However, the headlamp is run from the generator on an MX bike (1978) There are no circuit breakers or resistors or control boxes etc. it's a very simply wiring circuit/diagram. The ignition switch controls the circuit. Positon OFF : Engine off. Light circuits OFF position I : Engine running . switched lights only (indicators horns brake light) no headlamp. positon II : Engine running . All switched lights above plus HEADLIGHT AND TAIL LIGHT ON (today this would be called daytime running also) position III : Engine off. Tail light and parking bulb in headlamp ON ( Key can be removed from ignition bike left with minimum lights on for parking up at night) Here it is: once again colours are for a 1978 175 MX UK bike. the Ignition switch internal contacts are the black bars and dots. in position II the red wire from the battery is connected(by internal contacts) to the brown and red/blue strip lights/indicators etc. Whilst at the same time the yellow wire from the generator lighting coil goes to the yellow/purple of the headlamp and also to the regulator which 'clips' it preventing overvoltage to the lamp (a 6v regulator will clip it to 6v for a 6v headlight whereas a 12v regulator 'clips' it to 12v when a 12v bulb is used.) Also the generator white wire goes to the rectifier which in turn goes to the battery and charges the battery. It is noted that the white wire also goes to the switch but in postion II it is not connected. (In position I it helps prevent overvoltage to the battery.

I can't stress this enough but the colours and procedure is for the DT175MX range for the late 70's and early 80s models. Its unlikely that the colours used on the MX are an exact match to colours of another wiring diagram even if its built by the same company! so bearing that in mind, The C90 regulator uses three wires and an earth (dont forget the earth, the body was earthed to the frame on a MX bike, the C90 body is not earthed from inside, it uses the terminal) The C90 is wired using the two wires which went to the rectifier (red and white on 1978 MX) to one side. The other side has the earth and what ever wire connected to the regulator on the other side.( yellow on a 1978 MX, yours may be a different colour!) I don't have your circuit diagram in front of me but if you're saying the yellow/white wire went to the regulator then that's the wire which goes to the C90 combined reg/rect. The wiring colours below are those of a 1978 DT175MX....yours maybe different.

Hi Brett, welcome to the club, nice to hear the 'ol 12v conversion is still being read. The write up was aimed of course at MX models 10 years earlier than yours! so it may not entirely apply as the wiring is likely to be a little different. However, I guess if you've got so far you've taken that into consideration. if it was an MX I'd be thinking...... Is the 6.4v at idle without the effect of the regulator/rectifier in the circuit? This would be expected as shown in the 3rd post on the first page of this topic it would then go up as you rev the engine. As explained the purpose of the 6v regulator was to clip the voltage to 6v regardless of the output. Fitting a 12v one in essence clips the voltage to 12v instead of letting it get to 14v etc... if you're saying its 6.4v regardless of the revs then I also might be thinking you've got the 6v reg still in the circuit or the one you bought is a 6v one or faulty. Having said that, all this applies to the MX wiring circuit and may not apply to later models. Earlier models of DT have fancy things called avalanche resisitors and whatnot! (as mentioned by Cynic and Airhead in earlier posts) so it's not unreasonable to think you may have other accessories in the wiring which might effect the results. You also mention the tail-light lights up without the engine running, Well that is the same as the DTMX as its only the headlamp and charging circuit which runs off the generator. Everything else: indicators,brake light,tail light and horn all run off the battery. This may be of some help to you but equally just proceed with caution. Good luck

This has an air of familiarity for sure!....I certainly had a similar issue, I could rev mine over 5K + when its not under load, ie on tick over then whacking up the throttle and it run fine, however.....go for a ride with it under load and it didnt like going above 5K. Mine (although I wouldn't consider it at the time) was my exhaust pipe. ie the end can. I was given and fitted an original tail pipe, I was told it had been 'decoked' and I too cleaned it out with so called exhaust cleaner, and for a short time it did seem to be ok, but then the 5K problem started, it wouldn't run well at speed and top speed was only about 40~45 before it would play up, something was wrong but I carried on , but it didn't get better. After doing many things including new plug, carb, aircleaner, I eventually put back my rather noisey aftermarket can, and suddenly everything was back to normal, top speed and running all back to as it should be. Might be of some help?

the new rectifier/regulator..... Pattern part ? or Genuine?

What did you do in the end then Alex? did you hear back from Yamaha?

There's an interesting video on you tube from a fellow Oz suggesting the manual is wrong, i assume you've seen it? https://www.youtube.com/watch?v=l3q6wbct6-I

Hi Jonross, Might be worth looking at the parts lists for the R6 which may help you https://www.cmsnl.com/yamaha-yzf-r6_model16903/

I dated an imported bike once........from france if I recall.....boy was she rough!??

Nice, ....especially the brown carpet!?

Hi Emmert The three drain plugs are indeed one for the crankcase drain https://www.cmsnl.com/yamaha-ya6-1966-usa_model8299/partslist/A-05.html item no 17 is the drain plug and its corresponding filler top plug is item no 18. and the other for the transmission/clutch with item 15 being the drain plug and the filler cap being item 20 https://www.cmsnl.com/yamaha-ya6-1966-usa_model8299/partslist/A-06.html The third drain plug you mention is the actual drain FILTER plug, (item no 16) and is a seperate plug just with a drain screen fitted. The YA6 (like most motorcycles) is a wet clutch model, potentialy there can be 'bits' floating about from clutch wear. Back in 65 Yamaha thought it worthwhile to incorporate a drain plug to empty the crankcase and another for a filter screen, today it would be just one plug. Yamaparts provide a free pdf for personal use of the YA6 engine service manual, just click on the book image and it will download. You need to go to yamaparts.com / 2013 /01 /engine service manual its a bit dated but it might be of some help. I didn't know this but the YA6 was the first model to feature the Yamaha's dramatic new AUTOLUBE system!. You learn something new everyday. (Autolube was the separation of the two stroke oil into it's own little tank.) Member DirtyDT used to have one of these so he might be able to tell you what oil and capacities it uses but he doesn't often post these days.

Certainly drain and put in fresh petrol, Old petrol goes stale after about a year or so and loses it's 'ginger' ...it's ignitability! Equally if it's been sitting in the carbs it may well have evaporated by now leaving a rock hard shellac like deposit in the float chamber and in the jets! and disturbing the dry seals to inspect it will result in them requiring replacement too. The spark plug may well be okay, but for the sake of the few minutes to remove it and clean it all up helps elimante any problems starting it, ie "well I've checked and reset the spark plug" I left my 400/4 for a number of years and then set about getting it back on the road, like you it had been sitting in the shed for several years and all what you are doing is practically the same as i went through, having said that i was surprised how 'damp' the whole lot was even though its a dry shed, I'd recommend leaving it out in this sunny hot weather and get a free heat penetrating dry out, it will certainly help when it comes to starting her up. New battery fully charged, I moved over to the yellow gel battery and never looked back, well worth the slight extra compared to topping it up with water/acid etc. keep us all updated on your progress.

You don't mention whether you are looking for the round tube or square tube.( Earlier swing arms were round) but heres a square tube one on a frame, which you could buy and sell on the unwanted frame to someone else. Either way its an option? https://www.ebay.co.uk/itm/YAMAHA-DT-50-MX-FRAME-for-restoration-project-spares-or-repair-/153052149817