jattie

Comeon guys, someone must have some experience on this!

The idle screw is normally a big one on the side of the carb. In most cases the come out on a user friendly extension cable.

Pipes are normally in three section, the downpipes off the heads, into a second section up to the cans. If you have completely diffirent cans you normally have to get the connection bits to the downpipes as well.

Sorry, there's no easy way out, it's a big job, takes about 6 hours to fit, if done properly. Strip off a lot of stuff, connect the wires in so the dont corrode over time and tape it back up so it's hack proof. Most yamahas have the same wiring colour coding, look at the areas where the indicator wires are exposed, normally yelow and brown I think.

They're said to be able to to a top speed of 55mph. A timiong chaion tensioner is a spring loaded device with a ratchet mechanism that prevents it from being pushed back at all. or at least it should. It's normally held i place by two smaller bolts on the sides and a bugger cenrtral plug that can be opened and the springs taken out. Take out out and see if the ratchet mechanism is working as it should and make sure it locks properly when pushed out.

From what you describe I would be inclined to agree, sound like fuel starvation. Soemthing is stopping the fuel from getting to the combusion chamber. Close off the the tank fuel tap and open the drain valve on the bottom of the carbs, you might be lucky and flush it out. Repeat a couple of times. If that fails you might have to remove and clean the carbs.

I've had this kind of bahaviour before when a crakcase seal was intermittently allowing air into the casing below affecting the air faul mixture ration.

Adjusting the front sproket is easier if you want to play around with rations since one tooth in font does not affect the chain length and adjustment potential to keep it tight enough, otherwise you have to remove some chain links. The net effect would be a function of the ratio from front to back, for example say you have a 48 tooth sproket at the back and a 14 in front so a ratio of 14:48 i.e. 3.4285. So adjusting one tooth in front smaller you will get 3.6923, that is a reduction of almost 8%. (3.6923-3.4285/3.4285*100) You will get roughly the same effect by adding 3 teeth at the back, so the top speed will decrease by roughly 8% and the torque/excelleration that you experience by roughly the same amounts. 1. You get high performace reed valves (Boyesen - Fibreglass type) with a shorter lifespan, but increase in engine RPM and overall performance. They can resonate at higher frequencies. 2. Gafflowing in inlet ports, basically polishing the fuel inlets and widening them and widening the holes in the pistons that flows fuel trough the crancase. Make sure the crank case seals are leaktight and does'nt effect the fuel mixtures. 3. Use the Iridium type spark plugs and multispark types. 4. Increase the combustion presure by reducing the combustion chamber size. (skim the head - see below) 5. Build or buy a custom exhaust. On these bikes every little increase adds up to the overall performance, keep in mind that all these changes also leads to a reduction in engine life and fuel consumption. Skimming the head basically means reducing the cumbusion chamber size. The cyclinder head normally have a little ridge and a gasket. You hace to determine how much room is left for the piston to turn around on the top at speed and take away some of the spare capacity. An easy experiment is the remove the aluminium gasket. A millimeter of part of that make a huge diffirence. Be aware thou that the engine runs hotter and you can burn holes is the pistons if the fuel mixture is to lean.

With the piston on top on compression stroke i.e. valves closed the cam lobes should point outwards and the marks on the cam sprokets should align with the cam casing sides.

Conor, You are right, if top speed is not a factor, changing sprocket ration will creates an improvement in acceleration, but reduce the tope end. The easiest way is to change the front sprocket. They normally come in 13 14 and 15 toth options and bikes normally come out with a 14. Going down to a 13 will increase acceleration. There's also a 12 oth, but very scarce. There's lots of ways to improve the engine performance if you want to work on the engine. The exhaust makes a huge diffirence and the standard ones are very restrictive. A performance pipe will make a huge diffirence. If you dont want to spend lots of money, you can increase the compresionby skimmimng the heads.

Do you actually mean YD 250 or YZ 250. A CDI Unit is pretty much manufacturer dependant and very bike specific. The ignition timing is dependant on a magnetic pickup on the flywheel and an RC (Resistror and Capacitor) circuit changing the firing angle at varying RMP's. YD's (as far as I know) still runs of points and aYZ would run off a CDI unit. I've cross fitted some CDI units over the years, but you have to consider bike types, i.e. two stroke vs four strokes and the rpm's the engines run at. I would suggest getting a similar type CDI, IT 250 ar raptor 250, if it's a YD with a CDI retorfitted, you might be able to adjust the firing angle adjusting the points with a timing light.

I've a 1997 TDM with around 58k miles on the clock. It's regularly serviced and used for my daily commute for the past 3 years. A couple of days ago coming from work off the motorway I heard a strange knocking sound that seems to be related to speed and power applied, when you pull the clutch in she goes all quiet. I drove the last mile slowly home and put the bike up on the paddock stand. I noticed that there was a massive wobble in the drive chain especially in top gear at idle speed. I took the chain off and noticed that the knocking sound remains as soon as I put the bike in gear and especially in a higher gear. So over the past two days I stripped the heads down and was sure I am going to see a timing chain or big end issue and to my surprise they are all 100%. I am now totally stumped. I do not see any bearing issues on the flywheel, so short of dropping the engine and stripping the gearbox, any other ideas before I go down that road? Any ideas, suggestions and experience will be much appreciated. Thanks

Is there anyone with info on checking my TDM Valve timing? The Manual I have (http://dl.dropbox.com/u/6248918/service_tdm_96.pdf) does not cover this.