JimR

In the UK this was just a blank bolt see http://www.ebay.com/itm/Yamaha-AT3-125-2459-Cylinder-Head-/360519255448 but I have seen setups like this before (non yamaha) that just 'let the compression out' which in turn just stopped the engine (early kill switch) ... I have known other people intall a spare spark plug in place of it as it has the same thread as a spark pug http://www.ebay.co.uk/itm/151865172178?clk_rvr_id=1084552117386&rmvSB=true

In the UK the amount of 10w40 motor oil to be added to the gearbox was stamped into the casing just by the filler hole to check the level see this from memory there was 600 cc of oil in the gearbox but don't quote me

sounds like the battery charging system is at fault .. this would answer the point that a 7 week old battery failed ... it was not being charged and died !

perhaps its a ds6 ?

check the compression .. it is unlikley but remove the option of worn valve seats ... this can happen if the valve clearances are not done on time and to be fair the 30k miles between checking the clearances does seam excessive

.. oh OK it not blowing bulbs or boiling the battery then ?

There is no no actual 'read outs' .. so where have u mounted the resistor ?

I do

That's coz the dampers fucked !... most prob it has de gassed it'self

If you alter the spring, the shim stacks in the damper will be all wrong and it just wont work correctly, in fact you make the bike handle worse rather than improving it !

try talking to Kev at KB Racing he has at least 25 years playing with suspension ... I guess he could re valve it (change the shim stack ), and and work out the correct spring for you ... this way may be better than trying to work it all out yourself ... you could email [email protected]

PW80 and V80 are the same engine .. as the engine is short of the generator I am hoping the taper on the V75 crank is the same as the PW80 (this means your mag will fit) ... but it will bolt straight in

here's a motor for you http://www.ebay.co.uk/itm/Yamaha-PW80-Engine-Spares-Or-Repairs-/201366157698?pt=LH_DefaultDomain_3&hash=item2ee25bb982

this may help - http://www.ebay.co.uk/itm/Yamaha-V75A-1975-1979-Fully-Illustrated-Parts-Catalogue-V75-V-75-A-Moped-595-/310871351490

Back in the day I used to stretch the spring a bit (this encouraged the gearbox to change up earlier if people complained about the 'lurch' on gear change) ... the rollers in this clutch are ball bearings (great for playing marbles with ) maybe some lighter balls may help ?

so this is a V75A ... sounds like you will need to look at the clutch rollers & spring to adjust when the bike changes gear. However the bike out of the box would 'rev it's tits off' before it changed into second (this engine has just a 2 speed gearbox) and second being a lot higher than first you do need to get the bike to rev out in first The High/N/Low lever (the low option could only be set by pushing the metal clip back, your clip may have long since broken off) is for High normal riding N for starting the bike Low is only there for very steep inclines (if the bike stalled out in High). Regarding your question about tuning as this is a V75A and not a V75 (V75 had a 3 speed manually selected gearbox with an automatic clutch like the V80/90) you have a totally automatic gearbox, so altering the overall gear ratios (upping the front sprocket) will not work as you don't have the control over the gearbox that the V80/90 has ... The cycle parts are the same across V50/70/75/80/90 so in order to get this bike to go dump the V75A engine and put a V80 engine in the frame. Use a V80 as out of the lot of the V series it was the best motor

The V75 uses a reed valve block that fits to the crank case rather than the barrel which does not give much room to open the reed block up, The CDI unit may fit from the V80 model (you would need to alter the wiring loom to suit). I did, back in the 80's, some tuning work to a V80 .... top speed ended up at just below 60mph rather than the stock 45mph. V90 front exhaust pipe YG1 pattern exhaust system (cut and grafted to the front pipe) V90 Carb (it is so long ago I can not remember what I changed the jets to, but I did change them) reed block opened by 2mm front sprocket up by 2 teeth

As a V75 was never 'restricted' there is little chance of finding any technical on de restricting it but why would you want to tune a 1970's scooterette in the first place ?

try http://www.pjme.co.uk/acatalog/Yamaha_DT125LC_Engine_Parts_Bottom_End.html

the YB100 (dependant on modal year) had a resistor (hidden behind the number plate) to check if you have one look for a yellow wire with a black trace disappearing into the number plate mount.. if present they never normally gave problems but if the earth (via the rear mudguard) failed you could pop bulbs ! are you sure the head light blew first ?? it is possible the rear light blew first and sent 2 much to the headlight and switching to 'dip' just then blew the dip filiment Check the wiring harness by the head stock if the outer casing is cracked there is a chance that the white wire from the rectifier is shorting out (this problem popped bulbs also and boiled the battery) Check the connections to the rectifier (white & red wires) Check the white wire connection from the mag (under the L/H side panel) .... (this may be a yellow wire or yellow/black trace ... depends on the year)

Perhaps you could get them sonic cleaned ?

try cleaning the drillings in the carbs, when the choke is applied drilling(s) in the carb(s) are opened in order to draw neat fuel from the float chambers into the venturi ... this then allows the engine to start. adding fuel directly to the cylinders actually does the same as the choke (e.g rich fuel mixture) .... take the float bowels off and in the float bowel you will see a hole in the bottom (near the drain port) that is connected to the hole (in the float bowel) that the brass tube from the carb body lives in when the carbs are all together ... if the hole small hole (near the the float bowel drain) is blocked .... you get no enriched mixture to the venturi ,,, so in effect no choke !

not 100% true certain yamaha products do have a modular approach (eg any V model (within reason), 2 stroke scooterette and not XV ) can interchange motors. However I can not remember coming across the GT80 or 100DX in the UK so as you say this may become costly as they may not be modular. if anyone is interested I could compile a list of 70's ~ 80's UK models that are/were modular and others that need mods but still fit !

did you get any ?

don't forget there are many combinations of shells .... you need the con rod & crank number(s) to get the shell bearings with the correct oil clearance