1969 DS6, loss of power at top end

[ds69]

ive got a mint condition 1969 yamaha ds6 with 13,000miles. it runs like a dream around the street and hills. but i have one problem. at top revs it cant deliver the power.
going up the freeway in south australia it will only sit on 40 maybe 45mph. if its flat i can sit on 60mph but theres no more power to give. ive changed the sparkies, cleaned the air filters and baffles and the carbies. all i can think of is that ive broken a ring or something to do with the piston. i have taken the heads off and the piston looks alright, but im not to eager to take the whole pistons out and strip the motor cause i dnt wanna mess up the gaskets.

has anyone had this problem or does anyone know what the cure is.

thanks

[2TInstitute]

compression/leak down test.

Nice original bike

[ds69]

does anyone know where i can get depth adapter for a dial gauge. ive been searching the net and can only find ones for around $100. is there anyone or any place in SA that will do the test on it?

[ds69]

and thanks, it was a rare find but an awesome bike to add to the collection

[Grotty]

Look here:

http://www.ebay.com/itm/ws/eBayISAPI.dl ... 0757151075

[ds69]

thanks, just took off the heads and the gaskets look not too bad, theres bugger all carbon build on the head of the pistons. are there any places in Adelaide that can check/fix the timing on my bike. cause i dont mind paying for the adapter but im gonna use it on my bike then my dads and then its gonna sit on the shelf till my next bike. haha.

[Jeram]

just get an el-cheapo compression test kit off ebay for $30 bucks

http://www.ebay.com.au/itm/Petrol-Engin ... 385wt_1139

I think mine is like this one, cant remember, but it works fine.

sure it might be off by a little bit compared to the big $ ones but it is accurate enough to tell you if your piston/ring/bore is shagged

[ds6user]

Hi DS69.

Nice bike.
Have tried to reply before but not sure if message went (I am a bit of a Luddite with computers)
Some thoughts from a long time DS6 owner, pardon me if I am telling you the obvious.

Blocked exhaust ports / engine pipes.
Blocked exhaust baffles. (Already checked)
Blocked muffler pipes
Broken / worn rings. (Is there any sign of blow past on piston skirts) At 13000 miles could be due for rebore. Pistons and rings available on Ebay
Worn crankshaft seals (Right side more likely to fail due to overheating / out of true crank) Seals also available on EBay.
Incorrect ignition timing (Well best to use dial guage to set timing)
Carbies give little problems apart from occasional blocked jets.
Starving for fuel (Fuel line blockages or vacuum seal on tank)
Incorrect plugs (NGK B9HCS best for performance) Might be a bit cantankerous to start cold.
Incorrect final gearing (STD is 15 tooth / 41 tooth) I use 16 / 40 and run at just below 6000 rpm at indicated 75MPH (Actually about 110 K's) will go faster, but me and bike both a bit too old.
They only have good power range up to about 7000 RPM at most anyway.
Incorrect throttle cable. (Too much slack / not enough travel preventing slides from going fully up)

Some more thoughts:
Dial guage adaptor relativly easy to make using spark plug body and braising on an extension and drilling / tapping some holes.
Head gaskets resuable a million times, just heat over stove ring and drop in water
Base gaskets available on EBay or easy to make.
I have reproduction decals for frame and oil tanks, including "Autolube" if you want.
Also have parts and tuning book if any information is needed.


Good to see another DS6, especially one in such good order.

John I