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Motorcycle Repair/1970 Yamaha 90 ht1


QUESTION: Hi Wayne, This bike has been sitting for many years and I'm trying to figure it out. There is an oil tank on the left side with green oil in it,(it's just below the seat), then on the other side on the crankcase(?) there is a dip stick with clear oil on it. Is there 2 different oils for this bike? Sorry I don't know how to ask this better.          Thanks for any help,Ging

ANSWER: Hi Ging,

I like those old Yamahas, They are a great bike if you keep an eye
on a few things.

The tank under the seat is the supply tank for your engine oil injection
pump. This is how the engine is lubricated.

You keep some good quality two stroke or two cycle oil
in that tank. The oil will get used by the engine for lubrication
so you have to make sure you have some oil in that tank at all times.
The oil pump is attached to the throttle cable so the
engine always gets the right amount of oil at different engine speeds.

The other oil in the crankcase with the dip stick is the transmission
oil. This is used only to lubricate the clutch and transmission gears etc.

Just hold the bike upright and put the dip stick in and see if oil
touches the stick.  If not add some 10w40 motorcycle oil until
the oil level is correct.

The transmission oil has a drain plug for changing the oil.

The oil tank is okay as long as oil gets to the pump on the right
side of the engine.  There is a small screw on the pump which
can be removed to see if the oil is getting to the pump.
This is also used to bleed air from the oil lines.

Let me know if you need more info, I used to service these bikes
when they were new!


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QUESTION: Thanks for the answers.I see a screw next to where the throttle cable goes in to the crankcase, it has two flanges holding a cover, is that the hole to see if oils getting to the sump pump?

 Next question, I have emptied the oil tank with the green stuff in it, should I clean the tank with some kind of cleaner? Also the gas tank has rust that I can see and feel in it, can that be cleaned too?
         Thanks again, Ging

ANSWER: Hi Ging,

The two screws are holding the cover that encloses the oil injection pump.
Under the cover you will see the oil pump and also where the
throttle cable is connected to the pump.
If you turn the throttle you can see the metal wheel on the pump move.
The white plastic wheel can be turned one way to pump oil by hand.

You will also see the oil line coming in from the oil tank.

On the small pump itself is a silver colored screw with a tiny
gasket on it. This is the air bleed screw that if removed will
let the oil run through from the oil tank.

If you drain and clean the oil tank you will have to make sure
the oil line is full of oil and bleed and air out through the small
screw hole on the pump.

The tank can be flushed with any solvent like gas, varsol
or even hot dish soap and water,  just rinse and dry it well.

For gas tank rust you must clean the tank with hot soap and water
to remove the old gas varnush and then rinse with some two stroke
oil mixed with some gas to protect the metal.

If you want to do a really good job then buy some "Evaporust"
rust remover and soak each side of the tank until the rust is gone.

Clean out the fuel petcock valve on the tank also.
It has a small screen inside it.

If the fuel tank has alot of loose rust in it you can put some
small rocks in with the cleaner and shake it to remove the
loose rust. Count the number of rocks so you know how many
have to come out again.

If you have trouble getting the screws out you may need to buy
a hand impact driver. The case screws can be very tough.
If you damage them just pick up some metric screws the same length.
You can replace the screws with allen head or hex head screws
which will be easier to remove next time.


---------- FOLLOW-UP ----------

QUESTION: Hi Wayne, Well I did what you said with the oil tank and gas tanks, cleaned the petcock. I also took the carburator out and cleaned it. I cranked several times and I was amazed... it started.
  I only started a few times,(starts on the first crank)because I haven't found an impact wrench yet from anyone.
  My question now is I've noticed oil coming out of the engine between the engine and the exhaust pipe. There is a spring holding the pipe to the engine which seems loose, is it suppose to be loose? And is that normal to have oil leaking there?
  When it is running there is a lot of smoke, so I'm kind of assuming that the oil pump must be working because of the smoke and the oil from the  exhaust pipe. Thanks again for your help.  Ging.

Hi Ging,

There are a few possibilities for excessive smoke from your bike.

-make sure the fuel tank has only fuel in it and no oil mixture.
-the exhaust port or pipe could clogged with old oil or carbon.
-the oil seal on the crankshaft under the clutch cover side could be leaking.
this allows the engine to draw transmission oil into the motor.
-the bike may be flooded with old oil and fuel and just need some
running to burn off the old oil and gas.
-the oil pump cable may be holding the oil pump at too high of a volume.
The pump wheel has an alignment mark ("V" and pin) when held open I believe.
Also the pumps stroke can be adjusted with shims from Yamaha but
this is probably okay.

My first suspect would be as follows:

If the bike doesn't improve with some running
I would check the exhaust pipe flow and the exhaust
port on the engine for clogging.

Second, I would see if the transmission oil is going down
which means the oil seal is leaking on the crankshaft
and the engine is sucking oil in from there.

Make sure the carb is not leaking and flooding the engine with fuel.

Sometimes the exhaust pipes are so plugged they need to be cut open
and all the oil cleaned out and rewelded again.
Sometimes it might help to flush the pipe with a strong degreaser
or such to wash out the oil.
In my experience the pipe needs to be cut open on the backside
to clean it properly.

Once the pipe and seals are good then if it still won't
rev out the main jet in the carburetor can be lowered
slightly to reduce the fuel mixture.

Impact drivers should be listed online somewhere
or ask at a motorcycle shop.
Some auto parts stores carry them as well.

I got one one for about $10-$15.00 but
they may cost more depending on the store.

The pipe is held by the spring and may be slightly loose
if the spring is a bit weak. This is normal to some degree.


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Wayne S.


Licensed Motorcycle Mechanic, Knowledge of motorcycles from 1960 up, Japanese, British and most other brand motorcycle repairs.


Worked for Yamaha, Honda, Suzuki, Kawasaki British: Triumph, Norton, BSA Other: Most Scooters and Mo-Peds

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