XS 500 Problems

Hi all,

I recently aquired a Yamaha XS500 to restore.. admittidly its my first
'proper' bike (only had a honda C90 before)
Its not in bad overall condition, I just cant get it to start. My
thoughts are that the points are set badly, and maybe the cam timing
is out. There is fuel getting through, and spark, and it will pop and
bang a bit, but it wont catch.
Does anybody know the procedure for setting the timing of the cams and
the points? And any other tips as to why is wont start?

Ben.

 

as to why is wont start?

Your motorcycle has what are called "constant vacuum" or "constant
velocity carburetors", commonly known as "CV carbs"...

CV carbs don't have a proper choke plate like a car's carburetor.
Instead, they have a starting enrichener valve built into the side of
each carb...

When you lift the "choke" lever on the side of the carb, you are
opening a little throttle valve in a port that bypasses the throttle
butterfly...

The starting enrichener sucks gasoline right out of the float bowl
through its own starter jet, it doesn't use the idle set to get its
fuel supply...

But vacuum downstream of the throttle butterfly is very weak in a four
stroke engine. The throttle butterfly has to be closed all the way.
There should be a master idle knob between the two carbs. It may be on
top of the carbs or underneath. Turn that knob all the way
counterclockwise to close the throttle butterflies completely so you'll
get more vacuum to suck starting fuel/air mixture into the engine...

And, when you try to start the engine, avoid turning the throttle
handle at all. If the idle fuel/air mixture has been set correctly, the
engine should start without turning the throttle handle at all, and the
idle speed shouldn't race up too high when you have the "choke" lever
in the full ON position...

If you get the engine to start, you can nurse the engine with the
throttle to keep it running until it warms up, then set the master idle
knob back to where the engine idles at the correct speed when it's
warm...

But, your idle jets might be dirty and plugged up. The starting
enrichener needs the help of the idle jets to start the engine...

If the engine still doesn't want to start, you're better off trying to
hand choke it to get it running the first time. Just hold your hand
over the carb inlets while trying to start the bike. You'll know you're
sucking gas up out of the float bowls if your hand gets wet with
gasoline...

It's a lot of work to remove the carbs and clean out the jets if you
find that they are too dirty to allow the engine to run right.
I have described the process about 100 times at least, you can find it
by googling up "kaybearjr@aol +cv carbs +idle jets"

I recommend adding 2 or 3 ounces of Berryman's B-12 liquid ChemTool
carburetor cleaner to a tankful of gas and running the engine to see if
the idle jets will clean out. Avoid getting the engine really hot or
using high RPM while you're doing this cleaning process, the alcohol
and acetone in B-12 will wash the film of lubricating oil off the
cylinder walls and you could scuff the cylinder bores...

You can also get Berryman's B-12 carb cleaner in an aerosol canif you
just have to remove the idle jets for cleaning...