84 FJ600 Yamaha Mikuni 32mm carbs pilot screw setting

 Hey guys, I need to know where to start with the pilot screws on these
carbs. I have tried 1/2 turn out to 5 1/2 truns out and get all
different levels of starting. Anyone know what the correct number of
turns out is and I can fine tune from there?

Thanks

 
The starting enrichener is supposed to work all by itself, when the
idle mixture is set right, you should be able to start the bike by
pulling the knob all the way out (or moving the choke lever all the
way) and you shouldn't have to touch the throttle at all.

If the engine starts with no choke at all, you should realize that the
idle mixture is too rich and that the transition ports are uncovered
because the idle speed knob is turned too far clockwise.


there?

Some online parts fiches for Yamaha have carb tuning information on a
page called "technical information" or some such.

The FJ600 came with smallish #35 pilot jets, so the idle screws may
need to be opened as much as 2 or 2-1/2 turns.

Carburetors with #40 to #45 pilot jets are the ones that require as
little as 1/4 turn out from fully closed.

The general rule of thumb with constant vacuum (diaphragm) carbs is
that
3-1/2 turns is the maximum number of turns out from lightly seated and
that
nothing happens after that.

Most shade tree mechanics have the idea that their idle RPM should
keep rising as they turn the idle mixture screws further and further
counterclockwise.

But, at some point the idle speed starts slowing down and the exhaust
note becomes dull and thudding.

To keep the engine from stalling, they turn the master idle knob up.

Then the idle RPM will hang up at high RPM when they twist the
throttle and close it again, checking throttle reponse.

The engine is actually getting the extra fuel from the three
transition ports just downstream of each throttle butterfly.

If the idle RPM doesn't hang up like that, it may still hang up when
the engine gets hot. When that happens, newbie tuners scratch their
heads wondering
if they don't have enough slack in the throttle cable, or what,
because they don't know about the transition ports being uncovered by
the throttle butterflies.

I recommend that you start with the idle mixture screws turned out
about 2-1/2 turns from lightly seated and turn each of them
*clockwise* 1/4 of a turn, then readjust the idle speed if it
increases.

Then turn the screws another 1/4 turn and readjust the idle speed
screw again.

What you want to achieve is the highest smooth idle speed with the
least number of turns on the master idle knob.