Motorcycle Repair: 1985 yamaha xj700 maxim, vacuum leaks, air vacuum

Question
I have recently bought a xj700 and when I bought it the battery was dead so we jumped it it ran no leaks no ticks. Do I bring it home get a new battery for put it in it starts right up. So I jump on it take it around to the block it acts like it was bogged down so I cleaned he carbs out them back on start it up, runs no problem so I got to put a few tools away and it spontaneously just revs to like 6000 rpm stays there for a min the drops back down and dies then wont start for awhile, after that while it dose the same thing iv changed the plugs air filter on it and still the same problem. Do you have anglers what that would be thanks

Answer
Hi Aaron,

Here are a few possibilities for the high engine speed.

Check the throttle cable is not out of place
and that it has some slack or free play so the
carbs can close easily.

Check that the carb mounting rubber boots
are not leaking air. They may be kinked or
have cracks in the rubber or their may be
a gasket between them and the engines head
leaking air/vacuum.

Any air or vacuum leaks between the engine
and the carbs will cause a fast engine speed
like you mentioned. You can check around
the carbs/intake with a spray can of carb cleaner
to see if it changes the engine speed.

Also check for air leaks around the seals
on the carb butterfly valve shafts.
There are small o-rings that prevent
air getting past the butterfly throttle
valve shafts.

Try turning your idle down with the idle
speed screw between the carbs at the bottom.

The smaller screws between the carbs are
for synchronizing all the carbs with carb
vacuum sticks or gauges.
Sometimes getting the carbs syncronized can
help get the idle speed corrected.

You might try setting all the carb
fuel mixture screws at 2.5 turns out.

So,
Check a parts diagram online and make
sure your carbs have all the necessary
o-rings and check the throttle cable
slack and check the intake for air/vacuum leaks.
Get all carbs so they open at the same time
and pull the same vacuum.
this is called synchronization.
You can look that up online.

Good luck!
Wayne S.
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