Questionsir please help me.
i am lost. i recently bought this motorcycle and have been trying to get it run right for the past months.
the problem is that i can get the bike to turn on and stay on but in order to turn it on, i need to have choke all the way open while having the throttle wide open. the bike will idle at 4000 plus rpms. after it warms up, i can close the choke and it will idle at 2500 rpm - sounds high while idling. if i try to bring the idle down to atlease 1500 it dies. i then have to start it back up while hold throttle wide open.
i have cleaned the carbs two times, synced the carbs, searched for vacuum leaks, checked ignition spark, replaced spark plugs and just to be sure, swapped coils. i have all screws adjusted all the way in (i know this would make the bike run lean) but for some reason i do not feel,hear or see a diffrence if i have them out 2 - 2 1/2 turns. two things that throw me off; carburator number four(far left hand side), when i unplug wire off spark plug , bike does not really react in the same way the other 3 do. when i unplug one of the other 3, the bike dies. if i unplug that number 4, bike keeps running like nothing, barley notice a change. like i said. i swapped coils and wires to see if anything changed but nothing changed. also this spark plug seems to look darker than the others. i know its alot of reading but i appriciate any help you can give me, thank you.
AnswerHello Luno,
Since you are having so much trouble with
this bike I suggest you approach the
problem as if you were starting anew.
Often a problem is overlooked because
you may have thought it was already checked
out or dealt with.
First thing you need to get a good running
bike is reasonable cylinder compression.
Beg, buy or borrow a compression
gauge or get a bike shop
to check the compression on all the
cylinders.
If that one cylinder is bad then the
bike is never going to run well.
You have to check the cylinder that seems
weak and get it fixed.
Check it for compression, spark and fuel.
When all the pipes heat up at the same
rate then you can start tuning.
The VF500 uses a fuel pump so that
and the lower fuel tank have to
be checked out. The tank can be rusty
and the pump may not be working.
Also there is a fuel filter to check.
If the pump is no good any electric
pump will work like a 4 psi auto pump
or a VF750 fuel pump.
Once the pump is working then
you have to make sure the small
holes in the carbs center needle jets
are clean. Remove the center jets
and clean them by hand.
The best thing is to get Yamaha brand
carb cleaner and soak the carbs in it
for a few hours and blow out all the
passageways.
Check the carb slide rubber diaphragms
for holes. Check the intake rubber
tubes for hairline cracks that might
leak air into the engine.
A lean fuel mixture will make a bike
idle high speeds.
This is not enough fuel or too much air
leaking into the intake area in front
of the carbs.
Even a fuel petcock with a leaking rubber
diaphragm can allow the engine
to draw in excess fuel or possibly
air on the vacuum hose.
So to sum up,
Check the compression
Check fuel petcock, tank and fuel pump/filter.
Soak carbs in (safe) yamaha carb cleaner.
Clean jets by hand and examine carefully.
Check carb intake rubber for cracks.
If you feel you have covered most of this
thoroughly then check the compression
and the fuel pump for problems.
If the pump is not working your carbs
may be running low on fuel as indicated
by the need for the choke.
Good luck!
Wayne S.
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