QuestionI just bought a honda cb650 and it starts up and runs ok after about 10
minutes of warming up. The problem is that the engine will not idle very well
below about 2500 RPM, and when I try to accelerate, the engine bogs until
about 400 RPM and then it just takes off. I can't even start rolling without the
engine revving above 3500 RPM. I have cleaned the carbs of varnish. I was
told that it might be a vacuum leak, and if that is what you think it is, could
you recommend a good place to pick up the parts needed to make the
repairs? thanks for the help
AnswerJonathan,
-these bikes tend to have some bogging but
usually not that severe.
-Has the bike been modified at all?
If the stock air box is gone or the pipes
changed it may need bigger carb jets.
Try turning the idle mixture screws 2.5
turns out, see if it helps.
-check the choke operation.
-Were the idle jets cleaned out physically
well? They are small and need to be checked
very carefully or replaced.
-air leaks would be around the tubes where
the carbs attach. Sometimes spraying
some wd40 or such around the intake
will make the engine speed change, this
indicates an air leak. May need
new rubber there.
-any place there is a vacuum hose or
fitting could leak.
-make sure the carb slides are not sticking.
-get the carbs synchronized, this
can get the cylinders all pulling together
at the same time. Really helps sometimes.
-check under the ignition pulser coils,
there may be a mechanical advance unit,
these may get sticky also.
-make sure all the pipes are warming up
just in case one is misfiring.Don't burn yourself.
-replace spark plugs, check plug caps
for 5000 ohms resistance or less.
-check air filter(s)
-valve clearance should be .002"intake and .003"exhaust.
-your plug color can tell you how the bike is
running: rich=black plugs, lean=light colored plugs,
brown or tan color=good fuel mixture.
-if all else fails or maybe do this first,
check that the compression is around 150 psi
or higher. Get a leak-down test done
to check engine condition.
