QuestionQUESTION: I have a 1979 honda cb650 and I recently pulled the plug on my crankcase
breather, and a fair amount of gas came out. I am running my bike at about
5000 ft above sea level and haven't had a chance to re-jet it yet. Could too rich
of a mixture cause gas to be pulled into the crankcase breather. Thanks
ANSWER: Jonathan,
If your air filter is plugged
or the cover is being sucked in
it might restrict air flow
through the air box. This
might cause the engine to
suck more fuel or excess vapors
in through the oil breather.
Check your air filter and
the cover for weakness.
----
Do you mean the crankcase breather
tube from the head to the air box?
Or are you talking about something
else, like the oil strainer in the
crankcase? Either way it may be
an accumulation of engine vapors
over time or a leaking carb float
valve which would cause running
problems. Is the air box wet with fuel?
A rich mixture would not likely be enough
to saturate the crankcase.
Have you changed the oil? You should
do that and let me know what breather part
we are talking about. Look here:
http://cosky0.tripod.com/id3.html
---------- FOLLOW-UP ----------
QUESTION: So this is going to be a long explanation, but hopefully it will help you answer
my question. So the actually tube that I drained was the one that is found
right by the muffler on right side of the bike if you were sitting on it. The
airbox did indeed have fuel in it. I have been messing around with
everything lately to see if I can get it running correctly. I noticed if i put tape
over part of the air intake the engine idles better, and revs more redily. When
the tape is removed and i turn the throttle, I hear a kind of hissing noise
from the carburetor, but it sounds like it is inside the carb, not air flowing
into the boots. Then if i hit the throttle really hard the engine actually loses
revs, and eventually dies. I have the idle screws set at slightly more open
(2.75 turns) than recommended, and the bike seems to idle well. After the
engine warms up, and the choke is in, is when the problem is most apparent.
It seems like I am running a lean mixture, but the exhaust still stinks of
unburned fuel.
Sorry for the length description, but hopefully I will be able to get this bike
rideable soon.
Jonathan
AnswerJonathan,
that breather is connected to a little
liquid collection tank so it does
collect some fuel over time.
Have you had the idle and main jets
cleaned on the carbs?
If not you might want to fill
the carb float bowls with yamaha or other carb cleaner
and let it sit overnight.
It does sound lean. The needle jet
under the main jet may be plugged,
these have many tiny holes in them.
Fuel does not burn fully when lean,
this might be why you smell unburnt fuel.
Also make sure the fuel supply to the carbs
from the gas tank is good.
Do all the pipes feel warm when it runs a few
seconds? Any feel cool?
The carbs may have sticky slides
reach in the back of the carbs
and see if the slides lift up
and down ok. This may apply
more if they are vacuum slides.
Check this color chart to see what
your fuel mixture is doing in the engine:
http://verrill.com/moto/sellingguide/sparkplugs/plugcolorchart.htm
The air-cutoff valve diaphragms
may be shot. It is under a little
cap on the side of the carbs.
You should see it on the outside
of the far left carb. The rubber
part inside should not have holes in it.
These usually make the fuel temporarily richer
when decellerating to prevent backfire.
It may need the air box, filter etc.
attached to run properly.
Some bikes run terrible with these parts
off. The whole air and emission
system are designed to work together.
Make sure rubber carb boots are not cracked.
You can rub high temp silicon into them
to seal cracks. Any air leaks will
lean out the fuel mixture.
If the carbs are clean and set and it
runs bad, see if the spark is good
on all the plugs.
