83 Honda Shadow, again

Ok, I need to know if this is part of the problem. I have already
checked the fuel pump, seems to have adequate output. However, I
replaced the factory fuel filter (inline, before the pump) with one from
the local bike shop, but it is a generic, clear fuel filter, not factory
spec. It only has fuel in the bottom third of the filter. What is
level of fuel should be visible in the filter?

Symptoms: I'm trying to adjust my carbs. However, I can't get
consistent idle. It will idle for a while, then crash on me. I keep
having to adjust the throttle, since I seem to get runup in RPM when I
adjust the master idle screw. Am I not getting enough fuel to allow me
to adjust the idle, and therefore the carbs?

 

Clear plastic fuel hoses and clear plastic fuel filters are often only
part filled with gasoline, making the amateur mechanic wonder whether
there's a vapor lock, or what the heck is going on.

You don't want any loops in the fuel lines where you can have bubbles
form, and the filter should be below the fuel lines and the petcock.
You might want to disconnect the lowest end of the fuel line and blow
backwards with the gas cap off. If there is crud in the bottom of the
gas tank it may blow backwards out of the petcock into the gas tank.

Then when you allow gasoline to flow back through the filter again, it
may fill up, and after some running of the engine, that damned air
bubble will restablish itself! The problem could be crud in the petcock
again, or a vapor lock in the fuel line and filter...

Well, if you can't get the air bubble out of the filter, you can try
the old plastic hose trick to see what the fuel level is inside the
float bowl while the engine is running...

Just remove the float bowl drain hose from the spigot on the bottom of
the float bowl and stick about 6 inches of clear plastic aquarium
tubing on the spigot. Open up the float bowl drain screw and hold the
open end of the aquarium tubing up by the float bowl gasket area. The
fuel level should be withing about a millimeter of that gasket and
should stay there as the engine idles and the fuel pump keeps replacing
the fuel that's been burned...

 

thanks again for the help. I've taken the spark plugs out tonight, and
they were pretty carbon fouled after a very short time. Dry, black
coating. I cleaned them off, seemed to dispel the problem with the
engine falling out on me while trying to tune the carbs. Like I said
before, I'll get better plugs next paycheck.

I actually made progress, started about 1.5 turns out, ended around 2.25
to 2.5 turns out. Don't think I'm quite there, but it was getting late.
When I rev the throttle quickly, it seems like it is stalling out, but
when turned slowly, it revs just fine. I'm doing all this from
sound/smell, since I don't have a good tach or any fancy tools. But
like you've posted before, I'm trying to learn to do it the right way,
not just the "procedural" way.

Likely, I'll start again tomorrow from scratch, now that I have some
idea what I am looking for.

As far as the gas tank, I've pulled the main tank and cleaned it, but
the secondary tank hasn't been pulled. I'm sure it has some build up in
it, but it is not as easy to pull off as the main tank. To the
outsiders, yes, it has two separate tanks.

 

krusty kritter wrote:
snip

Could you be a little more specific on this technique. The gasket line
is about 45 degrees off horizontal on my 83 VT-500C Shadow.
How can we tell where on the gasket to make the measurement?

For making the relative measurement, you can use a much longer tube
taped to the gas tank and a big paper clamp on the end.
You can go down the road at speed, open the clamp to let the level
stabilize in the tubing, close the clamp, then stop to safely
read what the level was at speed.
Thanks, mike



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My Haynes manual shows how measure the fuel level with carbs mounted at
a 45 degree angle. It seems that there is a reference line molded into
the bottom of the float bowl on Mikuni semi-downdraft carburetors, so
the fuel level can be checked with the $pecial Expen$ive Yamaha $ervice
tool.

The tool is essentially a piece of flexible clear plastic tubing but it
has another piece of clear tubing in the end that's calibrated in
millimeters...