How do I measure carb fuel level from outside?

1983 Shadow VT-500C

How do you check the fuel level in the carb
without taking it off?
I wasn't able to get a good pix of the fuel,
so I'll have to describe it.
Here's a pix of the carb:

http://nm7u.tripod.com/homepage/carb.html

Note the black cross with center near the mating
line of the bottom piece.
Imagine a plastic tube hooked to the bowl
drain and running up the vertical black line.
the fuel level rises to the level inside the carb.
This level is represented by the horizontal black line.

So, now I know the level of fuel in the carb.
But what should it be? Is there a known outside
reference point that can be checked against?

It's a real pain to take 'em off to check the inside
measurement. And 20 year old plastic floats bend and warp
and absorb fuel, so I'm not completely comfortable that
the recommended measurement point is reliable.
Measuring the actual level from the outside should
be accurate.

Is there a reference point outside the carb?

Thanks, mike

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Get a clear piece of tubing about 8-12" long that you can fit inside the
screw hole in the bottom of your float bowl (Float Bowl drain). The
tube needs to be big enough to seal the hole when you shove it inside.

Shut off your fuel feeding the carb. Take the screw out of the hole.
Let it drain out to empty. Put the tube into the hole. Raise the end
of the tube so that the top of the tube is above the carb. Get a magic
marker and mark a line at the top of the float bowl seam and the carb body.

Release the fuel petcock and let the fuel fill the float bowl. The fuel
will also fill the clear tube. Mark where the fuel stops in the tube
with your magic marker. If you have done it right, measure the
difference between the two marks. You should have amount your bowl is
filling from the top of the bowl. The distance should be in your
service manual. Too much check your float or bend the float tab to make
it shut the needle valve sooner, check the bottom of the needle valve to
make sure it is sealing.

To do that, turn the carb upside down and put about 10psi suction on the
fuel feed. If it leaks air, replace the needle valve.

Too little bend float tab the other way. Your service manual should
outline the specifics for your bike.

Hope this helps.

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"Happy Hour" starts one twist of the throttle past neutral!
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Thanks for the response. I understand about the plastic tube...done
that. Fuel level in the tube is easy.
I don't understand about the other mark relative to the carburetor.
Notice from the picture that the bottom cover to carb seam
is not horizontal.
http://nm7u.tripod.com/homepage/carb.jpg
The distance specified in the manual is perpendicular to the carb body,
not the angled position of the fuel when it's mounted.
Even if it were perpendicular, the distance is for the float bottom.
The float must "sink" in the fuel enough to displace enough fuel
to support it's own weight plus the weight of the float valve.

What am I missing?
mike

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If it were me, I think I'd try to get new floats before I
wasted any time fighting with the old ones.

 

Not sure about your bike, but in my shop manual, the measurement they
give is for the fuel level, not for the float bottom. Having the carb
tilted adds a wrinkle, but the principle is the same: the fuel level has
to be high enough for the pick-up tube to get enough fuel at full
throttle, but not so high as to overflow into the manifolds.

I'm finding your explanation a little hard to follow--can you give us
the exact wording from your manual? If the distance measurement is truly
perpendicular to the carb body/float bowl seam, then you need to get out
the protractor, and just make a mark on the carb.

As well, my manual specifies checking with the bike running, as the
level goes down a bit then.

Are you sure the levels are wrong? I've read that 'Carburetor is a
French word for "Leave it alone".'

 

Not sure about your bike, but in my shop manual, the measurement they
give is for the fuel level, not for the float bottom. Having the carb
tilted adds a wrinkle, but the principle is the same: the fuel level has
to be high enough for the pick-up tube to get enough fuel at full
throttle, but not so high as to overflow into the manifolds.

I'm finding your explanation a little hard to follow--can you give us
the exact wording from your manual? If the distance measurement is truly
perpendicular to the carb body/float bowl seam, then you need to get out
the protractor, and just make a mark on the carb.[/QUOTE]

A picture is worth a zillion words
http://nm7u.tripod.com/homepage/carb2.jpg
Since they don't specify an angle or a position along the width of the
carb, perpendicular is the only direction that makes any sense.
I only have experience with a dozen bikes or so, and the dimension has
always been perpendicular.

Yes, it is possible to take it all apart, measure all the parts, do some
geometry, weigh the parts, calculate the displacement required to
support them and come up with a fuel level in the carb.

I was hoping there was an answer already out there is cyberspace.

This is just an aside. I have no idea if this is my problem. I posted
the whole shaggy dog story under the thread about floppy vacuum
cylinders. No suggestions so far.

And that's exactly why I'm asking before I mess with it.

Bottom line is that the Shadow has what sounds like fuel
problems and I don't know how to fix it. Swapping out the carbs
and whole fuel delivery system didn't fix it.
mike

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This is really the only way to set float levels, and this is the only
mesurement you will find.
You simply must remove the carb to do this, there's no other effective way
to set the float levels.
Unless you've replaced the float valve or the floats themselves it's
unlikely they need adjustments.
B

 

A picture is worth a zillion words
http://nm7u.tripod.com/homepage/carb2.jpg
Since they don't specify an angle or a position along the width of the
carb, perpendicular is the only direction that makes any sense.
I only have experience with a dozen bikes or so, and the dimension has
always been perpendicular.[/QUOTE]

Yeah, it looks like they are specifying a dry level, with the carbs out,
and their special tool. Haven't done one of these, although I've seen it
in various manuals. I tend to agree with Battleaxe--the level is
probably not out, unless the needle valve seat is worn.

I saw that. The symptoms were so varied, it was hard to think of a
simple cause.

This would tend to rule out the carbs as the problem, no? You've checked
the coils, high tension leads, etc.? I had a snowmobile that started
running weirdly, and it turned out to be a coil that was failing and
affected by temperature.