Gas spewing from carb drain tubes

I ride a 1981 honda cb900c. Love the bike, but the other day i had
some starting difficulties. The problem was the choke cable had slid
down and popped out. Anyways, i fixed this, but to see what it was i
had to remove the carburetor. Now i put everything back together and
voila it starts up, but spews gas all over my garage floor... dad was
happy about the smell.

So i've done some research on this problem and it sounds like i did
something to my float valves. What did i do and how do i undo it?

 

Maybe there was some debris in the passages or lines and it fell into
the openings and made the floats stick open or maybe they were already
somewhat sticky with gum. It might clear by tapping them with a
screwdriver handle or if you're energetic enough by bouncing the whole
bike from the rear of the seat.

Another mistake I make all the time is draining the carbs before I take
them off and then forgetting to tighten the drain screws, that has
similar effect.

 

If the other thoughts don't work right away, I'd just get it outside,
stub my cigarette and then look closely to see where the leak starts,
maybe the hose is leaking at the petcock or above the carbs (I know you
mentioned only one carb but I presume you have four of them) where the
fuel line splits.

 

I suppose there may be carburetors in which you can install the floats
upside down...

If you have to remove the carbs to check the float level, there will
be a tiny wear mark on the tab that pushes the float valve closed.

If you've somehow installed your floats upside down, you'll see that
little wear market facing you...

 

eg., if three carbs are sucking and one has a loose connection, it might
not be a stuck float at all.

 

You've got a stuck float. Unless you actually pulled the carb apart you
didn't do anything. It just happens, especially on older Hondas.

Recommended fix: pull the carb bank, invert, remove float bowl from
offending carb, remove float pin and float, check for wear on pin,
replace with new pin if necessary, reasseble.

Quick & easy fix: locate offending carb, and give float bowl a sharp tap
with (for example) the wooden shaft of a hammer. Frequently this just
frees the float off.

 

checked it out and gas is leaking from all four drain tubes. i turned
the drain screws all the way around the opposite direction, but that
didnt change anything. ill take the carb off and try to post some pics
tonight.

 

The float bowl drain screws are not a two-position affair, you have to
tighten them all the way to stop gasoline from leaking out the four
drain tubes.

The float bowl drain screws just have a cone shape on the end which
stops gasoline from leaking out when you tighten them all the way
clockwise.

But there is a little rubber o-ring on each screw which may have
perished from age, they are at least 29 years old, yannow.

The o-rings are part of a gasket set that you probably don't want to
buy at the price. You can get new o-rings for a few cents each at a
good hardware store.

http://www.bikebandit.com/assets/schematics/Honda/H00840036.gif

1: GASKET SET 216212-001 $39.56

13,14,18,19 TUBE, FUEL are the float bowl drain tubes

The float bowl drain screws come with the float bowl. If the conical
ends of the
float bowl drain screws are all pitted and corroded, you can chuck the
screw in an electric drill and hold the conical end against a piece of
sandpaper or a whetstone, turn on the drill and manufacture a new
conical end the isn't pitted.

If the floats are stuck, gasoline will come up through the float bowl
air vents.

Most carbs I've worked on have an air vent for each float bowl or, in
the case of four cylinder engines, one float bowl vent between each
pair of carbs.

Your carburetors only seem to have one float bowl air vent though:

http://www.bikebandit.com/assets/schematics/Honda/H00840034.gif

19: TUBE 224256-001 $6.04

 

Still puzzles me that only one 'carb' is mentioned. Also, I find it
hard to believe that all four drain tubes are leaking unless all four
drain screws are open. Seems unlikely that four separate float needles
would suddenly be blocked or stuck unless the carbs had been
dis-assembled and put back together wrong whereas the original post said
they were only removed. Also if the drain screws are turned all the way
out (counterclockwise), I'm pretty sure they will fall off! I wonder if
the above is talking about tubes above the carbs and screws not on the
float bowl.

 

I think the simplest solution is probably the most accurate. You haven't
tightened up the drain screws properly.

Krusty's right when he says O-rings deteriorate with age, but for all
four to go at the same time? Nah.

 

ok yes to clarify there are four carbs. i suppose i should have called
'it' the carburetor assembly? im new to this... anyways i definitely
didnt take them apart, only removed because my choke cable got loose
and was sort of dangling and the bike wouldnt start. being so new to
this, im a little wary about popping open my float bowls and fiddling
around. All my o rings should be new because (allthough its an 81) the
engine was recently rebuilt. The 'carburetor assembly' is very clean
and looks brand new. The guy i bought it from said essentially the
whole bike was new accept for the frame, the tank, and the instrument
cluster. might have been bs but nothing on it LOOKS thirty years old.
ok so is the new consensus that the drain screws all came out some
during the carb assembly removal and just need to be tightened? that
seems about as likely as something getting inside all of them and
blocking the needles... ill get out a digital camera and get some pics
on here.

p.s. i feel silly for thinking the drain screws were like an on/off
switch. i've been looking at carburetor assembly diagrams for days now
and they are clearly screws... sigh, chalk it up to inexperience! haha

 

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Can't get the photos to load for some reason, but the most likely
explanation is still that someone - not you, then - didn't tighten up
the screws before refitting the carbs. Just tighten them up. Caution -
nip them up carefully, because it's quite easy to strip the threads in
the float bowls.

Oh, and whichever forgetful sod forgot to tighten them up probably
forgot to tighten the choke cable assembly too. I wonder what else he
forgot?

 

Nice snaps, from the appearance of the screws (no gouging that I can
see), it looks like somebody was careful.

On the #2 carb, I see a hose is missing from what looks to be an
accelerator pump.

 

Did the 900C have accelerator pump carbs? Paging Mr Olson.

 

Sorry, I may have used the wrong name, meant the gizmo (is is
deceleration pump) that reduces backfiring when the throttle is closed
at speed.

 

6: DIAPHRAGM SET, PUMP 217860-001 $69.41

 

thanks, that's the name I was looking for.

 

Friend's CB750 is long gone, air cutoff on all four makes sense, just
trying to remember why the accelerator pump (which I think was what was
pictured) was only on one carb. Mark?

 

One pump is plenty to meet the requirement for extra fuel during low
vacuum conditions.

If you study the carburetor drawings, you'll see that there are rubber
tubes connecting all four carbs together. The accelerator pump output
goes to those tubes so all four carbs get a squirt of fuel when the
throttle is opened but engine vacuum is too low to suck fuel through
the idle ports and the needle jet.