Flooding Problems

I have a 2000 suzuki katana gsx750f and it is having some
trouble. It floods...a lot. So, at first I thought carbs...but now
I'm not so sure. I think it may be the vacuum actuated fuel valve or
possible the tank vent. So, I'll tell you all what I did to
investigate and all advice is appreciated.
I started by removing the tank. When the fuel line was
disconnected, gas sprayed (with decent pressure) out of the main fuel
line. Shouldn't the valve have prevented this? I think the tank may
be over pressurizing and forcing fuel past the shut-off valve. It is
supposed to be actuated by carb vacuum, so I figure the spring is
pretty weak and an over pressurized tank would fairly easily get by
this valve. Is this a correct assumption? Once I opened the gas cap
to relieve the pressure, the valve stopped the flow of fuel on its
own.
Next, I removed the airbox after draining the fuel out of it
(severe flooding). Then, With the carbs exposed, I tried a trick i
read about here. i hooked a little piece of fuel line to each of the
drain nipples on the four float bowls, pointed the hose up and opened
the drain valve to check the float levels. They all looked pretty
even. I kept fuel in the line from the tank to ensure that a bad
float would show here. It didn't as far as I can tell. So, I pulled
the carbs, set them on the work bench at approximately the same angle
and let them sit, with fuel in the fuel rail, to see if any of the
carbs was leaking gas somewhere. I didn't see any.
Next I removed the plugs, and eureka! plug 2 was darker than the
rest, so i assume this is the flooding cylinder, as the plug was
brown. So, I know which cylinder, but now why. Checked the carbs
again, still no gas leaking out.
Here is my theory, and please tell me what you think. I think the
gas tank is overpressurizing. The gas cap threaded and comes out
pretty hard sometimes. I think that this over pressure is forcing
fuel past the fuel valve and past a float valve, flooding the
cylinders and airbox. Is this possible? How much pressure should be
on the tank? How do i check it? Is the vent supposed to regulate
pressure? I am hoping to avoid taking the carbs into a shop due to
the expense. I would like to investigate all other possible causes
first. Thanks for everyone's help!

 

2000 Suzuki katana gsx750f wrote:
..

Yes it should have. The tank is supposed to be an open system, through
the gas cap and runs at atmospheric pressure. It is not pressurized.
When the petcock has a reduced pressure on it from the engine running it
allows the valve to open and gas to come out. If your gas comes out
when the engine is not running, and the petcock is not in the prime
position then it needs a new diaphragm in it. BUT even if the petcock is
leaking the float valves should cut the fuel off in each carb so if you
are flooding then the floats are bad, the height is wrong or they are
not shutting off. When you were checking float levels on the workbench
the carbs need to be in exactly the same orientation as they are on the
bike to see what the problem is.

Ian Singer

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The previous owner put in an aftermarket fuel cap that doesn't allow
pressure out. Do I need an OEM cap or something? There is a vent
tube on the bottom of the fuel tank, is the pressure a sign that this
is plugged?

Even if the pressure was too high. Is it possible that the diaphragm
is OK, but the pressure is causing the malfunction?

Again, could the pressure cause this? It isn't intended to be a
pressurized system.

I checked the levels on the bike first and they seemed OK. I don't
think they have ever been tweaked.

 

2000 Suzuki katana gsx750f wrote:
I have no experience with your bike or anything that new so hope I am
not getting in over my head

On the older bikes I have seen that "vent" is actually a drain in case
the gasket by the fuel level float leaks.

I suppose if it is pressurized you would have a problem, but how is it
getting pressurized besides from evaporation sitting in the sun?
Any pressure will force gas past the float valves and totally mess
everything up.

Ian Singer


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You can't leave us hanging like that....everyone will give you hell for
being short winded.

Ian Singer



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I'm not sure, How do I check?

I don't think so, but it's very possible

Where is the canister drain tube?

Is all this inside the tank? Do I need to take the fill cap off and
pull this hardware out? Is a new charcoal canister needed or can i
drain the existing one?

So, The water separator hose is all by itself on the right side of the
tank and drains straight to the ground. I thought this was a vent
hose.

I think maybe the evaporative control hose is the one shown next to
the number 1 on the fuel cock schematic.

http://houseofmotorcycles.bikebandi...id~987331~model_dept_name~GSX750FY+KATANA.asp

It goes from there directly to the carb throat. I didn't have this
part hooked up wrong, so a flooded canister sounds likely. I thought
this was some kind of a vacuum line that actuated the fuel valve.
Guess that was waaaay wrong. Thanks for the education.

Sorry about your tank, thanks for saving mine.

I'll pull the tank apart tonight and let you know what I find out.

 

Did you miss his comment about having a non-oem fuel cap?
My bet is that is the problem.
Along with one or more fouled plugs.

Others have figured out how to ride (presumably safely) with the cap loose
or off. Maybe the OP can too!

Isn't the evap. canister only present on California models?
If so, wouldn't it have been MUCH easier to just ask if the bike was
originally sold in Calif. ???

Oops, sorry, I forgot that you have this need to "baffle us with your
brilliance". ;-)

 

Albrecht and Ken,
Thanks for your input. After further inspection of the bike, I do
not have a california model (i'm in Nebraska). I coudn't find the
charcoal cylinder... So, is it the gas cap? yea, I could ride with
it loose, but is a vented cap that much of an expense? Where is a
good place to buy a lockable vented gas cap for this bike? I'm going
to put it all back together tomorrow and see if a loose cap fixes the
problem. Wow, I have had it in the4 garage for almost a month waiting
for the time to fix it...a tight gas cap would be a real kick in the
nuts for all the good weather that I've wasted.

Thanks again,

Tim

 

Well if the cap is not vented then air will not get in and gas will not
come out. Opposite of what your problem is. Sounds to me like your
petcock is in the reserve position, or it is leaking.

ebay of course. Don't forget though that you will also end up using two
keys unless you also replace the ignition and helmet lock ones as a set.
Locksmith might be able to rekey for you.

Ian Singer
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You missed the original post?

Recap:

2000 Suzuki katana gsx750f wrote:

I started by removing the tank. When the fuel line was
disconnected, gas sprayed (with decent pressure) out of the main fuel
line. Shouldn't the valve have prevented this? I think the tank may
be over pressurizing and forcing fuel past the shut-off valve. It is
supposed to be actuated by carb vacuum, so I figure the spring is
pretty weak and an over pressurized tank would fairly easily get by
this valve. Is this a correct assumption? Once I opened the gas cap
to relieve the pressure, the valve stopped the flow of fuel on its
own.
[End quote]

As for a new cap, I would certainly try to get an OEM one from the
dealer.........unless you want to mess around searching for two weeks just
to save a couple of $$$.

 

No I did not miss the original post. So as you are assuming I
misunderstood the question how does having a non vented cap cause the
fuel to spray out the main fuel line? It doesn't unless the petcock is
non functional and in that case it would also stop when it started
decreasing pressure in the tank.

Ian Singer

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=========================================================================
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I am near Toronto Canada, can I tell where you are from your reply?
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how does having a non vented cap cause the

First, from my understanding, given time to build, the vapor pressure
of Gasoline can be prettysignificant, not that it needs to be for a
fuel system. I think the non-vented cap is allowing the pressure to
build. I think Ian is refering to the vacuum caused by the evacuating
fuel. However, then the fuel wouldn't stop with the cap off, and it
did. I should have mentioned more clearly that the fuel stopped
spraying when the cap (and the pressure) was removed.

Follow up question:
Severe Flooding + a week in the garage = flooded cylinder heads
Flooded cylinder heads + another week= empty cylinders and flooded
crank case

I'm going to change the oil and filter, new plugs, cap full of oil in
the spark plug holes as reccommended. Is there something I've
overlooked? Oh...and a new gas cap perhaps.

Thanks guys.

 

Is that not what he said?

That IS what he said, isn't it?
What am I missing here?
Seems simple to me. He SAID there was (substantial) pressure IN the tank.
There should NOT be. I "think" the only possible cause for this, on a
carburated bike without Calif. emissions and with gravity flow fuel delivery
IS an improperly vented tank (CAP).
Again, what am I missing?

 

Oh...and a new gas cap perhaps.
Ya think? ;-)