Welcome to Netrider ... Connecting Riders!

Interested in talking motorbikes with a terrific community of riders?
Signup (it's quick and free) to join the discussions and access the full suite of tools and information that Netrider has to offer.

Tank overflow/drain tube - GSX750F

Discussion in 'Maintenance and Servicing' started by Mr Flibble, Mar 23, 2016.

  1. 2005 GSX750F

    I've had it a couple of months, and it won't go over ~4000rpm without coughing and spluttering.

    Haven't really had a chance to look at it until today, was hoping for a simple fix like needing a new fuel filter and/or clean the air filter and/or change the plugs.

    Air filter looks pristine, fuel filter had a bit of gunge, but didn't look too bad (bought a new one anyway). But the weird thing is what the previous owner had done with the overflow drain pipe from the tank. The end of it was plugged!

    So I thought that this might be the issue, not allowing air into the tank?... So I pulled the plug out and water started pouring out! Fark!

    Put the tank back on to see if it made any difference. She started first go, but still seems a bit rough over 3000rpm. Bugger. Stopped the engine and then petrol started pouring out the overflow tube!

    Now as I understand it, the pipe this tube connects to must run up through the inside of the tank to the top of the filler? So this pipe must be cracked? But why would it only flow after stopping the engine?

    My google foo has failed me, I don't even know what the pipe/tube is actually called...
  2. Nup, the tube is connected to the tank. I couldn't disconnect it so I pulled it up through the guts of the bike. The plug was a homemade affair, the end of it was cut with a hacksaw.

    The airbox drain tube is indeed plugged with a plastic screwcap.
  3. #5 jstava, Mar 24, 2016
    Last edited: Mar 24, 2016
    The two tubes coming from the tank are normal on that bike.

    One is the breather tube - allows air into the tank behind fuel which has been used. It terminates at some location inside the tank cap seal.

    The other one is the water drain tube, which terminates in the cap recess - it allows water, from rain or washing to drain from the area around the filler cap, avoiding it pooling in this area and getting into the tank.

    Neither of these should be blocked, or plugged. If the water drain tube is plugged, the water won't drain from the filler tank area and it would be expected that if this tube was plugged, it would contain water which would drain from the tube when the plug is removed.

    A previous owner may have taken itself upon himself to block the tube, having noticed fuel exiting a tube after overfilling their tank - overflow in this case would be normal. Either of the tubes may provide an overflow function depending on the level to which the fuel has risen. This can happen when cold fuel is filled right to the top of the tank on a hot day, the bike sits in the sun and the fuel expands, reaching the breather opening or by being forced past the tank seal (where the breather tube may be blocked) into the recess drained by the drain tube.

    In your case, it is possible that you have now got water in your tank. This needs to be removed. It can be done with a syringe and a long piece of plastic tubing. Put it down into the bottom recesses of the tank and pull a sample to check. You want this water out, as it will rust your tank. You can get as much of it as you can by syringing it out ($15 syringe available at any Supercheap or similar auto store - they have other uses, worth having) Finish by putting in a half a cup of metho in a tank of fuel that you will use in a day - metho will mix with water and the fuel and "carry" the water out as the fuel is burned, alternatively, put a tankful of E10 through the bike. Assuming the E10 is not already carrying a load of water, this will also "dry" your tank. I personally prefer using Metho.

    This is routine maintenance stuff, however and beyond the point really.

    Symptoms as you describe point to a blocked strainer in the fuel pump. In the Suzuki, there is a fine strainer which has a reputation for blocking. Suzuki forum owners discuss this issue, and how to remedy it. The fuel pump on Suzukis is a wonderful bit of over engineering and solutions to the problem as you describe range from:

    1. pulling the tank, removing the fuel pump (from the underside of the tank) and using a fine brush (usually a bit of insulated wire, stripped back a few mm to expose the strands which then can be used as a brush to clean the offending screen. Note there are two - one is a strainer - pre-pump, and a filter post pump. The filter is the one prone to causing problems such as you describe. Where the pump is starting to wear, this filter (it's just a very fine screen) will catch the bits from the pump. Suzuki's fix is generally expensive (replace the entire pump assembly)

    2. finding an aftermarket fuel pump which meets the spec, but does not include the post-pump filter. - this is often the preferred option for Bandit Owners who get tired of pulling out the fuel pump to clean the screen. (I have a Bandit. The pump is not identical, but it does have a similar fine screen downstream of the pump)

    This topic is well discussed on Suzuki orientated forums where you will be able to find more information - Oh, it's worth looking at on-line parts stores parts list which can provide a handy reference to what things look like and are called. For a quick look, I use the MrCycles one.

    I have no explanation of why fuel would gush from the overflow when the bike stops - possibly an issue with the location of the breather pipe. This should not happen.

    I hope this helps.
    • Winner Winner x 3
  4. Thanks jstavajstava

    I'll certainly look at the petcock filter (no pump on the GSX750F)

    But what I think has happened is the water/fuel overflow pipe inside the tank has rusted through or is cracked.

    This would account for the fuel leaking. Why it only starts leaking after the engine has stopped is a mystery - perhaps there is a slight vacuum inside the tank while the engine is running?

    The previous owner's solution was to plug the tube. Brilliant. Stops the leak, but water can get into the tank via the cracked drain pipe inside the tank.

    Perhaps (and this is just a guess) the problem getting over 4000rpm is caused by water in the carbies?

    Would I need to drain the bowls?

    I think I've been sold a pup. No wonder it was so cheap :(
  5. I took a bit of a punt on the year. My bad. My response was based on an assumption that you had a fuel injected motor. Carburetion is a different thing.

    As for your hoses. Metal pipes or hoses inside the tank? Good question. My guess would be plastic hoses due to cost of manufacturing. It's simply easier to manufacture the tank shell and add hoses. I would confirm that they are both open by blowing gently from the bottom end. Wasps like to build nests in the end of hoses - that frequently causes them to block where a bike is left standing for lengths of time. Blow only gently, as you don't want to blow muddy debris, if it is there, up into the tank. You should be able to determine which hose does what. If you can block the top of the overflow with your finger, you then will be able to determine whether it is cracked along its length within the tank.
    • Agree Agree x 1
  6. In addition to the above (as a prior GSX750F owner) I would also drain the carby bowls (the middle ones are a bit of a pain to get to though.
    • Agree Agree x 1
  7. I believe they are metal pipes inside the tank.

    When I get a chance, I'll drain the (remaining) fuel out and give it a closer look

    This refers to a 2008 Kwaka 1400, but shows the same potential problem

    Strange leak from gas tank

    "Here is an inside look at the gas tank plumbing. The overflow for the filler cap is on the pipe on the left. Notice the rust deposits on it. I believe the pipes were not properly treated/coated at the factory. And ethanol gas certainly hasn't helped matters any." large.
  8. A mostly blocked vent tube with cracks in it below the level of the fuel in the tank might cause symptoms like you describe insofar as the fuel coming out of the pipe is concerned. When sitting or running, there is no leak, but when you stop the bike the heat from the engine warms the tank, the fuel and fuel vapour heats up, expanding, and forces fuel through cracks in the internal hose or pipe which then escapes past the partial blockage.

    A partial blockage in the vent would be enough to limit fuel available to the running engine, limiting revs. Another way of testing this would be to go for a ride with the fuel cap open or ajar. Not a good idea with a full tank of fuel. This could tell you (barring an issue with a blocked petcock screen) whether the problem limiting revs is related to the fuel supply as far as the supply to the carburettors.

    Another way to test your fuel supply is to disconnect the fuel hose to the carburettors at the carburettor end. Provide a container to catch the fuel and open the petcock. One would expect that with a full tank of fuel, that if the vent tube is clear that the fuel would simply run freely out the tube until the whole tank is empty - Jerry can required, maybe more than one, if you drain it all. You can test the petcock, the main outlet and reserve this way. If the vent tube is blocked, it will run, then stop and start to "chug" once the elasticity of the air above the fuel is exceeded and the only way for air to enter the tank is the fuel supply hose. Normally one would expect fuel to run from the supply hose, where the petcock screen (or the head of the intake tube) is blocked, the stream will be a dribble. It is not so unusual in older bikes that may have had water in the tank in the past for the intake tubes to carry some corrosion if they are made of alloy.
  9. Just to update:

    It was the spark plugs causing the rough running. Previous owner had put in 8's, manual specifies 8's if your trips are less than 20km or its bloody cold. 9's for normal use, 10's if you're a revhead. I put in a set of 9's, runs like a charm now.

    As to the tank, The petcock filter had a little bit of rust flake deposit on it, but not enough to cause fuel starvation. I put in a replacement tank so the overflow doesn't leak now. The previous fuel filter (don't know if it was oem or not) was shaped like a coin and slipped in between carbies 3 and 4, the replacement is longer and needs to be a lot closer to the petcock to fit. The fuel line was kinked a bit, but it appeared to me the fuel was flowing OK. Barrrrp!!!. Put some fuel in, and took her for a run. Once she was warmed up, I gave her a bit. Seemed to be running fine... Then cough, cough, cough ...dead. Fark. So the kink was letting enough through but only for ~3000rpm. Back to the drawing board. Tried Supercheap, Autopro, and finally Repco to get an 8mm angle piece. After a bit of faffing about, I got it to fit, but only by running a longer bit of fuel line on a loop. Turns out it would have worked better without the angle, as it is pushed right up against the fairing and causes another little kink although apparently not enough to affect flow.

    So, I've got a red bike with a grey tank which has a ding in it and doesn't seem to fit up against the fairings as well as the original tank, but it runs!
    • Like Like x 2
    • Winner Winner x 1