Hitchcocks Forum

To my surprise i drained the carb/pipes into an opened container and left it outside in the garage.After 10 days 50% had evaporated and looked like a gel was forming,true enough after another 7 days with around 25% left and more gel it looked a bit frightening. The moral of the story is use a fuel stabiliser for the winter lay up or completely drain tank/carb.

No. If you are laying it up for the winter draining the tank will encourage the formation of rust. Fill the tank to the brim and tightly fit the cap. No eveaporation will occur and so no "gel" or whatever will form. Do however turn off the tap and run the carb until dry, and then do a manual drain to remove the last few drops. Better still use the thing all year round after all it is a motor cycle not a horse that needs to keep warm and dry.

What about the water trap in the very bottom of the tank? How can you fit the cap tightly when it breathes?

Hi jaffa90



I understand your thinking on this but Mike is absolutely correct, leaving the tank full will stop any rust forming in the tank, to get rust you need two things water and oxygen, with a full tank even if a bit of water is at the bottom it wont cause rust without the oxygen present, the small vent will not allow the petrol to evaporate enough to cause any problem.

Plus 1 when it comes to riding al year round... although I ain't exactly looking forward to the ride home tonight, it's certainly preferable to being crammed in an London underground train at rush hour (with very miserable commuters), even at this temperature!

jaffa, what water trapped in the bottom of the tank? There will be no water trapped in the bottom of the tank. If you had water in the bottom of the tank then every time you turned on the tap(s) it would drain into the carb. That would be a problem as water does not have any tendency to ignite in an internal combustion engine. If however you really meant a "water trap" in the bottom of you tank then I would have to ask....what water trap? There isn't one as petrol tanks are not meant to carry water. Breather hole in the cap.......for goodness sake nothing will evaporate through there, but if you think it will, then simply seal the hole with some tape for the time it is out of use. Frankly despite my advice, I never empty my carbs. I keep the tanks filled and I use my bikes as often as I can all year round......and that is not as often as I would like. HTH.

I use my BMW R100RT all year round and I find I get a regular build up of water/petrol emulsion in the bottom of the tank. The BM taps are multi function, that is, off/main/reserve. The problem only shows up on reserve when you've drained down far enough to get to the "soup" which settles to the bottom. The bike starts to run rough and you need to fill up with fresh stuff asap if you want to carry on as once the level gets well down into the emulsion the engine just dies. I usually drain it off about every 18 months (am doing it now, as it happens,) and it's vile stuff. This time I notice it's corroded the alloy of the taps too, and partly bunged the filters as a result! I've replaced the tank cap seals but it made no difference, I think it's condensation that builds up in a part full tank that does it. I even had to be recovered by the RAC once as the battery went flat trying to ignite the stuff. I ended up with about a gallon of the stuff last time so I thought I'd try an experiment and put it in the magneto sparked Bullet Trials. Fired up good as gold. Electronic ignition on the BM? No chance. Progress eh?! REgards, Mark

I understand oxydation, also water contains oxygen as in the O in H2O,also petrol can contain up to 2.5% oxygen which helps that water in the trap to perforate the tank as in my 5 year old XJ900 years ago.Also a reserve tap will not get rid of all in the tank.Fair enough condensation has less oxygen in it.As you know Ethanol (up to 5%) is causing problems with old fibreglass tanks and metal tank sealants and fuel lines.I wish i could ride all year round like i used to in the 70s but my arthritis & circulation tells me different.

Oxygen in H2O is part of a compond comprising 2 parts Hydrogen and one part Oxygen. It is not possible for the oxygen to be released from H2O. The fact is that as a constituent part of water it remains so. The great challenge faced by scietist is the extraction of Hydrogen from water in order to make Hydrogen fuel cells to produce an alternative to carbon based fuels. If and when this is commercially available the oxygen will be released to atmosphere, the very thing it cannot do from water, even during evaporation. Similarly Oxygen as part of petrol is also a compound and so the same situation occurs as with water. There may be fuel left in the tank even after running dry from the reserve tap......but why would you do that. It would merely expose the maximum internal surface of the tank to atmosphere and thus increase the risk of oxidisation of the surface. A perforated steel tank wis more likey to be the result of weld failure than oxidisation unless you create the conditions I have described to create an oxidised surface. You say "Condensation has less water in it". This is nonsense. Condensation is 100% water unless you condense other fluids at the same time. Evaporation and condensation are 2 different processes. Ethanol has caused problems on some machines, but in my experience mostly on those with so called sealant gloop in them. My bikes have tanks of steel, fibre glass and aluminium, with fuel lines made from copper, polythene piping (from my local aquatics centre) and black synthetic material The tanks injectors and carbs are on machines made on several continents and none suffer the E problem. Consider this, I keep my tanks filled and I do not have gloop in any of them. Sorry the posting is so long winded.

Not long winded at all,apart from the condensation bit about water/oxygen content.Just remembered my first pinhole leakage on a GN400 in the same place as the XJ900 inbetween the fuel tap and the seat,both away from any weld or seams which i call a water trap.