Fuel boiling

I was riding in the UK the last couple of days in wonderful weather. Beautiful roads, 30 °C and not a cloud in the sky. The only problem : The bike was running HOT. I mean superhot. Much hotter that I ever experienced in the last 14 years I owned this bike.

When riding uphill at 70mph in the 30°C heat, the engine started to cut out intermittedly. Heavy stuttering. The engine would alternate between full power and no power in maybe half a second. No exit in sight, so had to pull over on the emergency lane. The frame, the footpegs, the seat, but most importantly, both fuel tanks were superhot. Too hot to touch. Coolant temperature steady at 3 bars, fans switching on and off regularly. No warning lights on the instruments. My best guess was that the fuel was so hot, it must have been boiling in the injector gallery causing vaporlock.

I opened the fuel tank to let in some fresh air and to use evaporation as a cooling method. After 15 minutes or so, the bike started up fine again and ran fine for the remainder of the trip, even at higher ambient temperatures (up to 33°C). I added fresh cool fuel whenever the tank was half empty. The tank and frame continuously felt much hotter than I ever experienced before.

Can anybody think of a reason why the fuel itself could be heating up so much ? Maybe some kind of FPR, pump or injector failure that could increase the flow of fuel through the rails back into the tank ? Clearly something is different in the bike from before....

Sounds like you have a failing fuel pump, if you search you will find the problem gets worse in the heat. When you ride the ST in hot weather it is normal for the fuel to return back to the tank sounding like it is boiling.

Are you sure it was heat related and not fuel starvation? Is it possible that the fuel filter in the lower tank is becoming clogged and starving the engine for fuel? Or, maybe the fuel pump is starting to go bad? A lean engine will run hotter than normal.

Mine has done the same sort of thing today!! Running up the M1 motorway at speed and all was fine, then it started to pull back, like it was cutting out. More noticeable when trying to accelerate. I stopped and the bike ticked over fine, bike was hot but not too hot to touch. Temp showed usual 3 bars and no warning lights. I carried on slowly and the temperature went up by one Bar, which I have never seen before. I could still run at 70mph but had to take a while to gradually get there. Don't think it's electrical as it ticks over so well, so thinking fuel related due to heat or filter perhaps. How easy is it to get to the filter??? Any other thoughts please.

Filter is in the lower tank, I think. You will have to run the upper tank down (or siphon as much as you can out, then run the bike some more to lower the fuel level to the lower tank. Then pull the seats, take the cover off the lower tank and the fuel pump and filter are down there. I believe there is a relatively easy way to disconnect one of the fuel lines from the lower tank cover and use the fuel pump to pump the gas out, but I'm not familiar with the procedure. I'm sure you will get more accurate and detailed responses than mine. Try searching the site for fuel pump and fuel filter to read other threads.

I don;t have a picture handy.. or maybe...



Hose number 6, that is the return line that goes to the bottom of the lower tank. Undo the clamp, pull the hose and put on another piece of tubing that you run into your catch-can. It can siphon you down to just a smidgen of fuel left in both tanks.

Same happened to me last summer... check your gas pump, filter and look for dirt or rust on your lower gas tank... mine was really nasty and rusted. I changed pump, metal mesh, plastic mesh and gas filter. Cleaned the lower gas tank the best I could and still runing good. Cheers!!!