leaky petrol cap

jerry · 03-01-2018, 10:11 AM

no its not the green rubber or black round gaskets on the fuel tank insert , but the actual cap itself it clicks shut and locks down fully but with anything more than 3/4 it now sloshes fuel all over my legs and balls ...I have siliconed the rubber pad and lubed the springs , on the cap , is the rubber pad replaceable?? it is 17 years old mind u the one on my 750ss is 27 years old and it does not leak

the breather and overflow pipes are ok not blocked

jerry · 04-01-2018, 10:52 AM

i rode it today with tank only 12 litres in and no leak
now will top up to the full 14L and see what happens ????

jerry · 05-01-2018, 12:31 PM

full up it leaks like a pump its a pressure problem for sure when i open the fuel cap the leaking stops if i lose it fully it flows out the top of the tank , leaving a tiny gap to release internal pressure and all is well????

overflow is not blocked , im confused what to do next

Dennis menace · 05-01-2018, 03:05 PM

Jerry,

I may be wrong but on my old Monsters the fuel cap has what I can only describe as a flap valve system in the petrol cap to, I think, let air in via the cap. It looks like two round rubber discs in a recess. If the flaps are perished or split fuel could leak out.
I seem to remember that the flaps are exposed when you take out the pin that holds the lock latch in place.
Secondly, on my bike at least, there are two pipes in the tank, one is a return for spilt fuel via the recessed portion of the tank fuel cap holder and the second is the true air vent. On mine the true air vent was blocked leading to pressurisation in the tank. A blast of pressurised air in the vent pipe from the top of the tank cleared the vent pipe of rust. I could not get a wire down from the top as the path is too convoluted.

jonzi · 05-01-2018, 03:25 PM

Is it actually coming out of the fuel cap?

My SS was leaking recently, this was because the overflow tube, from the cap, to the overflow outlet pipe, had come away from the cap. so when the tank was over filled over a certain amount, the fuel just siphoned out.

If this makes sense?

I am not sure how a old monster tank is set up, but if it's any thing like the SS tank, then possibly worth removing the filler cap and mount and having a check

Mr Gazza · 05-01-2018, 04:44 PM

Quote:

Originally Posted by Dennis menace

I could not get a wire down from the top as the path is too convoluted.

Guitar strings are quite good for that.

jerry · 06-01-2018, 04:45 AM

took the whole tank system apart this morning and found a split overflow breather hose down inside ,, replaced , will fill up later and test ,,????

utopia · 06-01-2018, 09:19 AM

I believe Capo did a detailed investigation/write-up of the fuel cap function some time ago.
The pics are probably gone down the photobucket tubes but the words may still help, if you can find it.

03-01-2018, 10:11 AM	#1
jerry Old Git Join Date: May 2006 Location: Cricklade Bike: Multiple Monsters Posts: 2,831	leaky petrol cap no its not the green rubber or black round gaskets on the fuel tank insert , but the actual cap itself it clicks shut and locks down fully but with anything more than 3/4 it now sloshes fuel all over my legs and balls ...I have siliconed the rubber pad and lubed the springs , on the cap , is the rubber pad replaceable?? it is 17 years old mind u the one on my 750ss is 27 years old and it does not leak the breather and overflow pipes are ok not blocked __________________ MONSTERMAN

04-01-2018, 10:52 AM	#2
jerry Old Git Join Date: May 2006 Location: Cricklade Bike: Multiple Monsters Posts: 2,831	i rode it today with tank only 12 litres in and no leak now will top up to the full 14L and see what happens ???? __________________ MONSTERMAN

05-01-2018, 12:31 PM	#3
jerry Old Git Join Date: May 2006 Location: Cricklade Bike: Multiple Monsters Posts: 2,831	full up it leaks like a pump its a pressure problem for sure when i open the fuel cap the leaking stops if i lose it fully it flows out the top of the tank , leaving a tiny gap to release internal pressure and all is well???? overflow is not blocked , im confused what to do next __________________ MONSTERMAN

05-01-2018, 03:25 PM	#5
jonzi Mary Mary Quite Contrary Join Date: Mar 2012 Location: Berkhamsted Bike: M796 Posts: 1,398	Is it actually coming out of the fuel cap? My SS was leaking recently, this was because the overflow tube, from the cap, to the overflow outlet pipe, had come away from the cap. so when the tank was over filled over a certain amount, the fuel just siphoned out. If this makes sense? I am not sure how a old monster tank is set up, but if it's any thing like the SS tank, then possibly worth removing the filler cap and mount and having a check __________________ #48

06-01-2018, 04:45 AM	#7
jerry Old Git Join Date: May 2006 Location: Cricklade Bike: Multiple Monsters Posts: 2,831	took the whole tank system apart this morning and found a split overflow breather hose down inside ,, replaced , will fill up later and test ,,???? __________________ MONSTERMAN

05-01-2018, 03:05 PM	#4
Dennis menace Registered User Join Date: Nov 2013 Location: Farnsfield Bike: Other Ducati Posts: 300	Jerry, I may be wrong but on my old Monsters the fuel cap has what I can only describe as a flap valve system in the petrol cap to, I think, let air in via the cap. It looks like two round rubber discs in a recess. If the flaps are perished or split fuel could leak out. I seem to remember that the flaps are exposed when you take out the pin that holds the lock latch in place. Secondly, on my bike at least, there are two pipes in the tank, one is a return for spilt fuel via the recessed portion of the tank fuel cap holder and the second is the true air vent. On mine the true air vent was blocked leading to pressurisation in the tank. A blast of pressurised air in the vent pipe from the top of the tank cleared the vent pipe of rust. I could not get a wire down from the top as the path is too convoluted.

06-01-2018, 09:19 AM	#8
utopia No turn left unstoned Join Date: Jun 2010 Location: leicester Bike: M750 Posts: 4,546	I believe Capo did a detailed investigation/write-up of the fuel cap function some time ago. The pics are probably gone down the photobucket tubes but the words may still help, if you can find it.