paultsmith Posted May 2, 2009 Share Posted May 2, 2009 I am having an intermittent noise sometimes when I switch the ignition of my bike on. It is an 81 XS400. The noise sounds like a large puff or release of air. It only happens sometimes and occurs about a second or too after I turn the key to run. It happens before I start the bike. It also seems to happen when the bike has been sitting and moved around without turning it or starting it for hours. Any thoughts on what could be causing this? I thought it may be the battery breather venting or perhaps the engine breather releasing some pressure, but am not sure why it would happen all of a sudden once it gets the 12V of power. May also be the carb breather vent or gas tank venting???? It happens every once and a while and I cant seem to pinpoint the problem as it happens pretty quick Thanks Link to comment Share on other sites More sharing options...
Moderator drewpy Posted May 3, 2009 Moderator Share Posted May 3, 2009 great, get to post this of OG again I'm not too sure this is your problem though!! I think its from your gas cap and by turning the key you may just conicidently shake the tank and the petrol fumes just escape due to the disturbed petrol. check its not partially blocked, or try it with a loose gas cap and see if happens again? Link to comment Share on other sites More sharing options...
JimR Posted May 3, 2009 Share Posted May 3, 2009 I am having an intermittent noise sometimes when I switch the ignition of my bike on. It is an 81 XS400. The noise sounds like a large puff or release of air. It only happens sometimes and occurs about a second or too after I turn the key to run. It happens before I start the bike. It also seems to happen when the bike has been sitting and moved around without turning it or starting it for hours. Any thoughts on what could be causing this? I thought it may be the battery breather venting or perhaps the engine breather releasing some pressure, but am not sure why it would happen all of a sudden once it gets the 12V of power. May also be the carb breather vent or gas tank venting???? It happens every once and a while and I cant seem to pinpoint the problem as it happens pretty quick Thanks Hi Paul, it will be the gas/petrol tank cap venting out .... you only have one doing it you ought to get 5 or 6 together doing it The switching on is un related I guess as in the showroom no one was switched the bikes on but did appear to get worse as the temp increased it became a 'good alarm clock' in the summer as the sun would hit the showroom window about 11 am & heat the bikes to the level the tanks vented. But all in all I don't reckon you have a problem as these bikes have been 'sighing'' from new ! Regards Jim Link to comment Share on other sites More sharing options...
Ttaskmaster Posted May 5, 2009 Share Posted May 5, 2009 Is it more like a quiet buzzing, or a whispery rasping noise that slows to a stop? If so, it's probably yer fuel pump. No worries - The fuel in the line sometimes evaporates off, so when you turn teh ignition on, the pump puts a little down the line, ready to start. Obviously fuel stands a higher chance of evaporation if the teperature is warmer, or if the bike has been standing for a bit. I get it on my bike a lot. Not a problem, chap!! Link to comment Share on other sites More sharing options...
JimR Posted May 5, 2009 Share Posted May 5, 2009 Is it more like a quiet buzzing, or a whispery rasping noise that slows to a stop? If so, it's probably yer fuel pump. No worries - The fuel in the line sometimes evaporates off, so when you turn teh ignition on, the pump puts a little down the line, ready to start. Obviously fuel stands a higher chance of evaporation if the teperature is warmer, or if the bike has been standing for a bit. I get it on my bike a lot. Not a problem, chap!! Hi, did old XS400's have a fuel pump ? I think not so that could be discounted, the noise you mention with fuel pumped bikes where the pump will refill after the bike is left for some time or in high temp when the ignition is turned on is correct, but what happens with a bike with no pump ? XS400 used a vaccum tap which when the engine was not running, sealed the tank (no On/Off Reserve just On/Reserve/PRI) which in turn would allow the fuel to expand in the correct conditions and would then vent thro the tank cap ..... RD series bikes (250/400) had the same cap (or deritive) and suffered from the same noise if the fuel tap was in the off position, if left on there didn't seem to be the same problem, but as I cannot be sure that an XS400SH is a SOHC XS motor (worst culprits) and US DOHC motors may have a fuel pump (UK DOHC motors did not & still had the strange noise) it would be difficult to work out where the noise is comming from. Regards Jim Link to comment Share on other sites More sharing options...
Ttaskmaster Posted May 5, 2009 Share Posted May 5, 2009 did old XS400's have a fuel pump ? I think not so that could be discounted, Feck knows - I'm just doing my usual bit and chucking ideas about. Link to comment Share on other sites More sharing options...
JimR Posted May 5, 2009 Share Posted May 5, 2009 Feck knows - I'm just doing my usual bit and chucking ideas about. Hi TT not a problem I was just interested if the US had freebie stuff over theUK bikes ! Regards Jim Link to comment Share on other sites More sharing options...
barwell1992 Posted May 5, 2009 Share Posted May 5, 2009 quick way to check remove gas cap cover with a4 pice of paper then start bike if no sound then turn off then replace top then go back say a hour later then do it again if no nois then itsjust the gass cap's presure valv relising gasses Link to comment Share on other sites More sharing options...
JimR Posted May 5, 2009 Share Posted May 5, 2009 quick way to check remove gas cap cover with a4 pice of paper then start bike if no sound then turn off then replace top then go back say a hour later then do it again if no nois then itsjust the gass cap's presure valv relising gasses What's all this about ??? please explain !!! Regards Jim Link to comment Share on other sites More sharing options...
barwell1992 Posted May 5, 2009 Share Posted May 5, 2009 What's all this about ??? please explain !!! Regards Jim well to be sure that its the fule cap then do this the paper just stops any thing going in the fule tank when the cap is off thats all im just trying to make it safer for him to check have done this befor and worked (was with a nitro car but same princible) Link to comment Share on other sites More sharing options...
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