Michael Posted June 30, 2011 Share Posted June 30, 2011 Hey As written in the topic description, my XS400 looses enginepower after having driven around 110-120 km/h (around 75mp/h) for 20-30 seconds. The machine has fine power and runs great until it has run for 30 seconds, then I need to lower the speed of the bike because it looses all it's power. It feels like the bike isn't igniting in every rpm and therefore loosing power, just a thought, don't know if it's possible After having let go of the gas and the speed drops til like 80-90 km/h it runs fine again. Any ideas? Would be kind of useful to be able to run those speeds on the highway Link to comment Share on other sites More sharing options...
Mr Machinist Posted June 30, 2011 Share Posted June 30, 2011 Possible needle/jetting issue? i only say because i have read ( never had it happen to me... well there was a honda vt500e but thats a longer story!!) that if your jets are set for a certain rev range, they will fail to operate at higher revs, but im also inclined to think that this scenario only happens when modifications are done to inlet or exhaust settings ( new pipes, K&N filters that sort of thing) the drop in power could indicate starved of fuel. plugs? float heights? this might help : http://www.factorypro.com/tech/carbtune,CV,high_rpm_engines.html that is if you have cv carbs.... it is sounding tho like you have a float issue the more i think about it it definatly does sound like its starving for fuel at high rpm's will keep watching.... its buggers like this that make life interesting!! copyoulater neil Link to comment Share on other sites More sharing options...
kindest Posted July 1, 2011 Share Posted July 1, 2011 Hey As written in the topic description, my XS400 looses enginepower after having driven around 110-120 km/h (around 75mp/h) for 20-30 seconds. The machine has fine power and runs great until it has run for 30 seconds, then I need to lower the speed of the bike because it looses all it's power. It feels like the bike isn't igniting in every rpm and therefore loosing power, just a thought, don't know if it's possible After having let go of the gas and the speed drops til like 80-90 km/h it runs fine again. Any ideas? Would be kind of useful to be able to run those speeds on the highway also see Link to comment Share on other sites More sharing options...
Paulwhite Posted July 2, 2011 Share Posted July 2, 2011 check the float height then check the fuel pump if it has one ... it sounds like its sucking more fuel out of the carb then whats going in from the tank. also check the tank breather. Link to comment Share on other sites More sharing options...
Michael Posted July 2, 2011 Author Share Posted July 2, 2011 Thanks for all the replies, will definitely check out the float height. Never thought about that to be honest But.. How would the float height have anything to do with the drop in fuel to the carbs? Isn't the float height a standard height where the fuel isn't flooding the carbs when turned off? Just me being a newbie, sorry But yeah, when you think about it, it does kind of make sense. If I keep the throttle maxed out for a while, it will eventually suck the carbs dry if the fuel is running slower to the carbs than the engine is using. And therefore I would have to let go of the revs. Will go check it out. By the way, I have stock airboxes and filters but a homemade exhaust system with less restriction than normal system has I guess. Just to get that clear. Pics of the bike with the custom exhaust link Link to comment Share on other sites More sharing options...
Michael Posted July 4, 2011 Author Share Posted July 4, 2011 Does the XS 400 actually have a tank breather and where would it be? I have't stumbled across it so far.. :/ I got a fuel filter on the bike, would it have any effect? Link to comment Share on other sites More sharing options...
kindest Posted July 5, 2011 Share Posted July 5, 2011 Does the XS 400 actually have a tank breather and where would it be? I have't stumbled across it so far.. :/ I got a fuel filter on the bike, would it have any effect? i got a fuel filter on mine too no problem. i believe it vents from the gas cap. there should be a rubber seal with a hole in it. Link to comment Share on other sites More sharing options...
blackhat250 Posted July 5, 2011 Share Posted July 5, 2011 I got a fuel filter on the bike, would it have any effect? It will if its dirty, renew, always start with the cheapest simplist remedy"s. its an elimination process. , get a good fuel flow, pull pipe from tank, & see . the breather " you"l hear air suck in wen opening tank.[After symptom occurs] Link to comment Share on other sites More sharing options...
Paulwhite Posted July 5, 2011 Share Posted July 5, 2011 im not sure on your bike m8 but bike engines work off the same principle, have you tried taking the filter off? if its blocked then you wont get fuel to the carbs, just whip it off and connect the fuel line straight to the carb to see if it is the filter. the float stops the carbs from overflowing but it needs to be set at the right height otherwise the engine sucks up more than whats going in. its worth checking as you dont know what the previouse owner did to it. some people "adjust" the float height as some form of performance "mod". Link to comment Share on other sites More sharing options...
Michael Posted July 8, 2011 Author Share Posted July 8, 2011 Sorry for the late reply. The fuel filter is brand new so I don't think that is the problem. The float height on the other hand.. I have no idea about those. Had the carbs taken apart and cleaned, but it never occured to me, that the floats would have to be at a specefic height to be working optimal. Guess I'll take it apart again and take a look. Can you people recommend a height to set them in? Link to comment Share on other sites More sharing options...
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