xmastree Posted May 24, 2009 Share Posted May 24, 2009 Here's a funny one. My XS400 has been misbehaving lately. It will start but dies the second I release the starter button. If I hold the button in, it will rev happily (but I don't like doing that too much). The scary thing is, it only started doing this after I replaced a few things, specifically the LH switch cluster and some wider bars. Now, none of the switches on there have anything in connection with the ignition, but I may have disturbed something in the headlight. So, I've checked the supply to the ignition box, which is fine, and its earth connection too. I've even tried wiring directly from the fuse to the ignition, just to bypass the killswitch and ignition switch. The starter circuit is completely separate from the ignition, which is why it's perplexing. Now it gets weird though. I have a fuel filter, which was showing a rather low level of fuel. I turned it onto reserve and it was fine... So, could that be all it was? If so, how could it rev when the starter button was pressed? It just doesn't make sense to me... Maybe the problem is still there just waiting to bite me at the worst moment. I took it out today for abut one hour and it never missed a beat. Next weekend I'm planning a 300 mile round trip and I'd like to set off with confidence. Link to comment Share on other sites More sharing options...
Moderator drewpy Posted May 24, 2009 Moderator Share Posted May 24, 2009 check the fuel tap bowl for crud, it might be that and the starter forcing the fuel to flow via the vaccum system!! Link to comment Share on other sites More sharing options...
xmastree Posted May 25, 2009 Author Share Posted May 25, 2009 check the fuel tap bowl for crud, it might be that and the starter forcing the fuel to flow via the vaccum system!! Sucking fuel down the vacuum pipe straight into the inlet? Interesting concept, but I suspect it would only run on one cylinder if that were the case. Plus I can see fuel in the filter, and it fills up nicely. There's a little voice still telling me it's electrical... Like the ignition box can somehow sense that the starter's operating. Link to comment Share on other sites More sharing options...
Moderator drewpy Posted May 25, 2009 Moderator Share Posted May 25, 2009 Sucking fuel down the vacuum pipe straight into the inlet? Interesting concept, but I suspect it would only run on one cylinder if that were the case. Plus I can see fuel in the filter, and it fills up nicely. There's a little voice still telling me it's electrical... Like the ignition box can somehow sense that the starter's operating. sorry, didn't explain very well.. no, the vaccum pulls a diaphram in the petrol tap, which opens up the fuel flow into the carbs. you said the fuel filter had a rather low level and when you went on to reserve it ran fine!!! Link to comment Share on other sites More sharing options...
xmastree Posted May 25, 2009 Author Share Posted May 25, 2009 no, the vaccum pulls a diaphram in the petrol tap, which opens up the fuel flow into the carbs. So maybe the vacuum as only operating the tap when the starter was running... The trouble with that theory is that when I release the button it would stop dead, even at high revs. Just like the ignition was turned off. Presumably if the fuel was shut off it would splutter first. Although it's not as wacky as one of my theories. The ignition box can sense that the starter is turning and delivers a bigger spark for the duration. But there's no connection between the two so it would have to sense the supply voltage being lower than normal. So far so good, but revving it with the starter running should spin up the generator and restore the healthy supply. Link to comment Share on other sites More sharing options...
Moderator drewpy Posted May 25, 2009 Moderator Share Posted May 25, 2009 if you think its electrical, than its a case of checking all electrical connections including the coils. There may be a ballast resistor in there which is bypassed when the starter is used and reverts back to the ballast resistor in normal operation. If this is faulty or badly earthed, then it could give you the sinmptoms you descibe!! I don't have the DOHC manual but there is one in the sticky I made at the top of this thread drewps Link to comment Share on other sites More sharing options...
xmastree Posted May 26, 2009 Author Share Posted May 26, 2009 There may be a ballast resistor in there which is bypassed when the starter is used and reverts back to the ballast resistor in normal operation. If this is faulty or badly earthed, then it could give you the sinmptoms you descibe!!That was my first thought, but having checked he manual, there isn't anything like that. +12V goes straight to the coils and it's healthy. The trouble with the coils is that they're up inside the frame under the tank. Rather inaccessible, there's this engine thing in the way. I can get to the connectors though, and everything seems ok there. I don't have the DOHC manual but there is one in the sticky I made at the top of this thread Cheers, I have the official Yamaha one. Link to comment Share on other sites More sharing options...
Moderator drewpy Posted May 26, 2009 Moderator Share Posted May 26, 2009 is there a mix up with cut off switch and starter? did you check all the colour connections in the headlamp? is there anything else that runs off the solinoid and is taking power on the wrong side of the actuator, so will only power when the solinoid is energised? Link to comment Share on other sites More sharing options...
xmastree Posted May 26, 2009 Author Share Posted May 26, 2009 is there a mix up with cut off switch and starter? did you check all the colour connections in the headlamp?Everything checks out there. If it were that simple then the bike wouldn't run at all. is there anything else that runs off the solinoid and is taking power on the wrong side of the actuator, so will only power when the solinoid is energised? Not that I am aware of. Well, nothing on the diagram at least. The bike wiring may well have been messed with at some point in its life. But I suspect a wiring fault as such wouldn't allow it to run ever. This is intermittent... Link to comment Share on other sites More sharing options...
Moderator drewpy Posted May 27, 2009 Moderator Share Posted May 27, 2009 you never know what people have done over the years. I had a friend with a worn chain, turns out the previous owner "forgot" to put in the carrier bearing in the rear sprocket hub with potential dire consequences. have a look around the headstock where the loom gets chaffed, the insulation should be intact. Link to comment Share on other sites More sharing options...
xmastree Posted May 27, 2009 Author Share Posted May 27, 2009 you never know what people have done over the years. Indeed. The previous owner has been in the headlight. there are little masking tape 'flags' on all the wires... The interesting thing is on the indicator wires (even the front ones which go directly to the indicators, so there should be absolutely no doubt what they are) the flags say 'TRAF' which I presume means trafficator. Only someone of a certain age would use that word... I'm surprised there wasn't a label on the battery saying 'Accumulator'! Link to comment Share on other sites More sharing options...
xmastree Posted May 31, 2009 Author Share Posted May 31, 2009 I took it out today for abut one hour and it never missed a beat. Next weekend I'm planning a 300 mile round trip and I'd like to set off with confidence. Well, the trip went without too many problems. When I first started it, it was fine. So I put the side panels back on and it died the instant I clipped on the LH one. Hmm.. interesting. Off with the panel again, fired it up again and thumped the ignition box. It died. Started again and carefully replaced the panel. I then took a deep breath and set off on the journey. It was fine, never missed a beat the whole way. It seems to be happy once it's warmed up. On the way back next day it died just once, minutes after setting off. I restarted it and it was fine after that. Another problem manifested itself later in the journey, fuel starvation. I have a filter in the line so I can see what's going on. That came in really handy, especially as I can see it while riding the bike.When it first started misfiring I thought it was simply running out so I switched to reserve, but it didn't clear the misfire. I looked at the filter, which was empty and fuel was dribbling into it. Found a petrol station and filled up, but it was nowhere near empty. Turns out there is something blocking fuel flow and if I cruise at over 60 mph the flow is insufficient. I kept an eye on the filter and if it became too low I just slowed down. I'm pretty sure I can fix that by having a look at the petrol tap. The filter is probably gunged up. Was it a nice day yesterday, or what? Link to comment Share on other sites More sharing options...
Moderator drewpy Posted June 1, 2009 Moderator Share Posted June 1, 2009 looks like you had a great time. the place look gorge!! just check your fuse holder for loose connection, as these can fracture and cause intermittent faults. I'd also check the venting in the gas cap as this will reduce fuel flow!! drewps Link to comment Share on other sites More sharing options...
xmastree Posted June 3, 2009 Author Share Posted June 3, 2009 looks like you had a great time. the place look gorge!! It's here just check your fuse holder for loose connection, as these can fracture and cause intermittent faults. Last night I was out with a mate for a few beers and we were discussing this problem. One thing occurred to me. The starting circuit and the ignition circuit are completely separate. Therefore the intermittent fault is probably a short between the two. There's one wire from the starter button to the starter relay. There are six wires at the ignition box, excluding the supply (which I've confirmed are ok), they are two from each pickup and one to each coil. If the pickup wires are fed with a high impedance 12V from the box, and that wire was shorted to the starter relay wire, they would have the 12V when starting but once the button was released the relay coil would be connected to it. That may affect it and kill the signal to the ignition box. It's the only thing I can think of which makes sense. I'll try running a new wire for the starter and see how it goes. I'd also check the venting in the gas cap as this will reduce fuel flow!! Good idea. I can't believe I hadn't thought of that. Link to comment Share on other sites More sharing options...
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