What could be melting my main switch fuse

20-01-2020, 04:21 PM

Thanks again, much appreciated. I may have been confusing myself earlier on which fuse is key - ie, the 30A fuse melting is not the 'main' fuse (the big bugger on the left of the tank) but the 'main switch' fuse which sits in the fuse box. I've read that serves the ignition circuit. in any case, I'll change the stator and fuel filter, plugs too would be worth it by the sound of things.

Mr Gazza · 20-01-2020, 04:45 PM

I had assumed that your spark plugs would be in good order if you were chasing an intermittent misfire, as those would be the first thing to check. I give mine a 6000 mile service life, having found that after that they can cause less than crisp performance. (that said the current pair have lasted much longer this time.)

The plugs I was alluding to in the last post are the electrical connector plugs on the harness that plug into the injectors. I had trouble with mine, or rather the previous owner did! I bought it as a non-runner and traced the problem to those plugs. As I mentioned they looked in perfect order and signals were coming out of the plug terminals but not transmitting to the socket on the injectors. It was a bit of a swine to diagnose, as everything checked out, except the injectors were not firing. I twigged it by spraying switch cleaner into the plug. The engine fired and ran when the switch cleaner was wet, but when engine heat soon dried it out, it died again one cylinder at a time.. and there was the smoking gun! I replaced the Marelli plugs and it's been no bother since.

I'm not saying that is necessarily your problem, but the moral is; take nothing for granted when testing.

Also not sure how the alternator stator could have any effect on either of the problems you are experiencing, replacing that sounds like a waste of money to me and a red herring in the equation anyway.

Nickj · 20-01-2020, 05:06 PM

The main fuse is probably a short or maybe the regulator is a bit dodgy and fails when it starts to warm up. Possibly one of the diodes in it has gone bad, that could easily give you that kind of problem.
If this doesn't happen when you take the bars from lock to lock then the loom is probably OK and it is something that like above.
Alternator isn't likely to be the culprit, volts out do rise with revs (hence the regulator) but it shouldn't be a real issue. It ought to happen as soon as the revs rise.

Intermittent bad running.. plugs and injectors. Change the plugs maybe clean out the fuel system.
Both might be linked if the reg is dumping more random voltages, sometimes low but sometimes high enough to trip the fuse

20-01-2020, 04:45 PM	#2
Mr Gazza Lord of the Rings Join Date: May 2013 Location: Norwich Bike: M900sie Posts: 5,855	I had assumed that your spark plugs would be in good order if you were chasing an intermittent misfire, as those would be the first thing to check. I give mine a 6000 mile service life, having found that after that they can cause less than crisp performance. (that said the current pair have lasted much longer this time.) The plugs I was alluding to in the last post are the electrical connector plugs on the harness that plug into the injectors. I had trouble with mine, or rather the previous owner did! I bought it as a non-runner and traced the problem to those plugs. As I mentioned they looked in perfect order and signals were coming out of the plug terminals but not transmitting to the socket on the injectors. It was a bit of a swine to diagnose, as everything checked out, except the injectors were not firing. I twigged it by spraying switch cleaner into the plug. The engine fired and ran when the switch cleaner was wet, but when engine heat soon dried it out, it died again one cylinder at a time.. and there was the smoking gun! I replaced the Marelli plugs and it's been no bother since. I'm not saying that is necessarily your problem, but the moral is; take nothing for granted when testing. Also not sure how the alternator stator could have any effect on either of the problems you are experiencing, replacing that sounds like a waste of money to me and a red herring in the equation anyway. __________________

20-01-2020, 05:06 PM	#3
Nickj Too much time on my hands member Join Date: Jun 2007 Location: Forest Of Dean Bike: S2r Posts: 3,201	The main fuse is probably a short or maybe the regulator is a bit dodgy and fails when it starts to warm up. Possibly one of the diodes in it has gone bad, that could easily give you that kind of problem. If this doesn't happen when you take the bars from lock to lock then the loom is probably OK and it is something that like above. Alternator isn't likely to be the culprit, volts out do rise with revs (hence the regulator) but it shouldn't be a real issue. It ought to happen as soon as the revs rise. Intermittent bad running.. plugs and injectors. Change the plugs maybe clean out the fuel system. Both might be linked if the reg is dumping more random voltages, sometimes low but sometimes high enough to trip the fuse __________________ "The final measure of any rider's skill is the inverse ratio of his preferred Traveling Speed to the number of bad scars on his body." Song of the sausage creature

20-01-2020, 04:21 PM	#1
Skeldy Guest Posts: n/a	Thanks again, much appreciated. I may have been confusing myself earlier on which fuse is key - ie, the 30A fuse melting is not the 'main' fuse (the big bugger on the left of the tank) but the 'main switch' fuse which sits in the fuse box. I've read that serves the ignition circuit. in any case, I'll change the stator and fuel filter, plugs too would be worth it by the sound of things.