# Mysterious kill switch issue (FS450)



## Ibeatgodzilla (May 15, 2022)

Hi all,

I had a pretty odd problem on my FS450 the other day - as a general rule, my most reliable piece of kit. 
Got a full tank's work done, as usual, stopped when needing refueling, then it didn't want to start again. It popped once or twice but didn't want to actually run - it's never done that before, and I do use it a lot, all year round. So, I bring it into the shed and see what's up (once it had cooled down). Upon removing the plug boot, the boot decided it didn't want to hang on to the HT lead any more and appeared to be quite corroded inside. OK, so there's the problem - bad HT lead, no spark. Thankfully I'd ordered a spare coil with some other parts in foresight a while back, and thought it easier to change the whole unit.

New coil on; won't start, no spark. Eh? Why could this be? It only stopped running because it had run out of juice; no issues during use. Bad coil? Possibly? So, I put the original back on after having unscrewed the HT lead and plug boot from the new one and transferred it to the original. Still no spark. What? But... It was running just fine! I'm not sure what made me try it, but I removed the spade connector from the coil which goes to the kill switch circuit... And lo and behold, spark - it was fine after that! 
However that spade connector is a normal part of the circuit, it's supposed to be connected, as it was when I first went to remove the coil (again, it was running fine during use just minutes prior!)

How very odd that something in the kill switch circuit had failed at the exact same time as I ran out of fuel. My only theory is that it was a hot day, doing tough work, and as soon as it ran out of fuel, engine stopped, no more fan to cool the engine, and something melted causing a short circuit (?). However I can't see what or where. And I do use it regularly, intensive work not infrequent, and it never seems to have any particular overheating issues. All is fine inside the handlebar control (no surprise; why wouldn't it be?) and the little spade connector that's supposed to go to the coil can be seen going along the outside of the crankcase and screwed into an earth point later on, nothing appears bad with it except it's somehow shorting the coil and stopping it from sparking. There weren't any insulator washers on the coil that may have been forgotten upon reassembly. The coil is screwed directly to the casing, metal to metal. 

For now, rather than choking it which results in far more petrol than I'd have imagined flooding the system and making a mess of the air filter and the floor, I'm going to make a second kill switch by putting the spade connector to the outside of the casing (it does reach), and having a second little wire from the coil to the outside with a switch between them. Not the most convenient, but it'll work.

However admittedly I'm a little stumped at what's causing the issue here, and why when connected 'properly' the coil is permanently being given the kill engine signal; there is definitely no short within the control handle when in the 'on' position.


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## Ibeatgodzilla (May 16, 2022)

An update on this... I had some time so thought I'd better have a look at it and try to figure out the issue.
Upon further disassembly and inspection I noticed that the little wire going from the coil to the front of the engine casing (where it touches the bare part of the throttle cable to make the short loop to the handle control) had a section where the plastic sheathing was melted/worn off. Found the short! So, remove it, put some heat-shrink sheathing over it, now no bare metal besides the spade connectors, refit, reassemble (properly with wire back on coil) and try again. 
Problem not solved, and the plot thickens - plug removed and put against top of cylinder to check for spark. Start switch in 'start' position (when stuck at half throttle) = spark. At normal 'run' position, no spark... What? As well as off position naturally. Tried this a few times and same thing - spark when 'start' with half throttle, no spark at 'run' . Makes absolutely no sense to me. This implies something inside the handlebar control is shorting it when the switch is in the middle 'run' position - yet upon (again) taking it apart, no it isn't. The wires are are a good 1/4" away in the run position, nowhere near touching. Only in the 'off' position do the wires complete the loop. So why is there no spark in the 'run' position, yet spark at the 'start' position? Absolutely could not figure it out, this machine appears to defy the laws of physics. 
So, I gave up and went with plan B , disconnected the kill switch wire from the coil and positioned the connector outside of the casings, added another wire from the coil to the outside of the casing and put a second switch between these two wires. Now does what it should again, albeit the position of the kill switch being less convenient. If all goes well after its next use, I'll run some longer wires discreetly up the shaft and place the switch closer to the handle bars.


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