Never ending problem. Xs500 firing on one cylinder

Jay2903 · Scooby Slapper Joined: 03 May 2016 Karma :

Hey guys
I've been messing this for a few weeks now. I've replaced the plugs and ignition coils and checked them once I'd fitted them. I charged the battery for a bit and fitted the coils today. It started up first kick and idled fine for a bit then cut out and struggled to start. When it started again it seemed fine.

I took it out for a quick ride, as soon as i got to the main road and opened it up one of the cylinders cut out. I had to keep the revs up on the way back to keep it from cutting out and as soon as I stoped revving it , it cut out and wouldn't start again.

I've cleaned the carbs twice and the tank is fairly clean + it has a fuel filter

Not sure what else to check

Help greatly appreciated

jaffa90 · World Chat Champion Joined: 06 Apr 2016 Karma :

After a run out did the exhaust tail smell of fuel and was it cooler?
Are the carb slides lifting the same when revving?
I take it the valve clearances have been checked!

bypass2 · Spanner Monkey Joined: 12 Sep 2013 Karma :

Have you tried runing it without the fuel filter.

Bru · Trackday Trickster Joined: 01 Feb 2007 Karma :

Hi. I think this is a twin-coil setup. What I would do after the symptom manifested is firstly, *briefly* touch each downpipe to find out which is cooler, ie. that cylinder not firing. Then, I would swap coils over, and re-run the engine. If the mis-fire moves with the coil change, then that is your issue.

Old coils can break down under load (heat and electrical).

Of course, there is also the plugs to consider, as they can go: insulator cracks and when the plug heats up, spark shorts through crack to head instead of via the spark gap. So, that is a second option to test.

Jay2903 · Scooby Slapper Joined: 03 May 2016 Karma :

Jay2903 · Scooby Slapper Joined: 03 May 2016 Karma :

Jay2903 · Scooby Slapper Joined: 03 May 2016 Karma :

Jay2903 · Scooby Slapper Joined: 03 May 2016 Karma :

After the test run I left it to cool down and tried it again. It started up fist kick but only on the right cylinder. The left pipe completely cold 😕

Suntan Sid · World Chat Champion Joined: 07 May 2009 Karma :

Plug leads and earth connections Question

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bypass2 · Spanner Monkey Joined: 12 Sep 2013 Karma :

what about faulty condensor

Jay2903 · Scooby Slapper Joined: 03 May 2016 Karma :

Jay2903 · Scooby Slapper Joined: 03 May 2016 Karma :

jaffa90 · World Chat Champion Joined: 06 Apr 2016 Karma :

Jay2903 · Scooby Slapper Joined: 03 May 2016 Karma :

jaffa90 · World Chat Champion Joined: 06 Apr 2016 Karma :

jjdugen · World Chat Champion Joined: 03 Jun 2011 Karma :

One question...... WHY!!!!

Notoriously unreliable, the worst being cracked heads around the valves, oil leaks, poor running...(ahem), ugly, no spares at all, so....WHY?
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Jay2903 · Scooby Slapper Joined: 03 May 2016 Karma :

redeem ouzzer · World Chat Champion Joined: 06 Oct 2015 Karma :

Not as good as an RD of same period but look good, handle ok and as long as OP didn't give 4K for it it's worth a fiddle?
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Jay2903 · Scooby Slapper Joined: 03 May 2016 Karma :

I was gonna try what Jaffa was saying but I couldn't get it started today. I kicked for a good while. I pulled the plugs, the plug from the right cylinder was quite blackened the left one was slightly. I cleaned them a bit and stuck them back in. After a bit more kicking it started again and now on both cylinders again.
This is driving me crazy

Bru · Trackday Trickster Joined: 01 Feb 2007 Karma :

Hi. If you are convinced that your electricals are good, then it is back to the carbs. A severely blackened plug suggests an overly rich mixture.

Could be float height, as suggested earlier. Or a sticking float or float needle, not allowing fuel in the carb... Unfortunately as I have learned, carbs need to cleaned scrupulously. Despite cleaning the carbs out (and how well did you do it), the miserable things do like a good clogging; it could even be something irritating like muck from the tank clogging the carbs, depending on how good that fuel filter is (or if it was fitted from the start).

Clearance checks are vital; is there any chance that something is not opening, or opening too much, so messing up the running - along with any carb problem?

Air, fuel, spark... Have you tried spraying the outside of the carb rubbers (between carb and head) with carb cleaner, to see if the engine picks up? Could be an air leak running a cylinder lean... Constant refitting of carbs and rubbers can put a kink in the works.

Jay2903 · Scooby Slapper Joined: 03 May 2016 Karma :

Jay2903 · Scooby Slapper Joined: 03 May 2016 Karma :

I've noticed the problem did actually jump cylinders. At first before I replaced the coils it was the right cylinder that wasn't firing and now it's left.

temeluchus · World Chat Champion Joined: 01 Oct 2008 Karma :

could be knackered float needles, that would cause rich running and signs of over rich/flooding. If they are original they are almost certainly fucked by now.
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bypass2 · Spanner Monkey Joined: 12 Sep 2013 Karma :

take the plug out turn the ignition on being carefull wiggle the points with a screwdriver to see if plug sparks. may have a loose wire between the points to the coils

Bru · Trackday Trickster Joined: 01 Feb 2007 Karma :

Low-voltage wire from points to coil - how clean are the connectors, how good is the insulation around the wires, any kinks, any green corrosion?

Same from the coil to the plugs. If the problem has followed the coil, then it can only be low-tension, high-tension, or coil. Could be a cracked high-tension cable shorting to the engine or frame?