XJ600 misfire

[steer_rally]

I only bought my pre-division XJ600 a couple of weeks ago and already I've had to change the clutch and throttle cables, remove the exhaust and weld up the 4-1 collector box and renew the gaskets, remove and replace two exhaust studs that I managed to snap, trace an intermittent ignition fault (fuse had been removed and wires taped together!), and now she's developed a misfire. Before I throw the sodding thing into the nearest hedge and walk away, I'm hoping someone can make a few suggestions that I could investigate.

The symptoms: constant misfire, or at least rough running. It sounds as though it's only running on three cylinders. Won't idle unless I hold the throttle open a smidge. Dumps unburnt fuel down the exhaust resulting the occasional pop and fart. This occurs throughout the rev range whether in neutral or on the move. I can't take it for a ride on the road yet as I only did my CBT this morning and won't be doing the direct access for another couple of weeks, so have to be content with 1st gear up and down the drive.

Anyway, things I've tried so far: Removed the plugs - they're all covered in a dry, black sooty stuff, but not excessively so. All plugs are giving a spark. If I remove each plug lead in turn the engine note changes, revs drop, so I'm guessing that the problem isn't with the ignition side?

Sprayed easy start around the carbs and rubbers whilst holding the throttle steady, no change in engine note or revs, so I'm guessing there's no air leak.

I'll be buying an adaptor for my compression guage and colourtune in a few days to see what they show, but in the meantime, does anyone have any suggestions as to what else I could be looking for?

Many thanks

[Colin the Bear]

they're all covered in a dry, black sooty stuff,

Sounds like its running a tad rich.

[steer_rally]

they're all covered in a dry, black sooty stuff,

Sounds like its running a tad rich.

 

Yeah, I'd kind of come to that conclusion myself, especially since I cleaned the plugs last week (they were black and sooty then too), and I've only done about a mile since then and they're back in the same state again. I was hoping that maybe it was because I'm just pootling around in first gear and it might clear up once I took it out on the road and give it some stick. And the misfire has only just started a couple of days ago.

Also, the plot thickens - I've just found some mayonaise inside the oil filler cap. How can this happen in an air-cooled engine?

[zzr lon]

sounds like the bike needs a thoroughly good service .

the mayo is from lots of short journeys etc or 5min start ups.

oil and filter change will sort that.

have you looked at the air filter.

personally full service plugs filters oil valves and a carb balance etc and you will have eliminated most things.

you may have a carb prob but you need to do the other things first.

plus a check of all related wires earth's etc battery good igniter box plug caps coils

hth