Not running on all 4 cyclinders (intermittently)

[Dale]

Gentlemen, i'm really hoping you can help me out on this one please, as it's got me really stumped. I've tried allsorts, but the problem always returns after a day or 2.

So firstly heres the background story:-
95, XJ600 Diversion. Intermittently does not run on all 4 cyclinders.
Sometimes it does, then will only run on 3, and sometimes only 2

It's always the same 2 (or 1 - outer left ) cylinders that go down - the 2 on the left as your'e sat on the bike.
As you all know these 2 cyclinders are run off both coils, i.e. not the same one, so i ruled out the coils on this assumption.

What i've tried so far:- Checked for loose wires under the headstock area - cleaned and sprayed with WD40 the connector blocks. Problem solved for a day, then returned.

Changed the spark plugs on the 2 (non running cyclinders) - problem solved, but returned a day later - only running on 3.

So only thing i have'nt checked is the HT Leads as i dont know how - no info on this in the workshop manual.
Could it be this ? if so how do i refit new HT Cable ? - again nothing in manual on this.
Do you simply cut to length, strip back then is it push fit ? screw in ? or connector ?
Some mornings i start up and hey presto - it's running on all 4, then after 20 minutes or so drops to 3 or sometimes only 2. Always the same 1 (or 2)
I check this by simply touching the exhaust down pipes the one(s) not running are stone cold. And obviously when i'm on the bike, i can tell by the poor running / lack of acceleration ect.

Appologies for the long post, but i wanted to give you as much information as i can to hopefully get a correct diagnosis and solution / fix to this problem which has me well and truly stumped, to the point i'm tearing my hair out, and dont know what to do.

I would really appreciate your thoughts and solution to this, and many thanks for reading.
I'm hoping it's something stupidly simple and not exspensive to solve.
Cheers Guy's.
Regards,
Dale.

[neilmud Lord Protector]

Are you getting enough fuel check carbs.

Neil

[Dale]

Hi Neil, yes as far as i know i'm getting fuel as i drained the float bowls, (because someone mentioned that it could be a blockage / dirt ect, - then moved tap to "prime" to re-fill them.
But how would i check to see if they were indeed getting enough fuel ?

Cheers,
Dale.

[bobh]

As you say, these two cylinders run off different coils. So you may well be right about the problem being in the HT leads. Also, if the problem goes away briefly after "attention", that could also point to a dodgy connection or a break in the wire.

Before you do anything else, though try switching the leads from 1 - 4 and 2 - 3 and see if the problem moves across. You may have to take the coils off their mountings to get the leads to reach. You could also try switching the two coils over, again check to see ifthe problem moves.

I'm not sure, but I think the HT leads are potted into the coils, so it might be difficult to just fit new cables. I have a feeling that there was a post on this topic some months ago, but can't remember the details. But as well as the cables it might be the plug caps, and it is easy to fit new ones of those - the replacements should just screw in.

As Neil says, it could also be fuelling.

Hope this helps - good luck - Bob

[Dale]

Oh and sorry, i forgot to add to my original post:- I put some "REDEX" fuel additive in the tank to try and clean / free any sticking needle(s) in carbs. Again this appeared to solve the problem for about a day or two, then the problem returned.

Cheers.