96 replies to this topic

[JakeJakeJake]

obviosly what i said earlier is a diagnostic not a solution, if yon find that it makes no difference then you know that cylinder is not firing, and its an ignition related issue. try swapping the leads around see if it swaps the problem, from that you know its a faulty HT lead, then try swapping sparking plugs, if this swaps the problem, you know its a fault sparking plug, if neither make a difference, you have to start looking into more complicated issues...like Dizzy\valve clearances\lift and compression

Replaced leads and checked they work but connecting to a plug outside the engine, all spark fine.

Also I have 7 working plugs and have tried various combinations to no positive effect. Also cleaned them up and checked the gaps. I know sometimes they can fail under compression but I doubt they all would.

[liirge]

have you tried removing the leads from the sparking plugs when its running to test each cylinders working, as it can be a matter of them sparking but not at the right time this will help you diagnose that...


EDIT:
in fact all this test shows is how many cylinders the car is actually running on, and this is the useful bit! from that you can look at other things such as valve movement and compression on those specific non firing cylinders.

EDIT 2:

The plugs may work when out of the car, but they may be wetting up inside the cylinder and not able to fire, I had this issue with a 1098 engine would not fire on all 4 for the love nor money, fixed it in the end though!

Edited by liirge, 14 December 2010 - 12:21 PM.

[JakeJakeJake]

Took the carb apart to see if there were any problems there, managed to bend the carb needle I'm a bit clumsy.

Only thing I did find was the jet needle guide (or whatever its called) has a funny little notch sticking out, dont know if it's right or the rest has broken off.

[Phil-R]

From the sound of the video, the blackened internals and the needle holder it sounds to melike it's over-fueling. Could the needle have shifted position, causing the same effect as unscrewing the jet too much?

Try putting it back together and see if there's any play caused by the broken part.

[JakeJakeJake]

From the sound of the video, the blackened internals and the needle holder it sounds to melike it's over-fueling. Could the needle have shifted position, causing the same effect as unscrewing the jet too much?

Try putting it back together and see if there's any play caused by the broken part.

So that little black thing isn't right?

Hopefully that's what it is, will have to wait until tomorrow until I can get new parts.

[liirge]

if it is running VERY rich, then yes it will wet the plugs, and cause a lack of firing.

[grumpy2]

if it is running VERY rich, then yes it will wet the plugs, and cause a lack of firing.

an unlikely but possible cause may lie inside the dissy.

check the small 'pigtail' lead from the dissy base plate to earth, any movement will create an intermittant or resistive path to earth and regular misfire under any load. speak from 2 months experience tracking down a fault on an old MG.

like I say it seems unlikely from your simptoms but it's free and easy to check

G

[liirge]

well I was of more leaning towards the ignition side of things, and always will on a non firing cylinder scenario but the OP has not confirmed a lack of non firing cylinder.

[JakeJakeJake]

if it is running VERY rich, then yes it will wet the plugs, and cause a lack of firing.

an unlikely but possible cause may lie inside the dissy.

check the small 'pigtail' lead from the dissy base plate to earth, any movement will create an intermittant or resistive path to earth and regular misfire under any load. speak from 2 months experience tracking down a fault on an old MG.

like I say it seems unlikely from your simptoms but it's free and easy to check

G

Do you mean the black wire on the left here?


Is on the bottom when dizzy is mounted to engine, it is tight. Will double check anyway, won't take 5 minutes

Edited by JakeJakeJake, 14 December 2010 - 10:04 PM.

[starletman]

have you checked the valve clearence - if you have adjustable timing gear it may have worked loose and moved if it has'nt been locked of properly , set engine to No1 tdc , rotor arm at No1 lead and check that both valves on No1 cylinder have clearence , do the same for all four cylinders and also compare the amount of compression of each valve spring - if you have a soft cam it can wear the odd lobe ,

I would look down this route,timing chains can stretch over time and move the timing 1 or 2 degrees out.If you have a hot cam then it has to be very precise to work properly.

[minidaves]

for a hot engine i would say that needle looks quite chunky so would be running lean this will cause plug overheating and misfires also if that the dizzy for your engine because also the condensor looks like one from the dark ages

dave

Edited by minidaves, 14 December 2010 - 10:39 PM.

[samsfern]

i think you should reset the carb to a default setting and try some NEW ngk bp6es spark plugs! have you tried a new condensor as well?

Edited by samsfern, 14 December 2010 - 10:40 PM.

[JakeJakeJake]

have you checked the valve clearence - if you have adjustable timing gear it may have worked loose and moved if it has'nt been locked of properly , set engine to No1 tdc , rotor arm at No1 lead and check that both valves on No1 cylinder have clearence , do the same for all four cylinders and also compare the amount of compression of each valve spring - if you have a soft cam it can wear the odd lobe ,

I would look down this route,timing chains can stretch over time and move the timing 1 or 2 degrees out.If you have a hot cam then it has to be very precise to work properly.

Will def check this then, wouldn't think it would go from perfectly driveable to barely running in less than 100 miles

for a hot engine i would say that needle looks quite chunky so would be running lean this will cause plug overheating and misfires also if that the dizzy for your engine because also the condensor looks like one from the dark ages

dave

Deffantly no troubles with it being too lean, was rolling roaded not too long ago which confirmed this.

Picture is not my dizzy, just an example off the net to check I knew what wire someone was refering to.

i think you should reset the carb to a default setting and try some NEW ngk bp6es spark plugs! have you tried a new condensor as well?

Might try some new plugs, wheres cheapest? I found ebay was by a long way last time they were replaced. Pretty sure I allready have ngk bp6es's.

I don't have a condensor, have electronic ignition.

[haggz]

where abouts in herts are you.

[JakeJakeJake]

where abouts in herts are you.

I'm in Hertford