Rough idle

[lee_rob]

Hi all

My little moggy is troubling me. She has always been a bit reluctant to idle smoothly but recently it's been trying worse. I can't get her to idle smoothly at anything less than 1000rpm. If you drop the revs she gets rough and the tachometer drops sharply every so often like she's missing.
I have checked the plugs and they are a perfect biscuit colour and she's doing over 40mpg around town so I don't think it's fuel. I tried adjusting the timing thinking I may have it too advanced but retarding it doesn't help at all. It's on acu spark ignition with all new leads etc.
I'm stuck if I'm honest I can't think what would cause the rough idle. Any ideas?

Lee

[bmcecosse]

Rev counter dropping tells you it's losing the spark....so look for loose connections. Also - clean air filter? Breather pipe from rocker cover clear? Oil in the carb damper?

[lee_rob]

Air filte is clean, the breather pipe is clear. Oil in the damper yes. I shall check my connections tomorrow. It can't be the coil!!! ;>)

[jothina]

hi
I had the same prob, new dissy cap has cured it

john

[lee_rob]

It's had one of those unless of course it's one of those dodgy rotor arms

[bmcecosse]

Could well be....

[lee_rob]

Ok so I seem to already have one of the new Red rotor arms I forgot I had bought. I changed the dizzy cap but no change.

[lee_rob]

Still having this issue guys, cant seem to solve it at all. The problem now gets really bad when warm so much so I have to pull the fast idle out to keep it going. Feels like its missing a beat, also noticed that the cars judders on the over-run which I guess would indicate a rough idle. surely they should tick over at less than a 1000 rpm? and evenly ?

[bmcecosse]

Indeed it should......is the 'rev counter' still dropping to zero? If so - continue to trace Ignition problem - loose connections etc etc. Condenser/points gap/HT leads that sort of thing.

[lee_rob]

Doesnt quite drop to zero it just drops a couple of hundred revs then back up again, I checked the coil connections and all seem ok and tight. I have an accuspark ignition unit in so no points or condenser. I have put new champion plugs in which are gapped 25 thou. I even took the dizzy out and removed the base plate to check inside. Both advance bob weights seem to be working, the lighter spring is in contact first with the larger spring being slightly loose. then when you turn the dizzy the lighter spring stretches and the heavier one comes into contact. I take it the heavier spring should be loose initially?
I sucked in the end of the vacuum unit and the dizzy moves so that seems to be working ok.....confused

[bmcecosse]

Try a temporary wire direct to the Ignition from the battery - instead of the feed through the Ign switch etc. I think it's very unlikely...but I suppose it's possible the leccy ignition is faulty. Any chance of swapping in an old points dizzy to see what happens? It would also be worthwhile setting the valve gaps, and then running a compression test.

[lee_rob]

I have a brand new set of points in a box I could put back in and see if that makes any difference. I was thinking of running a wire from the battery to the coil separate and see if that works so I will try that next. compressions were all good when I checked recently around 160 on all cylinders but I can easily check again. I have also done the valve gaps opening up the exhausts just a tad to allow for expansion.
So frustrating really, but I am inclined towards something electrical, tempting to just buy a new dizzy really but you never know what the quality of the new ones is like

[bmcecosse]

I agree it's likely to be ignition.....