Lumpy Idle

[lee_rob]

Hey all,

Just joined the register as I have just acquired my first moggie, a 1968 2 dr in smoke grey. I wanted to get some advice on how to solve a problem I have with idling. The car goes really well with plenty of power and pull up the hills. However I cannot get the old girl to tick over properly, I have changed the plugs, leads and set the points to 15 thou cleaned the carb and checked the jet, did the tappets. Still she wont tick over slowly without being lumpy, at a bit of a loss now as to what the problem could be.
Any ideas?

Lee

[bmcecosse]

" plenty of power and pull up the hills. " - you sure you have a Morris Minor?? Perhaps it's been fitted with a high performance engine - hence the rough idling????
Otherwise - you need to check the vacuum advance is working on the dizzy...and then twirl the dizzy back and forth to get the best/smoothest idling... Then road test and listen for pinking...If none - try a little more advance, if pinking -retard the timing until it's 'not quite' pinking... And then -adjust the carb for best idle, and follow up with a good road test and immediately whip out the plugs and check the colour.

[JOWETTJAVELIN]

If and only if timing, clearances, plug gaps etc are spot-on, then try adjusting the carb for fast idle and/or mixture. You can adjust the idle speed without altering the mixture by turning the throttle-stop screw.

[Dean]

Also check the dash pot has oil in it.

[olemikeyd]

Hi, just a couple of ideas for you. Is the lumpy idle with black exhaust and maybe black smoke ? Lumpy idle is often over rich mixture. If you have a workshop manual, take off the float chamber top and check that the float is set correctly. Also, I would remove the carb dashpot, then, whilst looking down to the jet, wind the jet back up until flush with the outer tube. Now, counting the spanner flats under the carburetor. wind the jet down by six flats. Reassemble. This now gives you a starting point to tune from. If the car is too lean, wind the jet down a flat at a time, too rich wind up. But remember how many flats and which way or you will just be guessing whats happening ! Hope this helps. Best wishes MikeyD

[minor65]

If all of the above ok/checked. A compression check on all cylinders to see if any are a bit low might be useful.

[lee_rob]

I have checked the timing and its set around 7 degrees BTDC static, I havent checked the vacuum as yet so thats the next job. Plugs, points etc are all ok and the plugs are a lovely golden colour when i took them out after a long run so the mixture seems fine. No black smoke out of the exhaust and it picks up fine.
I realise you can adjust the idle without affecting the mixture, I set it up at a fast idle (around 1000rpm I guess) and adjusted the flats until when i lifted the piston with the built in lifter on the carb I got a slight increase in revs followed by a drop which is how I set up my vintage cars on SU Carbs. Dash pot has oil in it.
Oh and when I mean plenty of power up the hills i realise this is all relative lol but it impressed me anyway considering the size of the engine.

I am wondering if it is an air leak somewhere in the vacuum system so I will take that apart tomorrow and have a look.

Thanks for the help guys its always good to get ideas

[bmcecosse]

Mix from plug colour is fine - as is your setting of the idle mix.. Check the vacuum advance and if ok, then set the timing to 'not quite' pinking.