SLIGHT MISS

[bleddyn]

Hi,Previously had problems starting my moggy,but after some excellent advice everything there now ok,but'''''had previously changed all electically imaginably possible,and stripped down carb,cleaned put back together and ajusted accordingly, but after taking out for 5 mile spin,have still got a slight miss, have adjusted timing, idles very well,does'nt seem to miss at about 40,but when putting foot down slighty to 50, has this miss,and scared to take on longer spin just in case i'll have breakdown as previously when all my troubles started about 6 months ago, any advice please, thanks

[PSL184]

Could just be carbon build up in the combustion chambers. Run a bottle of Redex through the fuel tank and give it some good hard acceleration between gears and a good high speed blast down the motorway.....

[bmcecosse]

Hmmm - remind us what you have changed - and is there anything NOT changed?

[mike.perry]

Have you checked that the carb. piston is lifting and dropping smoothly?

[Dean]

I had a slight miss on mine once and the responses were:

A leak in the inlet manifold, can't remember how to identify if it's this, I think someone said spray WD40 on the inlet manifold while it's running and smoke will identify a leak. But someone should confirm this first before trying.

My problem though turned out to be...... a dodgy spark plug . It just wasn't sparking as good as the other three, not very noticable to the naked eye, but made a difference to the running. To correct this, make sure all plugs are tight against the block and make a clean contact on the block. Give the block a bit of a clean where the copper washer sits. Or buy another spark plug.

[beechford]

bad practice to change just one plug ,do all or none.ok for diagnosing but not for everyday use . now watch me get shot down from north of the border.

[autolycus]

Nope: well south of it...

Why is it bad practice to change one plug? How does one plug "know" anything about the condition of another one?

Kevin

[bmcecosse]

Seeing as you are in Tasmania BF - I'm not too sure which 'border' you refer to! Most of us will be 'north' of you anyway!! But - on the off chance you are thinking of ME - Why would I shoot you down ????? Getting a bit paranoid there BF !! I agree - it IS likely to be dodgy plugs - and yes - fit a new SET. I've just be-rated a lad on a Mini forum for fitting 'A' new plug!! The old ones don't happen to be NGKs - do they ??

[beechford]

to change 1 plug would be like changing 1 brake shoe .they come in sets for a reason dont you think? by changing only 1 you will lose track of how much work these parts have done and when they need tossing away at the end of useful life.

[Dean]

If all the plugs are old yes I agree. What I forgot to add is all mine were new, but one was dodgy, I think the thread originator had renewed all his too. So he may have been sold another dodgy spark plug (like me) or it's not earthed properly to the block.

Sorry, should have explained myself better.

[bleddyn]

if you remember,had problem starting,no spark,but put cap full of fresh petrol down carb and started instantly,changed everything electrically,thanks

[bmcecosse]

Could be many things - have you checked the valve gaps - and a compression test would be a good idea just to confirm general engine condition. Is it now running on 'new' petrol - or still using up old stuff in the tank ?

[bleddyn]

mixture of both, new and old petrol,also just occured to me bought a complete service kit from bull motif and the plugs were not champion or any other well known make, also have been suggested oil in damper could be to low, thanks

[bmcecosse]

Try a different set of plugs - even an old set - would be good to burn off the old petrol, although I think that's unlikely to be the cause. It's usually something 'ignition' wise! Nut -if say a valve seat was burned - or gap closed up - that would cause uneven idling!