My mini has developed a mis all of a sudden. It appears to be running only on cylinders 1 &4. There seems to be spark coming from all 4 plugs yet when i pull the leads off cylinders 2 &3 the engine makes no change, unlike 1 &4 which nearly make the motor stall when i disconect them. (thats what makes me think its cylinder 2 & 3 thats not working. Any ideas whats happened? Could i have a blown head gasket between 2-3 causing the spark to blow out?

Yep youv'e done a head gasket.

Certainly sounds like it ....unless the points/dissy cap, spark plugs or Ignition Leads to 2 and 3 are absolute crap!

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"Show me the Mini!"

Do a `bush compression test'- remove plugs, put your thumb over each plughole in turn while someone cranks the starter.
If gasket is blown, it will be obvious-

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

thanks for that. Hey kev, i tried the bush test, but they all seem to have compression,ie they all force air past your thumb. However, does it only work if u have all the plugs out at the same time? i just took 1 out at a time. Should that make a diff? I can't seem to find anything else that may be causing it. Maybe i'll have to take the head off.

If they all feel the same gasket is OK. Usually when it's blown there's F'all compression in 2 adjacent cylinders.
Are these 2 plugs wet?

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

I would go and change all the ignition stuff, thats the first thing I do when a problem like this occurs. Change the points, condensor and plugs. Check the leads (shouldn't have much resistance) and do so when they are attached to the dizzy cap (so you know the connection between the cap and the leads are fine).

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only number 3 looked a bit wet, not 2.

Maybe take the rocker cover off and adjust all the tappets?

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ok. i'll have a go tomorrow when the shops are open. could be an excuse to get the head done up lol. It has pretty high compression anyway so changing the head gasket might still be a good idea.

Before you do anything else, I'd put 2 new plugs in there.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Cheers doc! all going! weird cause the plugs were giving spark when i checked them, maybe just not at the right time or something.

It takes more volts to fire a plug in a cylinder with fuel mix under pressure than it does out in fresh air.
Cheers, Merry Xmas!

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

1. Fill the radiator to the brim and see if bubbles come out.
2. Any condensation under the oil filler cap?
3. The best and quickest way is to find a gas analyser and stick it in the neck of the radiator. If it registers mixture then there is a compression leak to the cooling system.
4. Swap the plugs from the cylinders firing to those that aren't.

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Chris

Everything I like is either
illegal, immoral or fattening.