Hey i recently replaced the cylinder head on my mini from leaded to unleaded, i replaced the spark plugs the oil and the gaskets and now when i start it, its really rough it. it doesnt idle very well at all. Would it be the spark plugs or the adjustment of the rockers?
Thanks for any help
Blake

Did you change the actual head or have your head modified? If a different head the combustion chambers could be a different size and the compression ratio different

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David L


My greatest fear in life is that when I die my wife will sell my Mini and tools for the price I told her I paid for them!

Assuming you adjusted the rockers when you put them on then a very slight misadjustment shouldn't affect it too badly. If they are a long way out it can affect the idle. You should adjust them according to the manual though. Adjust the gaps too small and you can end up burning valves. Gaps too big and they rattle and hurt the valves and rockers.

New plugs should be Ok but I have heard of the odd new plug not performing properly. Pretty rare.

My money would be on an air leak in the carbie or inlet manifold. Maybe the manifold gasket. You can check this by spraying around the joins with WD40. If it has an air leak the WD will fill the void for a few seconds and make it run smooth.

Good luck.

Pete

Get your WD40 and do as Pete suggests. The tappets gap should be 12 thou but check this when they are cold - not just after you have done the WD40 check.

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Rod
http://smg.photobucket.com/albums/v607/Rodney/

I completely replaced the head. I adjusted the rockers to i think the gap was 0.38mm and its running better still not the best but its running better. Its just running abit rough now but i think it should be fine. I will check for air leaks around the manifold. Thanks for your help

As Wombat suggested, if you completely changed the head you could have larger combustion chambers, which will lower your compression ratio. What head did you put on it, and what did it replace?

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Gareth.

Have you re-torqued the head since you first fitted it

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"Show me the Mini!"

Or they could be smaller thereby uping the compression ratio, resulting in a too high CR or to advanced ignition timing resulting in pre-ignition...

However this is unlikely because unless you go for a worse head than the one you had before the combustion chamber will probably be bigger.
One way to do it would be to go from a 12G295 on a 998 to a standard 998 head...

Or from a 202 to an original 850 head

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David L


My greatest fear in life is that when I die my wife will sell my Mini and tools for the price I told her I paid for them!

Im not sure what head i replaced it with but i went from a standard 1100cc head to whatever i put on. I ordered the unleaded head from mini and moke world in sydney. I asked them to send me an unleaded head and they sent me one and gave me a guaranty that it was unleaded. If they are bigger is that a bad thing? will it do any damage?

Take the rocker cover off and have a look for the head casting number , 12G202 or similar , and post it here so it can be identified and will at least put that worry to bed . Was there anything else changed at the time you swapped heads , did you try another carb or needle or exhaust ?

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Yes Please

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Stop Licking the Dog...I Don't Care Who Started It

i cant read the numbers because it goes under the engine support at the top right hand side of the engine all i can see is a 20........ then im not sure on the rest. Ive started the car a few times now and it starts alright but the idle is still abit rough ive guessing it has a bigger combustion chambers. Will this do any damage to my engine?

You can try reading it with a mirror, or try to use a piece of paper and a pencil lead or something to try to do one of those tracing things primary school kids do with coins (put the coin under a piece of paper, draw on the top and get a picture of the coin).

I tried these methods before on one of my engines, but can't remember what the result was. I suspect it didn't work.

Larger combustion chambers will lower power and reduce fuel economy, but apart from that it will be fine. Smaller combustion chambers will increase the risk of pinging, but improve power and fuel economy. You might want to adjust your ignition timing as well if the combustion chamber size has changed.

Went and had a geek at Blakes Mini...head is a 12A1456 with bolts holding it down....so 998cc head.

Engine is an 1100 with a 1 1/2 SU.

Not a bad little unit overall...for an early white clubby

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"Show me the Mini!"