Hi all,

The mini was running badly over the last few weeks - it just progressively got worse over about two months. First it started misfiring at about 4000rpm, and it got down to about 2000rpm the other day when I decided I had to look at it - I couldn't go much faster than 60km/h.

After playing around with the timing, the fuel and checking the plugs, it was no better. So I tried taking off the air filter - all fixed. It seems that the filter had been the issue all along.

What's strange is that the filter looks good as new. It's a K&N filter like this: http://www.minisport.com.au/prod394.htm

I've looked up a few links about cleaning them, but once they were clean, they looked just like mine. They recommend cleaning once every 80k - I've only done about 20k.

All I can think is that I have been parking the mini in the weather, and that water may be running from between the body and the bonnet onto the air filter, which has somehow blocked the filter. Has anybody heard of this happening before?

I've not, but over-oiling K&N filters is very common. Just enough oil to taint the cotton to the right colour. I feel that water should just dry off with the heat of the engine.

Also make sure the port which vents the SU dashpot to atmosphere is clear of obstructions.

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

Yeah, I've heard that over-oiling is a big issue, but it came pre-oiled, and I haven't touched it since. I'm only guessing it's the water, but it went from perfectly fine to choking the engine in the space of a few weeks!

The oil should exclude the water by its own nature. What about fuel being spat out of the carb clogging it up?

I would give it a wash, re-oil it and give it another try over the next few weeks. Make sure that damper port on the mounting face is nice and clear too.

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

Yeah, I was going to clean and re-oil it along with the carby and see how it goes. Both look fine, but obviously it's not as it appears.