I have noticed on my 998, that 2 and 3 cylinders don't fire very well down low. This is seen through via the exhaust temps, but also when I stick a gunson colortune on to have a look at either of the two cylinders. 1 and 4 fire just fine however at the same time.

I ask as I am trying to improve the pickup from low to mid range, and have noticed that this is not helping.

Whats are common reasons for this?

Mick

Standard twin 1.25 SUs, AH2 needles, GR RE82 cam, stock rockers, mildly ported head, 10.5:1 comp ratio.

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SooperDooperMiniCooperExpertEngineering

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

I've seen something like this on a motorbike once. It had something to do with play in the moving ignition parts. Shaft on the dizzy okay?

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Behold! The mighty 850!

All the gaps the same size? Heck, you probably already looked at all these.

If this was me, the first thing I would do is number everything and start swapping bits around. Grab a known working spare coil and check the regulator. Process of elimination will rule out everything that works leaving the probable cause. Also check for parts that could be affected by vibration. Something I've experienced with motorcycles.

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Behold! The mighty 850!

IMO it is because of charge robbing due to the siamesed intake ports. The bigger the cam duration the more pronounced it is. I get this effect even with all 4 cylinders showing the same compression pressure.
I think it's also the cause of spark plugs 2 & 3 burning richer (with SU carbs).
With a modded A series you can't use the old Alfa trick of checking your carb synch by pulling the plug leads off in turn and expecting them all to drop rpm equally....

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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, the plugs are new, and the coil seems good too. Through the colortune I can see that their is a good strong spark.

I figure Doc is correct from what I have seen, is there any way to minimise this? Is it a case of closing gaps a little more or running a little bit richer?

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SooperDooperMiniCooperExpertEngineering

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

My MK2 S does the same I'm running standard su's with AH2 needles and a very mild cam, at idle if you pull the leads off one at a time no's 1 & 4 drop substantially whereas with no's 3 & 4 there is hardly any change comps are all the same have swapped plugs and leads around with no change.

I think the Docs diagnosis is on the money..

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1970 Mk 2 Cooper S