My 1968 Mini 850 is running lumpy on load. Fine at tick over but struggles to reach speed and going up hills.
All four plugs are sparking but after removing and inspecting the plugs, I noticed the the plug from cylinder 1 is clean as new, there is only clean unburnt fuel on the plug. The other 3 are all sooty. Replaced the plugs and still the same thing happening, cylinder 1 spark plug is always clean. There seems to be nothing happening in the cylinder.
I have checked the gaps, done a compression test (125 psi at all 4 cylinders). Set valve clearance 0.30. News points, new condensor. Timing done, static and strobe.
The only fault that I have found was the vacuum diaphram isn't working, considering that the distributor is almost 50 years old, I will buy a new one. The coil seems to be the only thing never changed from new (1968).
I have no idea, please help.
Thanks. Rob

How does the dizzy cap look? Does the #1 contact look ok like the others? The spark plug might be sparking in open air when you test it but the spark might not be jumping the gap under running conditions if it is a weak spark.

The vacuum diaphragm would have nothing to do with your problem. By all means replace it but it won't change anything for your issue.

You said you changed the points and you've also said that the distributor is 50 years old (sounds like it has never been rebuilt or run up on a dizzy testing machine), did you install the points with the use of a dwell meter to check for 57-63° of dwell angle (check that figure) or did you just set the points to the standard gap? I'm wondering if the coil is getting enough time to charge as you've made a good start into replacing the usual suspects. I don't even know what points gap I run as I always set my points with a dwell meter as this overcomes any wear in the dizzy.

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"In two years time your car will be like a lady's clothes, out of date, my car will still be in fashion when I am dead" - Sir Alec speaking to Pininfarina

confusing...

if you've done the timing using a timing light, then you must've clipped the timing light onto #1, and it couldn't have flashed unless there was some spark going through it

edit - try some new leads...

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did I tell you that I won a trophy?

The dizzy cap is new. You are correct in saying that the dizzy has never been touched in fifty years. The points were installed using the standard gap with a feeler gauge.

All four plugs are sparking including cylinder 1. I could try new leads. Thanks

I'm intrigued how do you know that all the plugs are sparking. I take it you have removed them, connected the leads and physically seen the spark.

Yes, I did exactly that and all 4 plugs had a good spark

have you tried changing the plugs and/or leads around to different cylinders.

to see if either the plug or the lead is bad?

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1975 Hairy Lime/White Clubby
Build Thread: http://www.ausmini.com/forums/viewtopic.php?f=3&t=80657

something to note with testing of spark plugs, inside the cylinder it is harder for the spark to jump the gap due to the compression/fuel mix, so it is possible for a spark plug to spark once you have taken it out to test and for it not to spark in the cylinder. the best way to test if you have spark is to take a spare spark plug, file/grind of the ground electrode and test it that way, this makes it harder for the spark to jump the larger gap and is more indicative of the spark required inside the cylinder.

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2015 Ducati 899 Panigale

Check the plug lead resistance. Old suppression ones go high resistance, this reduces spark intensity.
Should be under 2K ohms when new, I'd bin them if over 5K, or 10K tops.

If buying new leads, go for inductive core ones, Bosch or whatever. They do not have this problem.

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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.

Did you change the rotor. Does it fit tightly on the dizzy.

Also have a look to see if the electrodes in the cap are evenly spaced same size. The last couple of caps i have purchased have been of poor quality.

Coil was my last problem. Lost power under load.

Yes, new rotor arm, new dizzy cap,condensor etc. Leads and coil are the only things not changed.
I will try a new set of leads, check all new components.
The coil seems to be the original factory fitted one from 1968. Would it be worth trying a new coil, I have a spare ballast coil in the garage. Would it be possible to use it on a non ballast system?
Thanks to everyone for the excellent advice. It is all part of the joy of having a mini. We have all be there!

Do not use a ballast coil (1.5 ohm) without a ballast resistor. It will overheat, and wear the points bad.
If you want to use it, buy a 1.5 ohm ballast resistor and put in series with the coil.

I would borrow another std coil off someone, to test.

If buying new, I think Bosch ones (GT40, GT40T or Bosch Blue) are better made than the current Lucas ones.

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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 try a new coil. They do not last last for ever and your one is 47 years old after all.

One thing you could check is the coil hot after a run. Buggered if it is.

I had a simular problem with my moke. Changed everything but the leads and coil. Swapped the coil for a spare I had. Made no difference. Swapped the leads and no difference. Brought a new coil problem sorted. Started loosing power than finally a miss developed.

Please let us know what the issue was once you have sorted it.

Sorted, changed the leads, made no difference, changed the coil and the problem resolved.
Thanks.