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MG MGB Technical - proper plugs and gap

I have a 1968 engine bored thirty over. I am looking for the best spark plug and the gap. I am running smog free so it would be like in the old days, (yea). Thanks in advance
Peter Murray

Try the NGK Triple or Quad electrode plugs, no need to set them and the engines seem to like them!!
K Harris

NGK it is. The standard plug uses a .025" gap. RAY
RAY

I take out more platnum plugs than you would beleive. It seems the ignition system even ifs a electronic type does not have enough power for these plugs. This was brought to my attention by a mechanic that works at a VW dealer. It seems they have the same problems with the older Rabbits & golfs. I use champion N9Y in all the MG's
Jim Pelletterie

Hi All

We tend to stay with NGK basic plugs such as BP6ES or BP7ES at 35 thou plug gap. We had too many Champion plugs breaking down under load on the rollers.

Peter
peter burgess

Peter, is there a big difference between 35thou and the 25thou setting in the book?

I only ask as I wonder if I can use bigger plug gaps to give another dimension to setting the car up. if the gap is bigger, is it the same as retarding the ignition slightly, or will it just give a better spark (due to the increased voltage to bridge the gap).

I have a 1965 B with a 123 MG dizzy (with vac advance) and am struggling to get rid of flat spots! I think my main mistake was buying the MG dizzy and not the general one! I have BP6ES plugs, new leads etc and seem to have rough tick over (currently set at 1,000rpm to keep it smooth), then have a flat spot around 1500-2000rpm. The car picks right up around 2500rpm and runs like a dream, it just seems to be at lower rpm I have the problem. I was going to try a different curve in the dizzy, I think I set it at number 1, maybe number 2 would be better with more advance at lower revs.

Regards

Chris
Chris

Hi Chris
Try setting 6. You are right you get a better spark with the bigger gap which helps burn the fuel better. What carbs filters needles?

Peter
peter burgess

I've had quad-points in my roadster for yonks and they don't seem to be wearing at all i.e. no change in gap. The last Champions I used had insulator ribs with flat faces and sharp corners rather than the usual rounded ribs I had always previously seen, and I broke three taking them out at a service so have never used them again.

Chrome bumper cars (25D4) were 25 thou, rubber bumber (45D4) were 35. You will get higher HT voltages with the latter so it will seek out any weaknesses in HT leads, cap and rotor. Plug gap won't affect timing (unlike changing the points gap), but under acceleration and higher cylinder pressures the plugs become harder to fire so the HT voltage will increase, which means that marginal HT bits can cause mis-firing under acceleration. Had problems with that on two cars. Can't see it causing flat-spotting itself which is usually a mixture thing though.
Paul Hunt

This thread was discussed between 04/06/2009 and 26/06/2009

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