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Sooty Spark Plug on Cyl 1


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'70 CP. Just fitted MU after re-build and have done around 60 miles. All injectors pulse same and cone spray is same. However on cylinder number 1 (at the front closest to the rad) the spark plug is dry sooty. All other plugs are fine with fawn/light grey. Car has bags of torque and goes well apart from a little low speed lumpiness (30mph'ish in top) Plugs are NGK BPR6EIX (Iridium) and have been in for last 5k miles. Gaps at 35, Coil Bosch Blue, on 124 Dizzy. MU rebuilt due to ruptured diaphragm. Starts from cold on all six  (full choke) Any suggestions before more serious investigation ?

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16 hours ago, JohnTB said:

'70 CP. Just fitted MU after re-build and have done around 60 miles. All injectors pulse same and cone spray is same. However on cylinder number 1 (at the front closest to the rad) the spark plug is dry sooty. All other plugs are fine with fawn/light grey. Car has bags of torque and goes well apart from a little low speed lumpiness (30mph'ish in top) Plugs are NGK BPR6EIX (Iridium) and have been in for last 5k miles. Gaps at 35, Coil Bosch Blue, on 124 Dizzy. MU rebuilt due to ruptured diaphragm. Starts from cold on all six  (full choke) Any suggestions before more serious investigation ?

Hi John,

Change that plug with another like from number 3 if that goes sooty, check HT lead resistance, or change the injector, it may be something simple. Finally a compression check may be required. A 0.035" gap may be too large for your ignition system as no1 lead is the longest.  I am not familiar with the 124 dizzy so I have no experience of using them. But I have used the NGK Iridiums and was not happy with the results that I had from them ( some of the plugs were sooty) but my MU was on the way out at that time?

Bruce.

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Thanks Gents. I will swap the spark plugs around and see what that brings (should have thought of that as I had tried swapping the injectors 1 to 2 to no avail). Did meter the plug leads and they all seem fine. The suggestion to look at the sparks on all cylinders is a good one, not thought of that. I have just checked that the hole at the back of the butterfly on number one, to the air bleed tube is not blocked and that seems OK. Going to be Sunday before I can go for a run so will report back. Thanks for suggestions.

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