5 replies to this topic

[gcos93]

Hi All,

 

I have an interesting problem:

 

I just fitted a 1275 engine to my mini and have set ignition timing, fuelling and idle speed and the car idles nicely and seems to drive fairly well.

 

However, I pulled the plugs earlier and noticed that one of them (cylinder #2 I think) was sooty and black but the rest were a nice grey colour (as expected).

 

I adjusted the valve clearances before installing the engine (I could have messed one cylinder up I suppose but not very likely).

 

I have also done a compression test and all cylinders were evenly matched around 150psi even with the starter running a bit slow on a low battery.

 

I have also checked the dwell angle, gapped the points and checked the mechanical advance with a timing light.

 

The car seems to run well with no misfiring or hunting so this all seems rather odd.

 

Is anyone able to point out any possible causes? I did wonder if a vacuum leak might be the source of the problem but I cant see how it would affect one cylinder only due to the siamese port arrangement and it should lean out the mixture rather than enriching right?

 

-- Edit: Plugs are brand new NGK BP6ES gapped at 32 thou (~0.8mm) they all had gaps preset... I just checked them and there was no need to adjust so presumably this is the standard gap for a BP6ES.

Edited by gcos93, 10 February 2015 - 01:19 PM.

[KernowCooper]

For a points system those gaps are to wide, reset them to 25thou, have you checked the leads with a meter? to see if they have aged and the ohms per foot is outside what the manufacturer states? leads age and there are lots of cars running about with duff leads.

 

Spray wd40 around the inlet manifold joint to see if its allowing in air and causing those cylinders to run weak

[gcos93]

Thanks for the input Dave,

 

I'll check the plug gaps and leads tomorrow and see how it goes :)

[Dusky]

Were it NGK plugs? I had some of those go bad recently..

[gcos93]

Hi All,

 

Thanks for all the input, just a quick one to finish this off:

Took the car down the motorway today and after the return journey I removed the plugs in order to check and gap them... All was fine! They are now all a lovely grey. I have now re-gapped to 25 thou as suggested above so hopefully this is problem solved.

 

I can only guess that my previous runs round the block weren't enough to burn off the carbon generated during the initial setting up period.

 

Pictures of all plugs are attached for interest and comments are welcome. The car hesitates slightly under load so I've tried lowering the Jet quarter of a turn and will take the car out tonight to test. I am also going to try an AAA needle rather than the AAM currently in the carb.

 

I am eventually going to have the car rolling road tuned at SRE but want to fit megajolt first and want to get the fuelling as close as I can to drive the car in the meantime.

 

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[gcos93]

Follow up to my last post:

 

Car was great on the run, no more hesitation flat out but idle is ever so slightly too rich... I'd rather have rich idle than lean full throttle so I think that'll do 'til the AAA needle arrives!