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MG MGB Technical - Lead free conversion

I have recently had the cylinder head on my 1973 MGBGT gas-flowed and converted for lead free fuel. Due to bolting problems, I have removed the cylinder head after about 1500 Kilometres and I have found that there is a substantial coating (about 1mm thick) of hard black soot in all of the combustion chambers.
Because I had changed from LRP to unleaded fuel, I re-adjusted the carburetors using a “Colourtune” device, so I am pretty sure that the mixture at fast idle at least is OK.
The spark plug insulators are chocolate coloured which to me indicates an ideal mixture.
In 1500 Kilometres the engine has used no oil.
Is there something that I am missing here? Maybe different needles?
C.S. Barrow.

Hello Chris,
I understand that LRP 'is' unleaded, at least that is the terminology down here. I wonder, have your adjustments got her running rich at running? My plugs show a tan rather than chocolate colour, though I concede that may be only a semantic difference. Others may have experience of your situation and be able to offer more.
Regards
Roger
Roger T

LRP in the UK had one of the chemicals tested by the FBHVC, although it wasn't the most effective. It's also not recommended to mix additives (one of them being the chemical in LRP) so I never used it, preferring to use high-octane unleaded with the Castrol additive, which gave the best results in the FBHVC tests. I did try the octane boosting version which costs quite a bit more but found no benefit when using the basic 95 octane, so stick to the 'standard' additive in higher octane fuel. I've never had my roadster head off but have been using unleaded now for 10 years with no ill-effects. I did have the heads off the V8 about eight years ago after running on unleaded with no additive as soon as it was available, and found a similar amount of carbon on the pistons. I scraped this off just leaving a ring around the edge, but again had no combustions problems before or since. The tail pipe on both cars is black, which would have indicated a rich mixture on leaded, but you can't go by that on LRP or unleaded, with or without additives. I just set my carbs to give the correct response to the lifting pins, and that is all.

If the plugs are as you say, and there are no running problems, then I'd say you are worrying unnecessarily.
PaulH Solihull

All bets are off when using a Colortune with unleaded fuel. The colors indicated are for leaded fuel and trying to get a satisfactory reading, from your spark plugs, is next to impossible. Don't be put off by the deposits on the head. These are normal byproducts from the burning of unleaded fuel. RAY
rjm RAY

Thanks for the input guys!
C.S. Barrow.

This thread was discussed between 17/06/2011 and 20/06/2011

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