Is it serviced?ie filters/plugs etc,quite an old motor this and you may be able to adjust the carburettor and check the needle valve/seat etc isn`t worn and maybe give it a clean out,a compression test may be worth doing also as it is an old motor,if you are struggling to get the readings for an mot a fuel conditioner is worth a go also and may help clean out your fuel system.If all else fails you will need to decide if it is worth repairing against scrapping the motor.
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