I had just sent off my carbs to gerber who has been mentioned on here for good refurbish when blow me down I read an article about ohm resistance and plug spark, well I went too the garage and not only do I have resister plug caps but also resistor sparke plugs, this apparently gives around 10,000 ohms of resistance which results in weak spark! So maybe a combination of carbs and plugs or it could of been just the plugs I will never know As I'm sorting both!