If the engine has high HC with CO being OK is it lean or rich, or could it be either?.

hc is hycrocarbons? if so, its unburnt fuel, which means too rich. CO should be high too though...

Is hc too high when it is burning oil? I know one of the tests is for this.

But if it was too lean there wouldn't be enough O2 so surley some of the fuel would still be unburnt???

If it is very lean, all the fuel is burnt, but you get o2 in the exhaust as there was insufficient fuel for all the o2 to be used up. The hc's can increase as the combustion is hotter, the oil gets thinner and some is ejected on the exhaust stroke from the rings.

Cheers mark,

Was tired last night. I realised I spouted Bo***ks as soon as i woke up. Thanks for your help.

Steve,

With marginal CO and high HC you're running lean. All the fuel doesn't get burned because the flame propagation (spelling?) speed is lower with a lean mixture. Therefore the mixture is released into the exhaust before it had the chance to fully burn.

Depends on the definition of high HC's.

to make any objective reasoning values really need to qouted for
CO
HC
CO2
Lambda

also what engine/fueling



Enjoy. 69 Days & counting

High HC's and ok CO can also be caused by one or more cylinders misfiring, due to e.g. duff spark plug, sticking valve etc.

Thanks Seb, That is exactly what I wanted to hear!

You were right Seb. I blanked off some of the air box with gaffa tape and now it pulls sweet all up the rev range. I will now order bigger jets 124's and 126's as they only cost £1.50 each.

not sure if this is any use as problem seems to be solved but for general interest...

Chart was of help.

Changed jets to 126 today and boy, what a difference!!!!

Goes like brown stuff of a shovel