mixture

[minor65]

I know this has been discussed many times, but here we go again.

I thought I had the mixture set correct on my 61 948cc. On Saturday when going home from the mot centre i took it a good run, but before i got home i pulled in and remove a spark plug to check the colour. It was starting to go a digestive biscuit colour. And on using the lifting pin, when the piston was starting to lift the engine revved a bit quicker. So i thought the mixture was correct. Though i took the car to work today which is a 3 mile journey each way. On returning home tonight I removed a spark plug and it was black again. It was not sitting on the choke and averaging 30mph. Would you expect the plug to be black if the mixture was correct on that short journey? So thinking the mixture was too rich I decided to weaken it a bit. Meaning now that when I lift the pin the engine dies out, so to me that means it is to weak. Although it still sounds good.

[bmcecosse]

The biscuit colour on a good run is ideal , could maybe go a tiny bit weaker for best economy - more towards a Rich Tea. Lifting the pin should pretty much do 'nothing'. When the ignition is first switched on - and the pump ticks - does it stop completely after maybe 2 or 3 clicks ?

[minor65]

As far as I know it clicks a couple of times and stops (as it should) but will check. The handbook says that if the lifting pin is used and the engine revs increase slightly the mixture is correct. Which is what was happening even though the plugs where black tonight. Could it be an over fuelling issue with the float ?

[chesney]

Are you sure it's not 'oiled up'? Generally, if you can wipe away the 'black' easily with your finger, it's oil.
Also, due (in part) to the siamese porting, the middle two cylinders get a slightly different mixture to the outer two, which could be affecting your results.

[minor65]

No it's not oil, it's black soot and all plugs are the same. At first the pump clicks twice, then with the ignition on (engine off) the pump then clicks once every 8 seconds.

[bmcecosse]

That was my thought - if the float valve is leaking slightly, it affects the idle/low speed running as in 'traffic' but on the open road (is there such a thing these days....) the fuel is used up and the correct running mixture displays on the plugs. Just noticed your 8 seconds - that probably does indicate a slight leak. A new valve won't go wrong, and you could lower the float level slightly - but not too far or it will splutter on corners.... Just ignore the short run plug colours - heavily affected when you start up on the choke, and maybe not run long enough/hot enough to burn off the black. And yes - any oil burning will affect more in traffic/stop-start than it will on a good thrash ! Have you optimised the ignition timing - so it's 'not quite' pinking ?

[minor65]

OK. I have ordered a new float valve from ESM. So will give that a go and then we'll see after that. Thanks men

[Trickydicky]

OK. I have ordered a new float valve from ESM. So will give that a go and then we'll see after that. Thanks men

If it's a brass float you can drain any fuel in it and solder the hole up, eliminating the need for a new float.
Is it brass or plastic?

[bmcecosse]

I doubt there's anything wrong with the float - the ticks would be much worse than the '8 seconds' . The valve will have a wee lip on the taper - after all it could be 40+ years old !

[katy]

Though i took the car to work today which is a 3 mile journey each way. On returning home tonight I removed a spark plug and it was black again.

and maybe not run long enough/hot enough to burn off the black.