Moss Motors, Ltd

Darrel,

I think the likely clue is the two plugs. Replacing them temporarily cleared things up. Which ones were they? It appears as though whatever is going on causes them to foul or break down. How do they look? Lean? rich? green? (seriously) You may need to invest in yet another set of plugs to make sure this is repeatable. This can be a valuable diagnostic. Let us know.

It was number 2 and 3 cylinder. Three of the plugs were slightly fouled.  I did not think it serious as I had had a problem with overfueling - which I had sorted with a new needle and seat valve.  So those plugs were in when that problem occured.  Number 4's plug was a text book colour.  I will take out the new plugs this evening and let you know how they look.

I pulled all the spark plugs.  Number 2 and 3 cylinder - badly fouled.  Number 1 cylinder fouled - but not badly.  Number 4 cylinder - text book perfect!  Bear in mind that these plugs have done no more than 20 miles!

Why are the plugs so different?  Any solutions to this persistant problem?

Darrel,

By "fouled", do you mean fuel fouled (velvety black) or oil fouled (dull greyish black and smelly)? Also, refresh my memory. What do you have for a carburetter?

Fouled velvety black.

Single SU HS2

Darrel,

Sorry I dropped you there, buddy. I've got a lot of plates spinning. It seems as though you've got an overly rich running condition. Fuel distribution has not been a strong point with some of the single carburetter manifolds fitted to Minis, which may account for the uneven coloring at this extreme. Check your float height, and err an the low side if adjustment is needed. If you have tuned the mixture at idle and still get this fuel fouling it's possible you have the wrong metering needle for your application or that your fuel pressure is too high. Also check to make sure your float valve is working reliably and definately. Any of this sound like a possibility?

No need for apologies. You do us all a favor by offering your time and advice here.

I have set the float.  But will check again and err on the low side. The mixture was tuned at idle with an exhaust gas analyzer.  I recently replaced the float valve. 

I have had some serious suspicions about fuel pressure.  I know it should be no more than 3 psi.  Ideally between 1.5 and 2.5?  Am I correct?  Is there an easy way to measure this - like using a flow rate per minute?

Not sure about the metering needle?  This is the needle in the main jet?

Darrel,

You'll need a fuel pressure gauge. They are available pretty cheap at parts stores. You should have no more than about 2.5 pounds of pressure available from the pump. Volume is not important as long as there is enough, which it seems like you certainly do have. The metering needle is, as you thought, the long needle that plunges into the main jet.

Darrel take the needle out of the piston (via the three screws on the dashpot) and get the letters from the top of the needle three letter at the very base (the big end) lol

Let me know what you got! it is very possible the needle and the mian jet are badly worn or it has the wrong needle fitted! this should have shown up on the gas tester? failing that the best way to check the fuel is old school with a colour tune kit!  

http://www.moss-europe.co.uk/Shop/ViewProducts.aspx?PlateIndexID=9198&SortOrder=1

Hi Darrel,

From a second row bystander, --- have you tried substituting hotter plugs just for the ones that are fouling up?? If this appears to work I suggest a compression test is then in order, a good idea anyway!

Cheers

steve

Just an update on where I am.  Bill: Battled to find a fuel pressure gauge with small calibrations - mostly up to 10bar!  Eventually found one calibrated to 7psi.  This will make things easier to read.  Should arrive this week.

Oz:  Took out the needle.  It has EB stamped on it - which I take to mean standard mixture.  However, I rolled the needle over a smooth surface and it appears to be bent.  Does not turn smoothly.  I am sure something like this could cause an issue?

Put a new needle in, and new spark plugs again - so will let you know if that makes a difference.

No news on the fuel pressure gauge though and I wanted to do everything at the same time