8 replies to this topic

[Tifferrobinson]

Some of you kind people may remember I had a problem recently with my mini shuddering on load, well I replaced the spark plugs and got a colourtune and the problem went away. It came back a couple of weeks later and I checked and two of my spark plugs were carbon fouled (too rich) and two were completely spotless (which the Haynes says means too lean). I gave the fouled ones a little scrub and the car was fine again. Now there is more shuddering, and I am very very worried about the unequal fouling - why would the inside two be rich and the outside two be lean?

Thanks


1992 Mini City E 998cc

[wile e coyote]

This is typical of five port design & particulalry occurs using std manifold 2 & 3 are directly in fuel path , 1 & 4 being further away - without running twin carbs you'll always get this. Colourtunes can be deceptive mini engines almost always, even when rr tuned and in perfect order will have carboned plugs ... you may be running too rich though..

[998dave]

This is typical of five port design & particulalry occurs using std manifold 2 & 3 are directly in fuel path , 1 & 4 being further away - without running twin carbs you'll always get this. Colourtunes can be deceptive mini engines almost always, even when rr tuned and in perfect order will have carboned plugs ... you may be running too rich though..

Ports are outward though, I thought 1 + 4 would be richer as the fuel is denser then the air > more likely to continue outward with momentum.

What carb, spacer, inlet manifold are you running?

Dave

[Ethel]

I think the biggest issue with 5 porters is the firing order, as with injection on them. The outer ports get a quarter of the time to fill as they follow the inners in the firing order. 2 carbs won't alter that, and for the reason Dave gives, the bias of a single carb manifold could help to even things out.

It's worth looking at other things though, a compression test may show something.

[Jupitus]

Could also be a leaky manifold gasket...

[998dave]

Could also be a leaky manifold gasket...

This is very true. or loose nuts on the inner manifold bolts.

[tomswain17]

just a thought: have you checked your valve clearences?

[Tifferrobinson]

Thank you all for your suggestions. What do you mean by valve clearances? The spark plugs are all pretty new.

"What carb, spacer, inlet manifold are you running?"

I am not sure what you mean sorry, it's a standard SU sealed type carb, and other than that I am fairly clueless about what I have, it's all fairly standard for a J-reg 1992 Mini City E.

The inner manifold? Can I find out how to check that in Haynes?

It is likely to be something wear and tear related, as it was off the road for a year and developed all sorts of issues. If as wile coyote says it is just inevitable which plug socket should I do the colourtune to? I am worried about how lean the outer two are as I think that can actually damage the engine, whereas I don't want to have to buy new spark plugs every couple of weeks for the middle two.

[Ethel]

You can clean sooty plugs, overheating them will kill them. A compression test will identify most major issues. Assuming the compression is ok and it's not sucking oil down the inlet valve guides it's most likely an induction issue. Does it need an air filter; is the breather hose in good condition; & the gaskets; are the throttle spindle bushes leaking?

If you have a Haynes look up adjusting valve clearances / tappets.