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MG Midget and Sprite Technical - Lean running

My 1275 is as follows
MG metro head MD266 Cam and lcb manifold with hif44 carb & K&N cone filter.
I am no way an expert but I was reading one of the mini sites and the same set up they recommend a BCE needle.
I am currently using a BCV which is much richer than the BCE but while the car runs fine if I take the plugs out after a good run the porcelain is bone white.Does this actually mean it is running much too lean.
The plugs have no build up or anything else,they actually look as new.
I accept a rolling road would be the answer but living in Italy it is not so easy and of course I would have to drive it to the UK.
Oh another point is that my rocker cover was cracked so I managed to get another one but this one I am using has a breather outlet on it which I connected into the original set up with a Y piece,could this also affect things.
manian

If the plugs are running a bit hot that can give the same symptom. Generally, if your compression ratio is raised you may find you need to go to a colder grade of spark plug. The execat one will depend on the actual engine spec.

As an example, we had a 1275 engine with the compression raised to 9.6:1, a mild camshaft and an LCB exhaust. We found that we had to move to N6Y Champion or BP8ES NGK.

I've had many other equivalent examples. One way you can detect if the plugs are too hot is to find a long steep-ish hill and drive the car up it at full throttle. If the plugs are too high in heat range the car will run OK initially, but after a while it will start to misfire a bit, then progressively get worse.

If you need to try a colder plug and you go for plugs which are too cold, then the idle will be affected and/or the plugs will tend to foul on slow running. If this happens try something in between.
Paul Walbran

Thanks for that Paul
I will try the BP8ES as I am currently using the BP7ES.
Do you think that the extra breathing arrangment I have affects this at all?

Thanks
Ian
manian

Id watch for oil leaks from the rear main engine seal, would be more of an issue then anything with this set up

I want to say no, that a differant differant evacc setup wont have effect on the carbs running lean...But I cant say that for certian as i know that venting thur the valve cover does have some effect on the rpms but that is air vacume not the air its self, OTHO its taking more vac. to make the higher rpm so so does that mean more air in the carb, or is the air just moving Faster....I can do this all day, LOL

In all honest, perhaps leve a bit of hose and shove a bolt into it it to block off the breather opening and go back to the correct method for evac

If its an old needle destained for the file 9, you might try filing the end off just a hair, appeartly this will make it run much richer, in what range, hard to say...a little goes along way on the filing is what I understand.

Prop
Prop

I had a Kent MD266, 1:1.5 Rockers, HIF44, K&N and LCB but Std head. I tried a BCE and it really wasnt quite right. A BDL worked much better.
Dean Smith ('73 RWA)

If you have no restrictor on that, then you probably ARE sucking a lot more air into your carbs and leaning out the mixture. I would certainly try blocking the Y-pipe from the carbs and see what happens.
David "need more details on the venting" Lieb
David Lieb

I also have learnt just know that even though a needle may be richer at the thin end we usually only use about the first 50% of the needle if we drive normally up to about 70-80 mph so perhaps I need a needle that is richer in the middle rather than the end.
I am not saying the above is fact, but I would be interested in anyones thoughts.
manian

Manian
That is a good point. I should have looked up my needle chart earlier!

BCE is significantly richer than BDL all the way down the needle.

However, BCV is richer than BCE only at idle and at the full power end of the needle. Between that is is significantly leaner, leaner even that the BDL, so I would say that your car probably is running lean.

My comment above is still valid if reading mixture from spark plug appearance - the plug heat range affects the appearance too so you need to be sure it is correct in order to get a good steer on the mixture. I would try out the prolonged load test on the BP7ES plugs first before trying something else.

The midget of ours which has similar spec - Metro head (but well modified), 266, 1.5's, LCB - went reasonably well on a BDL but had a small gasp when initially accelerating at low engine speed. I mislaid my notes so I can't remember what we changed to ... and this is the car we keep in England for when we visit so I can't simple walk out the door and check it!

I'll contact it's foster home and get back
Paul Walbran

Thank Paul, I would appreciate that
By the way I drove at about 65-70 mph for 2 hours with the BP7ES plugs and inspected them.The porcelain is still bone white.
manian

I've just spoken to Clive (who looks after the car) and it is fitted with a BGA needle. This one is leaner than BDL at positions 1,2,3 (which is where it runs under light cruising, say constant 60mph on the flat) and then similiar to BCE for the remainder, though slightly richer for the bottom half.
At positions 2,3,4 it is not too dissimialr to the BCV you have. However, BCV is considerably leaner from there until position 10. On the road, this means that it would be leaner at that 65-70mph mark especially if you were doing the odd bit of overtaking, encountering hills etc.

I arrived at BGA after extensive road testing of a range of needles. With this needle it is not perfect, but returns 40-50 mpg and has no flat spots. Clive has a copy of the notes I can't find and on them I have noted that the car was still a bit rich around 2000 RPM. However, seeing the car only intermittently as I do and given it goes well and is economical I'm much more interested in driving it than making it perfect when I finally do meet up with it!

I forgot to mention, compression ratio is around 10.5:1

Did you manage a prolonged load test?
Paul Walbran

Paul Thanks again
I will study these needles in deatil.
What is a prolonged load test, sorry but I am not sure.
I'm not so interested in perfect either,I just want to be able to drive it knowing I am not damaging it.

Thanks
Ian
manian

Prolonged load test - see my post above:

"One way you can detect if the plugs are too hot is to find a long steep-ish hill and drive the car up it at full throttle. If the plugs are too high in heat range the car will run OK initially, but after a while it will start to misfire a bit, then progressively get worse."

If you don't have a steep enough hill, you can load the engine with a bit of left foot braking - however after a while the brakes might get a bit on the extra warm side!

If all else fails, a rolling road is the ideal way to sort all this, but then it costs.
Paul Walbran

This thread was discussed between 14/05/2009 and 15/05/2009

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