SP Workshop Manual Wrong Again

[Ian Hastings]

Apologies if I am teaching Granny to suck eggs but I have found the workshop manual to be incorrect. I have searched and not found any reference to this anomaly. Normally when I set the carbs on my SP I do it by the book then go on a test drive, stop and remove plugs to check their colour and adjust the relevant carb to richen or weaken as necessary.
Going by the info in the workshop manual this has led to totally confusing and incorrect results causing many days of frustration and bad language; but I have now discovered why.

The left Hand carb feeds cylinders 1L 2R 3R 4L
The Right Hand carb feeds cylinders 1R 2L 3L 4R

This is not what it says in the workshop manual, the manual is incorrect.

[Paulkennedy]

I understood that when the manual refers to left and right in reference to the engine it is as if you were sitting in the car, not when standing at the front of the car.
Paul

[Brian-H]

^ ignoring the numbering....

if I stood in front of the car, carb on my left would feed the centre two cylinders on my right
if I sat in the car and looked at the setup from there, carb on my right would feed the centre two cylinders on my left

So it makes no difference which is left and which is right ?

[Paulkennedy]

Brian, it plainly does make a difference the manual is referring to the the left hand carburettor as viewed from the drivers seat, then if you are adjusting the left hand carburettor standing in front of the car, you are adjusting the wrong carburettor.
Paul

[Brian-H]

Paul, maybe Ian has two left-hand gloves which, on one hand, is great, but on the other, it’s just not right.
Other than that, I've got a Gunson's colourtune which makes life a whole lot easier.
Brian.

[John-B]

The manual says you have to raise the needle at the side of each carb 1/16" and see whether the engine revs are constant or rise or fall, then check the other carb. Have you tried that?

It won't tell you if the plugs are connected in the wrong order, you will know that because the engine will be lumpy if that is the case.

[Ian Slade]

The raising of the needle only refers to the idle configuration, getting the mixture and balance correct is quite involved, balance the carbs at idle, then set the mixture recheck the balance it can change, once the balance is correct at idle set the throttle lever arm to 3000rpm, check the balance, if necessary adjust the individual carbs at the short linkages until balanced, the mixture should be equal on opposite cylinders but won't be the same on all cylinders the end cylinders will be weaker than the centre ones. Ensure that the extremity cylinders are not too weak as this can burn valves, if necessary richen the mixture at idle to overcome this, off centre jets will cause mixture and balance problems.

[Ian Hastings]

Paul. I am well aware of the orientation of the engine and not only that the cylinder numbers are cast onto the various ports of the manifold for easy identification.

Brian. You are absolutely right, the opposing carb feeds the center two cylinders on one side and the same set up on the other side.
This is not what the manual says, it states that:-

Left Hand carb feeds 1R 2L 3R 4L
Right Hand carb feeds 1L 2R 3L 4R
This is incorrect and certainly does not match the two manifolds I have sitting on my bench. One is from an SP and the other a v8 250 and they are the same and have the distribution as listed in my first post.
So the manual is incorrect.

John. I tune the carbs in the conventional manner as you describe then road test it and check the plug colours to confirm everything is OK. I have not connected the plug leads to the wrong plugs. For instance, going by the manual if I removed L1 plug and found it sooty the manual indicates that the right hand carb needs adjusting, but this is not the case, it should be the left hand carb.

If you don't believe me, next time you have a manifold in your hands check out the distribution from the carbs, you will find the workshop manual is wrong.

[Brian-H]

btw I wasn't joking in the sentence about Gunson's colourtune. These sell on ebay for around £50, some as B.I.N. and some as auctions. I would guess that for a twin-carb engine, two would be great.

I have just one, and admittedly I've only ever used it on single carb engines, but it makes setting the mixture (and even the timing at a stretch) such a joy. It's only a fancy spark plug with a glass viewer built in, but it enables you to see the colour of the flame, which goes from light blue (lean) to dark blue (stoichiometry) to orange (rich).

If anyone does consider getting one on ebay (I don't think they're available anywhere else) condition is probably not important as long as the glass is not badly sooted up (which can be cleaned using IPA and a small brush) and that the relatively large electrode is good enough to adjust for a good spark. You'd also need the thing that looks like a small wand, which is an extension piece so that the plug lead sits several inches out from the "colourtune plug" so as to see the flame behind the glass more easily.

As said already regarding lean on outer cylinders, if you set the centre cylinder(s) to dark blue you do usually see light blue in the end cylinder(s) - if that's an issue then set the end cylinder(s) to almost dark blue and then you'll see the centre cylinder(s) just about orange (with some blue still in the flame).

PS for standard car engines you'll want the 14mm version, not 12 mm or 10mm - AFAIK spark plug threads are 14mm in most cars right the way up to and including modern engines e.g. FSI, VVT etc - it's only the hex size that varies on 14mm threaded spark plugs

[John-B]

The left Hand carb feeds cylinders 1L 2R 3R 4L
The Right Hand carb feeds cylinders 1R 2L 3L 4R

This is not what it says in the workshop manual, the manual is incorrect.

I think you are muddling the firing order with the allocation order from each carb.

My service manual for an A spec. only gives the firing order IL, 4R, 2R, 2L, 3R, 3L, 4L, 1R for plugs both sides of the engine (not the carb position).

and the left side is L1, L2, L3, L4 and right side is R1, R2, R3, R4 numbering from the front as viewed from the driver's seat

which corresponds to 1L left carb, 4R right carb, 2R left carb, 2L right carb, 3R left carb, 3L right carb, 4L left carb, 1R right carb. Note that the middle two each side swap to the carb on the other side.