Carburettor switch

Post by **psjorge** » Wed Dec 03, 2008 9:31 am

Hi,

Along the years several carburettors were used, as everybody knows...

Are they all interchangable? If so what are the possible advantages/drawbacks of doing so?

Many thanks,
Pedro

Post by **Shawn** » Wed Dec 03, 2008 8:27 pm

Basically, yes, you can interchange them, along with the matching inlet manifolds.

They are often one of the first things changed, and can result in more power, but you should also then be looking at a bigger exhaust.

Whatever you switch to needs to be in good condition and properly tuned/jetted or you'll just be wasting petrol.

Post by **psjorge** » Fri Dec 05, 2008 10:38 pm

Thanks for your answer.

You know, my problem is the following:

My car is an early '54 (built date of January '54 or December '53, I'm not exactly sure) Series II, 4 door saloon, LHD export model. This means it should have a 803cc engine with a H1 1'1/8in carburettor.

It should but it doesn't! Someone, sometime,for some reason swaped it for a 948 cc!

As far as the carburettor is concerned I'm not quite sure wether is a H2 1'1/4 or a HS2, used from 1960 onwards. I assume that the engine should be from a date later than February '59 because it has the saucepan-type Cooper's paper air filter.

To further complicate things, the union on the pump's linkage to the carburettor is of the type that uses a threaded pattern. I don't know exactly when it changed to a push-on type, so I can't date it more accuratly.

As you realize, I'm stuck with a bit of a mess!

What should I do? Should I use a HS2 carb or a H2 (although both are correct-for-the-engine-incorrect-for-the-year...)? Which is the correct for my engine?

Or should I use a correct-for-the-year-incorrect-for-the-engine H1 and, if I eventually get hold of a 803 cc engine, I allready have the correct carb?

I would value your advice...

Pedro

Post by **bmcecosse** » Fri Dec 05, 2008 10:41 pm

The H1 will strangle the engine horribly - so DO use an H2 or HS2 - it doesn't really matter! Obviously the later HS2 is an 'improvement' over the earlier carb - but there is no difference in air flow.
Be very glad you have a 948 engine - it's a very much better engine !

Post by **psjorge** » Fri Dec 05, 2008 11:07 pm

Thanks for your wise advice bmcecosse!

Your basically saying that I should keep my 948cc engine and the hell with originality! You're not the first pointing out the low performance of the 803cc engine... The first person was the mechanic that's restoring the car for me!!!

Having said this, I must explain that I bought this Minor on impulse in a VERY bad shape... without my wife's knowing about it (don't advise anyone doing this... for the obvious reasons!)

Anyway, once the car is restored it will join my '66 MGB roadster.

As I do have another car to use on a dailly basis (actually I have two...), the Moggie will not see much action as it will be a sunday-drive car.

This means that performance is not a major concern. I value originality instead.

If I find a 803cc engine for sale at a convinient price, I'll probably change the 948cc one for originality sake. Or maybe I won't, can't honestly say!

Independently from all this, from the info I provided, can you say if I have a H2 or a HS2 carb? At least I should try and have a correct-for-the-engine carb, don't you agree?

Pedro

Post by **mike.perry** » Fri Dec 05, 2008 11:25 pm

The H2 carb has the float chamber bolted on to the bottom of the carb. On the HS2 the float chamber is connected to the carb by a plastic pipe.
The standard needle for an H2 carb is a BX1 and for an HS2 is an M. Unless you are desparate to keep it original stick with the 948 engine, it is generally reconned to be the smoothest engine of range.
What gearbox are you using? The 803 was not a very good box and had a nasty set of gear ratios.
If you still have the original diff you may find the overall gearing too low with the extra power of the 948 engine

Post by **psjorge** » Sat Dec 06, 2008 8:43 am

I'll take a closer look at the carburettor to check for the differencies you've mentioned.

As far as the gearbox is concerned, I'm unsure which one is it. What sould I be looking for to set them apart?

The diff I also don't know but I would risk saying that it is original that came along with the 803cc...

Post by **mike.perry** » Sat Dec 06, 2008 10:10 am

Have you got a long gear lever or a short gear lever coming up vertically in front of the hand brake? The 1st type is an 803 gearbox, the 2nd is the 948 gearbox.
I am not sure how to tell which diff you have without stripping it out when the ratio will be stamped on the crown wheel, but if you have the 803 diff you will soon notice that you are revving the engine at speed.
I would advise you to buy a workshop manual, you are going to need it.
I think you can download one.

Post by **psjorge** » Sat Dec 06, 2008 2:41 pm

I must have the 948cc gearbox then!

The gear lever is not that long but is unquestionably straight. On the other hand the gearbox tunnel cover has the square rubber cover gaiter which must also mean a 948cc 'box...

Regarding the diff, as you say I'll have to confirm it when driving the car. It was revised, painted and put back on the car...

I bought the car in a VERY bad condition, stored under a shed for many years, so I never drove the car!

And yes, I already have a workshop manual.

Thanks,
Pedro

Post by **bmcecosse** » Sat Dec 06, 2008 4:41 pm

The 803 engine is very short of power - and very weak too. The crank has been likened to a 'bent piece of wire' - so be very glad you have a 948. You could confirm the final drive ratio by jacking up a rear wheel - and then find how many turns of the prop shaft it takes to make 1 rev of the wheel. The diff will X 2 this because only one wheel can turn. The correct ratio for a 948 car is 4.55 - so you can expect 2.28 turns of the prop to make that one turn of the wheel. To get a decent result - it may be better to go for say 4 turns of the wheel and then divide back.
The H2 carb is in fact more relaible than the later HS2 - where the pipe bringing the fuel from float bowl to carb can develop leaks. As far as running is concerned there really is no noticeable difference.

Post by **psjorge** » Sat Dec 06, 2008 5:48 pm

Ok, ok, I shall not mention the 803cc engine again!!!

Independently from which differential is actually fitted to the car, I'll keep the existing one, for the moment, even because I don't have another!!!

However, it's important to know if it is the correct one or not and you gave me an execelent idea. Brilliantly simple!

Regarding the carburettor, I have to check if I have an H2 or an HS2. Independently from this, I'm thinking on buying a new one because it will be better to have a new carb on a car that has been completely dismantled and reassembled... and VAT is down in the UK as well as the pound's exchange rate for euros which makes them cheaper now for continental buyers such as myself...

Many thanks!

Post by **rayofleamington** » Sat Dec 06, 2008 7:55 pm

Ok, ok, I shall not mention the 803cc engine again!!!

They are slow and weak, but they don't lack character ;-)

Post by **psjorge** » Sun Dec 07, 2008 1:01 pm

They are slow and weak, but they don't lack character

Ah! The smoothing intervention of the moderator!

Deep inside I'm an 803cc fan hardened by incisive comments by... almost everybody!

Maybe there should be a 803cc section on the forum, eh, eh, eh!

Regards,
Pedro