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MG MGB Technical - MGB carb change point

Does anybody know what vin numbers crabs changed over at.
I have a late 72 regstered GT I have just bought and still trying to work out if it is a 73 model year or a 72.
The cabs ion it are biased HS4's but I think it should be HIF4's?
The VIN is on the change point at GHD5 301xxx.
Its only a problem because I need to rebuild the carbs t solve a running problem and if I am going to spend up to 80 on a rebuild kit I may as well change the cabs to the correct ones and rebuild these.
Anybody know exactly what VIN number HIFs were fitted from? The engine number is no use as its missing and there is some weird number on the V5!
Neckieman

I'm afraid there is probably no definite change over point. BL probably carried on using "what was on the shelf" until it ran out and also export models got changes at different times to the home market cars.
Allan Reeling

Not car VIN number but engine number. Clausager says this in his book "Original MGB":

"HIF4 carburettors were introduced on home market cars in November 1973 with engine types 18V-779 or 780."
Mike Howlett

Unfortunately my engine number is gone, it is probably an 18v but the actual number is missing.
However my car was registered in Nov 72 so while I think it is a 73 model year car, going from what you are saying it would have had biased needle HS4's?
This is what is fitted although the actual carb number is also missing............
I should have the riginal engine number is a few weeks once the heritage certificate appears.
Neckieman

The trouble is very few engines, distributors and carbs are the original ones as the cars have been 'messed' with over the years. Allan is also spot on saying BL fitted what was on the shelf at the time. We have seen this in engines, carbs and distributors. Unless you are seeking originality and your car should have shipped with biased needle HS4 carbs the HIF4s work better. Get the workshop manuals out and start reading and learning and enjoy the journey.

Peter
Peter Burgess Tuning

My roadster was built September 72 i.e. a 73 model with a chassis number 297nnn, but wasn't registered until June 73 so the first registration date is no guide at all. The BMIHT certificate will give you the true dates, but without an engine number you won't know whether it is the original engine, and even if you did have the engine number tag it could still be a different engine.

Clausager gives the chassis number change point for the change from HS to HIF on non-North American cars as starting at 332033 and finishing at 336650 approximately i.e. there was considerable overlap. As such that was after the start of the 74 model, which began in August 73, so from your chassis number you should definitely have HSs. Spring-loaded needles were used when 18V engines were introduced.

Whilst HIFs were marginally better for the environment HSs are significantly easier to live with. If I had to choose between the two I would always select the HS.
Paul Hunt

I am awaiting the heritage certificate to get a build date. However the reg date of Nov 72 means that it had to have been built before that date, even if it was some months before.
When it comes to reg dates I am well aware of the differences and unreliability of the data.
I have two midgets, both built in Mar/Apr 72. One was registered in Oct 72 but the other, which is the slighly earlier March built one, was registered in Sep 75!
It looks like the biased needle HS4's are probably the correct ones for the cars age, so with simply rebuild those.
While I am not anal about originality when I am changing or repairing parts I do like to rebuild it as far as possible to the original spec when repairs are required, particularly when parts need replaced.


Neckieman

I guess your petrol is 10% alcohol. Whatever you decide, the refit is an opportunity to fit alcohol proofed floats.
Roger Walker

The existing floats are white plastic, I had a look last week.
Why would the petrol be different up north or am I misunderstanding something?
The last time I had an MG of anysort 4 star had just been deleted at the pumps......
Neckieman

The introduction of ethanol into petrol has a corrosive effect on some fuel system components. It's currently 5% in the UK, but this will rise to 10%, where I believe it is in the States. Might be worth Googling some US sites on the subject.
P A Allen

It's currently 5% MAXIMUM in the UK, unless the pump states 95 E10, in which case it can be up to 10%. Higher octanes e.g. 97 and higher have no ethanol for the time being as they are classed as 'petrol protection grade' for older engines.

However producers have said in the past that they can meet their statuary requirements for renewables in the UK purely through biodiesel, and have no plans to introduce it in petrol. That could change at any time of course.
Paul Hunt

mine is Nov 72 also.
I have AUD 429, biased needles.
consistent with all i have read.
VIN GHD5 303xxx
a pair of new HIF will set you back £350-400 if you can get them as they have stopped production. used, you might get worse than you have ... needing rebushing....
HS series is much easier to service too, and troubleshoot.
technically, i read that HIF are superior, but i very much doubt if you would notice nay running difference on the car.

Graham
Graham Moore

I may have found part of the problem. When I bought the car a month or so ago and drove it home from London to Inverness I filled it up with the higher octane "superunleaded" the last fill I was unsure what pump was this and it seems on looking again that it was 95 octane.
On filling the tank today I refiilled again with 97 octane and the running, after 25 miles or so is much sweeter.
I am pulling the engine and gearbox for a refresh in a few weeks and have the carb rebuild kit now anyway so with rebuild the carbs while it is out, if nothing it will make them easier to balance and tune.
Neckieman

If your ignition is set to get the best out of 97+, then you ARE likely to have running problems on 95.
Paul Hunt

Its not the whole solution though, still have some poor running only at small throttle openings and especially when cold.
I am going to pull the whole engine gearbox shortly and service,repair a pile of bits to freshen it all up, will be more worried if its still there when I have finished that!
Neckieman

This thread was discussed between 25/03/2016 and 08/04/2016

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