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MG Midget and Sprite Technical - HIF carb update

As the floods, ice and road debris have lessened somewhat up here in the Tundra, I took the opportunity yesterday to test drive the midget with its new HIF 44 fitted. I have to say that intial impressions are very favourable. Much better pull from low down, a seemingly freer revving engine, and slightly improved acceleration.

Drive spoiled somewhat by a BMW - why is it invariably a BMW by the way? - up my exhaust pipe on a twisty road with no hope of passing, and I was moving a bit, but all in all a good improvement. Too soon to see if whether fuel consumption has improved, but all of the above and a slightly smoother running engine are good indicators.

I was fortunate that the good condition HIF 44 from fleabay (80 quid) needed little attention, apart from a needle change, and it also came with the standard manifold - that fitted with no further modification to the engine inlet profile - but thanks anyways Steve C....I can only assume that engine mounts/bonnet were changed out sometime.

Pic shows the installation. Yellow hose is the breather, braided hose the fuel, and the clear tubing for the overflow. All routed so as to minimise the bends, and fill the void left. They need a wee bit of further attention for sure. Choke is from a Morris Minor - with special homemade wooden chock at the dashboard end for holding it out on start! Throttle cable from Metro, with additional spring for beeter "feel". Took about a day to fit up and fiddle with mix/idle/fast idle. Greatly assisted by the manifold needing little attention.

So far a very worthwhile improvement. I would recommend it highly...

Mark O

Mark - yes so much easier to tune & maintain in addition to performance & economy advantages.

I've now routed my coolant through the manifold - some advise against this on the basis that it will warm the air in the throttle chamber making it less dense. On the other hand I believe the reason BL (& Titan Motorsport) manifolds use this pipe was as an aid to cold starting. I assume BL tested these aspects & chose to do the logical thing (?). Personally, I've tried it both ways & could not tell any difference but then I only have a standard 1275.

Only minus is perhaps the aesthetics of a pair of twins - but I can live with that.

Gavin Rowles


Yes absolutely agreed wrt maintenance/set up. Cannot say I have encountered any problems with starting - so I will leave coolant ex manifold - as is. Aesthetically yes, pair of beefy SUs very nice, but then under the bonnet is not really on show most of the time.
Mark O

the only thing I wonder is whether you are comparing a set of worn twin carbs to a rebuilt single in which case you'd expect some improvements

with my previous twin set up, which wasn't as good as my present set up, and a 4-speed box I got 50mpg at a steady 50mph for a 100 miles of M6 (yes it is possibly to drive below 70 mph on motorways!)

I used the motorway as the test road as after initial take off there's no gear changes, braking or real acceleration

we were using the M6 to go north for a weekend tour, I discovered my wife lacked the necessary discipline to be a patient passenger for the two hours of this test

after refilling from the test my mates caught up with us and we followed them at higher speeds (Honda S2000 and Toyota Supra) and next refill showed 25 mpg

I keep meaning to do an mpg test on my present set up but I can't resist giving it some beans
Nigel Atkins

To be honest Nigel, I am comparing the HIF44 to a pair of entirely non-standard 1 1/2 inch old SU carbs - as fitted by the PO. However, reading around quite a bit, pretty convinced they would also be an improvement over standard SUs, especially with my upgraded head and higher lift camshaft.
Mark O

secret with twins is to get everything on the car including the twins sorted, set up and running well and keep up the full servicing, maintenance and repairs and then importantly leave the twins alone don't fiddle with them and drive the car frequently

it would be interesting to see, on a fairly standard car, a good set of twins RR tested then swapped with a single on the same car and tested on the same RR

mainly because the fuel tank is so small I wish I got more mpg out of mine but I do enjoy the soundtrack that comes with more spirited use

Nigel Atkins


That looks a nice installation, especially with no manifold or bonnet clearance problems.

If you still have your old 1 1/2" SU's and manifold and don't want to keep them, I may be interested as my 1 1/4's are a bit small for my set-up. A bit like me, they run out of puff before the engine does, and I've wanted to try twin 1 1/2"s rather than going down the HIF44 route. I'm looking for a nice matched pair.

If you're interested you can e-mail me at: peter at pbca dot co dot uk.
Peter B

One of the best advantages (having reconected the exhaust and carb manifolds on Sunday) is the ease of fitting the stud nuts. It's so much easier with the single carb than with the twins.
frogeye Gary

Why the exhaust wrap?
Guy W


It was on when I bought it! Why not???


Mark O

those that know more than I (most of the population) suggest that the exhaust wrap does more harm than good, IIRC holding more heat in the head
Nigel Atkins

So which manifold did you use? You say "standard" but would be interested to know which standard. This seems to be an area with a lot of experience gained around the BBS but with a wide variety of different conclusions about what works and what doesn't.
G Williams

By standard, I mean the one that came straight of the original car - with the carb attached. I seem to remember a standard Metro - not MG Metro - in the EBay ad. From what I have read, most manifolds will push the carb top too high and foul the closed bonnet - I think I was lucky in that my engine mounts have been lowered and this combined with the replaced bonnet on the car originally gave the clearance required - thus no awkward machining on the manifold cylinder head mating face.
Mark O

It's an MG Metro Metro manifold I think. I'm fairly sure the non MG Metro's had a cast iron inlet and exhaust combined, my 1.0 HLE certainly did. Might possibly be from a Mini Cooper but not sure on that one.
John Payne

It's definitely a MG Metro one, minus the steel coolant pipes which have normally rusted away. The Standard Metro all had cast iron combined manifolds. You've been lucky that it fit without fouling the bonnet. May indicate knackered engine mounts.

This thread was discussed between 03/01/2013 and 15/01/2013

MG Midget and Sprite Technical index

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