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MG Midget and Sprite Technical - Air filters for 1¼' SU's

Hi everybody, I would appreciate some advice. Apologies in advance for my lack of knowledge of the oily bits. I'm a learner!

I have a 1971 Sprite with a 1275 engine, an MGOC rebuilt unit, that is standard. It has twin 1" SU's (I tried to upload a picture, but the system tells me that the file I specified is too large, so sorry you will have to make do with my poor description). I have the air filter assembly that was on when I bought the car, which is one of those in fluted metal that bridges across both carbs, and says 'SPRITE' on it. This is secured by two bolts, one towards each end. One of these has consistently come loose since I have had the car. I have replaced the bolts, replaced the nuts, added washers, and have had it looked at in the margins of other work by a few specialists, and still the same bolt comes loose and needs tightening after every long run.

So basically I'm tired of it, I never much liked the look of it anyway (it looks a little big and heavy against the engine to my eye) so I'd rather replace it with a pair of individual air filters, ie. one on each carb. The MGOC magazine came this week, with a separate pamphlet listing lots of parts with pictures, and in there there are pictures of K&N air filters (two small chrome pancakes, basically!) and a second type of air filter, which has 'SU' in big letters on each one. I like the look of both, so wondered if I could pick your collective brains for a recommendation? Are the SU ones intended for earlier cars (like T series?) or for 'our' period cars? Would either type perform better/suit my 1275 engine better? I have been advised to fit stub stacks with these, is this good advice? And could I fit these myself, or will I run out of talent before I get the job done?

Sorry for all the questions, I'd just rather not take a misstep, and the advice on here is so sound, as it tends to represent the thoughts of a knowledgeable group rather than a knowledgeable individual, so, er, any thoughts much appreciated. And apologies again for the lack of picture and resulting length of posting!

Piers
Piers Colver

Sell your existing one on ebay & with the money buy a couple of chrome K&N filters, from said cheapo site.

cheers
Brad
Brad (Sprite IV 1380)

I just slap on the cheapo ones as used on a Triumph Spitfire.

Peter
Peter Caldwell

I think that the dual one that you have works well, it has the advantage of having built in stub stacks. Is it the outer nut which keeps coming off? It happened to mine all the time till I used some red nut lock glue (is it called tablock)? and it worked fine after that.
Later I used another method. I used a nut which had a slightly larger ouside diamiter and actualy locked itself against the ribbs on the outside of the cover. It is quite easy to do as the rubber filter will allow you to compress it a bit then it will then push out and lock the nut in place. To undo the nut you simply compress the filter a bit and then undo it by hand.
Possibly not the clearest description but I know what I mean.
G Lazarus

Threadlock is the name, Loctite do the best.
Brad (Sprite IV 1380)

Yes it is a very common fault with that type of filter. In fact with the majority of K & N filters. Once recognised it is a simple fix with loctite although the over size nut described by Gary is rather ingenious.

IMO Stub stacks are fine, but in the rolling road tests I have done with them I have found difficulty in actually measuring an increase when fitted. But maybe I am wrong :-(
Robert (Bob) Midget Turbo

I prefer the longer ones that can take a bit of stand off, but stub stacks are better than no stacks.
Brad (Sprite IV 1380)

Just a question.
Would lack of forward momentum on a rolling road (and no big fan at the front as my car wasn't overheating) make any difference to the amount of induction into the carbs between a moving and static car?
G Lazarus

Little or none Gary.

Mark,
M T Boldry

Hi piers! This is the proud owner of GAN5UB91179G a US spec 1971 MG midget! You have the kind of car I dream of. An austin sprite. It would confuse the hell out of every car club in the area. First of all I have been seraching for the badges and horn push to do the conversion. If you can tell me where I could find such parts I would be much abliged.

As per your question. I have the stock "cooper cans" They are what came with your car. they were black and fit canister style air filter units that are about 3-4 inches around and 3 to 4 inches deep. The air cleaners had a cone shaped air inlet on the site and they were two separite air cleaners bolted together at the middle. The sprite branded one is one that I have seen before. I to think it's gaudy but in a classic 1980's sort of way. I like the OEM look a lot better but I did once try to make my own air cleaners out of some plastic wall bumper disks 9 used to protect the walls from doorknobs when the door opens too far.) No noticable improvement in performance. I have used the K&N stock size filters for years and they work VERY well. Totally reusable, saves a ton of money over the years and there is a noticable improvement off the line upon installation.
S.A. Jones

What's the general opinion on having to fit richer needles with K&Ns due to the reduced resistance to airflow? Or can you just fit 'em and forget 'em?

-:G:-
Gryf Ketcherside

Seth,
Piers' filter assembly might look "gaudy" to you, but its performance far exceeds your originals, whose snorkels severely restrict breathing. Don't forget, your VIN would immediately betray the fakeness of your Austin Sprite conversion. The very first letter would put the lie to it. Besides, you would also have to convert it to RHD. AND, anyone who noticed would already know about the AAN.

Piers,
I agree with those who say to retain your current filter, but only because it would cost too much to swop for an original set with me ;-) If you were a bit closer, I would do my best to convince you that it is utter rubbish and you should trade with me.

Gryf,
I have heard that as often as you have, but none of my cars really cared beyond a flat or so of the adjuster nut. Certainly not wanting a new needle.
David "I like the filters that Bugeye Barn sell" Lieb
David Lieb

Fit a side draft then your never have to worry about SU needles ever again :-)
Brad (Sprite IV 1380)

Everybody: thank you for the various responses, very helpful to get a snapshot of your collective thinking.

Seth: The front grille badges are very difficult to find, my car had a good one on it when I purchased the car, and I have never seen another come up for sale. Boot badges seem to survive better, so come up for sale from time to time (three or four on Ebay in the past year), but seem to go for £80-£150 or so, so aren't cheap and quality varies. I bought mine in poor nick, paint-wise, but fortunately the ever-helpful Guy Weller on here kindly put me in touch with someone who could restore the paintwork, not easy on a near-40 year-old plastic part. As for faking an Austin Sprite, I have nothing against reps (my father runs a classic replica as he could never afford the real thing and he loves it to bits) but the '71 Midget is a lovely car in its own right, so personally I would keep it as a Midget, as you have an original, but then the great thing about this hobby is that we would all do different things to similar cars. 'Though if you're really commited, I do have a friend thinking about selling an Austin Sprite boot badge, as he has seen the recent prices on Ebay. His is in a badge collection, so he thinks it might be worth more to him as cash than a badge! Anyway, not sure whether he is going to sell, but if he does he will do it through my Ebay account as he doesn't have one. I also haven't seen it, so don't know how it looks... Might come to nothing, but thought I'd mention it, certainly worth monitoring Ebay for those.

Anyway, sorry to ramble on, thanks again for all the responses,

Piers
Piers Colver

This thread was discussed between 04/03/2009 and 08/03/2009

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