MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG Midget and Sprite Technical - Ewin 11/2 SU's

Spent an afternoon yesterday on Slark's rollers trying to tune in a pair of 11/4 SU's on a lightly modified 1293. Got it reasonable in the end but the idle is a bit rich. The problem is the engine wants to breath more and the carbs are just a bit small. I was wondering on fitting a pair of twin 11/2's Yes i know about the value of a single big one but I have a good pair of 11/2's with the take off so I can retain the existing 1275 crankcase breather. Any body done it and any tips. I don't have a manifold yet. Its going on a frogeye and space under bonnet is very limited.
Bob Beaumont

Bob
I run 1.5 SU's on my Sebring rep. They sit on a modified MGB manifold. I have had to modify a panel to accomodate the float chamber.
Alan
www.maskent.org



Alan Anstead

excuse thread drift, Bob - do you still need a pair of stub axles?
David Smith

Thanks Dave but i am sorted now!
Bob Beaumont

Alan

Could i have an image of your set up? Thanks

Bob
Bob Beaumont

Bob
The black bit at the bottom is where I have had to alter the panel where the float is. I cant get a good picture of the manifold amongst the clutter. The manifold is MGB cut and tig welded lengthways and machined on the head inlets. Not one that I have done myself but modded by CCK.
Alan


Alan Anstead

Thanks Alan very prompt!

Its all a bit tight! I wonder if a narrower spacer would avoid the problem with the float chamber. I don't want to modify the panel. Leyland ST did a manifold for 11/2 SU's I wonder who made it? Moss also do one I see.

Bob Beaumont

Bob,

Unless you want to retain 'twins', a single HIF6/44 has the connection for the crankcase breather hose directly from the timing case oil separator. Works very well on our 1380.

Richard
Richard Wale

Thanks Richard

I have a pair of twin 11/2" which was why I was going down this route. I think the issue will be getting the right manifold. It may be that a big single is the only real option.
Bob Beaumont

Bob

I certainly see the attraction of retaining twin SUs, but upping the size. Could be a good move for torque as well as keeping the look (a rather period mod) as well the run of needles to tune with (i know the latter point applies to HIF44 carb).

Maniflow sell a twin 1 1/2 inch SU A Series engine manifold:
http://www.maniflow.co.uk/index.php?view=product&from=162&product=1194

Alan's modification of MGB manifold is a great idea, if you can sort the welding. And MGBs a good source of the carbs (but you have them).

Alternatively second hand manifolds do come up. I picked up an Alexander one last year for a future 1293cc engine build for my MkII Sprite.

Are your air filters and exhaust suitable spec and condition? Guess you want twin K&Ns, long-centre branch exhaust manifold and an RC40 exhaust to allow everything to breath nicely. Got a reasonable modded head too?

I guess twin large SUs fell out of favour when single Weber twin choke sidedraft carbs became the racing norm in modified midget classes.. I am not sure whether twin 1 1/2 SUs were ever homologated for rally or racing Minis (or Midgets).

Cheers
Mike

M Wood

Bob

Things like this pop up:
http://www.ebay.co.uk/itm/Classic-Mini-CT-Tuning-London-Twin-SU-Or-Stromberg-1-1-2-Bore-Inlet-Manifold-/281778828007?hash=item419b53b2e7

Not sure if too angled up for a Midget installation (the problem for Mini 1/34 manifolds)

Cheers
Mike
M Wood

Bob, we have seen 1 1/4" twins feed over a 100 at the wheels on MGOC 1328 engines (modded standard valve size head and free cam apart from lift), around 115 bhp at the engine is that not enough? To be honest the small twins are very sharp on pickup compared to the big singles and the twin 1 1/2"s especially below 3000 rpm. Can you not source needles to give the required fuelling? What needles are you running and are they standard or have they been modified to get the fuelling close?

Peter
Peter Burgess Tuning

I had twin 1 1/2s on my A series. Went well. I made an adaptor and used the original manifold.
Rob Armstrong

Mike,

1 1/2" SUs [H4 not HS4] were / are homologated for Cooper S's and therefore used for racing in FIA Appendix K.
Doug Plumb

Thanks All for the comments, Much appreciated. As mentioned I have a pair which have the take offs for the timing chain breather, its really a question of the right manifold. I will try Maniflow. As mentioned all the mini ones are too angled. I have got access to the one Mini spares sell (c-AEG 489) so may try that but not hopeful. Clearance under a steel frogeye bonnet is very limited

Peter, I must admit we tried hard to get the 11/4's to work on Slark's rollers. The engine is not that hot, Polished and flowed Slark head, 36mm inlets 29mm exhaust 10.75cr, Kent 246 cam,LCB etc. The problem was that it tended to run lean mid range but rich at top end, great for flat out but not so good for normal road use.That was using AEM needles. Managed in the end to get a needle (will check) to work but it was a short one which meant the jets are flush with the bridges and it runs slightly rich at idle. Buzzes up beautifully though. Its giving 60bhp at the wheels and 76lbs torque which is fine. Slark felt bigger carbs would solve it and I thought the twin 11/2's look quite period.

Any other bright ideas welcome although I'm off to Angouleme with it in a couple of weeks so will probably leave as is for now.

Bob Beaumont

Just a thought, is the bridge modified where the jet is? Or is the inlet manifold polished?

Peter
Peter Burgess Tuning

No the carbs are completely standard on a standard spridget manifold
Bob Beaumont

Bob - saw this and thought of you - any good?
http://www.ebay.co.uk/itm/Ultra-rare-MITCHAM-MOTORS-Twin-1-5-SU-manifold-MG-Midget-Austin-Healey-Sprite-/201418555039
David Smith

Thanks Dave Interesting.I'll keep track of it. Mitcham Motors was a reasonably well known tuning firm which closed a few years ago. Its a tyre dealer now.

I spoke to maniflow and they do one. The guy there said he had sold many over the years and never had one back with any fouling problems. The problem with the maniflow one is it will need a throttle linkage fabricating.
Bob Beaumont

This thread was discussed between 29/08/2015 and 06/09/2015

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.