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MG Midget and Sprite Technical - Weber choke changes

My 1293 midget is fitted with a 45 Dcoe weber which makes a lovely noise and goes very well at the top end but it has a slight hesitation under hard acceleration and I need more bottom end for classic rallying. I intend decreasing the choke from 36mm to 33mm and rejetting the main and idle jets. I am fairly confident about changing the jets but have noticed the wee bolts holding the chokes are wired...presumably to prevent losening by vibration. Are these easy to remove/replace, can you reuse the wire and is it possible to do the job without removing the carb from the manifold?
Thanks,
John S
J Sloan

Easy enough to remove, but you're unlikely to be able to reuse the lock wire. You could always use a drop of Loctite on the thread, if you don't have lock-wire pliers.
Dave O'Neill 2

There are books with this stuff in...

36mm chokes is borderline to use a 45. You don't say what cam is in the engine so hard to say if the engine needs a 45.

Assuming a Kent 286 or equivalent cam then money spent on a CV exhaust manifold would give you such a massive bottom end you'd be fitting 38mm or 40 chokes and pulling up power on the top end.

Also and in addition to or on their own, fit proper Full Radius rams from ITG - They'll pull up the bottom end enough for the 36mms not to be a concern and maybe still think about 38s

The engine in my car has over 100bhp at the wheels and will pull cleanly from 2000rpm in 5th on a 3.9 diff with 175/70 tyres.


Daniel Stapleton

I have never used lock wire on mine. That's what the jamb nuts are for, no?!

When you say "hard acceleration" do you mean when you floor it from low revs it hesitates the picks up? If so, maybe it is a pump jet issue (too large/small).

DCOEs are awesome carbs but the only way you will get it totally right is by visiting a rolling road.

Are you using a vac. advance?

Cheers,
Malc.

Malcolm Le Chevalier

Daniel,it has a scatter cam, stainless large bore lcb.it also has long rams and a large sponge filter.
For classic and targa rallying you need to get off the line on the loose and tarmac pretty sharp but it currently needs the accelerator feeding in to get away smoothly_hence going for more bottom end torque. No vac advance connected.
I planned to measure the acceleration from a standing start before and after the change to see if there was much difference.
Probably last event for this year on Sunday so I have tomorrow and part of Saturday to sort it or leave it as it is and do it over the winter.
Thanks for the discussion...
John
J Sloan

I've just had a thought...some webers used lock tabs instead of lock wire. Might be a simpler solution.


Dave O'Neill 2

John
What emulsion tubes, mains and air correctors
have you got in there at present
It could be a combo of emulsion/mains that is working against you
It should suck 36's ok
Make sure you rewire them screws though if you have them out no Loctite required or recomended --just wire them
They don't run very well with the chokes spinning round in there------------half way through a rally
willy
William Revit

The lip of the ram will make a bigger difference than the length on a 286 Scatter cam. So long rams won't be as effective as Full Radius rams unless they are long Full Radius rams.

There are a bunch of variables around Aux venturi and jets as well pump jets and everything else.

My road car had 40 main venturi and you could floor the throttle from practically any rpm from 2,500 upwards without any hesitation. Sure it takes longer to build rpm at 2,500 in fifth than it would in any other lower gear but it never hesitated.

Without the CV manifold (and rams) it didn't like a full throttle much below 3500rpm with 34mm rams and the CV absolutely transformed it.
Daniel Stapleton

This thread was discussed between 13/10/2016 and 14/10/2016

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