Weber 45 problem | MG Midget and Sprite Technical

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MG Midget and Sprite Technical - Weber 45 problem

I've got a misfire which I'm now convinced is carb related.
Anyway, when I turn one of the mixture screws while engine is running, there is no change in the engine.
When I turn the other one, the engine speed changes.
I can screw the first one right in & the engine still runs, so it's doing nothing.
I have cleaned the jets, but maybe I need to do more thoroughly or do I need to strip the carb.
I assume a blockage, but where should I be looking guys.
thanks.

Mallorcaben

Ben,

You might want to check the state of the idle mixture screws as on a mates car 2 out of the 4, twin DCOE Ford X flow, had the mixture screw tips lodged in the carb body. We suspect someone had overtightened them when closing them and as they are quite fine the tips broke off. Same symptoms, they didn't have any effect on the engine running. He removed the carbs and managed to lever the tips out from the inside IIRC and replaced with new and they worked again.

David Billington

Just taken the adjustment screw out completely. The tip is not broken off.

Mallorcaben

Ben,

Did you compare the 2 against each other. In my mates case only the tip of the tapered needle section had broken off so if you didn't know better you might think it was normal. If not that then likely a blockage in the feed passage.

David Billington

Ben
If you undo the butterfly nut on the top of your carby and remove it and the round cover you will see four screw heads inside the carby two large and two smaller, Undo the two smaller ones and pull them out, they are a couple of inches long. on the bottoms of these are the idle jets that you can give a good blow out and clean , it sounds to me that one of these could be blocked
Hope this helps Willy

WilliamRevit

Ben

I can't see any Misab plates/Thackery washers between your Weber and the inlet manifold - Webers need some movement with their mounting otherwise you get fuel frothing... (forgive me if they are there and I have misinterpreted the photo)

James

J A Bilsland

Yeah James, the washers are there.
William, I've already cleaned all the jets.

Mallorcaben

Ben, I agree with James, that carb is bolted tight up to the manifold. On these engines, they NEED to be flexibly mounted or they will froth and give symptoms of bad running.

As for your bleed screw adjustment, you need to check that the throttle shaft is not twisted. The butterflies open a series of progression holes at very low throttle positions. IF it is twisted, that progression will be out of sync and alteration of an air bleed screw may not have any effect at all.

The Weber carb is NOT a simple piece of equipment and can cause endless troubles to those that are not familiar with their workings.

Mark.

M T Boldry

OK Mark, so I should strip it down eh?
(see pic, lol)

Mallorcaben

Only problem I see is the carbs in your pic aren't Weber - otherwise pic very useful.

A

Anthony Cutler

So only the lid is weber then, anthony? 'Cause that says weber?

Alex G Matla

The cartoon pic Alex, the cartoon ;)

Jordan Gibson

Oh. oops. I'm not that observative obviously, he he.

Alex G Matla

Ben

look at this picture
you can see the weber and the manifold are not touching
the is a ruber o ring in between

you do not seem to have it
if you do it looks like you over tightend the bolts and compressed the o rings to mutch so they lost their dampening action

Onno Könemann

Onno, I need my eyes testing I know.... but that pic is VERY small....

Mark.

M T Boldry

yeah i know it is a cut out from a biger one
but the midget is in pieces in a garage 15 min drive from me and i won't be there until sunday
so until than this has to do

lets just say with my setup you can clearly see the rubber o rings between the weber and manifold
and i can't see them on ben's picture

Onno Könemann

Dito. here here. 8^)
The gap that is, not the eyes.

Alex G Matla

There's not much to see but here's a different pic of a Weber setup from something else, notice the 2 mm "gap" thats created between the carbs and manifold by the rubber O ring gasket.

D Prince

If the weber is causing problems I would definately talk toe Keith in sidedraft central at yahoo..
His methods sort most of the issues with webers
Tim

T Dafforn

Having made 3 sidedraught manifolds in the past I can't see any evidence of the appropriate washers fitted. IIRC the term for them could be thackery washers which I used on the first 2 manifolds, the last one I used Alfa Romeo bonded rubber mounts which require a different flange orientation but work well with the OE quality fittings.

David Billington

some manifolds have a groove to take the rubber rings, the 'spectacle' seals work OK with these