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MG MGB Technical - Throttle/choke spindle & cam settings, HS4.

A question if I may, referring to Paul Hunt's excellent discussion and photos showing the relationship between throttle and choke shafts and levers. This is after following the usual procedure for fitting new jets, centreing needles, achieving the desirable "soft metallic clunk" of the pistons, and getting ready to finish off by refitting the jet levers.
I'm having trouble matching the orientation of my choke shaft and the position of my fast idle cam and my jet levers to your photos Paul. I understand the peculiar path of the jet lever, behind the jet assembly and then appearing at the side; but in order to line the holes up (jet assembly and lever), I currently have to pull down strongly against the tension of both the lever returning spring and the cam spring. I don't want to risk hurting the plastic at the base of the jet. Your notes say that the holes should line up, and without "raising" the lever - whereas I have to pull my levers down strongly to have any hope of lining the holes up. Also, my fast idle cam is not oriented correctly when I look at the Hammer & Spanner photos.
I have not tried to alter orientation of the shafts themselves (for fear of making things worse). I'll be grateful for Paul's and anyone else's preliminary thoughts, following which I'll try to get it right.
First photo tonight just shows the fast-idle cam not really where it needs to be.
Sorry this is not very clear - it reflects my current frazzled state of mind.
Thanks all. John.



J P Hall

I can't remember which one(s) I posted so I'll post this of the choke pushed fully home fully connected up.

On mine in order to attach the cable the choke spindle has to be rotated quite a long way from it's natural resting position just to get to the starting point, i.e. the start of the fast idle cam just at the fast-idle screw, in your picture it's way back from that.

That will govern where the cable lever arrowed in the second picture has to sit, this is 'choke pulled' as in the 'choke in' picture it's hidden by the shaft.

Also although I can see the lever B in your picture I cannot see the jet operating bar which has a pin going through the hole in that lever and a spring-clip to retain it.

I would say that needs to be fitted first, and the lever to the jet, with any return spring to the heat-shield disconnected.

I would also say that as long as the jet slides in the jet bearing (make sure it is fully up before you start, it should be about level with the top of the jet bearing) the the force of the jet operating lever on the jet itself will be minimal. When the choke cable is connected that will taking the 'weight' of the return springs, not the jet itself. The fast idle cam should operate independently of the jet lever for part of its rotation, when fully connected the cam will rotate and lift the fast-idle screw before the cam starts to push the jet lever and the jet down. With your cam rotated as far back as that the cam should have a lot of movement before it starts to push the jet lever down, with only the return spring on the lever trying to pull it back, not the one on the choke spindle. However if the choke cam is not yet connected to the jet via the lever than that might allow the cam to go even further back, so you may have to turn the cam against it's spring before the lever holes will line up with the jet. That shouldn't take much effort though. Make sure any 'handing' of components has been taken into account.






paulh4

looks like it needs to go 90deg anti clock to me--that little line near the A of the part number on the cam lines up with the speed adjuster screw when in the rest position-
William Revit

Spot on, Willy - the cam arrived back in the right orientation once I corrected the choke lever orientation, set wrongly by a p.o. . Thank you Paul - your article and some great photos on Dave Braun's site helped me to see what should go where. It still took a good 3 hours today to get the result.
A couple of comments : the little push-on retainers on the top of the choke lever should be BANNED - the bar-stewards ping off and disappear into the wide blue yonder. I was tempted to try a small hole and a keeper, but thought better of it. Order far more than you need. The self-tappers into the plastic base of the jets - I've replaced them with a little M3 bolt & nut, less risk of damaging the plastic base. At the same time, I found several of the pinch-bolts on the shafts to be badly worn, so am replacing them all.
All in all, very relieved to have the setup right. Just got to even up the lift of the carb pistons (front carb lifting more than rear), and of course adjust the mixtures after all the disassembly and reassembly.
Thanks as ever, Paul and Willy - don't know what I'd do without you.
John.






J P Hall

John, can I get you to do a little job for me please. I've got a bit of a body job going on here and need a measurement centre to centre of the headlights of an MGY if you could please, not over accurate just within a few mm will do it -thanks
William Revit

Pleasure Willy o'the South: my lamps are the correct 8" YA lamps, and appear to be aimed pretty well straight: allowing far any slight variance in straightness, the mounting studs centre to centre look like 700 to 702mm. Similar measurements between the centres of the Lucas glass, and between the little brass pips on the rims. Hope this helps. John.
J P Hall

certainly does--thanks.
William Revit

This thread was discussed between 15/01/2024 and 16/01/2024

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