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MG MGA - Tight jet

Hey all, I am assembling, (finger tight), the engine manifolds and carbs.

I have found that the front carb's jet does not slide back in after releasing the choke. I swapped the return springs and found they both work well on the rear carb.

The piston drops freely. Where do I go from here?

Thanks, Tom
Thomas McNamara

Loosen and re-centre the jet. It could be dragging on the needle?
Art Pearse

If he air float drops freely the jet is centered well enough. Sticky jet = dry seal or corroded jet OD. You can likely fix this on the cheap. Remove the tension spring and the clevis pins underneath, and lower the choke arm out of the way. Pull the main jet completely out from the bottom. Clean the OD of the jet with solvent and rag. If needed, polish with a touch of oil and super fine emery paper (~1000 grit). Clean jet again with solvent, add a touch of oil to the OD, and reassemble it.

If that doesn't free it up, find more details here:
Barney Gaylord

I used Barney's teflon o-ring idea to replace the rubber or leather top and bottom seals, and polished my jets with 1000 grit until they slid in and out easily, and yet they still don't leak.

I bought a carb rebuild kit, and the jets that came with it are too large - they stick hard in the bores - so I had to reuse the old ones, which cleaned up nicely.

AJ Mail

Looking at Barney's link shown above, I was interested to see his successful use of twin PTFE O-rings for the jets. This is going to be very useful with ethanol on the increase soon here in the UK.
I have been looking into this for us UK guys.
The PTFE O-ring size Barney describes (0.239"I/D x 0.070" dia)or 6.07mm I/D x 1.78mm is actually a standard BS.010 O-ring in the UK. I have located a local supplier who has these ex-stock for 30p each.
Barney recommends x2 O-rings in place of each jet gland = x8 O-rings per MGA.
You won't get many spares as cheap as that! Who's fitting theirs first?
P N Tipping

I bought the teflon o rings Barney suggested. They are very tight and very hard. I had to polish the needles with 600 grit more than I wanted to.

The moss o rings I bought started to get soupy with exposure to gas. I think the gas has 10% ethanol.

I might just use cork next time.

The teflon o-rings seem to be wrking ok but I haven't had a chance to do much driving since the rebuild.
Fred H

I highly recommend the Teflon solution...has been great, with NO leaking.


AJ Mail

Thanks for the verification Fred and Jim. I got a couple of sets of O-rings (16) yesterday - nice to know they'll fit. This PTFE is a great friction reducing solution for the jets as well as solving the ethanol problem; as the original cork glands would be attacked by the stuff. So that's one bit sorted, now we have the zinc based alloy (carbies & tank sender unit), brass (jets, floats, needles butterflies & Throttle Shaft), solder (floats), rubber (fuel tubing & carb seals) to sort out now - all of which will be attacked by 10% or above ethanol.
Regarding the cleaning up of jets I polish mine to a shine with brass polish to give the 'glands' both a good seal and a freer sliding 'choke' motion.
P N Tipping

I have Teflon lined fuel hoses from Moss Motors, circa 1986, 25 years, 240K miles, using 10% gasohol for the past 20 years with no problem. Standard rubber fuel hoses around my aftermarket fuel pump get changed every 10 years or so. Carb jet seals are Teflon O-rings in place 14 years 120K miles, no stick and no drip. Float bowl grommets are now Viton parts from Moss motors, no problem for 2-1/2 years years so far, already a big improvement, time will tell.

I have no problem of any kind with the fuel attacking any metal parts, including original 1958 fuel level sender unit and original carburetors with original soldered brass floats. I think that issue is grossly overblown. I suppose pot metal exposure to humid air is more corrosive than being wet with fuel. The cars do not like long term disuse with no fuel present.
Barney Gaylord

Pete, please can you let me know where you got the seals?
N McGurk

Barney, I agree totally with your choice of materials for ethanol. As I am sure you know, in the UK we are only at 5% max here. It looks like 10% around 2013 so classic car owners here are getting a bit twitchy. I think your inovative use of twin PTFE O-rings on the SU jets is simply superb. Its also nice to know you have had no real metallic problems over 20 years at 10% - that is good news. Thanks again for your continued input Barney - we all appreciate it.
P N Tipping

This thread was discussed between 10/02/2012 and 25/02/2012

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