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MG MGA - Sticking jet/choke

I've been trying to work out why I'm running rich and I've found that whilst the back carb jet returns as it should when the choke is released the front carb jet doesn't. This clearly isn't right and could explain the rich running. The photo of the front jet hopefully helps explain the situation. Is this a jet centering issue? I've tried pushing the jet up manually but it doesn't want to budge. If it is a jet centering issue can I work on this with the carbs in situ? I'd welcome the thoughts of the forum. Thanks.

Tim (61 1600 MGA Coupe)


Tim Prime

Tim
Doesn’t sound good that you can’t even push the jet up - “it doesn’t want to budge”. A bit stiff or sticky, ok, but won’t budge is strange. Sounds like more than jet centering problem Perhaps start by disconnecting the jet linkages and see if the problem is really the jet alignment or something to do with the linkages. Then go from there. Good luck.
Bruce.
Bruce Mayo

Tim
Are you saying you cant lift the piston? As I am sure you know, if it is centered, the piston should lift and fall down freely
Graham V

It is the jet that won't travel that last 8-10 mm up the carb body so that when the choke is closed the fork is level with the bottom of the adjustment nut. The jet goes up and down okay otherwise by operation of the choke. The piston rises and falls just fine.
Tim Prime

Tim
I am not an expert, far from it. But I dont think it needs centering. I think you will need to strip it down, maybe the seals need replacing.
Its not a bad job to do. If you do, I would recommend viton seals, I bought mine for just a few pounds.
Graham V

Obviously you need to check all the mechanical connections on and linked to the carb(s) are all free moving but I had one carb out of two (different SU carbs and linkages) with an internment sticking choke even after taking the carbs off and cleaning them.

I reset and took that carb off two more times and cleaned and checked its full range of movement off the car and all linkages and cable but couldn't find any reason for the sticking. With road use of the car it stopped sticking but I've no idea why or why it started sticking. Other than perhaps the way an idiot, not me but another paid idiot, had put the return springs and not replaced a ballsed-up choke cable which I noticed when I lifted the bonnet at their premises - British motor trade at its usual very low average workmanship and attitude.

I can recommend avoiding Burlen as much as possible for parts, apparently they make more money with pedal car parts so not bothered with their other monopoly, another sorry example of a British company and how they view their customers, not just my isolated view.

Nigel Atkins

I've experience this before with the earlier H Series carbs. It's the interface between the jet, cork seals and jet bearing. It gets a bit gummed up. I've tried to fix it by using a stronger return spring (the one the end of the lever), but it doesn't cure it. The only way is to take it apart and clean it, polishing the outside of the jet.

Obviously, if jet is off centre then the jet needs centring iaw the manual. If you're careful you may be able to re-use the seals.

Your seals don't seem to be leaking, but some at this stage might convert to Burlen's ethanol proof bearing kit (not cheap for a pair of carbs). I found a chap (by Googling) who'd converted a pair of carbs to neoprene seals (v cheap!). I'm experimenting with this mod on a carb, but have yet to put into use.
Peter Allen

Thanks for all the helpful comments. I removed the jet this morning and as it has a definite kink near the fork I'm pretty sure that is the cause of my problem. See attached photo. New jet required! Tim

Tim Prime

Defo, Tim!
Peter Allen

More like a banana or boomerang, I'd check all the connections and linkages have free movement, dissemble, a good clean and lube of carbs, linkages and cable might be in order.
Nigel Atkins

Tim,
Replace the jet(s) with the new design to accept the newer ethanol resistant seals. Burlen redesigned the seal, but it has to have the redesigned jet; better than two viton ‘O’ rings.

Regards
Colin
Colin Manley

Tim
Pleased you have found the source of the problem
Graham V

How the h#ll does a main jet become bent like that?

Even with my heavy right foot, I never managed to bend one!

I'm lost for words (for once!)

Cheers
Colyn
Colyn Firth

Hi Tim
I have spare jets which you could come and get, or alternatively I am in Edinburgh today. Could meet you in Traverse Theatre bar around 2 as we are at lunchtime show.

Paul
Paul Dean

A trick to working on carbs is to remove them as an assemby complete with inlet manifold and heat shield. You can then work on them on the bench, centre the jets, adjust the mixture levers without having to be a contortionist. You need an offset ring spanner to access manifold nuts.
Mike
Mike Ellsmore

Hi Tim,
Sorry, I just re-read my last post and I realised that it may have come across as a criticism.

I was just so surprised to see a main jet that was bent like that and I can't see that it is possible for this to happen whilst it is actually fitted to the car.

I am equally surprised to think that someone had fitted a bent main jet and not noticed.

But I am pleased that you have found the cause of the poor running and I am sure that you will find the car should run much better in the future.

See you at Scottish MGA Day this year?

Cheers
Colyn
Colyn Firth

Mike - I agree with your suggestion but I have always managed to do it with open end spanners.

I am now on train to Edinburgh but I have jet and a pair of new cork gaskets in my pocket. Let me know if you can make Traverse at 2 as we won’t be hanging around otherwise.

Paul
Paul Dean

Thanks for the latest comments. Big shout out for Paul Dean who I met at lunchtime and who kindly offered a spare jet and cork gaskets. Will hopefully have time over the next week or so to get the car up and running again and carbs tuned. Colyn - no problem, no criticism taken at all. How the jet became the shape it is will probably remain a mystery! Yes, hope to be on the MGA Scotland trip in July - also hoping that this year I'll complete the day in the A and not on the back of a low-loader!
Tim Prime

This thread was discussed between 29/03/2022 and 31/03/2022

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