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MG MGA - Too rich!

My MGA1500 is running very rich no matter what I seem to do, the carbs were overhauled a year ago suggestions please
p whitehouse

PW

I suffered a similar problem for a long time until I discovered that the very poor quality 'Chinese' filters supplied with my repro canisters were the culprit. I replaced with good quality elements and the problem went away. It's a starting point for you.

Tell us a bit more about your carbs, filters etc and I am sure you will get sound advice
Steve Gyles

PW,

Did the "overhaul" include new needles? Worn needles caused the same always too rich problem for me in a previous car. New needles solved it.

Jim
Jim Ferguson

Another cause could be worn float needles but that would normally be accompanied by flooding float chambers. Check that your floats have not partially filled with petrol (due to leaking seams) by taking them out and shaking them, and check your float lever settings, although that shouldn't have altered.
Lindsay Sampford

I had the same problem recently. It turned out that the choke wasn't fully releasing, even though it looked ok from in the car as the knob returned all the way
GrahamMV

Graham could be on the right track. I had this problem on my '57 for a short time in the past. Reach under each carb and give the jet a firm push upwards. If one is sticking you will feel it move, and if the engine is running you will hear the change right away. It doesn't take much, even stuck a tiny amount will make it run very rich.
Good Luck,

Ralph
Ralph

Ralph,
Where exactly do you push?
Nigel Munford

Thanks for all your input I will adjust/play and fiddle this weekend
p whitehouse

Nigel,
The jets #11 (if the picture is clear enough) are right nesr the bottom of each carb in line with the center. You can see the hex nuts #13 near the bottom of each jet. Connected to the very bottom of the jets with pins are the choke levers #27 & 28. When you pull on the choke knob it pulls the levers, pulling the jets downward to enrich the mixture for cold starting. When you push the knob all the way in, the springs on the ends of the levers pull the jets back into their normal position. (At least in theory). You can push upwards on the levers just below the jets to see if they are sticking slightly.

Ralph



Ralph

Thanks Ralph. It's easier to see when then picture is 'exploded'
Nigel Munford

Probably what your carb would look like shortly after striking a match under there!
Lindsay Sampford

Just a thought from my similar experience with a SU H6 carb. After checking that the jet is against the nut with the choke pused fully home, make sure that the cork washer above the jet adjsustment nut is fully compressed. It should be hardly visible. If it isn't compressed, the jet will be too low to allow a lean enough mixture. Also, check the jet with a dial caliper, it should be no more than about .050" below the bridge as a static adjustment Others might chime in with a different measurement from experience.
Berry Price
BTP Price

Hi guys after striping the carbs down and rebuilding/resetting it is better but still rich.How far should the top of the jet be below the top of the upper bearing when the jet is pushed up tight mine looks about 2mm,the jet also says 6 on the bottom is that std
p whitehouse

"The Book" says the jet should be 0.09" and the needle a GS.
Lindsay Sampford

It should be possible to screw the jet up until it is flush with the bridge in my experience and I just checked the SU manual and it says the same there. Lindsay.
Lindsay Sampford

See my previous post. The jet is too low and is probably the cause of the rich mixture. The jet is stamped 9, which means .090" dia. and is correct.
Berry Price
BTP Price

Mr Whitehouse,
All the jets for MGA are the same size - .090" (90 thou). Yours might be marked "9", ie, turn them the other way up!
Needles should be "GS" for MGA 1500. (this is stamped on the needle right at the top where it is clamped in the piston).
Regards, Peter.
P. Tilbury

Just a final thought before I slink back to the Triumph board and leave the MGA people in peace. As others have mentioned, it should be possible to get the top of the jet flush with the bridge. If not, it is possible that the cork washer #17 isn't fully compressed,also there should be only 1 very thin washer #24 under the shoulder of the upper jet bearing, or the jet is slightly shorter than the original spec.
Berry Price
BTP Price

Peter,

Although it does not relate to this post, only the pushrod MGA always has a 0.090" jet. The mga twin cam has a 0.100" jet.



Mick
M F Anderson

Check that the shoulder of the needle is flush with the bottom of the pistons. If they are pushed up it will be richer.
Ed Bell

Berry's mention about the depth of the jet below the bridge is actually worth expanding upon.

Once the carbs have been tuned by whatever method you choose, it is worth noting the depth of each jet as Berry described. Whenever I have subsequently stripped and rebuilt my carbs I have adjusted them to the same setting on the workbench. I have usually found that no further adjustment has been required when bolted back on the car.

Steve
Steve Gyles

Illustration from the MGA Workshop Manual, page D.12. The top of the jet bearing and jet are not flush with the bridge. You could substitute a thinner copper washer, but it wouldn't be as intended.


John DeWolf

This thread was discussed between 10/06/2009 and 19/06/2009

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