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MG Car Repair/54 MGTF carb running rich


Hi Barrie, got a sweet original paint tf from a dear friend's estate.
John had done a lot of work- new head,carb etc. smoked badly. had the motor rebuilt, 60 over. the motor still smokes- black sooty smoke-too rich. the mechanic tore the carbs down twice but couldn't get it less rich. we are wondering if the carbs are too large? the bore is 1 3/8th".
Mike wash suggests a 1 1/2" carb. National carb builders (50 years in business) immediately said floats a too high.
I am looking for ideas that we can check out.
What carb number is a 54 TF 1200cc ?
any other ideas on what to check? car runs nice, just very rich.

Hi Richard
Please could you tell me the chassis number of your TF?
The early TFs up to chassis number 3494 did not have dampers in the tops of the carbs.

All TFs had H4 carbs with a bore of 1 1/2".  This is measured at the back of the carb.  
The diameter at the front where the air filters go will be slightly smaller.

Inside the carb there is a large spring which sits on top of the piston.  
The free length is about 6 inches, and the TF spring has a light blue colour on one end.
When it is compressed inside the carb it should produce a pressure on top of the piston of about 2 1/2 oz.

I have seen several TFs and modified TDs fitted with Red springs.  They are 4 oz.
If you have the stronger springs this will cause the engine to run very rich.

Remove one of the springs, put it on the kitchen scales and compress it to about
3 inches.  (Please protect the scales with tissue paper or else you will dirty the scales).

If the scales read 2.5 oz they are correct, if they read 4 oz you have found the problem.

Other possibilities:

Floats should be set with a 10mm (3/8") bar.

When you push the choke knob fully in, the carb forks must both go fully home against the bottom of the adjuster nuts.  If one of them has a gap then the linkage bar needs adjustment.

If one of the jets is flooding, then the float could be partially full of gas.  
This happens a lot with modern gas containing Ethanol.
Either replace the float or empty it by immersion in boiling water and sealing it with modern no-lead solder.  Do not do this on a gas stove near a naked light.

Let me know what you find, and please tell me your chassis number.  

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Barrie Jones


MG Sports Cars from 1949 to 1980 - Including MGB, MGBGT V8, TF1500, TF, TD and modern Midgets. I also specialise in SU carburettors, Lucas wiring, suspension, steering & brakes.


I have owned my 1955 TF1500 since 1966. Technical specialist for the TD and TF with the MG Car Club T Register. Also owned 20 MGBs and currently own an MGBGT V8. Written 3 books on MGs and produced a DVD on how to strip and rebuild the TD/TF gearbox.

MG Car Club.

Barrie's Notes on the 1953-55 MG TF (author). /=====/ Barrie's Notes on the MGB (author). /=====/ Barrie's Notes on the MGB GT V8 (author). /=====/ The Essential Buyer's Guide to the MG TD, TF and TF1500. (author)

M Phil, C Eng, BSc (Eng).

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