MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG TD TF 1500 - Carburetor tuning

I have a 53 TD which I drive most every day. I rebuilt the carburetors last week and replaced most all of the gaskets.
My question is that although the engine sound perfect when reved up, I notice that when climbing a slope in 3rd gear the engine will sputter a bit unevenly. It is when there is a stress put on the engine.
Does this mean the carbs are set too lean or too rich.
I used the synchro vacuum gizmo and also tried lifting the piston slightly as is recommended to try and set the lean/rich adjustment screw.
Any suggestions would be appreciated.
Thanks,
Bill
W Chandler

Have you checked that the full level is correct in the float chambers? When labouring up hill the throttle valve is wide open and manifold vacuum is low. If the fuel level is low you may get weak running.
Dave H
Dave Hill

Pull the choke a bit when sputtering- if lean it should smooth out. Above suggestion good. Many carb problems actually ignition. Make sure oil in dashpots and dampers working, check for air leaks. Tuning procedure in the NEMGTR T series handbook great too. George
George Butz

Thanks for the comments.
How do you check the fuel level in the float chambers?
Do you just take the top off of the chamber after the engine has been running?
Bill
W Chandler

No. The regular method is described in the Workshop Manual, though there is a better way. See dbraun99.com
Dave H
Dave Hill

Suggest surfing archives, volumes in there about setting float level. George
George Butz

Nothing like chasing your tail around trying to get your carbs to run right by setting the float height just exactly right according to the book. There are so many variables that will throw that adjustment off. Maybe a close starting point can be got that way if you have new parts of the correct sort?

Your floats can be set "perfect," but that means nothing if the fuel height in the jet is not where it should be. If the fuel height in jet too high, drop the float height a little. If too low a fuel level in jet then raise the float height a bit. Too high a fuel level WILL make the carbs run rich, and too low WILL make it run lean.

And did you check the throttle shafts are not worn-- and leaking (air in) when they feel like it?

The following link, on page 29 works every time if you can figure a way to check the heights and can read between the lines. .060" to .065" comes out to 1/16" (.062"). Some people will object to this method of adjusting SU carbs. Trouble is it works every time.

Do be sure the "jet securing nut" at bottom of carb has compressed the cork gasket to 1/16" or so. You did soak the corks in oil overnight prior to rebuilding the carbs?
http://www.namgar.com/images/uploads/Chapter_Newletters/Vintage_Racers_Newsletter30.1.pdf
D mckellar

Nothing like chasing your tail around trying to get your carbs to run right by setting the float height just exactly right according to the book. There are so many variables that will throw that adjustment off. Maybe a close starting point can be got that way if you have new parts of the correct sort?

Your floats can be set "perfect," but that means nothing if the fuel height in the jet is not where it should be. If the fuel height in jet too high, drop the float height a little. If too low a fuel level in jet then raise the float height a bit. Too high a fuel level WILL make the carbs run rich, and too low WILL make it run lean.

And did you check the throttle shafts are not worn-- and leaking (air in) when they feel like it?

The following link, on page 29 works every time if you can figure a way to check the heights and can read between the lines. .060" to .065" comes out to 1/16" (.062"). Some people will object to this method of adjusting SU carbs. Trouble is it works every time.

Do be sure the "jet securing nut" at bottom of carb has compressed the cork gasket to 1/16" or so. You did soak the corks in oil overnight prior to rebuilding the carbs?
http://www.namgar.com/images/uploads/Chapter_Newletters/Vintage_Racers_Newsletter30.1.pdf
D mckellar

The fuel level in the jet should be 1/8 to 3/16" below the top when the jet is fully raised. Its not super critical, but should be thereabouts. Lower the jet until the meniscus is level with the top and the amount you lowered it should be in the range given above. To get it right you have to bend the lever that rests on the float. Remember each time to lower the level of fuel in the float chamber and refill. It can take several attempts to get right.
Dave H
Dave Hill

The plus or minus 1/32" range for fuel height is not too critical, like Dave says, as long as you are within. First the relationship between top of jet (no choke) and the bridge must be established. This 1/16" is critical for the other adjustments to have any relevance. Soaking the "jet securing nut" cork in oil first allows for that 1/16" difference to be established when re-assembling the carbs after a rebuild.

What I find helpful is clean paper towels and a container like an oil drain pan. Good garage ventilation. When going about adjusting the fuel height in the jet, a paper towel soaks up enough fuel from the float bowl so that each new adjustment of the float height can be checked when the float bowl lid is bolted back on, and the fuel pump is activated.

No good way to paraphrase the one paragraph instructions in the link, as it is as simply stated there as is possible. page 29 at:

http://www.namgar.com/images/uploads/Chapter_Newletters/Vintage_Racers_Newsletter30.1.pdf
D mckellar

I figured out the problem was that the jet on the front jet was sticking down when choked. I was driving with the choke "on" on one carb!!
Runs perfect now.
Thanks for input.
Bill
W Chandler

This thread was discussed between 27/02/2017 and 07/03/2017

MG TD TF 1500 index

This thread is from the archive. The Live MG TD TF 1500 BBS is active now.