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MG TD TF 1500 - Idle-rpm problem

My '52TD runs great, but no matter how I try, I can't seem to drop the idle below 1200 rpm....Even with the idle screws all the way up...
The carbs were completely rebuilt less than 1000 miles ago...
I'm not as familiar with the "T" series SU's as with the "B" series ....
Thanks for the suggestions.
Edward
E.B. Wesson

Edward, I had the exact same problem when I got my car. Turns out the 2 butterfly valves had been installed BACKWARDS! Since they are beveled on one side, installing them backwards made it impossible for them to fully close which kept the idle artifically high regardless how low you set it! I discovered this when I rebuilt the carbs. You can probably find this post in the archives from a few years ago. If this is your problem whomever rebuilt them can flip the valves around I'm sure.

Hope this helps,
Ed
efh Haskell

Did the problem set in right after the rebuild?

Look down the bore and see if butterflies are closing down to a crack. Were they synchronized so one isn't open farther? Your throttle wouldn't be holding them open, would it?

You might have vacuum leak. Shoot some starting fluid around the intake, (from below, too) and see if rpms crank up.
Jim Northrup

Edward - Even if the throttle plate are installed in the proper orientation, they may not be seating properly. Look down the bores as Jim suggests and if they are not closing all the way around, loosen the screws and reposition them until they close perfectly all the way around. Cheers - Dave
David DuBois

This may be too obvious to mention... you backed the idle adjustment screws out, but did you check the fast idle linkages?

Do let us know what you find.
Jim Northrup

Edward,
Did you losten the interconnecting linkage between the carbies????? The high idle migh also be air leakage,,,
SPW
STEVE WINCZE

If the throttle shafts were replaced, make sure there is clearance between the carb body and the brass piece that the adjustment screw goes in. It is possible to mid-pin that piece, and with the screw backed out, the brass still contacts the body not allowing the plates to close. Also, try what Steve said (loosening the connecting link), and make sure each shaft snaps shut- if the end return spring isn't wound up enough the plate won't close. Remove the pedal linkage also from the back carb to check for binding there. George
George Butz

Typo- should be "mis-pin" above.
George Butz

Thanks guys...
Sorry for not responding sooner....
I have not had the carbs off...they were rebuilt by the previous owner...He was very careful, based on other things he did, but anyone can make a mistake....
I have rebuilt HIF-4's, but never this type carb....
When I tried to tune them, I did release the links, so I could adjust air flow independently...But , even with the same air flow, there was no change....
I am planning on an engine removal, this Fall, and will probably wait till then to check the butterflies.
Edward
E.B. Wesson

Edward another thing to check is that the jets are returning all the way up after the choke cable is released.
They tend to stick down a little after a while from buildup on the shafts of the jets.
You can lift up on the jets from under the carb with your fingers. If they are sticking some, pull the choke all the way out, and clean the jet shafts with some carb cleaner and then apply a little Vaseline.
Also some of the jet return springs sold have not been the correct length and do not always return the jets all the way.

Dallas Congleton

This thread was discussed between 16/08/2011 and 17/08/2011

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