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MG TD TF 1500 - Carb Balancing

The throttles on my carbs are joined together with a short rod and two "U" shaped clips which are tightened with small nuts and bolts. There are coiled return springs on the outer sides of the carbs and these are secured / tensioned with clips as above. The left carb has a screw with a securing spring fitted to an arm on the throttle spindle to which the accelerator actuating rod is fitted. This screw can be used to adjust the throttle opening. The other carb has a shorter leaver with two adjusting screws, one for the throttle and the other to speed up the engine when the choke is used. I am attempting to re-synchronised the throttle butterflies. I slackened off the choke screw fully so it had no effect. I then slackened one of the "U" clips which joins the throttles together so they could operate independently. I then adjusted the coiled return springs so each throttle snapped back with approximately the same force. I then screwed the adjusting screws on each carb by approximately the same amount so each throttle was open slightly. I then started the engine, which I had previously run to warm it up. Using a manometer I checked the airflow through each carb and adjusted the stop screws so the suck was the same. I then tightened the "U" clamp so the throttles would work in unison. On retesting the sucks were no longer balanced. I tried and tried to get them the same and eventually achieved sort of balance. I then slacked off one of the stop screws and used the other to set the tick over. The sucks were again out of balance. I then adjusted to other stop screw but this threw the balance out even further. I appears to "U" clamps are some how twisting the throttle shafts. Also is tickover set using one or both of the stop screws. It would be very difficult to get both of them in perfect unison. Is it possible I have set the return coil springs with too much tension and the is causing the "U" clips to bend? Any advice will be really appreciated.

Cheers

Jan T

J Targosz

Jan -

You don't mention having performed other preliminary steps such as centering the carb jets,cleaning the dashpots and oiling the dashpot dampers. I would also start with adjusting valves, setting timing/advance, checking float lever/fuel levels and then checking the airflow on the carbs.

Just go back and complete the basic tune up - to answer your question directly though, it sounds as if you have a carb piston that is hanging up due to misalignment of the jet or the dashpot cover.

Good luck!
DLD

I have had that problem before. With connection loose, get idle correct on each carb (ie balanced perfectly at the speed you want). Try holding both the throttle stops down firmly(may need a helper) as you tighten the last nut. BTW, are the throttle shafts worn? That makes it harder to do. George
George Butz

Thanks for the replies. My carbs are brand new, the car has a Stealth electronic ignition kit fitted and I have timed the ignition using a dial in strobe. I now think the spiral return springs on the outer sides of the carbs are out of balance. If one is tensioned more than the other this could cause the joining clips/connecting bar between the two throttles to twist and throw the synchronisation of the butterflies out. I am going to try slacking the springs off fully and see what happens. On my car these springs are the only mechanism for returning the throttle. Should there be another spring on the accelerator pedal?

Cheers

Jan T
J Targosz

Tie two equal wights on each spring and compare the length of the springs.
Bela

Yes Jan. The return spring bracket is mounted on one of the starter motor bolts. This is the only pic I have from a recently restored car here that shows the bracket & spring. You can just see it below the horn. I have a photocopy to scale of an original stashed away somewhere in both plan & side elevation that I used to make mine. Cheers
Peter TD 5801

P Hehir

Jan,

You can certainly over tighten the shaft joining clamps but it sounds like you are being too careful. I can not remember a case in 50 years where I have had a clamp slip when tight. My technique is, with the carb throats open and the clamp loose use a finger to press the throttle plate closed. (Idle screws fully backed off.) Then retighten the clamp. Also check that the factory did not install a throttle plate backward. They are machined with a tapered edge to fit the carb throat. If there is no binding one throttle spring will close both carbs.

Keep trying,


Jim Haskins 1953 TD
J M Haskins

Check the archives for 'throttle return spring' Bud
Bud Krueger

This thread was discussed between 28/02/2016 and 29/02/2016

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