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MG TD TF 1500 - Idle problems - sticky carb spindles

'51-TD. A slight misalignment of the carburetor spindles was causing an idle problem when the engine had reached temperature after running for about 15 minutes. When dropping back to idle, one of the spindles would 'stick' slightly off the home position, causing the engine to settle at faster than idle speed.

Tightening up the spindle springs and pedal return spring fixed it, but unfortunately this brute-force method resulted in a 'heavy' accelerator pedal.

I then focused on the short interconnecting spindle with its 'universal' u-shaped clips, which I assumed were supposed to compensate for spindle misalignment. The Workshop Manual (fig. B.12) shows both u-clips installed with a matching alignment about the spindle axis.

After a bit of experimentation, I found that the u-clip is not ideally 'universal', as they each bend easier along the axis of the 'u' bend than across the clip, i.e. 90 degrees to the 'u' bend. Therefore, if installed with matching alignment as per the Workshop Manual, the required 'universal joint' functionality of the assembly will not be achieved.

I then reinstalled the clips onto the spindles with one clip rotated 90 degree about the spindle axis from the other clip -- problem solved!

This one is worth a try if you're having trouble with sticky carb spindles and idle problems.
David Padgett

Hi David,

What an excellent observation. I have had exactly the same problem with my TF and even went to the trouble of removing the butterfly shafts and inserting a long rod into both carbs to check alignment. Trouble is with spacers and several soft gaskets it is impossible to get the spindles to line up consistently.

It makes total sense to position the clamps at 90degs. Mine are all set in line so I will be out later today to do some adjustment.

Cheers

Jan T
J Targosz

Agreed. Its obvious now that you mention it!
Dave H
Dave Hill

Thanks for your comments.

Jan, let me know how you go with this. Success may depend on how far out the spindle alignment is, or if there is excessive binding between the spindles and carb housing bushes.

cheers,
David
David Padgett

Hi David,

If you are ever in Scotland there is a Glengoyne Malt whisky waiting for you. I am now able to take my foot off the accelerator pedal and the tick over drops to about 700 and unlike before consistently. This is after removing the extra return spring I had fitted between the linkage and starter. I am now just using the springs on the throttle shafts and have been able to slacken them off. Overall a great success, thank you.

Jan
J Targosz

David can you post a pic showing your alignment solution? Cheers
Peter TD 5801
P Hehir

Peter, picture as requested below.

Jan, most pleasing to hear that it worked for you. This type of clip is more designed to accommodate heat-expansion issues, which would be a real problem with interconnecting a twin-carb system. However it's clear that heat-expansion and spindle misalignment go hand in hand.

It's also interesting that your arrangement does not require use of the accelerator return spring. Now, is that with both return springs removed or just the extra one which you fitted?

I had noticed previously that the accelerator pedal/arm assembly is quite well balanced when disconnected, with very little force required to pull it back to the rest position. Seems you may have proven that the spindle springs alone can do the complete job. I will try this out also.

...and I'll look forward to that Glengoyne Malt!

cheers to both,
David



David Padgett

Hi David,

I have now improved the pedal action even further. I have fitted small universal joint between the buterfly spindles. I bought this on eBay for £4. I have been able to back off the return springs even further and can set a reliable tickover from zero upwards. The pedal action is now nice and light. You can see from the attached photo that the two shafts are not in perfect alignment.

Cheers

Jan T

J Targosz

Well done Jan,

You obviously now have the optimum solution, with the u-clip for heat expansion compensation and a true universal joint for misalignment correction (albeit, over 70 years late - ha,ha!!).

Thinking about it further, the next question is - does the accelerator lever spring, which you are not using now, have any other function apart from assisting the spindle springs?

Could there be a safety issue of some sort, or is it really just a belt and braces solution to the original idle problem?

Also a suggestion, keep an eye on the uni-joint to see if it develops any looseness or slop. This would of course cause a carb imbalance, especially when applying the throttle.

Again, great work!

cheers,
David

David Padgett

Jan,
Have you checked why you have this misalignment?
I had the same problem on my TD then I first acquired it 26 years ago. In my case the reason that the carbs were misaligned was the the rear flange of the rear carb had been skimmed by about 1/8 inch, I assumed because it was deformed. My solution was to make and fit a spacer between the carb and the manifold. I did this and it worked fine. Some time later I found a good body and used it on my rear carb. If you have the same problem you can skim some material off the front insulator to realign. I couldn't do this, as TDs don't have insulators.

John
J Scragg

Just a thought

often the carburettors got new bushes while using a reamer.

If this is done for each single unit may be the axis is out of line.

W_Mueller

My carbs were brand new, genuine SU ones and were fitted a couple of years ago so I don't think there is an issue with spindle alignment. I seem to remember that the holes in the carb flange were bigger than the studs in the manifold. It may be possible to turn the carbs clock/anti clock to align the spindles but I have't tried this.

Jan
J Targosz

This thread was discussed between 01/01/2019 and 11/01/2019

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