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MG TD TF 1500 - Carb piston problems

I overhauled my carbs and fitted new jets, needles seals, the lot. When I put them back together I centred the needles and each of the pistons fell freely with a nice thud. They both fell at the same rate.

I've now filled the dash pots with 3 in 1 oil and the pistons no longer fall at the same rate. The rearmost piston now takes longer to fall but they both make the same satisfying thud.

Does anyone have any suggestions please? I used the same oil in both and filled them to the same level.

Thanks

AJ
A R Jones

Check the dampers that sit in the oil, are they the same type or maybe they are worn.

Hope this helps,

David
David Tinker

AJ, the conventional wisdom is to swap them around and see if that cures the problem. I remember reading somewhere that the pistons were often matched to the cylinders they sit in and sometimes get inadvertently switched over.
Tom Bennett - 53TD 24232

AJ, are both dampers the same type (vented/unvented)? Bud
Bud Krueger

Try this...
Loosen both screws on the rear dashpot....Then tighten only one, and check to see if the other has a gap (using a feeler gauge), between the screw-foot, and the body of the carb...Do this with both front and rear screws....
I found a .003" gap on mine, and it was preventing the front piston from dropping at the same rate as the rear....
Simple fix, make a shim of the correct thickness, to seat under the offending side...It's such a small gap, that there is no air leak.
I'm pretty sure that mine was an original factory defect, that was never caught...Caused the carb to always run slightly rich. Now both run correctly.
Edward
E.B. Wesson

If the jets were centered and pistons fell with a good thud before you put the caps back on the cambers, check that the dampener rods are straight and at right angles to the cap. You can remove the little c clip and remove the cup on the bottom of the dampener. Then chuck the end of the dampener rod in your battery drill (or lathe, or drill press) and turn. If it is bent or misaligned it will wobble.
Dallas Congleton

AJ,
Bud suggested checking that the dampers are the same type, along with that, check to see that the vent is clear,,, also, I found on our carbies that one of the the dampers was installed upside down on the rod,, it was dampening on the upward stroke rather than the downward stroke,,, I reversed the damper and "all is good",,,
I have a very good SU article some where, and as soon as I find it I will post it,,,,,

SPW
STEVE WINCZE

Here is the link to the SU Article,,,
http://jcna.com/library/tech/tech0006.html

SPW
STEVE WINCZE

Thanks guys, it's always best to know what you're talking about. I found the technical section of the SU website useful. I now understand how these things work.

Dallas wins the prize this week. One of the damper shafts was slightly bent and dragging on the piston as it fell. Amazing how sensitive they are.

Both dampers are the same and they are vented. The holes are clear.

Thanks for your help.

AJ
A R Jones

This thread was discussed between 22/11/2011 and 23/11/2011

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