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MG TD TF 1500 - Low speed idle

It has been a LONG time since I have been back to the forum which was amazing when I did a total rebuild of my '54 TD. Since then I learned to sail and captained my own boat across the Atlantic and up the Caribbean to Florida. However, I am back with a question I hope someone can help me solve.

My engine, even when warm, hesitates when accelerating for idle. The idea speed seems fine, the timing is right, the distributor was rebuilt by Advanced Distributors, and the coil, wires and plugs are new. The engine runs fine once underway and produces good power. It just hesitates from idle. IF I give it a little choke, the problem goes away. What do you think may be improperly adjusted.

All help appreciated

Dave
54 TD in the San Francisco Bay Area
Dave Rome

Welcome back, Dave. Those are the symptoms of a sticky piston in the vacuum chamber. One of the common causes is a needle not being centered in the jet. Another is just 'stiction' of a piston in its chamber. Sometimes it's a matter of having too heavy an oil in the dashpot. Bud
Bud Krueger

Thanks Bud. I investigate and report back.
Dave Rome

That made a huge difference. I added about a tablespoon of "damper oil" and the hesitation on acceleration disappeared. The pistons were basically dry, so I assume the pistons were not staying up which resulted in a lean mixture on acceleration. Two questions if I can be so bold:

(1) The idle speed increased when I did this, is that normal or did I add too much oil.

(2) Related to 1, when I added the oil I noticed it took a bit of push to get the pistons down. Both took the same effort. Is this also an indication of too much oil?

Thanks again.
Dave Rome

The oil will “self level” if over serviced..being drawn into the intake airflow.
Regards, Tom
tm peterson

Dave, if you don't feel a need to be pushing against something, you haven't added enough. It sounds as if you added a reasonable amount. Bud
Bud Krueger

and yes, it's normal for the idle speed to change-
Before you added the oil the pistons would have been flapping around in there giving a lean mixture and the flat spot --adding the oil works like a shock absorber and stabilizes the pistons keeping the idle mixture stable as well and slightly retards the movement of the piston as you open the throttle which gives a momentary little richness to eliminate that flat spot on takeoff
--all good and yeah, i like to have the oil level at a point where there is about 1/2" of resistance when refitting the dampers,
willy
William Revit

Thank you to everyone, everything makes sense and gets me over another one of those stumbling blocks towards better.
Dave Rome

This thread was discussed between 28/11/2020 and 29/11/2020

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