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MG TD TF 1500 - Thickness of Upper and Lower Jet Bearing Washers

Several recent SU discussions have brought up the need for an accurate specifications for the thickness of the upper and lower jet bearing washers.

I had asked about this a while back but have yet to find any specifications.

Dave Braun had mentioned in an earlier thread that .016 was an approximate thickness for the upper jet bearing washer.

I would imagine that the lower jet bearing washer would have a greater impact on the range of adjustment for the jet adjustment nut - as a thin lower washer would move you towards a rich adjustment (the thin washer would drop the lower jet bearing - and hence the adjustment nut) A thicker would allow for a more lean adjustment - (as the thick washer under the shoulder of the lower jet bearing would raise the jet bearing and the adjustment).

As asked in the earlier SU thread, are there any definitive specifications for the:

Upper Jet Bearing Washer
Lower Jet Bearing Washer


I have never seen a specification in any of my SU books or MG manuals. I have only seen reference to "thin" ones and improper "thick" ones.

Interesting discussion. I also appreciate Dave's mention of a lower fuel level for the modern fuels - he mentioned .020 depth below bridge and I plan to try that measurement for improved running.

DLD

Yes, please... I'd love to know the correct thickness of both!
kmclemore

Here is what I found from Jim Taylor's page on SUs.

1. On the H series carbs the upper jet bearing copper washer is supposed to be 0.016" thick. Many after market kits have this washer 0.025" or even 0.033" thick. This holds the complete jet assembly down farther away from the needle than intended and defeats about 1/2 turn of the mixture adjustment nut (ability to lean out).

If we could confirm this with Dave Braun and then get a spec on the lower washer, I think this would be very helpful to folks.

DLD

If this is true then thousands of us with the Moss rebuild kit have this problem. My adjusters do almost nothing as well. Car runs fine though! Maybe it's not a problem?
efh Haskell

I will try to get the specifications for the Moss washers, Joe Curto's washers, and Abingdon Spares. I will see what Burlen Fuel Systems (SU) has to say as well.

This is a situation that impacts fine tuning capabilities (rich/lean) rather than something that would disable a car.
DLD

All,

I had the same problem a few years ago, I solved by lowering the needle in the piston by about 0.015".
I decided to do this by trial and error and 0.015" was my first attempt


John

52 TD
J Scragg

Last year, Geoffrey Baker recommended removing the top washer completely to lean out the carbs.
Seach the archives for ...
2014042601083424760

The top jet bearing washers that came in my "SU Master Rebuild Kit" (Moss part #375-518) were 0.015" thick. (the correct thickness according to Jim Taylor). The old one that I removed were 0.033" thick. (too thick)

Link to Jim Taylor's SU article:
http://www.jcna.com/library/tech/tech0006.html

Link to TSO carburetor. See "Inability to Achieve Lean Enough Mixture" on page 39 for more reasons for rich idle (but possibly overly lean at highway speeds.)
http://www.mg-cars.org.uk/imgytr/hints&tips/carbtune.pdf

Lonnie
TF7211
LM Cook

With an upper bearing washer of.016, it is necessary to use a somewhat thicker lower bearing washer - this to prevent the lower jet bearing from spinning in the carb body after tightening down the jet securing nut, beveled washer and cork (or viton)gasket.
DLD

This thread was discussed between 12/05/2015 and 13/05/2015

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