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Tips
Tips

Mixture Control

pdplot

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TR-6 runs fine but seems a bit rich according to plug color. When I try to adjust mixture, nothing happens. Manual says when you lift the piston 1/4", idle should speed up and then die off. When I fooled with SUs back in the '50s, that's the way we tuned them, but these Stromberg's don't make any difference what I do, even when I screw the needles all the way in or back them way out. The idle speed just falls off right away, indicating too lean. Any ideas?
 
You could stick with reading the plugs. Adjust them leaner, take it out for a 10 mile run and check the plugs. Rinse and Repeat...... This would be a fun testing method.
 
Make sure that the needle is still threaded onto the adjuster. From fully Clockwise with the Allen wrench which is full rich to the disengaged point is slightly less than 2-1/2 Counterclockwise turns.
Start out about 1-1/2. Lift the air valve about 1/8 inch and observe the IMMEDIATE reaction of the engine. Taking a couple of seconds to decide will cause the engine to flutter and give the false impression that the mixture is lean.
BTW, I rely on the reading the plugs after getting the mixture close with the air valve. The reason is by driving I go thru a variety of conditions. Very little idling, a lot of acceleration, a little downshifting and some cruising.
About 30 miles on old plugs should be enough to develop a color change.
 
When that happens on my TR3, it usually means there is a problem somewhere else. Valve lash, ignition timing, clogged air filter, etc.

If you can't find anything else, double-check the valve timing. I've never seen it on an LBC, but I have seen other engines slip a tooth on the timing chain, which will cause the plugs to show rich (or even carbon foul).
 
poolboy said:
Make sure that the needle is still threaded onto the adjuster.

That's my first reaction as well.
 
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