TR2/3/3A SU carburetor running rich

[Grainger 268]

My 1960 Tr3 carburetor is running rich. Rear carb. Front seems okay. Ive adjusted jet all the way up and still have engine speed up when lifting carb piston. Plugs also show rich.
Any ideas? Tim

 

[cguild]

I have the same issue with 1960 Morgan with SU carbs on Triumph TR3 engine. Plugs and exhaust show excessive carbon. Tried leaning up the carbs with no luck. Haven't messed with jets or ignition timing but car was supposedly recently tuned in a restoration shop.

 

[CJD]

Have you already followed the tuning procedure in the manual? Just trying to get an idea of where we are starting.

 

[Grainger 268]

As far as I know - timing,dwell per manual. Iv checked float needle and seat.

 

[CJD]

Then, no...

Here is the quick and dirty.

1) With the air cleaners off, look in the throats of both carbs where the needle enters the jets...right after shutting the engine down. The fuel should be just below the top of the jet. If more than 1/8 low or, especially, if flowing out of the jets, then adjust your float level. This takes precedence over the 7/16" lever setting in the book.

2) Run both mixture nuts in (up) fully, and then open both 3-1/2 flats.

3) Disconnect the throttle linkage between the carbs and start the engine.

4) Set the idle settings on each carb to get a 700rpm (max) idle, with both carbs drawing equally. (by sound, or better with a tool).

5) Turn the flats equally to get the highest idle possible. Occasionally gun the engine to clear it as you work on it. Lean will surge. Rich will run rough and gradually slow in RPM. DO NOT ADJUST THE CARBS SEPARATELY!! Keep the number of flats equal, or you will end up with one carb working at idle and the other shut off.

6) Reset the idle speed, with equal pull from each carb, and then repeat steps 4/5.

7) once you get the highest rpm, open both nuts 1 flat to the rich side.

Once you have the idle at 700 (max), equal draw, and one flat rich of highest idle speed...then reconnect your throttle linkage.

Now, all the above assumes you have no issues...like sticking pistons, wrong needles, worn jets, needles not centered. If you have any of those problems, then fix them first.

 

[cguild]

Thanks. I'll give it a try.

 

[bobhustead]

Check that the choke lever on the bottom of the rear carb is returning to jet full up position from choked. Just push the jet up by hand.
Bob

 

[sp53]

The choke linkage on SUs hangs up sometimes and will not let the jet return. Take your finger and push up on the clevis pin at the jet to make sure the jet returned to the base. The spring is supposed to do that, but sometimes the jet assembly or choke linkage does not fully return.
steve

 

[Grainger 268]

Then, no...

Here is the quick and dirty.

1) With the air cleaners off, look in the throats of both carbs where the needle enters the jets...right after shutting the engine down. The fuel should be just below the top of the jet. If more than 1/8 low or, especially, if flowing out of the jets, then adjust your float level. This takes precedence over the 7/16" lever setting in the book.

2) Run both mixture nuts in (up) fully, and then open both 3-1/2 flats.

3) Disconnect the throttle linkage between the carbs and start the engine.

4) Set the idle settings on each carb to get a 700rpm (max) idle, with both carbs drawing equally. (by sound, or better with a tool).

5) Turn the flats equally to get the highest idle possible. Occasionally gun the engine to clear it as you work on it. Lean will surge. Rich will run rough and gradually slow in RPM. DO NOT ADJUST THE CARBS SEPARATELY!! Keep the number of flats equal, or you will end up with one carb working at idle and the other shut off.

6) Reset the idle speed, with equal pull from each carb, and then repeat steps 4/5.

7) once you get the highest rpm, open both nuts 1 flat to the rich side.

Once you have the idle at 700 (max), equal draw, and one flat rich of highest idle speed...then reconnect your throttle linkage.

Now, all the above assumes you have no issues...like sticking pistons, wrong needles, worn jets, needles not centered. If you have any of those problems, then fix them first.

Thanks for the help. I'll give it a try

 

[DK66]

I had that same issue on my TR4A while tuning, the rear carb would not let me level the jet with the bridge. Further I could push up on the bottom of the jet and there was plenty of movement. Unlike the forward card - no movement. So this is a new to me car with rebuilt carbs and after many tries and questions - it was the choke cable hanging up and not allowing the jet to level with the bridge. Once I slacked that off no issue with the jet and proceeded to balance everything nicely but it took a few iterations to make the choke/cable release and not bind