Marvel Carburetor Disection

[Jeff in BC]

Continuing with the idle system and the upper portion of the carb.



Photo 8 – Interior view of the upper portion of the carb.

At the center of the photo is the passage (10) where the idle well enters.



Photo 9 – View into passage (10) for idle well.

I removed the idle adjusting needle to shine a light in, as this passage is too deep to get a photo any other way. The threads for the needle can be seen at the bottom.



Photo 10 – View from top of carb with throttle valve (6) closed.

The bright dot (7) at the center is the tip of the idle adjusting needle; this is the primary idle orifice.

Now I removed the throttle valve.



Photo 11 – Throttle valve parts.

Note the wear at the ends of the throttle shaft (~ 0.010”). This may be a problem for rebuild (air leakage). Also there aren’t any seals.

Now back to the idle system.



Photo 12 – View from top of carb with the throttle removed.

The primary idle orifice (7) can be seen and just below is another orifice. This is the secondary idle orifice (8).



Photo 13 – Another view into passage for idle well.

The above shows a wire placed in the secondary idle orifice; below it are the threads for the idle adjusting needle.



Photo 14 – Idle adjusting needle.



Photo 15 – An attempt to show the fuel passages into the upper portion of the carb.

6 – Throttle Valve in closed position
8 – Secondary Idle Passage
7/12 – Primary Idle Passage/Idle Adjusting Needle Seat
10 – Idle Well/Passage
13 – Idle Adjusting Needle

There is one more passage to show, this is an air passage.



Photo 16 – Interior view of the upper portion of the carb showing the air passage (copper wire) into idle well passage with the gasket in place.

Note the small cutout in the gasket, this is important for correct airflow.



Photo 17 – Side view of the upper portion of the carb showing air passage.



Photo 18 – Diagram from Service Manual.

For an explanation of the Idle System refer to the TSX Service Manual page 3. A link to this manual is at the beginning of Post 1.

Now for a little fun.

How does this all fit in with the magic number, 1536043, on the side of the carb? Lets have a look at the patent. A link to this patent is at the beginning of Post 1.

On Figure 1 The primary idle orifice (54) and the secondary idle orifice (53) are shown and an explanation of their function starts on page 3 line 80 (correction page 3 line 43). Continuing on to page 5, starting at line 28, are claims made by the inventor, claims 1 thru 4 refer to this type of idle system.

The explanation given in the TSX Service Manual, on page 3, are a little easier to follow than the explanation in the patent. It should be noted that both of these explanations refer to an “Air Adjusting Needle Valve”. The carb we are looking at uses a “Fuel Adjusting Needle Valve”. There is an explanation of the differences in the TSX Service Manual on Page 8, lower left paragragh.

The next section to be covered will be the Power Fuel Feed System.

That’s all for now.
Jeff