An over-rich mixture will cause the engine speed to fluctuate through more or less regular periods from high to low speeds; the engine will seem to be mis-firing and there will be noticeable a strong odor, as well as, usually, a heavy black smoke from the exhaust.
LEAN MIXTURE
The best adjustment is obtained with the fuel and air valves set as described. It must be remembered that too lean a mixture as well as an over rich mixture causes over-heating and loss of power and is not as economical as an adjustment which provides just the proper proportion of gasoline and air.
CAUTION
It must be remembered that the low speed needle has been carefully calibrated to notch in disc handle and guide post above it, at the factory and that in making an adjustment that the needle must be so set and the rest of the adjusting done with the air screw as described, never varying from described needle setting unless in extreme cold weather, when a little more gas may be carried, or turning off a little when casing head gas is used in hot weather.
MARVEL CARBURETER
MODEL "S"
Nash Series 691 Sixes Parts Price List
| Part No. | Name | Price |
| 10-80 | Carbureter Body | $ 6.00 |
| 10-580 | Carbureter Assembly | 22.00 |
| 11-537 | Insert Assembly | 7.00 |
| 12-77 | Accelerator Lever | .40 |
| 12-78 | Throttle Lever | .40 |
| 14-2 | Throttle Fly | .25 |
| 15-5 | 10×24×1⁄2 Insert Lock Screw | .05 |
| 15-6 | Bowl Support Screw | .05 |
| 15-14 | Ratchet Spring Screw | .05 |
| 15-15 | Bowl Cover Screw | .05 |
| 15-23 | Throttle and Choker Fly Screws | .05 |
| 15-28 | Throttle Stop Adjusting Screw | .05 |
| 15-29 | 6-32×1⁄4" French Head Screw | .05 |
| 15-32 | Pilot Set Screw | .05 |
| 15-43 | Square Head Set Screw | .05 |
| 16-5 | Bowl Cover Gasket | .05 |
| 16-14 | Strainer Gasket (fibre) | .05 |
| 16-16 | Strainer Gasket (Copper) | .10 |
| 16-35 | Flange Gasket | .10 |
| 16-48 | Insert Gasket | .10 |
| 21-519 | Throttle Stop Damper Control and Shaft Assembly | |
| 22-1 | Heater Jacket Plug | .20 |
| 23-8 | Air Screw Shell | .50 |
| 24-6 | Choker Spring | .15 |
| 24-116 | Air Valve Spring | .30 |
| 24-28 | Flusher Spring | .15 |
| 24-50 | Metering Pin Spring | .15 |
| 24-51 | Ratchet Spring | .15 |
| 25-524 | Choker Shaft and Spring Assembly | .75 |
| 27-10 | Choker Fly | .25 |
| 30-504 | Float and Lever Assembly | .75 |
| 33-501 | Float Shaft Assembly | .20 |
| 35-501 | Float Valve Assembly | .45 |
| 36-4 | Strainer Connection to Bowl | .40 |
| 38-501 | Insert Connection Screw | .50 |
| 43-508 | Gasoline Adjusting Needle Assembly | .50 |
| 44-1 | Gasoline Adjusting Needle Packing | .10 |
| 45-1 | Gasoline Adjusting Needle Packing Nut | .15 |
| 49-56 | High Speed Jet | .30 |
| 56-508 | Bowl Cover Assembly | .75 |
| 58-501 | Flusher Assembly | .15 |
| 64-1 | Bowl Support | .10 |
| 65-1 | Brass Bowl | 2.50 |
| 65-502 | Brass Bowl Assembly | 6.00 |
| 66-3 | Metering Pin Lock Wire | .05 |
| 67-1 | Strainer Body | .30 |
| 67-502 | Strainer Assembly | 1.00 |
| 78-1 | Throttle Shaft Washer | .05 |
| 78-5 | 3⁄16 Lock Washer | .05 |
| 79-8 | Metering Pin Housing Space | .20 |
| 80-3 | Metering Pin Plug | .15 |
| 81-16 | Strainer Nut | .15 |
| 82-1 | Cotter Pin | .05 |
| 83-2 | Manifold Stud | .05 |
| 84-3 | Metering Pin Jet | .35 |
| 95-1 | Strainer Gauze | .20 |
| 119-504 | Dash Pot Plunger, Plunger Rod and Washer Assem. | .80 |
| 125-2 | Metering Pin Spring Seat | .05 |
| 158-2 | Metering Pin Housing | .15 |
| 167-502 | Metering Pin Stem and Wire Assembly | .10 |
| 173-529 | Metering Pin and Lock Wire Assembly | .45 |