Demon Fuel Systems 1905 - Manual (Page 14)

14
Long Duration Camshaft Tuning
Long duration or radical camshafts generally need more idle air than a stock or mild camshaft and require the throttle
plates to be opened more than that of a stock or mild engine. Excessive throttle opening at idle coupled with low manifold
vacuum makes it possible that the metering rods are in the up/rich position at idle. If your engine has a radical camshaft,
check the manifold vacuum at idle, if it is
above 10” Hg the stock step-up springs will work fine. If the engine vacuum at
idle is less than 8- 10” Hg it will be necessary to change to a lighter or lower vacuum rated step-up spring. It may be
necessary to try a couple different springs to determine which is best for your application.
Tuning for Elevation
Street Demon™ carburetors are calibrated at sea level. When going up in elevation, the air is thinner and the carburetor
may run rich. As a general rule of thumb, for every 2,000 ft. in elevation, the metering rod diameter should be increased
.002” on the lean and rich steps.
Removal and Installation of Metering Rods, Step-Up Springs and Jets
Metering Rod and Step-Up Spring Replacement
1. Loosen the step-up piston cover screws.
2. Twist the step-up piston cover plates to the side (Fig. 20).
3. Remove the step-up piston, metering rod and spring.
4. Re-assemble in reverse order of removal.
Figure 20
Primary & Secondary Jet Replacement & Float Level Check & Adjustment
1. Remove carburetor (refer to removal of existing carburetor) on page 4.
2. Remove the metering rods and step-up pistons as outlined in (metering rod and step-up spring replacement)
3. Remove the two Phillips head screws from the top of the carburetor (Fig. 21).
Figure 21