Owners manual
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3. Start the vehicle.
4. Loosen the lock screw at the top of the assembly.
5. Turn the adjusting nut while holding the screw in place until the fuel level is at the bottom of the sight plug hole. A slight trickle should be
seen at the threads. Turn the adjusting nut clockwise to lower the fuel level and counter-clockwise to raise the fuel level.
Figure 3
6. Tighten the lock screw while holding the adjustment nut.
7. Replace the sight plug and lightly tighten with a screwdriver.
8. Flush the fuel bowl by revving the engine a few times with the transmission in neutral.
9. Remove the sight plug to confirm your setting. A slight trickle should be seen at the threads. Adjust, if necessary. Replace the sight plug
and tighten.
IDLE SPEED SCREW:
The idle speed screw in most cases is the only screw you should adjust. The Idle screw controls the throttle plate position at idle, which in turn
raises or lowers the engine rpm by allowing more or less air/fuel mixture into the engine. It does not control the air/fuel mixture. Here are the
proper steps for setting the engines idle speed.
1. Find the proper idle rpm on the underhood decal of your vehicle. If this decal is not available, find a service manual that references your
vehicle and engine and find the recommended idle rpm.
2. Start the engine and allow it to warm up.
3. Connect a tachometer, if your vehicle is not so equipped.
4. Make sure the parking brake is on and the wheels are blocked. Place the automatic transmission in drive, the manual transmission in
neutral or as stated on the underhood decal.
5. If the idle speed is slower than recommended, turn the screw clockwise to speed up the rpm. If the idle speed is too fast, turn the idle
screw clockwise to slow down. This adjustment should be made to both the primary and secondary screws in equal amounts, so that the
throttle plates are opened the same amount.
NOTE: There is a Holley secondary idle adjustment lever, P/N 26-137, that allows the secondary throttle plate to be adjusted without
carburetor removal. The Holley 4150 HP Ultra Carburetors have this feature already installed.
Figure 4 Figure 5