How to Time a Mopar 400ci 4bbl

by Sam Jenkins

The 400 cubic-inch Mopar is part of the Chrysler's "B" engine family. It was introduced in 1972 and was used on everything from Plymouth Road Runners to Dodge pickups until its end of production in 1978. Performance models such as the Dodge Charger and police vehicles had 400-cubic-inch engines fitted with four-barrel carburetors. In order for your 400-cubic-inch Mopar to run properly, its ignition timing must be set accurately. Incorrectly set ignition timing can result in poor engine performance, low fuel mileage, or damage to your engine. Timing a 400-cubic-inch Mopar is fairly easy and only requires a few tools.

Step 1

Locate your distributor and loosen its hold-down clamp. On a 400, the distributor will be on the front of the engine. At the base of the distributor will be a hold down clamp, which is bolted to the engine casting. Loosen this bolt with your 1/2-inch wrench just enough so that you can rotate the distributor. Be careful not to rotate the distributor too far from its original location as you test the looseness of the clamp.

Step 2

Remove the vacuum hose which attaches to your distributor. This is the hose that controls your vacuum advance. Remove the hose at the distributor end, and stick a bolt, nail, or other small object into the hose to prevent a vacuum leak.

Step 3

Locate the timing marks on the timing chain cover, on the the passenger side of the engine, next to the harmonic balancer. The balancer is behind the bottom pulley at the very front of the engine. The balancer will also have one or more timing marks etched into it. Clean this part of the balancer and apply chalk to highlight the timing marks.

If you are having a hard time getting at the timing marks on the balancer, rotate the engine by bumping the starter with your key. Be sure to remove the coil wire before doing this, to ensure the engine doesn't start. This is the wire that goes into the center of the distributor cap. Remember to replace this wire afterward, as it is necessary for your engine to run.

Step 4

Put on your parking brake and start the engine.

Step 5

Attach the timing light. Your timing light has three wires. Two of them are clamps: one black and one red. These attach to your battery, red going to positive and black to negative. The third wire is the spark pickup. This attaches to the No.1 spark plug wire, usually by clamping around the wire. The No.1 spark plug wire is the front-most wire on the driver's side.

Step 6

With the engine running and your timing light attached, point your timing light at the harmonic balancer from the passenger side and pull the trigger. The timing light will flash in rapid succession, flashing once every time spark is sent to the No.1 spark plug. With the strobe light shining on your harmonic balancer, you will see a timing mark on the balancer hovering in one spot.

Step 7

Rotate your distributor. With the timing light pointed, watch the timing mark move up and down on the balancer. This is how you adjust your timing.

Step 8

Turn the distributor clockwise. Note the direction that your timing mark travels. This is the direction to advance your timing. It differs from year to year, but your 400 should be set to between 10 and 12 degrees advanced, or before top dead center. Rotate the distributor until the mark on your balancer lines up with the 10 degree mark on your timing cover in the advanced direction. Note that your idle speed rpm may increase.

Step 9

Tighten down the distributor clamp, reinstall the vacuum line, and readjust your idle speed on the carburetor, if necessary.

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