1972 300SEL 4.5 tune up

[Clunker]

I replaced the water pump on my 300 so I had to remove the distributor. I got real confused putting it back together. But, with help from SHOP FORUM and my brothers I was able to get it to run some what. It is running very rich. I have the shop c.d.rom and some tune up knowledge (limited) and tools. Does anyone know the best way from begining to end to adjust the mixture and tune her up?

[psfred]

Clunker:

Just did the same thing on my 280 SE 4.5. What a pain in the butt, having to remove the distributor! Don't tighten the PS/water pump belts by prying on the PS pump -- there are two belts on there to keep the required tension low enough to avoid wrecking the water pump. Hand power on the PS pump ought to get them tight enough.

Assuming the car ran well before you changed the pump.

Step by step:

The only thing you could have changed is the timing, so get that right first.

What you need to know: timing at cranking speed (ground the high voltage lead from the coil so it won't start) is 7 degrees before top dead center. Check your vac retard diaphram to make sure it works before you set the timing. Requires a timing light. If the retard is working, timing is 5 degrees AFTER top dead center at idle.

Connect the timing light to the battery, and clip the pickup onto the spark plug wire to #1. Keep all wires out of the fan...... Loosen the bolt that holds the distributor down, then start car and shine the flashing light onto the pointer on the water pump (the thing you nearly stabbed your hand on). The degrees are marked on the balancer -- before TDC is to the right, after TDC to the left of the 0 mark. Rotate distributor clockwise to retard, counterclockwise to advance timing.

When set, shut off engine, tighten distributor hold down, and then recheck to make sure you didn't move the distributor.

If the engine still runs rough, make sure you have the wires on the cap correctly -- the firing order is on the valve cover, I think. At any rate, the plug wires go onto the cap in the following order, clockwise: 1-5-4-8-6-3-7-2. If the order is correct, check for proper condition -- if the wires were old, bending them can make them leak. Will cause irregular miss and smelly exhaust.

Check the cap and rotor, too -- if they got oil or water in them, they can carbon track, causing missing.

Next, check for vac leaks, and make sure the wires to the temp sensors are in place. Some of these will run very, very rich with the air cleaner temp sensor disconnected. Make sure the wires and connector are ok and properly hooked up -- I seem to forever be forgetting mine and yanking the wires off.

The door lock system, the booster line, the tranny signal line, and the vac line to the retard diaphram can all cause leaks, check the rubber hoses (all rock hard and leaking on mine) -- replace any that don't look or feel good. Check the lock system to make sure it holds vac -- you can plug it temporarily if you need to.

I assume you have the rad full -- if you are short on coolant, the system will think the car is cold since the sensor is in the intake, and won't have enough coolant running past to keep it hot.

From there, you need a CO analyzer to set the mixture, there is no way to do it otherwise. There is a Phillips screw on the top of the control unit -- I think clockwise is richer, but you will find out fast enough with the CO analyser.

Good luck -- at least you didn't have to repair the block and radiator!

Peter