Timing question.

Hello I hope everyone is well today. I apologize in advance for asking such a basic question that has probably been covered here but, I can't find it. I want to know the proper way to set timing on a 1974 450 sl. The car runs fine now. This is not a troubleshooting question. I have to assume there are slight changes in the procedure and degree settings because over the years the d-jet was replaced. The catalytic converters were added. I'm sure there are several changes over the years that could affect the timing procedure. Can anyone tell me how to set timing on a 1974 450 sl specifically? Thanks for helping.

Here you go with and without vacuum:

Thank you. Now I'm ready to set it. One follow up question, I'm assuming that the 5 degree initial setting is best for emissions. Will the car run better with a little advance? Or will the d-jet make it best at 5 degrees?

Richard450sl said:

Thank you. Now I'm ready to set it. One follow up question, I'm assuming that the 5 degree initial setting is best for emissions. Will the car run better with a little advance? Or will the d-jet make it best at 5 degrees?

Click to expand...

You are correct. The 5ATDC is for emission reasons. And that is with vacuum connected via the switchover valve on the line from the throttle body to the distributor. That valve is actually closed if the A/C is switched on. So first thing - Turn A/C off while setting timing. Remove the vacuum hose from the distributor can and plug it with a golf tee or similar.

I once crawled under car and using paint, marked the balancer at TDC, 5degBTDC & 30deg BTDC. (the graduations can be seen, but the marks help) By the way, remember that the marks appear backwards when looking from below! BTDC marks are to your right when looking down from above. Also mark the current position of the distributor so that you can put it back where it was if the adjustment doesn't help!

Another thing is to make sure you have a hex key that matches the distributor hold down bolt as well as a long extension that will stay connected to that key. I have a magnet on mine so that if the bolts is removed, it doesn't get lost. You will only have to loosen the bolts, so maybe don't need the magnet!

Car should be warmed up. Hook up your timing light to battery and clip to cyl #1 HT lead (passenger side front). The timing light I have is an older basic one. I know there are newer fancier ones, but I am not familiar with those.

Figure out how to to shine the timing light beam on the balancer. It is a bit hard to find just the right angle. Shine it just below the pin that is there to mark TDC.

Now you know where to shine the light, slacken the distributor hold down bolt just a little. Enough to be able to rotate with some friction.

Now run engine at idle (~750rpm). Rotate the distributor slightly with light on balancer until you get timing close to the 15BTDC mark. Vacuum will pull that back about 10-14deg, so this would be like setting idle at about TDC with vacuum. Clamp distributor. Now try revving engine and note where you get to at 3000rpm. You should be at about 27degBTDC if the centrifugal advance is working properly (it must!). Now, hook up the vacuum. You should be advanced a bit beyond TDC. I have found that my car runs best when set to about 5DegBTDC at idle with vacuum.

Now you have vacuum back on, you can fine tune it to achieve somewhere in the 2-8BTDC range. Car should run well!

You can also start off with vacuum still connected. Set timing to about 5BTDC, then disconnect and plug vacuum tube and see where it is without vacuum at idle and at 1500 & 3000rpm. I have done it both ways.

Haven't done this for a few years, so hope I covered everything. Probably more than you need!

Thanks for the help on this.