[Reynis]

Im a newbie and have been following this form to aquaint myself with the new toy I purchased, 1973 450 SL. Great reading. I drove my 450 for about 500 miles without problem. Then it started loping at start up and backfiring under power. I was on the road at the time and disconnected the air cleaner sensor. It quit backfiring under load ????? Any ideas for a newbie ?:bowdown:

 

[XXTi]

Air cleaner sensor??

 

[MBGraham]

Air cleaner sensor??

There is temperature sensor on incoming air. It is used as part of several inputs to ECU for mixture control. Disconnecting it makes a difference when car is cold or at idle.

That loping is usually caused by stuck aux air valve, but first try reducing idle speed. The loping occurs when rpm gets above about 1500rpm.

The backfiring would likely be due to timing being out. Check that cam/balancer & distributor timing marks are close to lining up at TDC. Then get a timing light and set timing at idle at about TDC. Then rev engine to 3000rpm and see if timing advances. (it should go to about 25BTDC) If you don't see the advance, your distributer weights may be stuck (see sticky on how to free them up)

 

[Reynis]

Thank You! I had just had it serviced at the local MB dealer and they had also set the timing?????????? it was idleing at close to 25 to 30 ATDC. I set the idle and now it just runs rough. Any idea what else they might have screwed up??

 

[rowdie]

Thank You! I had just had it serviced at the local MB dealer and they had also set the timing?????????? it was idleing at close to 25 to 30 ATDC. I set the idle and now it just runs rough. Any idea what else they might have screwed up??

25-30 degree advance at idle? IIRC timing is TDC at around 750 rpms warm with vacuum disconnected from dizzy and plugged. AC off also.

 

[MBGraham]

25-30 degree advance at idle? IIRC timing is TDC at around 750 rpms warm with vacuum disconnected from dizzy and plugged. AC off also.

He said 23-30 ATDC - Isn't that retarded?

At idle, he should be at about TDC or slightly advanced. Say 5 deg BTDC at Idle with vacuum plugged. Then at 3000rpm, he should be advanced to say 22-30 deg BTDC.

Not sure how he could be 25 deg retarded.

If Cam and Balancer (flywheel) marks approx line up, the distributor should be clamped so it is turned almost all the way CCW. It won't be quite at end of clamp bolt slot, but head/washer of clamp bolt will cover the slot.

I just set mine like that and then check the timing.

This pic shows position on slot (the other arrow is where the rotor points at TDC)

 

[rowdie]

He needs to clarify. I doubt it would even start with 25-30 BTDC or ATDC.

 

[Reynis]

I,m a newbie so I may not have explained correctly. Sorry. I checked the timing as MB suggested. On the part that has the timing marks also has a little tit that was lined up with the stationary needle on the block (at about 28 whatever) I moved the distributor clockwise so the TDC mark was opposite the stationary needle. Please bear with me. You guys are the experts!

 

[rowdie]

The part with the timing marks is the vibration (harmonic) damper. My '73 does not have the "tit" you describe. The pointer should point to "0" when timing at idle.
Model 107.

 

[Fonzi]

5 degrees atdc is spec.

http://www.benzworld.org/forums/r-c107-sl-slc-class/1608047-engine-timing-my-us-d-jet.html

I now understand the idea of tuning the timing other ways that by spec, like the antenna or feeling the vibration of the engine. I understand that spec is not the rule.



Sent from my iPhone using AG Free

 

[rowdie]

I hate to disagree. Well, not really.
http://www.startekinfo.com/StarTek/outside/11883/PROGRAM/Engine/107/M117_45/075-500.pdf

 

[Reynis]

I believe I got myself into a very interesting hobby. I hope I will be able understand (over a period of time) exactly how this thing works. Thanks and on my way to buy some more testing apparatus and tools. Learning the manual is a project in itself!