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75 280S will only start and run with timing fully advanced

Started by postman70, 19 December 2014, 01:30 AM

postman70

Hello all, I have a M110 engine in my car. My problem now with this car is that it will only start and run decent with distributor fully advanced. It dont run that bad but the idle is about 1000 Rpm's and the idle speed screw is turned out all the way. What would cause something like this? My friend thinks maybe distributor was removed at some time and put back in the wrong spot..but i am not so sure of that ..car runs pretty decent but im concerned about it slamming into gear all the time cause of the high idle..

djenka018

Strobe light can confirm correct timing (or wrong distributor gear mesh).

I guess it must be lapsus, on M117 idle screw out = makes more rpm.

On some cars there is a double vac advance/retard bellow and incorrect connection (as well as advance for AC at idle) and mixup there can further mistime the ignition.
Vitamin C for SL... the SLC

s class

You need to put a timing light on it to see what the timing actually is before making conclusions like 'will only run fully advanced'. 


[color=blue]'76 6.9 Euro[/color], [color=red]'78 6.9 AMG[/color], '80 280SE, [color=brown]'74 350SE[/color], [color=black]'82 500SEL euro full hydro, '83 500SEL euro full hydro [/color], '81 500SL

koan

On a carburettor engine (280S has a carb?) there's a bit of a trap with timing. If someone ups the idle speed with the throttle screw at the carb, it can uncover the vacuum advance port giving full advance. Then they check the timing (with vacuum lines connected) and see lots of advance and back it right off.

What you end up with is an engine that's hard to start, ignition retarded because there's little or no vacuum till engine runs and when it does start it drives badly as the advance jumps all over the place with throttle changes.

Best way to work out what's amiss is to remove the vacuum lines from distributor and set the ignition timing, TDC is a good start if you don't have the correct figure.
Boogity, Boogity, Boogity, Amen!

postman70

Will that brings about another thing that I dont understand..my distributor does not have any vacuum lines going to it..nor is there any nipple for a vacuum line..on the tag under hood it mentions something about setting the timing with the vacuum advance connected..am I suppose to have vacuum advance? Maybe distributor was changed at some time..idk

koan

Doesn't sound right.

Have a look in the online manual.
Boogity, Boogity, Boogity, Amen!

postman70

I will check out the service manual..For the hell of I checked Rockauto.com and took a look at a replacement distributor and that one has no vacuum advance either..not sure what to think now