Points or Pertronix pointless

[Steve_in_NV]

Greeting Gentlemen,

First, thanks for the information posted it has been informative. I'm new to Mercedes, but not new to auto mechanics, this car is sophisticated. I have cleaned, changed, renewed various items on my car. 1972 280SE (W108)
99700 miles. The car runs ok, I change out the points to a Pertronix unit it seems to idle smoother, but cranks a little longer to start after the change-out from points I have noticed within the first few miles what seems and sounds like a "backfire" through the throttle body, it then clears up but the motor seems to hesitate and just doesn't seem to have power. The lack of power was evident before the Pertronix the backfire is new any thoughts? I have kept everything as it was just in case I want to return back to stock. Thanks in advance for any help or suggestions.

[ggenovez]

After you changed from points to Pertronix did you retime the vehicle? Points affects timing and with the replacement it will definitely make a difference

[meltedpanda]

warm her up and set timing by ear, find the sweet spot . ggenovez, is correct you must retime with electronic points, and remeber the specs are for regular points and not these new fangled gizmos

[mosu]

What should one look for when timing by ear? Highest idle point? Or do you aim for the highest idle point then back it down incrementally until it doesn't ping under load?

[meltedpanda]

I always tune it to a solid steady idle and then pump the gas to check to see if drops with quick fuel and air flow. If it does I may try to advance a bit.
you can also hook up a vacuum guage at teh MPS and the setting with the highest vacuum at idle is usually pretty close

Take it one way till the idle gets unsteady then the other way till it happens agains, somehwere in between you will hear it even out ( provided you have no vacuum leaks ) Take it out for a spin and see how she feels. I have been known to carry my tools , stopping at every accelration trial and adjust on the side of the road
Most of these ol gals run better with timing set before top dead center
AND All this assumes cam timing and chain stretch are within spec.

[Graham]

It would be best to time properly using a timing light.

Try TDC or even 5BTDC at idle (700rpm) with vac retard line disconnected and plugged. Then rev engine up to 3000rpm and check what the timing is there. It should be about 25-30 BTDC. This will show if the mechanical advance is working. Sometimes the centrifugal weights get stuck.

Without a light, I would use a vacuum gauge on the intake manifold as MP suggested. Tee into line to MPS or use one at back that goes to door locks etc. Rotate distributor to position that give max vacuum, the maybe back off just a hair.

BTW - Assuming this car has 4.5L D-Jet engine! If not ignore my post and several others

[mosu]

In my case it's a carbed motor, but I'm assuming that the process is the same. Thanks guys.

[vandor]

>warm her up and set timing by ear

I can't believe you are recommending this. Maybe someone who has timed the same vehicle 100 times might be able to do it, but in reality its nearly impossible.
Most people who set it by ear will advance the timing way too much. Since the idle keeps rising with more advance it 'seems' better. With the low stock compression it will not ping even if the timing is too far advanced by 10-15 degrees. I've seen cars that had 25-30 degrees of timing at idle!

Get a timing light and do it right!

[meltedpanda]

now now, Vandor mind your manners we are a friendly lot, and we all have opinions. I have done it this way for over 30 years. To each his own. It was a suggestion .I have all the gizmo's timing light included. fact is these gals run best BTDC , more than the 'books' tell you , these car have 40 years under their hats, like I said , timing chain, cam's, valves all have to be within acceptible range. Use a vacuum guage if you really want to dial it in

[Steve_in_NV]

Thanks guys. I do have a timing light and I will try to set this weekend. I'm bummed because they are predicting some snow. I did install new plugs and wires I also readjusted the valves, but they were close. New fuel filter new fuel pressure regulator new fan belts new air filter new oil new antifreeze. It has been fun and i always look forward to working on it. Again thanks.

[Steve_in_NV]

One more thing I forgot to mention. I drove it work 30 miles one way when driving home I barely made it, the engine stalled I got it restarted and limped home about a block. This is before any ignition issues. I noticed a buzzing under the car I believe it is a diaphram I series with the return line anyway I removed the gas cap and either it was pressure escaping or something equalizing I'm not sure. Unfortunately after that I have little confidence in reliability. Has this happened to anyone before? I thinki I hijacked my own thread.

[meltedpanda]

the fuel pump will buzz on these cars, was it from the engine bay or under the car ?

[Steve_in_NV]

Originally Posted by meltedpanda

the fuel pump will buzz on these cars, was it from the engine bay or under the car ?

Thanks for the suggestion except the buzzing was happening with the ignition off.
It looks like the factory service manual calls it a "damper container". I haven't heard the buzzing since the first time, but I haven't driven that far since.

[vandor]

Sorry, I didn't mean to be obnoxious. I do believe that you can do it, but the likelihood that some else can are very slim.

[Steve_in_NV]

Originally Posted by vandor

Sorry, I didn't mean to be obnoxious. I do believe that you can do it, but the likelihood that some else can are very slim.

Thank you for your vote of confidence, I only reached out in the hopes that possibly someone else may have had these symptoms. My guess is someone has, but they may no longer follow the forum or haven't read my problem. I didn't take your reply as obnoxious just not very helpful. And you are correct I will figure it out hopefully sooner than later, like everyone that tinkers with these classics I would like to enjoy the ride.

Steve