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MERCEDES W107 The R/C107 coupe and roadster from 1971-1989 (280SL, 280SLC, 300SL, 350SL, 350SLC, 380SL, 380SLC, 420SL, 450SL, 450SLC, 450SLC 5.0, 500SL, 500SLC, 560SL)

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Old 25th March 2019, 08:34 PM
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Default k jet 450 Vac Advance/Retard diagram non-smog

Does anyone have a diagram of the vacuum lines for the M117 450 K Jet for the rest of the world models? I've got the vacuum diagrams for both the AU and US models complete with EGR and lots of retard built in. For reference mine is a 1977 model.

Since the EGR is long since disconnected on my car (and it always uses 95 non-ethanol fuel) I am trying to fix some of the broken vacuum lines and looking to see how the system would be set up with out it.

specifically i am trying to work out?

1) Is there any vacuum retard on the non smog 450 (e.g. to raise idle with A/C on?)
2) does the vac advance plug into the vac source above or below the throttle butterfly? As far as I know there are three sources, two above and one below. I gather the non-smog engines have the unused sources capped.

It seems that if you don't care about idle emissions you wouldn't need the retard function and the advance function would be plugged in below the throttle, not above it like in the smog system.

A very simple system may no vac retard at all and a single advance line going via a thermal valve to the vacuum advance on the distributor.
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Old 26th March 2019, 06:45 PM
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Default Re: k jet 450 Vac Advance/Retard diagram non-smog

For reference this is the vacuum diagram for the australian version, for model year 1977.




these are the corresponding timing specs



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Old 27th March 2019, 11:32 AM
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Default Re: k jet 450 Vac Advance/Retard diagram non-smog

To add further, I am also trying to work out in the diagram I have annotated, what is plugged in where on the regular K-Jet 450.




On the Aussie one, A is vacuum advance, which means there is NO advance at idle, and peak advance at moderate throttle openings (i.e. cruising on the motorway)

B is vacuum retard, which is max at idle and then turns off after idle.

C is air pump, which is unaffected by the throttle butterfly.

I am not sure where various stuff is plugged in on the regular car.
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Old 27th March 2019, 11:34 AM
sean sherry sean sherry is offline
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Talking Re: k jet 450 Vac Advance/Retard diagram non-smog

Bryce , I think you will get a better result with 10/11% static advance using 98 octane fuel. Though the total mechanical advance is the important number. somewhere in the low thirties and up to 35 % if the engine is relatively carbon free in all the combustion chambers. Sometimes one cylinder has a build up of carbon and it will cause pinging.
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Old 27th March 2019, 11:41 AM
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Default Re: k jet 450 Vac Advance/Retard diagram non-smog

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Originally Posted by sean sherry View Post
Bryce , I think you will get a better result with 10/11% static advance using 98 octane fuel. Though the total mechanical advance is the important number. somewhere in the low thirties and up to 35 % if the engine is relatively carbon free in all the combustion chambers. Sometimes one cylinder has a build up of carbon and it will cause pinging.
Thanks - right now I have 95 in the tank, and as of now the vac advance is plugged in to port A on my diagram, I have not connected up the vac retard and I tried advancing the timing a few degrees. This was fine under load, but it pinged at cruise, probably because of the vac advance. I have put it back a bit, but not yet taken the car for a test drive, and I want to use up more of the 95 before I try a tank of 98 so I get the full benefit.

I need to find some caps to cap off the ports for EGR and Air pump as these were disconnected years ago but the lines left uncapped.
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Old 27th March 2019, 08:22 PM
sean sherry sean sherry is offline
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Smile Re: k jet 450 Vac Advance/Retard diagram non-smog

Good..... now you know where you stand.. if 98 sorts the light pinging the timing is spot on.
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Old 2nd April 2019, 06:20 PM
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Default Re: k jet 450 Vac Advance/Retard diagram non-smog

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Originally Posted by c107 View Post
To add further, I am also trying to work out in the diagram I have annotated, what is plugged in where on the regular K-Jet 450.




On the Aussie one, A is vacuum advance, which means there is NO advance at idle, and peak advance at moderate throttle openings (i.e. cruising on the motorway)

B is vacuum retard, which is max at idle and then turns off after idle.

C is air pump, which is unaffected by the throttle butterfly.

I am not sure where various stuff is plugged in on the regular car.
Hi Bryce
I believe B through changeover valve is actually vacuum advance with a/c compressor engaged, it advances timing 10 deg to raise idle speed when comprsssor cuts it
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Old 23rd June 2019, 09:43 PM
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Default Re: k jet 450 Vac Advance/Retard diagram non-smog

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Originally Posted by Helmet View Post
Hi Bryce
I believe B through changeover valve is actually vacuum advance with a/c compressor engaged, it advances timing 10 deg to raise idle speed when comprsssor cuts it
Thanks Helmet, sorry I had not seen your post.
Are you referring to the european spec cars?
I can't find a proper diagram for them, but from what I can tell the only function for vac retard on them is A/C related.

On the aussie one, the manual seems to refer to B as the retard, unless I am not interpreting it correctly? The colour of the original vacuum lines is what I am using to make this interpretation.






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Old 23rd June 2019, 09:48 PM
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Default Re: k jet 450 Vac Advance/Retard diagram non-smog

Yesterday I had a bit more of a play with this.
I have filled the tank with 98, and the pinging is a lot less, but is still there.
it happens at around 95 km/h or more at slightly open throttle.
My assumption here is that the combination of the mechanical advance and the vacuum advance is too much.

Next thing I tried is to put a cap on the now disconnected retard line on the vacuum canister on the distributor. My thinking was that the diaphram would harder to move with that port closed. Don't think it made any difference.

My next thought is probably to retard the ignition a little. My thinking is that this is preferable than disconnecting the vacuum advance. The car does seem to have quite a bit more pick up and go since I re-connected the broken advance and disconnected the retard.

I also need to plug the unused lines for the EGR. This was disconnected years before my ownership, but the lines not capped off.
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Last edited by c107; 23rd June 2019 at 09:54 PM.
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Old 24th June 2019, 09:43 AM
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Default Re: k jet 450 Vac Advance/Retard diagram non-smog

These do make interesting reading & prompt a thorough analysis of how your particular engine is setup. Not uncommon to see these stuffed up with the passage of time & inexperienced mechanics.

BTW I’m now of the opinion EGR is best served in the bin since it often fails leaving the exhaust gases constantly entering the inlet or worse still deposits choking the inlet over time. Do your engine a favour....
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