My uncle tried helping me time the 4.5 and when he pulled off the vacuum, I believe it retarded the timing. I can't remember if he said it retarded or advanced it, but it did the opposite of what he thought it would do (if it is in fact a timing advance on the side of the distributor). The vacuum line goes to an electric solenoid on the firewall, is this correct? There is a two-wire electrical plug and another vacuum line that goes to the air sensor (?) in the middle of the intake. I just put on an intake manifold gasket and couldn't remember where the advance vacuum line attaches. Any help with these questions is greatly appreciated.

Merry Christmas,

David

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2000 Honda Accord V6 137k miles

1972 300SEL 4.5 98k miles

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If your car is the same as my 74,it only has a single line running to the distributor.This is a RETARD unit,timing is set at 5 degrees ATDC with the line connected.
Some models used a dual diaphragm with both vacuum advance and retard,(I think only later models IIRC)
The line to the distributor should get ported vacuum from a port just above the throttle plate.It may run to a thermal switch on the firewall for delay under cold conditions.
I remember some threads,possibly in the SL forums about setting timing with the line disconnected.I don't recall the exact specifications,I believe it was about 8-10 deg BTDC at idle with around 30-36 degrees total advance at 2500-3000RPM.
That ought to get you "in the ballpark" at least

That's about right. Remove and plug the vacuum tube. Then adjust timing so you get about 30deg BTDC at 3000rpm. You will have to turn distributor almost to end of the slot. I don't quite get to 30 - usually about 27deg.

The vacuum is a vacuum retard. It only really works at idle. If you check timing at idle (700rpm) with vacuum reconnected, it should be in the 5ATDC to 5BTDC range. I think mine is about 2Deg BTDC.

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

Thank you very much gentlemen, I will get to the matter tomorrow and let everyone know how it goes.

One last question, my ballast resistor was smoking because some oil, etc. was on it. I understand it gets really hot, but the wires are getting pretty warm as well, is this normal? Finally, what is the small computer for that is located right by both ballast resistors? It's smaller then the ECU on the other side of the radiator.

Thanks again and I appreciate your input.

Best Regards,

David

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2000 Honda Accord V6 137k miles

1972 300SEL 4.5 98k miles

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The wires may be warm due to heat transfer from the resistors but if they are hot enough to make the insulation pliable, there is something wrong.

The "ECU" looking box is the ignition switch gear. It's an early electronic ignition. It's not a capacitive discharge type but instead uses a big transistor to switch the coil rather than the points.

Michael

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Usta haves '69 250/8, '76 280C, 1971 250C 114.023, 1976 450SEL 116.033
Current have, 1983 300SD 126.120

Thanks for your post, Michael. I should be able to get this stuff taken care of in the next couple days.

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2000 Honda Accord V6 137k miles

1972 300SEL 4.5 98k miles

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Check that the centrifugal advance weights respond quickly to the throttle when doing a high rpm timing and how fast is snap to idle.
Check the stability of the light at 3000.
The weights get crudy and slow. Then it always seems retarded.
Clean and lube the trigger points cam.

Where exactly is the trigger points cam? I know they're below the distributor, but how do you access them?

Thanks,

David

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2000 Honda Accord V6 137k miles

1972 300SEL 4.5 98k miles

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You have to remove the distributor. The wire that goes down the front of the engine between the engine and the distributor is the one that the trigger points are attached to.

Those points cannot be adjusted. You can clean them. But only necessary after you have eliminated ignition problems.

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

I tried timing the car today and was unsuccessful. The car will not idle on its own without someone at least barely hitting the throttle. The car idles at just over 600 rpms. The closest we can get this thing in time is 25° ATDC. The thing is, however, that's without the vacuum retard working since the car can't be left at idle. When we used a mity-vac to apply vacuum to the retard unit, it slowed the engine down further but did somewhat smooth it out. There is no more adjustment left to the distributor and no one's had the distributor out. If the PO did, he would have had a well-known Germanic mechanic in town do it. Could this be indicative of the timing chain being off a tooth? We tried rotating the order of the wires to compensate but that definitely didn't help.

Finally, we replaced the points but had to use a feeler gauge since I don't know the dwell setting. What should it be set to?

Thanks for your help everyone, I appreciate it.

Best Regards,

David

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2000 Honda Accord V6 137k miles

1972 300SEL 4.5 98k miles

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25 deg ATDC????? Which way are you turning the distributor? You need to turn it almost completely counterclockwise. If the distributor has not been out, it is hard to see how you would not get 20-30 deg BTDC at 3000rpm unless the weights are jammed.

Has the timing chain been out? Unless something like a guide has broken, it can't jump a tooth. It is easy enough to check the cam timing. Just pull the passenger side cover - There are timing marks on the front of the cam assembly. Line those up and check what the marks on the Balancer say. If near TDC, then the distributor rotor should also point toward it's mark at about 1 o'clock.

BTW - put the wires back to spec. Do you have the specs?

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

It may have been 25° BTDC. If I remember correctly, it's turned just about all the way clockwise. Turning it counter-clockwise made it worse. We were getting this timing around idle rpm's but with me lightly touching the throttle. Where is the idle adjustment on this car or is that controlled electronically?

I don't think the distributor or cam is a tooth off, either. It has had no work in the past several years to either of these areas. One possibility that did come up is the possibility of a burnt valve which might explain the backfiring, etc.

Thanks,

David

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2000 Honda Accord V6 137k miles

1972 300SEL 4.5 98k miles

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You may want to check cam timing as mentioned and also make sure that if there are two pointers for the timing marks that you are using the correct one. Seems to me that there may be two of them but I've been wrong before.

I'd bring number one piston to TDC (feel for pressure buildup at sparkplug) and check that the rotor points to the mark on the distributor and that the cap is on correctly and that the pointer you're using is the correct one. I assume you've double and triple checked the firing order and wires.

Grab the rotor and make sure that it moves the mechanical advance and that the weights are still working. You've proved that the vacuum can is pulling the plate already.

Can't help with idle speed with any assurance since I have the mechanical injection but on mine, there is a natural nylon screw to my right of the tor radiator hose and nestled down among the mass of hoses.

Do check out w116.org, the CD manuals are online and will help out a lot.

Michael

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Usta haves '69 250/8, '76 280C, 1971 250C 114.023, 1976 450SEL 116.033
Current have, 1983 300SD 126.120

Distributor must be almost all the way counterclockwise. See approx location in picture.

If you can't run with it there, then something else is wrong. Go back and line up cam marks (#1 at TDC). Then check that balancer is also indicating close to TDC and that rotor point to mark on housing at 1 o'clock.

Idle adjustment is in front of engine - large slotted screw.

Did you read the link "specs" in my previous post. It would help if you read sections 07.4 and 07.5.

Attached Thumbnails

 

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

Also, make sure the mechanical advance in the distributor is not stuck. You should be able to move the rotor clockwise, and it should go back on its own (it may not go back all the way). If this does not happen then the stuck mechanical advance may be causing you to have to be at the end of the adjustment range. If applying vacuum helped the timing, it's probably 25° BTDC, I don't think the engine could run 25° ATDC. It would backfire like a beast at 25° BTDC. IF it could run at 25°ATDC, your headers would be cherry red.

Check to see if your timing is off a tooth. If the engine has 400k miles but never had the chain replaced, do it now. I have a DIY article on here that's easy enough for you to follow & shouldn't take more than 2-3 hours to do even for a first-timer taking their time. The timing rail replacement is what takes a while.

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