1975 280 W114 Emissions

[rump]

Hello all!

I'm finally getting around to digging back into my 1975 280 and I have some questions. First some info on the current condition of my car (all done by previous owner):

- Replacement Weber carburetor installed
- A.I.R. (smog) pump seized and shorter belt installed to bypass
- All vacuum control hoses going to EGR, A.I.R., and fuel evap control devices disconnected, but everything seems to be there

The car runs, but not smoothly - especially on acceleration. I want to make some adjustments so I can feel confident about driving it.

Now for the questions:
1. Should I try to get all of the emissions gear connected and working again? (Of course I would have to test everything, and repair the smog pump bearing.) I do like the idea of trying to save the environment, but I doubt I'd be driving it enough to make much of an impact in that regard. Also, I don't have to get the car inspected here in Virginia (antique registration), so no worries about legal issues.

2. If I eliminate the emissions gear, I'd rather remove everything and store it for the next owner to reinstall if they want or need to. What should I leave intact, and what should I remove?

3. Do I need to worry that the catalytic converter would be negatively affected by the emissions removal/bypass?

4. Do I need to set the timing, etc. differently if the emissions gear is bypassed?

5. I have plans to make the ignition more reliable (Pertronix module, new spark plugs, wires, cap, and rotor). Should I stick with the stock ignition module/coil/ballast resistors after I make those ignition improvements?

Thanks for all of your help!
- Greg
Richmond, VA
1975 280 sedan "Sage"

[Frank Reiner]

Re: Questions
1) Do not trouble to restore the emissions devices; your registration does not require them.
2) Remove & store the components.
3) If you can correct the Weber carb to operate close to stochiometric the cat will be OK.
4) The distributor has centrifugal advance only; set timing to 38 BTDC @ 3500 RPM.
5) As long as the OEM ignition is working, keep it.

[rump]

Hi Frank,

1. OK.
2. I'm guessing I need to plug any of the connections that are left hanging when I disconnect the smog pump, EGR valve, etc.?
3. That's good to hear. I didn't want to have to find a replacement manifold to delete the cat.
4. The timing marked on the plate under the hood says to set the timing to 7 deg BTDC. I'm guessing that number is only good when the emissions stuff is in working order?
5. It seems to work OK, so I'll leave it.

You mentioned getting the Weber carb working properly. I've heard that it can require re-jetting to do that on this engine. Do you know if that's so, and what jets are recommended?

Thanks for your help!

[Idle]

If your car has a catalytic convertor I would stay with that as they are a hassle to remove. But you could and just go with a straight pipe, or, as I recall, two of them. I am basing this on the 1977 280e I used to own.

If you have a big can like thing on the exhaust manifold under the hood then start shopping for a newer exhaust manifold that will fit and get rid of the thermal reactor a lot of 1975 German cars used. These things will crack and allow hot gasses to escape where the gasses will burn the paint off of your hood.

I don't know if the 280 used these, but the 1975 230 did on the California models.

[Frank Reiner]

Originally Posted by rump

3. That's good to hear. I didn't want to have to find a replacement manifold to delete the cat.

You mentioned getting the Weber carb working properly. I've heard that it can require re-jetting to do that on this engine. Do you know if that's so, and what jets are recommended?

If you can possibly do so, find some exhaust manifolds from a M110 that did not have the configuration that you have now. The engine mounted cat was an expedient for the US market; it is simply a terrible idea - high underhood temperatures and very poor flow.
Candidates for a replacement source are 107s, 123s, and 126s with the M110. The 107s & 126s are gray market cars; 123s w/M110s were US market cars 1977-1981.

All carbs can be re-jetted. Weber made thousands of different models of carbs. Specifics are required as a first step.

[rump]

My car does have the converter just next to the engine. Would it be possible to just knock-out the catalyst structure and reinstall it to get more flow and less heat in the engine bay? (I know some people do this when their converter gets plugged.)


As for the Weber - it's a 38DGAS. Just curious if there is a "known jet size" that works well with this engine?

[Idle]

Originally Posted by rump

My car does have the converter just next to the engine. Would it be possible to just knock-out the catalyst structure and reinstall it to get more flow and less heat in the engine bay? (I know some people do this when their converter gets plugged.)


As for the Weber - it's a 38DGAS. Just curious if there is a "known jet size" that works well with this engine?

I don't think that is a cat converter. It is a thermal reactor. They are two different things.

Thermal reactors have a ceramic body surrounded by a stainless steel case. On in some cases a cast iron case. The ceramic cracks and allows hot gasses to reach the metal container which burns through. Then the gases torch your hood and burn the paint off.

The best solution is to replace the manifold. And when doing so look for one from a Euro car as they do not have a port drilled into them for the EGR valve.

[Frank Reiner]

Originally Posted by rump

My car does have the converter just next to the engine. Would it be possible to just knock-out the catalyst structure and reinstall it to get more flow and less heat in the engine bay? (I know some people do this when their converter gets plugged.)

It is a catalytic converter; only '74 California cars had the reactors on the M110. The cat structure is the lesser of the problems; the point at which the front portion of the exhaust manifold turns upwards (and then aft) creates a substantial choke.

As for the Weber - it's a 38DGAS. Just curious if there is a "known jet size" that works well with this engine?

A complete run down of all the variables in the carb is the starting point - main jets, main air correctors, emulsion tubes, aux venturis, main venturis, idle fuel jets, idle air correctors, power valve. A real plus in sorting out a Weber is 30-50 years experience!!

[rump]

Ah, I did notice that bend - that makes sense that it would be a restriction. I'll see what I can find for earlier manifolds...

I know there is a lot that can be tinkered-with in the Weber. I'll give it a go with what I've got and see how she runs.

Thanks for the help!

[Idle]

Originally Posted by Frank Reiner

It is a catalytic converter; only '74 California cars had the reactors on the M110. The cat structure is the lesser of the problems; the point at which the front portion of the exhaust manifold turns upwards (and then aft) creates a substantial choke.

A complete run down of all the variables in the carb is the starting point - main jets, main air correctors, emulsion tubes, aux venturis, main venturis, idle fuel jets, idle air correctors, power valve. A real plus in sorting out a Weber is 30-50 years experience!!

That's good to know about the thermal reactor. I know mine cracked and when I was shopping for a new one the cheapest one I could find was $1600. And that was in 1994 or so.

I just replaced the whole thing with a manifold from a 1971 230.