1977 450sl fuel mixture adjustment screw is stuck. - PeachParts Mercedes-Benz Forum

jonbosler · #1 04-16-2015, 10:36 PM

I have a '77 450sl that has a difficult time idling. Before … it was flooding, then I replaced leaky injectors (8 new ones). That helped me at least get it started. Then I had the FD and the WU rebuilt by german star for a small fortune, followed by a new fuel filter and new fuel pump. I actually wanted to have all of that stuff replaced anyway because this car sat winters (in Minnesota) and those were likely necessary fixes. All the vacuum lines look okay, but I ordered more just to replace what I can. I also replaced o rings and holders for the injectors and checked all the relays. Maybe overkill, but what the hell.

So, as it turns out, I can get it to run now but the idle is not there. If I turn ignition on and push down on the sensor plate (to prime the injectors) the car starts and runs for 5-10 seconds. That is long enough for me to jump out and depress the plate again just a couple of mm to maintain an idle. it will idle all day if I hold my finger there and depress 2 mm. If I let go, it closes up and dies.

I checked the idle mixture screw (air supplement?) and cleaned that out. adjusting that has no effect on the idle or lack there of. I moved on to the fuel mixture adjustment screw just btwn the FD and the sensor plate opening…but the darn thing was seized up in there. It is obvious that the previous owner or mechanic worked it too much. (it's a standard screw head instead of the 3mm hex I expected to find there) So…Now I am going to have to disassemble all of that business to see it from the bottom side.

any ideas? My only guess is that this is the adjustment I need to make, but unfortunately can't.

hmmmph. (thanks in advance!)

meltedpanda · #2 04-17-2015, 10:01 AM

it sounds like a FD issue, it is the "heart" of the Kjet system.
Sounds like you are not getting sufficient fuel to the injectors, the FD routes and meters fuel to the injectors. If you are getting good pressure/fuel to the FD chances are it is the culprit or it is fine and the fuel meter to intake ( the screw you mention) is the problem. That screw is usually matched to the engine build to meter properly. Standard screws do not belong there

Frank Reiner · #3 04-17-2015, 03:53 PM

Quote:

Originally Posted by jonbosler

I have a '77 450sl that has a difficult time idling. Before … it was flooding, then I replaced leaky injectors (8 new ones). That helped me at least get it started. Then I had the FD and the WU rebuilt by german star for a small fortune, followed by a new fuel filter and new fuel pump. I actually wanted to have all of that stuff replaced anyway because this car sat winters (in Minnesota) and those were likely necessary fixes. All the vacuum lines look okay, but I ordered more just to replace what I can. I also replaced o rings and holders for the injectors and checked all the relays. Maybe overkill, but what the hell.

So, as it turns out, I can get it to run now but the idle is not there. If I turn ignition on and push down on the sensor plate (to prime the injectors) the car starts and runs for 5-10 seconds. That is long enough for me to jump out and depress the plate again just a couple of mm to maintain an idle. it will idle all day if I hold my finger there and depress 2 mm. If I let go, it closes up and dies.

I checked the idle mixture screw (air supplement?) and cleaned that out. adjusting that has no effect on the idle or lack there of. I moved on to the fuel mixture adjustment screw just btwn the FD and the sensor plate opening…but the darn thing was seized up in there. It is obvious that the previous owner or mechanic worked it too much. (it's a standard screw head instead of the 3mm hex I expected to find there) So…Now I am going to have to disassemble all of that business to see it from the bottom side.

any ideas? My only guess is that this is the adjustment I need to make, but unfortunately can't.

hmmmph. (thanks in advance!)

See highlight.
This sounds as though the spring loaded adjuster screw and tower have been removed. If that assembly were missing, what would be visible, would indeed be a slotted screw in the middle of the arm between the airflow sensor plate and the fuel distributor (FD). That arm has a joint in it, and the slotted screw adjusts the angle of that joint.
Is the slotted screw below the top of the casting on which the FD is mounted?
The possibility exists that your engine is equipped with a system that predates the spring loaded adjuster. If so, there would simply be a small plug in the casting above the mixture adjusting screw, and the screw would indeed have a hex socket.
Can you post a picture of that area?
Is the FD iron, or aluminum?