Where to buy a new throttle plate/flap

[Berggreen]

Hello everyone

I have a throttle house, where the brass throttle plate/flap is worn and not sealing the air-intake when the throttle plate/flap is fully closed - I can see light around the plate/flap, when it is closed, and "pirat-air" is therefore leaking into the intake-system at idle.

i can see that the plate/flap is just mounted with two screws, but I have searched around the i-net for a new plate/flap, but without any luck.

Any tip, where I can buy a new one?

Thanks,

Christian

[Tyler S]

The throttle plates do not seal 100%. If you can still adjust your idle down to spec using the idle air screw then dont worry too much about a little leakage at the throttle plate. These engines do not have any upstream sensors like modern cars so it is a non issue. Set the throttle plate stop screw until the throttle plate just drags in the bore. Then slightly screw it back in about 1/8 a turn or until it no longer drags. However if you still cannot get the idle down to spec using the air screw on the intake manifold you may also want to look elsewhere for a vacuum leak.

[Berggreen]

The throttle plates do not seal 100%. If you can still adjust your idle down to spec using the idle air screw then dont worry too much about a little leakage at the throttle plate. These engines do not have any upstream sensors like modern cars so it is a non issue. Set the throttle plate stop screw until the throttle plate just drags in the bore. Then slightly screw it back in about 1/8 a turn or until it no longer drags. However if you still cannot get the idle down to spec using the air screw on the intake manifold you may also want to look elsewhere for a vacuum leak.

Thanks Tyler!

Unfortunately, I cannot get idle speed down using the idle screw, and the only way currently to get the idle speed down is to "drown the pump", thus increasing the rod length linkage to the injection pump, so that it does not go into zero position. But I guess that this is not an ideal solution!

I have been looking around for a possible vacuum leak, but unfortunately without luck. So I thought I had found the issue with the throttle plate not sealing completely. I have already adjusted the throttle plate position with the stop screw, but no effect on the idle speed.

Do you know where to buy a new throttle plate to try to minimize the leak there?

Thanks,

Christian

[Tyler S]

I dont know where to buy a new plate. It is not a common failure point. Have you verified your timing at Idle? If the switchgear or vacuum retard system is malfunctioning it will advance the timing and no amount of adjustment will compensate to get the idle within range. Also, One more place to look for a vacuum leak is the brake booster.

[Berggreen]

I dont know where to buy a new plate. It is not a common failure point. Have you verified your timing at Idle? If the switchgear or vacuum retard system is malfunctioning it will advance the timing and no amount of adjustment will compensate to get the idle within range. Also, One more place to look for a vacuum leak is the brake booster.

Thanks Tyler - appreciate you advice! 

Yes, I checked the timing, and I have around 5 degrees ATDC at idle, increasing up to around 30-35 degrees ATDC at 3000 rpm.

The US switch-gear system has been disengaged and a 123ignition installed instead sourcing vacuum from the US configuration side port on the throttle port, giving constant vacuum. I have not yet changed to the the port under the throttle house (Euro configuration) with declining vacuum with rpms, instead of the US config. side-port with constant vacuum. But I don't think that should have any influence on engine behavior at idle. It should however give me more advance a lower rpms, as vacuum will reduce with rpms, when sourcing vacuum from the (euro) port under the throttle house.

Or am I wrong?

Good point about the brake booster. Any good way of checking this?

Thanks,

Christian

[Jonny B]

Checking for a leak in the brake booster is straightforward. With the car running, press on the brake pedal. If there is a marked increase in idle you most likely have a leak.

[Berggreen]

Checking for a leak in the brake booster is straightforward. With the car running, press on the brake pedal. If there is a marked increase in idle you most likely have a leak.

Thanks Jonny, I will try this out!

What do you think of my "vacuum port plans"? Am I on the right track?

Thanks,

Christian

[Tyler S]

Yes thats one way the booster can leak. It can also leak on the manifold side of the chamber. Easy way to eliminate it as a possible source is to simply disconnect the vacuum line and plug it for testing purposes.

Christian, your timing reading of 5 ATDC and 30-35 ATDC doesn’t make sense. Are you meaning “ BTDC” (Before top dead center)? Try setting your timing at Zero (0). If your timing is really at 5 BTDC then setting it at zero will lower the idle. Easy test.

Depending on which model 123 Ignition you have will determine if you will be able to use manifold vacuum for MAP advance purposes. Only the 123 “Tune”and “Tune +” can be set up this way.

[Berggreen]

Yes thats one way the booster can leak. It can also leak on the manifold side of the chamber. Easy way to eliminate it as a possible source is to simply disconnect the vacuum line and plug it for testing purposes.

Christian, your timing reading of 5 ATDC and 30-35 ATDC doesn’t make sense. Are you meaning “ BTDC” (Before top dead center)? Try setting your timing at Zero (0). If your timing is really at 5 BTDC then setting it at zero will lower the idle. Easy test.

Depending on which model 123 Ignition you have will determine if you will be able to use manifold vacuum for MAP advance purposes. Only the 123 “Tune”and “Tune +” can be set up this way.

Thanks Tyler, I will try that as well to rule out the brake booster as the source of "pirate air"!

No, I mean ATDC, so plus (+) 5 degrees. In the service manual, Mercedes states that timing at idle has to be +3 degrees ATDC with vacuum connected (for a 051 BOSCH distributor). See picture from service manual below.

If I had 5 BTDC and pushed it up to zero, wouldn't the idle speed increase, because you supply more advance, when you push the timing towards the ADTC regime? Or did I get something wrong here?

I did try to push the idle down by retarding the timing to zero and also into BTDC (minus regime) to try to lower the idle rpms. But with that setting the car was running horribly, and with cut-outs when pulling at medium rpms, clearing lacking enough timing advance.

But maybe by changing to the (euro) vacuum port below the throttle house, I get more advance at medium rpms, and I may therefore be able to push idle timing further down towards zero and thus lower idle speed. What do you think?

I have a standard vacuum retard 123ignition, and I am running it in program 8, corresponding to a vacuum retard 051 BOSCH distributor and euro throttle house with the vacuum port under the throttle house, and thus max. vacuum at idle and decreasing vacuum with rpms. I have heard this is the standard setting for a euro 280SL, which will give you the best performance. What do you think?

Thanks,

Christian

[kampala]

Christian

Tyler is correct - if you have the tune or Bluetooth version of 123ignition, you can use the side “vacuum all the time “ port but if you have the pre-programmed 123 and are using program E, it usually does exactly what you are experiencing.    Program E expects all emissions equipment to work and the two way valve to control vacuum. 

If you are using program 8 you need to have vacuum coming from below the throttle body like a euro 280 or any 250. 

Also once vacuum is correct you would time the car so at idle you are few degrees BTDC since you are not using any emissions equipment. 

Are you using side vacuum port or have you modified to have the port under the throttle body available?

[Berggreen]

Christian

Tyler is correct - if you have the tune or Bluetooth version of 123ignition, you can use the side “vacuum all the time “ port but if you have the pre-programmed 123 and are using program E, it usually does exactly what you are experiencing.    Program E expects all emissions equipment to work and the two way valve to control vacuum. 

If you are using program 8 you need to have vacuum coming from below the throttle body like a euro 280 or any 250. 

Also once vacuum is correct you would time the car so at idle you are few degrees BTDC since you are not using any emissions equipment. 

Are you using side vacuum port or have you modified to have the port under the throttle body available?

Thanks, very helpful.

I am still using the US throttle house with the constant vacuum side-port, and I found that using program 8 was the best compromise. I also tried program E, but found it even worse with the configuration I currently have!

But I have (over the winter) found a euro throttle house on Ebay, which I am currently restoring, but I also here see light around the throttle plate, when the throttle plate is closed, so I would also like to find a new plate for this house as well. Actually, when comparing the US and Euro throttle houses, they are actually physically identical, and both have both vacuum ports. However, on the US one, the (euro) port below the throttle house is blinded off, but I think there is still a vacuum channel, as i can see the small hole just next to the throttle plate on the engine side. Same for the Euro throttle house, it also has both ports, but the US port is here blinded off. Looks like Mercedes just made one house with both ports physically there, but blinded off one of them depending on the market (US/Euro). Have you seen this too?

Back to timing: Just for me to get on the same page as you guys, because I think I may have misunderstood how to read BTDC and ATDC using the scope. Up to now, I thought that, when I increase the rpms, and looking at the degrees on the scale using the scope, I see the degrees increase on the scale, and I though this was + degrees in the ATDC regime, and when degrees went in the other direction and down below zero, I would be in the BTDC regime, like _after_ zero (ADTC) and _before_ zero (BTDC). Am I wrong here, so that it is actually opposite?? 

The timing degrees in the picture from the service manual above is actually for a euro 280SL with an 051 distributor, thus without the emission control system. As you see, it says 3 degrees +/- 1 degree ATDC at idle.

For the US emission control version with US throttle house config and an 062 distributor, which my manual 280SL had, before I replaced it with the 123ignition, see the similar idle speed timing below, where it says 8 degrees ATDC!

What do you think?

Thanks,

Christian

[kampala]

The casting for the throttle bodies apprear the same to me as well.  I ended up drilling the port under the throttle body as I matched it to my 250 throttle body.  It’s better if you have a euro body and don’t need to drill.  Your problem seems to be the vacuum port.  That’s why you cannot get the idle down. 

Timing - what I do may not be the right way but the car runs good so I just keep doing it this way :  once the vacuum is connected correctly, I leave everything connected and time it at close to 35-38 degrees BTDC at 3000 rpm and lock it off.  Then I just adjust idle to get to correct rpm at idle.   Usually this means that at idle timing will be 5-8 degrees BTDC.

Car runs great with this method so I just do it like this.  May not be correct but it runs good and plugs look correct color. 

[Tyler S]

Christian, a higher number from “0” into the BTDC range is Advancing the timing. A number below “0” ATDC is Retarding the timing. So when you rev the engine you are advancing the timing into the BTDC range. (Before top dead center is earlier/advanced timing)
As far as your two late throttle bodies, yes they are identical in that they both have their ports on the engine side of the throttle plate.
However, The earlier throttle body that was paired with the 051 distributer had its port just aft of the throttle plate so that when the throttle was cracked open just slightly, vacuum would immediately raise to atmosphere. This is a different setup and function and is not achievable with the late throttle body and standard 123 ignition because the vacuum never goes to zero except maybe at wide open throttle. They can be modified as Oz states above or replaced with an early 051 type unit.
Yes, when you retard the timing the car will not idle well. You need to go back and adjust the air and fuel mixture in order to compensate for the removed timing advance.

[Berggreen]

The casting for the throttle bodies apprear the same to me as well.  I ended up drilling the port under the throttle body as I matched it to my 250 throttle body.  It’s better if you have a euro body and don’t need to drill.  Your problem seems to be the vacuum port.  That’s why you cannot get the idle down. 

Timing - what I do may not be the right way but the car runs good so I just keep doing it this way :  once the vacuum is connected correctly, I leave everything connected and time it at close to 35-38 degrees BTDC at 3000 rpm and lock it off.  Then I just adjust idle to get to correct rpm at idle.   Usually this means that at idle timing will be 5-8 degrees BTDC.

Car runs great with this method so I just do it like this.  May not be correct but it runs good and plugs look correct color.

Good to hear you have seen the same about the casting of the US and Euro throttle houses. I will investigate further, when I get the US throttle house off. Then I will try to open up the blinded Euro vacuum port and check by sucking, if there is a channel drilled - looks like it, but will double check.

I can clearly hear from what you write, that I have mixed up BTDC and ATDC! So advance means towards BTDC and retard means towards ADTC. Right?

But if so, then if you are to follow the timing numbers from the service manual for a Euro spec 280SL, I need to push the timing further down to 3 degrees below zero with vacuum connected. This will not work now with the US throttle house, as I would not have enough advance at higher rpms, because the constant vacuum from the US throttle house is retarding the timing too much even in program 8, especially for the low to mid rpms. But maybe when I change to the Euro throttle house, I will have more advance, because vacuum is now decreasing, and then I will reach the advance I need at higher rpms faster and more aggressive. Sounds like a theory, right?

Don't you lack acceleration (torque) at low rpms, if you have 5-8 degrees BTDC at idle? I have heard that you need low advance at low rpms to get enough torque for acceleration, and this is also why you retard the timing at low rpms. Correct?

Which 123ignition do you have, and which program do you run your 280SL in?

Cheers,

Christian

[kampala]

You cannot run a preprogrammed 123 on program E nor program 8 if you continue to use the side “vacuum all the time” if you are not using the two way valve to control the vacuum.  I have not been able to make it run right but others claim they can run.  I could not. 

On my 1971 USA 280, I am using a pre-programmed 123 with program 8.  I have bypassed all emissions and bypassed two way valve.  I have modified my throttle body to match my 250 throttle body with vacuum from underneath.  I did it very carefully but I had my 250 as a sample of what to do. 

[Tyler S]

But if so, then if you are to follow the timing numbers from the service manual for a Euro spec 280SL, I need to push the timing further down to 3 degrees below zero with vacuum connected. This will not work now with the US throttle house, as I would not have enough advance at higher rpms, because the constant vacuum from the US throttle house is retarding the timing too much even in program 8

You got it. This is exactly why the standard 123 does not work correctly with a late switchgear system thats inoperative or disconnected.
If your replacement throttle body was originally for a 051 distributer car then this will solve your issues.
Yes you are now correct in regards to ATDC and BTDC.
Remember that the 051 had a different curve than the 061/062 so trying to compare numbers for advance wont wont work. As far as the specs in the manual they are often strayed from in order to achieve a better running engine.

I have a 123 bluetooth in my 250sl with a custom curve that I made.

[Berggreen]

Christian, a higher number from “0” into the BTDC range is Advancing the timing. A number below “0” ATDC is Retarding the timing. So when you rev the engine you are advancing the timing into the BTDC range. (Before top dead center is earlier/advanced timing)
As far as your two late throttle bodies, yes they are identical in that they both have their ports on the engine side of the throttle plate.
However, The earlier throttle body that was paired with the 051 distributer had its port just aft of the throttle plate so that when the throttle was cracked open just slightly, vacuum would immediately raise to atmosphere. This is a different setup and function and is not achievable with the late throttle body and standard 123 ignition because the vacuum never goes to zero except maybe at wide open throttle. They can be modified as Oz states above or replaced with an early 051 type unit.
Yes, when you retard the timing the car will not idle well. You need to go back and adjust the air and fuel mixture in order to compensate for the removed timing advance.

Thanks Tyler!

Now it makes sense, and I clearly see that I have mixed up how to read ATDC/BTDC with the scope!  

But as I have discussed with Oz, it seems that the mismatch of US throttle house and Euro 123ignition program settings are messing up my advance, so that I don't get enough advance at mid-range rpms, especially in the 1500-2500 rpms range, where the car is misfirering, if I push the idle timing to zero or below, as the service manual demands. Hopefully, changing to the Euro throttle house and then lowering the idle timing to the required 3 degrees ATDC, while running in program 8 on the 123ignition will work.

The Euro throttle house I have is exactly as you describe. The port below the house ends in a small hole just behind the throttle plate on the engine side. The US throttle house has the same small hole just behind the throttle plate, but even though the port on the outside of the house is there, it is blinded off, and there is no tube for the hose. But I think, that if you take out the pin that blinds the port, and instead mount a tube, and put the pin into the US port and blind it, the originally US throttle house will be identical to a Euro house.

I think the very late Euro 280SL's still used an 051 distributor, and it was combined with the "dual" Euro/US house, I now have, but using the vacuum port in the bottom of the house for the Euro model. I don't think the older throttle house from the 250SL and early 280SL was used on the very late Euro 280SL's, but only the "dual" house with the two optional ports, but with the US port blinded off. Or what do you think?

As far as I have understood by reading the manual for the (standard) 123ignition and communicating with the 123-staff down in The Netherlands, program 8 corresponds to an 051 distributor with decreasing vacuum with rpms (thus a Euro throttle house), whereas program E corresponds to an 062 distributor with constant vacuum (thus a US throttle house) and with the vacuum cut-off mechanism working.

Thanks,

Christian

[Berggreen]

You got it. This is exactly why the standard 123 does not work correctly with a late switchgear system thats inoperative or disconnected.
If your replacement throttle body was originally for a 051 distributer car then this will solve your issues.
Yes you are now correct in regards to ATDC and BTDC.
Remember that the 051 had a different curve than the 061/062 so trying to compare numbers for advance wont wont work. As far as the specs in the manual they are often strayed from in order to achieve a better running engine.

I have a 123 bluetooth in my 250sl with a custom curve that I made.

Thanks Tyler and Oz, we fully agree now and are on the same page - great help from both of you, thanks a lot!!

I think I am almost there. I am already running program 8 and all the US emission things have been disconnected. I just need to make the Euro throttle house work, I found on Ebay, or alternatively open the Euro port on my current US throttle house and then blind off the US port. I think both will work on these late "dual" throttle houses.

I will make some pictures of the two throttle houses, when I have them on the table next to each other.

I may however still be sucking "pirate air" from somewhere, because the idle adjustment screw is not working with the linkage set correctly. Only when increasing the linkage to the injection pump and thus avoiding it to go to zero, I can get the screw to work slightly, but screwed almost all in. That may improve somewhat, when I get the timing/vacuum thing fixed, but I doubt it will solve the full problem. So I will check the brake booster possibility too searching for "pirate air", as well as try to remove the leak around the throttle plate by finding a new one with less leak.

Thanks,

Christian

[Pawel66]

I have a 123 bluetooth in my 250sl with a custom curve that I made.

  Your custom curve, also for 280 is now used by half of the world, I am sure.  Thanks for it!

[Berggreen]

Your custom curve, also for 280 is now used by half of the world, I am sure.  Thanks for it!

Fantastic....is that the curve that fits a US throttle house with constant vacuum, but with all the emission control things disconnected?

[Pawel66]

I have 051 and euro throttle. I got lost at certain moment in this (I do not have education as a mechanic), but I received three pieces of advise on the forum:
1. Forget all you learned about 051 and vacuum retard
2. Install 123 (bluetooth, programmable) and mechanically set ignition timing (may not remember correctly - 8BTDC idle, 38 3000rpm, everything connected)
3. Curves from Tyler

I did it all and it works. The car runs very well, although I had my ups and downs related to fuel delivery and fuel mixture, also recently.

[Tyler S]

Fantastic....is that the curve that fits a US throttle house with constant vacuum, but with all the emission control things disconnected?

Christian, No it is not the same curve as the one that replaces the 051 distributor.  I did make one for the late system with disconnected emissions gear but It also requires the programmable bluetooth version of the 123 Distributer. The curve can be found in the link below.  Though it could use some slight real world tuning specific to each car. The key ingredient in making this work is being able to set a starting point RPM. In the pic below it is set at 1000 rpm. That way the vacuum signal is ignored until throttle is actuated. Similar to the old 051 system. 

https://www.sl113.org/forums/index.php?topic=23210.msg214545#msg214545

[Berggreen]

I have 051 and euro throttle. I got lost at certain moment in this (I do not have education as a mechanic), but I received three pieces of advise on the forum:
1. Forget all you learned about 051 and vacuum retard
2. Install 123 (bluetooth, programmable) and mechanically set ignition timing (may not remember correctly - 8BTDC idle, 38 3000rpm, everything connected)
3. Curves from Tyler

I did it all and it works. The car runs very well, although I had my ups and downs related to fuel delivery and fuel mixture, also recently.

Great!

Tyler, how different are your curves and then Program 8 on the standard 123, which also is made for an 051 distributor and euro throttle house?

I did also considered getting the BlueTooth version a couple of months back, as a friend wanted my current standard 123. But I “chickened out” by the prospect of a BlueTooth 123 with no pre-installed curves and having to trial-and-error myself to some curved that would work. Had I known about Tyler’s curves, then I had probably jumped on it.
I did ask the 123-staff down in The Netherlands, why they do not put the standard curves from the standard 123 onto the BlueTooth version, so you have something to start out with. But apparently the current hardware will not allow that - not enough storage capacity to house them, as the unit can currently only store two maps! Hope they will improve on that in the future.

[twistedtree]

Back on your "pirate air", you can also pull off the vacuum line to the brakes and plug the manifold opening.    Also check to be sure the warm running device (WRD) is not stuck and allowing air to leak past.  Again, I think the easiest way to test is to disconnect the line and plug the hole.  I bought an assortment of rubber bottle stoppers at our local hardware store and they are very handy for plugging vacuum ports.

[Tyler S]

The Map curves between the two are different. Not so different that the car wont run but the starting RPM and point of initial advance relative to vacuum is very different. There are published curves for the 051 distributer on 123’s website. They are very easy to input on the bluetooth version. Basically its just inputing 5 numbers into the fields on the app and hit save. I’ll post my 051 curve below. Note the RPM set point is set at zero. It is not needed with the early/051 throttle body because vacuum control is still retained. 11 degrees of map advance and 22 degrees (not shown) of centrifugal advance with static timing set at 5BTDC for a total advance of 38 degrees.
 This is the one I have had the most success with.