Author Topic: Fine tuning WRD  (Read 6551 times)

wwheeler

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Fine tuning WRD
« on: October 26, 2009, 20:14:57 »
I have had a small problem with my WRD since I have had my car. The fuel mixture when the engine is cold and at idle is rich and the engine speed is only about 800 to 900. This is only slightly higher when warm and thought it should be closer to 1000 RPM. When warm, the mixtures are great.

I know the mixture is supposed to be slightly richer when cold than when warm. If I split the linkage and open the air venturi, the engine speeds up quite a bit. Same result if I turn the air screw counterclockwise. If I remove the WRD air filter, there is no change so I believe it is OK and besides, it is fairly new. I have also changed the shims on the air valve and this is about as high as I can get the RPM to go. The problem with just changing the air valve shims, is that it changes both the fuel and the air volumes. I just want to increase the air volume.

I was thinking about removing a thin shim from on top of the air valve, and placing it below the air valve. This would raise the air valve to increase the opening (allow more air in) while keeping the fuel rod at the same position thereby leaning the mixture. Has anybody ever tried doing this?

There is no keeper for a shim in the bottom of the air valve, but the spring loaded plunger nests inside the cavity in the bottom. This should hold the shim in the valve. What do you think?

Wallace
Texas
'68 280SE W111 coupe
'60 220SE W128 coupe
'70 Plymouth Roadrunner 440+6

wwheeler

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Re: Fine tuning WRD
« Reply #1 on: October 28, 2009, 15:24:40 »
I swapped the air valve shims around on a spare WRD assembly I have. It had a total of .039" worth of shims on the top of the air valve (piston). I installed the thermostat (cold position) and measured the plunger length coming out the bottom of the housing and the height of the air valve in the housing.

I then removed a .010" shim from on top of the air valve and positioned it below the air valve. Now the total shim thickness is the same (.039") but there is a .010" shim below and a .029" shim above the air valve. I then measured as above and as expected, the air valve moved up by .010" but the plunger length did not change. I know this makes common sense, but sometimes things don't work out as planned. Given the results, this should increase the air volume (leaner) during cold operation without increasing the fuel volume. My only question now is will the shim on the bottom of the air valve be OK without a keeper. It seems to be in compression from the spring in the injection pump.

One last question. If you change the height of the shims on the air valve, doesn't that effect the overall mixture just as the oval shims do on the WRD housing? It seems to me that both shims in effect, change the height of the plunger that changes the mixture in the IP. Any thoughts?   
Wallace
Texas
'68 280SE W111 coupe
'60 220SE W128 coupe
'70 Plymouth Roadrunner 440+6

jeffc280sl

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Re: Fine tuning WRD
« Reply #2 on: October 28, 2009, 17:45:21 »
Can you breakdown for us what you are doing when the engine is cold and warm?  You indicate that you removed the fip air filter and there is no change.  Is this when the engine is warm or cold?  When you split the linkage and idle increased was this with a cold or warm engine?

wwheeler

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Re: Fine tuning WRD
« Reply #3 on: October 28, 2009, 19:53:00 »
Thanks for the reply Jeff,

When the engine is cold, it runs about 850 to 900 RPM and a little shaky. If I split the linkage when cold and add air, the engine speeds up to a max of 1200 RPM. When the engine is warm, it runs at 800 RPM and smooth. If I split the linkage when warm, the mixture is only slightly rich at idle and good at the other RPMs. When driving, engine runs well and plugs look normal.

I removed the fip air filter with the engine cold and felt a strong suction, but the RPM did not change. When warm, there is virtually no suction. That seems normal. 

My goal is to try to increase the cold idle speed to 1000 or 1200 RPM. Decreasing and eliminating the air valve shims made only about a 50 RPM difference. But when I open the venturi or open the air screw, the idle speed goes where I want it. Problem with using the air screw, is that my warm idle would then be too lean. I am trying to find a way to add air to the cold idle without adding fuel thereby leaning the mixture.

I hope that helps!
   
Wallace
Texas
'68 280SE W111 coupe
'60 220SE W128 coupe
'70 Plymouth Roadrunner 440+6

jeffc280sl

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Re: Fine tuning WRD
« Reply #4 on: October 28, 2009, 21:41:26 »
Do you have the BBB sections concerning the warm running device?   If not send me your email address and I'll send it to you.   
It is my understanding that the switch point of the heat feeler can be adjusted by inserting or removing the upper smaller shims.  I think the switch point is referring to time in this instance.   In other words when the engine is cold you can increase the enrichment time period by adding shims.  In this way the enrichment phase will occur until higher temps are reached in the collant water and the heat feeler is fully extended.   These shims do not change the air fuel mixture.

The lower shims do change the air fuel mixture.  With a cold engine adding shims will increase rpms by adding fuel.  Removing shims will decrease fuel and rpms. As you know shim changes make very small adjustments to rpms.

I'm back working on the barometric cell operation and its shims.  Maybe that is the next area for you to look at also.

 

lurtch

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Re: Fine tuning WRD
« Reply #5 on: October 29, 2009, 00:08:48 »
Hello,  Wheeler,    I also  went through the same circles of h@ll that you are going through. Tried all the same fixes and all the same tweaks.

You could do what I finally did:    After hours and hours of tinkering and road testing , which resulted in more frustration than measurable improvement - - I GOT RID OF IT !

I have been running this way for several years now and all is fine.

Good luck, Larry in CA
Larry Hemstreet  in  N. Cal.

1966  230SL  (restored) Met. Anthracite w/ Maroon leather
1981  300TD-T (Concours condition, 86K, GETRAG 5sp.)
1982  300TD-T (parted out)
1986  560SEC (totaled)
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Shvegel

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Re: Fine tuning WRD
« Reply #6 on: October 29, 2009, 02:07:36 »
It's been along time since I got mine to work properly so I can't remember much but I will offer this advice.

Use a new warm up regulator and filter on the warm up air intake. That way you have a baseline and the regulator probably won't die 2 days after you get it perfect. As for the air filter I had one that disintegrated and caused a wicked intermittent running problem.

glenn

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Re: Fine tuning WRD
« Reply #7 on: February 06, 2012, 07:21:51 »
Lurtch, That's why MB/Bosch had the turn on/turn off bolt on the early control valve housings.

Benz Dr.

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Re: Fine tuning WRD
« Reply #8 on: February 06, 2012, 15:20:35 »
I couldn't get one to run right until I gave it a lot more fuel at the adjustment knob which allowed me to open the air screw. Once the engine was warm I was able to adjust the idle speed by turning the air screw. Small adjustments on the back of the pump brought it to a point where it would idle smoothly. Once it was cold it started and fast idled about 1,300 RPM.
I think 1,000 RPM is too slow for the cold start idle. It might be OK for a 280SL but it wouldn't be fast enough for a 230SL. Some of these engines won't idle properly at 700 RPM when hot and seem to run better at 900. Why then would they run properly at 1,000 while fully cold? 
1966 230SL 5 speed, LSD, header pipes, 300SE distributor, ported, polished and balanced, AKA  ''The Red Rocket ''
Dan Caron's SL Barn

1970  3.5 Coupe
1961  190SL
1985   300CD  Turbo Coupe
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1965  230SL
1967 250SL
1970 280SL
1988 560SEC