WRD Shims and Washers

[ctaylor738]

There have been a couple of posts recently about adjusting the behavior of the Warm Running Device.  The conventional wisdom seems to be as follows:

Add or remove small washers on the top of the slide where it contacts the thermostat's pin.  This will alter the timing of the enrichment.  Adding washers will cause the slide to cover the air hole sooner in the warm up period.  Removing washers will make it close later.  The thinking seems to be that this only affects warm-up.

I have attached a picture of a taken apart WRD.  I think that if you change the thickness of the washers in the slide you will change the timing of the warm-up, but also change how far down the pin will push the lever in the pump.  More thickness, lever is pushed further, leaner mixture.  Less thickness, lever is pushed less, richer mixture.  So in this respect, it is like adding or removing the shims under the WRD and it will affect the mixture under all conditions.

Help me if I'm missing something!

Cheers,

[alchemist]

Chuck: I agree, adding more round shims will lean the starting mixture. This is indeed the case in my 67 230SL. Because the valve (slide) is not completely closing the air passage when becomes hot, I added more round shims, more than reported. The engine starts cold with lean mixture (550 RPM) and in few minutes when the engine gets hot, it runs normally at 700 RPM. I am not sure if I should keep it as is or reduce the round shims. Perhaps, I should increase the oval shims. What do you think?

[Novamonte]

As far as I understannd from other posts the lever in the pump under the WRD only affects mixture until it reaches a certain position. If it is pushed further down (e.g. by adding round shims in the WRD) there is a spring that takes up the additional movement without leaning the mixture further. 

[wwheeler]

Chuck,

Adding round shims does push the piston and pin assembly down and reduces the time it is open and the fuel. But it also reduces the air as well. Look close at the WRD housing where the air comes in. You will find a stepped opening comprised of three rectangular shapes. As the piston moves from the top down, the size of the opening decreases and therefore less air. So as the piston is dropping, you have less fuel but also less air.

Now is that A/F ratio the same? Probably not. On that thermostat, can't you use the nuts to adjust instead of using round washers?