Barometric Cell setup help please

[jedwards]

My car was delivered in the UK, spent most of its life in the US, came to Melbourne and is now living in Perth, close to the beach.
My BC is functioning correctly and currently has 4.4mm of shims, which is probably not correct for where the car now lives.   
I have read the excellent articles and help on BC function in this forum, but am still not clear on how to calculate shim thickness for seas level. 

At sea-level, (737mm HG) should the BC exert any downward force on the rack at all?  Should I set it up at sea level so it only just touches the rack, or is there a specific amount of pre-tension necessary at zero feet?  Mine currently pushes quite hard on a cold rack which would be upsetting the entire rack adjustment setup.

Jeff

[w113dude]

Jeff,

Why don't you do the split linkage test at 2000 and 3000 rmp to see how the pump functions? This will give you an idea of your climate. BTW I have over 4. mm shims in my FIP as well.

[ja17]

Hello Jeff,

The BC is set up at the factory. It automatically adjusts for altitude no mater where you live. It only needs to be adjusted if it is replaced. However it can be used to adjust the injection if all the typical adjustments have not worked. Make sure everything else is correct first. As mentioned, the split linkage test can tell you where your injection is as far as mixture and at what rpms. Let us know what you find.

[jedwards]

Thanks for the advice.
My concern is that the BC in my car is working correctly, but was set to another location completely.  In terms of warm running, it is running well, if a bit lean.
However, my problem is cold starting, even though all components of the cold start system checkout perfectly as I suspect that the BC might be overriding the efforts of the WRD and the FIP Solenoid.

My understanding is that during cold starting, the WRD is trying to move the rack to its most rich setting, as well as adding idle air. The FIP solenoid is also contributing during cranking by adding even more force to the rack to ensure it moves to its most rich setting. But the  BC, which is also acting on the same rack, is pushing in the opposite direction and trying to lean out the mixture.
If the BC is set up incorrectly, then  you have substantial force  acting against all the efforts of the WRD and the FIP solenoid to enrichen the track. 

One way to test this might to remove the BC and to install an adjustable speed screw, as proposed by a number of owners, but again is raises the questions of whether the BC would be applying force to the rack at seas level or must it have a degree of pre-loading?

[w113dude]

Jeff,

You mentioned you have 4.4 mm shims under the barometer, that is actually very rich, I'd suspect problem maybe elsewhere. I see you live in Perth, nearly warm/hot all year round plugging FIP it with a screw wouldn't hurt.

[ja17]

Hello Jeff,

What problems are you having with the engine?  

There is not a set dimension or shim thickness for a particular altitude. The shims on your pump were originally added or subtracted at the factory or during a IP rebuild, depending on the characteristics of your particular pump. In this way BC shims may vary from engine to engine even though they are at the same altitude.

The extension of the plunger of the BC itself should be the only constant.  Shims and thickness may vary.

[jedwards]

The problem I was trying to solve was excessive richness during warm-up, even after removing all the oval shims under the WRD.

Eventually, the penny dropped!   (getting a bit slow in my old age)
I had been blaming a poorly set up BC when in fact my problem was with the WRD. So I went back and set the BC shims using the split test and driving so that I had a good mixture at around 2K when fully warm.

Now I could turn my attention to the WRD, which appeared to be performing perfectly, but in fact was way out of adjustment. My problem was that someone, somewhere, had removed any shims that should have been between the piston and the thermostat, so she run excessively rich during warm-up , no matter what I did. 
Having now thought my way through the relationship between the WC , the WRD piston/shims, and the WRD mixture enhancement pin length, I can now see where I had gone wrong.

My plan is to start with a 0.5mm shim, which according to many forum discussions, appears to be the “default” thickness the factory used.
I will run a full temperature test to ensure the piston is fully open when cold and fully closed at 85c, but I expect this to restore my ability to lean out the warm-up mixture.

Does anyone know the approximate range of piston shim thicknesses found in the WRD?

Jeff

[wwheeler]

I have played the WRD shim game and it can be confusing indeed. Right now I have .032" worth of oval shims and .035" worth of round shims. I have found that on my engine, I must have a minimum of .025" worth of round shims in order for the air flow to shut completely off. As Joe said, every car IS different but this may give you a rough range idea. I also have .090" worth of BC shims and the BC does work.

The round shims determine how long the WRD stays on and the oval shims determine the mixture of the WRD. NOTE: These mixture settings and adjustments are only applicable during warm up. Removing round shims does increase the fuel in the mixture, but it also increase the air. Not sure if the ratio is one to one and I kind of doubt it. To me finding the minimum shim that the WRD shuts off at is helpful because you know you can never go below that.