w108 280 SE sedan 1972 BC

[jim 56]

Awhile ago I my car was backfiring a little as I was accelerating around 30 MPH. I assumed it was too lean. I read on this site that if I put shims under the BC it would enrich the mixture. Well that is what I did and it took care of the problem. I now have a good amount of shims under there. I would like too remove some of them to get close to the original amount which was three of them. I think to do this I have to turn the screw that adjust the FIP in all ranges(not the big one ) out . Is this correct? Thank You
Jim

[wwheeler]

If it were me, I would leave the shims and move on. Having extra shims hurts nothing. Having the BC shims does the exact same thing as adjusting the full range screw and a whole lot easier to reverse if needed. The full range screw isn't as easy to adjust as say the idle mixture knob. It is a little vague in my opinion and hard to know when you are really turning it. Just my $.02 worth.

[jim 56]

Thanks I was a little worried about leaving it but now I will.
Jim

[Benz Dr.]

If it were me, I would leave the shims and move on. Having extra shims hurts nothing. Having the BC shims does the exact same thing as adjusting the full range screw and a whole lot easier to reverse if needed. The full range screw isn't as easy to adjust as say the idle mixture knob. It is a little vague in my opinion and hard to know when you are really turning it. Just my $.02 worth.

I completely agree. Mark the top of the BC housing so you can tell where you started so that the mark shows how far in or out you've turned. Because you have to completely remove the BC, it's very easy to loose all of your initial settings without a reference point.

[jim 56]

Thank you yes I did mark it

[bracurrie]

I have been told that the Bosch FIP will fail rich.  I have a similar situation that manifests itself at warm startup.  So for me and I suspect possibly you that its a fuel supply issue.  I really have read very little about BC failures so we need those that have diagnosed and dealt with BC devices.
If logic applies then extra shims pulls the BC plunger up which simulates higher BP, but if the BC is not working right you would end up extra rich should the BP drop or if you drove at some altitude.  Why not diagnose and repair the BC?  If the car stays at sea level and is not driven very often then leaving it as is also works. But that BC is really to this non-mechanic one of the magic parts of the MFIP.  Air density as a function of fuel/air being compensated real time is damn clever.
Brad