Increase idle a bit?

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RDSChicago

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Hi,

I'm not mechanical in the least but wanted to increase the idle a bit on my 1971 2800cs (upgraded to a 3.5 engine from a 1989 535i). When the engine is warm, it's idling at around 300 and feels like it will stall. It has dua Weber carburetors if that helps. Can anyone provide instructions? I'd like to get it up to 650 rpms in neutral. Thanks in advance.
 
You’ll need a synchronmeter to make sure both carbs are breathing the same amount of air. Also an rpm gauge, the one in the dash is not reliable or can show small changes.

Basically:

1. Check condition of vacuum hoses and for leaks at the base and distributor if running advance and/or retard.

2. On each carb, screw the mixture screw clockwise until the rpms drop then back it out until the rpm stops increasing. Then out another 1/8 turn. This may end up increasing your idle speed depending on your state of tune.

3. Each carb also has a throttle plate adjustment screw. Get a reading on the synchronmeter for each carb and if the idle rpm is still below 650 (this seems low-do you have an auto transmission?) then turn the throttle screw in on the lower breathing carb till it matches the other and the rpm increases. Repeat this process until both carbs are pulling the same air at the desired rpm. If pulling same amount of air but still too low (high) on rpm then increase (decrease) them equally.

4. Final adjustments are made with the mixture screw adjustments repeating step 2. If this results in a higher or lower desired rpm then repeat steps 3 and 4 until finished. Mixture is always the final adjustment.
 
Found a terrific mechanic in my new home state of Colorado who adjusted the carburetors for me last Sunday. Great guy if anyone is looking for a mechanic in the Denver metropolitan area.
 
My coupe is idling at 2000 on start up, after warming up 1500-1800. After a brisk hour drive and letting it sit it's around 1200 rpm. I suspect the vacuum hoses is leaking. Does the forum agree?
 
Are you running Weber 38's? My initial thought is that the linkage is holding a throttle plate open.

First check for vacuum leaks (throttle shaft area too) and that the timing is correct. Then look at the balance between the carburetor barrels on the front and the back.

Assuming that you have Webers you need the STE 40 tool to do this properly. Disconnect the linkage and make sure the accelerator pump linkage tab isn’t holding up movement of the throttle plates.

Check your synchronization of each barrel on one carb ( front for example) and then do the same on the other carb. It is easy to have a disparity between the barrels which can be adjusted by loosening the locking screw on the sector gears (picture below).

1776513122654.png


My guess is that the throttle linkage is out of adjustment.
 
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