Howdy. I've just aquired this car, which idles at around 800 rpm (normal)when just warmed up and the choke in fully. At the first step of the throttle (it has the M46 transmission), the idle never goes below 1500 rpm. Otherwise, the idle is very steady with no fluctuations or surges.

I'm not sure how it is for power though. I am used to a '91 740 turbo, so the 240 naturally feels sluggish to me. I did a compression test on the 240 with what I beleive are excellent results:
#1 150 psi #2 147 psi #3 155 psi #4 151 psi

Can anyone suggest a trouble shooting plan to lower the idle?

Also, what sort of ajustment or maintenance does the carb require?

Thanks

Way to go! they're great cars... motors are the definition of reliability.

Spray silicone lubricant (not wd40) on your linkages to the throttle.

If you run the car with the hood up you can see the mechanical cable pulling a spring to open the throttle. Spray it, and spray the moving parts of the carb, whatever it is.

I wouldn't screw :) with the mixture yet. Check the mechanical stuff. This is the great thing about a b21a - you know it is not a stupid computer/sensor thing; everything is mechanical; again, reliability.

Next would be loosening the air box from that side of the carb and checking that the throttle plate opens and closes smoothly (probably does but it is an easy check).

--
Stef -- 1981 245 B21A SU M46 'fat chrome' roofrack 319000km my volvo pages

Hello

I have a 1981 244DL, B21A with Zenith-Stromberg 175CD Carburetor and BW55 Auto Transmission.

You did not specify which Carburetor you have, either Zenith-Stromberg 175CD 2SE or the Skinners Union. I am not familiar enough with the SU Carburetor, but they seem simple, as compared to the Zenith-Stromberg.

On the top of the Carburetor is Bell-shaped housing, with a large Black, but possibly Brass Screw Top. Put ATF in there to 6mm below top of inner sleeve.

If you need to adjust Mixture, you will require a special tool to do this, because under the Bell-shaped housing is a Rubber Diaphragm that can be torn. Setting the mixture, even with the proper tools IS a fiddly pain in the butt. It is really hard to feel that any adjustment has been made. If you take it to someone, be sure that mechanic has the proper tool.

There are three places (four really) where Idle can be adjusted and like Microsoft Windows, they seem inextricably interlaced. The one down by the Choke supposedly was factory set, but folks usually adjust idle there, by the time we get the cars. It should be set with 1.5 threads showing through the bottom . . . there is also a feeler gauge setting. The Large Brass Plug-type Screw at the top of the Throttle Plate 11 o'clock position is the Main Idle Adjustment. Fiddly, in a word. There is an Idle Trim Screw, near the Temperature Compensator. It should be approximately 1/4 turn CCW from the full in position. The Temperature Compensator, read up about it, before playing with it.

Next, the Large Spring has two different positions, one for Automatic Transmissions and one for Manual Transmissions.

There is quite a bit of information on the internet, but not nearly enough complete information, mostly referring to MGs and TR6s.

Good luck