Idle problems

[knirk]

I have just finished replacing my distributor 010 (newer type with 25 deg. retard) with the proper 051 which I got rebuilt from Cees. I use a Crane pointless ignition. I could see right away that it was producing a much more smooth centrifugal advance since the timing light was nice and steady at all rpm’s. But even after adjusting the vacuum retard to the correct 3 Atdc at idle and at the same time 30 Btdc at 3000 rpm, I can’t get it to run smoothly at idle. As soon as I increase the throttle to about 1000 rpm it is smooth. Any suggestions?
My centre muffler is making a strange noise at / close to idle. I have listened underneath the car and it seems like something is loose inside it. I don’t know how it looks inside and have a faint theory that perhaps a panel could partially block the exhaust thereby causing my idle problems – but this may be a long shot….


Per G. Birkeland
69 280 sl aut 834
Norway

[ja17]

Hello knirk,
Make sure the linkage is completely seated and set correctly. Something may be throwing the fuel mixture off at idle. If you have not checked the linkage stop on the venturi (see previous posts) do this. Next you can check the mixture at idle by separating the linkage rod going to the injection pump. Let the engine idle and push the separated rod to the pump down. If the engine increases  more than 100rpms, the idle mixture is too lean. If the engine stalls or faulters the idle mixture is to rich.
The air large slotted air screw on the intake will lean the idle mixture. The knob on back of the injection pump will richen the idle mixture (only adjust this with engine off). Keep us informed.


Make sure everything else has been checked and the car is in good tune before tampering with fuel mixture! Count the turns of the adjustment screws so you can put things back if needed.

Joe Alexander
Blacklick, Ohio

[knirk]

Joe,

The linkage was set and worked OK before the distributor change, but I will recheck it and also try the "separating the linkage" test. With the old distributor I had to do a lot of adjustment to get the engine to run, including adding shims under the cold start valve housing. Maybe it would be a good idea to remove these again and start from scratch. I'm off to work for two days, but I'll be back.

Per G. Birkeland
69 280 sl aut 834
Norway

[ja17]

knirk,
Do the linkage test with the engine completely warmed up.

Joe Alexander
Blacklick, Ohio

[knirk]

I ended up checking everything. At idle I noticed that the timing light on wire number 1 was erratic in accordance with the idle misfire. Checked the other 5 wires which were nice and steady. Tried to swap wires – no change. Changed the distributor cap and rotor – no change. Then I found the screw holding the Crane optical unit a little loose. After tightening and adjusting the timing again it now runs much better. Still not perfect and it also backfires a lot when I release the throttle while driving.

Per G. Birkeland
69 280 sl aut 834
Norway