Engine missfire when cruising

[BRDownes]

Hi, I have recently rebuilt my 1971 280SL 4 speed manual and now struggling to tune the engine. When the engine is cold it performs perfectly, sometimes a little difficult to start but not serious. But when the engine is hot it misfires about 2400rpm upto 2800 rpm when cruising with small pedal depression, but it still accelerates from 2400 rpm very well when I push the pedal down. I have new injectors, a fully restored injection pump, I have tried a different coil, a different distributor, points, rotor, plugs, HT leads. I have checked the plugs and they look a light grey. It suggests to me that the mixture is too weak when the engine is hot but i don't know if this is the only possible problem. Please advise. Thanks, Barrie

[BRDownes]

I didn't get a reply from anyone, perhaps you were all as confused as I was.

Anyway, I read the post by Joe Alexander with the linkage tour information and pictures by Matt Merrill, thanks guys I have sorted the problem.
I checked and adjusted the rod connected to the injection pump lever and it was 229mm when it should be 233mm, I also checked that the venturi butterfly was closed without sticking which required some minor adjustment, and I also checked the progressive regulating linkage which was not exactly correct.
With all these adjusted correctly, even though there was only minor adjustment required the car now runs perfectly at any rpm.
Proof for me how critical the linkage setup is to get perfect performance.
I am not sure about the fuel mixture setting, but I don't feel too confident to start adjusting this yet.
Cheers, Barrie

[Cees Klumper]

Glad you sorted it out Barrie. I had read your initial post but nothing obvious came to my mind. Like you, I had an experience once where I had forgotten to properly torque down the bolts on one of the brackets that hold the transverse control rod in place and the engine ran terrible, to the point of fouling out the plugs so bad I had to replace them after driving less than 1 km. So, yes, the linkage system adjustments and functioning are critical to the proper operation of the injection system.