Difficult to start

[Smithy]

I have a 1969 280 SL. It is very difficult to start when left standing for any length of time. When cranking it seems like it only fires on 1 or 2 cylinders and splutters along for 15 seconds or so until all 6 cylinder fire. Once it starts it runs and drives beautifully.
I think it is fuel starvation during start up. My guess (probably wrong) is that the pressure valves are leaking and draining fuel from the injection lines which must then be filled again before fuel can reach the cylinders. Any ideas?

[Pawel66]

What is in general advised here on suspicion of low fuel supply is to start with checking the fuel flow at the end of the return line. Should be more than 0.6L in 15 seconds minimum. Preferably 0.8 to 1.0 L. Then, if it is low, you go through all the filters that are on the way (3 of them standard) and check if the return line is not clogged.

[Smithy]

Thanks, I will give it a go.

[Pawel66]

If indeed it comes to check valves, a simple test is described here in the posts a couple of weeks ago. In essence: clean up the fuel lines area at FIP, undo the fuel lines, blow remains of fuel out of FIP fittings with air, push the rack backwards till it stops, hold it and switch on ignition s that the fuel pump starts working. Watch if you see if fuel is appearing and its level raising in the fittings. If it is - check valve is bad.

But it is good to start systematically, cheaper and faster diagnosis.

[ja17]

The cold start solenoid on the intake manifold should activate during cold starts. Hook a meter or test light to it to see if it energizes with a cold engine. Let us know what you find.

[teahead]

starts up fine when warm?

If so, then CSV is suspect.