Follow up on hot restart

We purchased a 1985 380 SL with 64k miles in May.
The car had problems with primarily hot restarts, occasionally cold starts.
The prior owners replaced the fuel tank at 52k and the fuel injectors at 53k miles. (We suspect a fuel contamination issue)

Maintenance we have performed so far:
Clean the idle air valve, car now idles smoothly at 500 rmp after warming up (seemed very rich until warm)
Replaced cold start valve and thermoswitch. Car runs smoother during warm up.
Still had hot restart issue (seemed lean)
Read multiple threads here and on tech forum, especially re accumulator.
Leak tested accumulator- it leaked, a lot
Replaced accumulator, fuel pump check valve and filter.
Car usually starts fine, both hot and cold starts.

But:
When starting, you sometimes get a fair amount of black smoke (exhaust pipe). I am sure the valve seal leaks a little but this does not smell of oil. Also, for about a block, if you press the accelerator hard (not slamming it but just pressing it), the car bucks and you get a big cloud of black smoke. After a block, no problems, car runs great.
I do not have a pressure tester and am unwilling to replace other parts without more knowledge. Any suggestions?
Also, saw a reference to the thermovacuum valve. What exactly does this do?

[maheath]

Have you pulled the plugs and checked them? Leaking valve stem seals will leave oil on the plugs and possibly foul them.

Plugs show no oil. They are tan in color which I think means the car is probably running a little lean. Cold compression cylinder checks are all good at 150-150 psi.

[jaybirdw]

May I ask:
What did it cost you for parts and labor, to get the accumulater and check valve leak tested, then replaced.
Thanks,

[aharley1]

It just cost me $243 to have the accumulator replaced on my 88 560SL...which, of course didn't help my hard hot start problem.

[maheath]

A fuel pressure gauge would tell you if the problem was pressure related. If it was pressure related, the primary culprits would be the fuel accumulator and/or the check valves on the fuel pumps. If it's not fuel pressure related, then the next step (or maybe the first depending on your perspective) would be to check the ignition components. Look at the distributor cap and rotor.

[Otto w. Coers]

Black exhaust smoke points to a 'rich' condition.Grey/White smoke is due to oil, water, trans fluid or brake fluid entering the combustion chamber.

[AF300E]

Tan coloured plugs suggest that the mixture is fine. Black is rich and white is lean. (The old fashioned way to tune those carbs!)

[230/8]

"But:
When starting, you sometimes get a fair amount of black smoke (exhaust pipe). I am sure the valve seal leaks a little but this does not smell of oil. Also, for about a block, if you press the accelerator hard (not slamming it but just pressing it), the car bucks and you get a big cloud of black smoke. After a block, no problems, car runs great."

You do not specify whether this is a hot or cold starting problem. If cold, then re-check your cold start valve to see whether fuel might dribble out after the start period. As I recall, these are supposed to shoot fuel for about 10 seconds to aide cold starts, then stop. They operate only below certain temps. If it continues to run fuel, check your time switch, too. There are several temp sensors involved (air, coolant) so check the book for testing values (resistance at certain temps) and run through each of them to ensure proper functioning.

FYI, my 350SL 4.5 is also a bit rough at idle when cold, but runs fine otherwise. I just chalk it up to age (like my wife does with me).

Your tan plug color is a sign of a perfect mixture setting for when the engine is warmed and operating normal. You won't get great gas mileage, but the power will be excellent. Be happy...

230/8