280 SL engine power loss

My 81 Grey Market 280SL has lost it's power. I have checked the fuel pump, replaced the fuel pump relay and fuel filter. Plugs are new and nothing appears amiss. The problem: The throttle feels "mushy" and when opened rapidly the engine coughs through the air intake, stumbles, and tries to die. There isn't enough power to get out of the neighborhood. Looking for hints or access to a good (with pictures) trouble shooting guide. Any clues will be greatly appreciated.

[engatwork]

What's the condition of the throttle linkage? Not sure if it can make it feel "mushy" or not (I only feel "mushy" around my old girlfriends LOL) but I feel it can keep you from having "making power" types of problems if something is wrong with it or it is out of position/sequence.

Throttle linkage is pretty much pristine. Same effect occurs from the cockpit and from the engine-mounted bellcrank near the end of the chain. I'll take another look though. Thanks

[engatwork]

Someone will come along with more knowledge than me on these particular models. Sounds like a fuel delivery problem to me. Not enough fuel for the amount of air being put into the engine which can be caused by a dirty fuel filter but it sounds like you covered that.

Agree. That's why I started there. But the coughing kinda' points to something messing with the timing or the the whole ignition system acting up. Problem is, I don't have enough clues to go beyond shootin' a timing light. No specs and no trouble shooting guide. Thanks for keepin' the problem in your thoughts. Cheers, Clip

Generally the fuel system is the last thing you should be looking at. In order to nail down your problem you should start with a compression test to verify that the engine is mechanically sound(check the sparkplugs while the're out). Ignition timing comes next along with testing or replacing the plug wires. If eveything checks out then you should suspect or adjust the fuel system.

Reply to greasy Mystic. Thanks for the response.
The engine is solid as a rock and the plugs are new. The wires all read the same resistance. Haven't put a light on it yet but was wondering what, other than vacuum changes, can alter the timing? If there's a computer lurking in this grey market model, I haven't found it or the usual bevvy of sensors to feed it. Any clue there? Could the electronic ignition have a brain (or an attitude)?

[neileg]

I don't think there's much in the way of clever electronics on the 81 280. Despite your info and the other postings I suspect either a big air leak somewhere on the intake, or a clogged fuel filter or duff fuel pump.

You say you checked the pump? These can fail intermittently. If it's at all noisy, I'd replace it.

Hey I just thought of something. Are you sure that the plug wires are in the proper order. You engine sounds as if it may have a couple of wires swapped. I regularly switch a couple of wires on purpose to cause just such a reaction(I use the backfiring to clear clogged idle passages in the carb)

For Neil and Greasy,
Regarding an intermittant fuel pump, it's humming with the symptom present. Noisy may be a player. I can hear it over the exhaust with my head under the car. Can't remember if that was always true. I did replace the filter on this go. Plugs are wired correctly. I'm the only one who touches 'em and I just ran wire checks and looked at firing order while I was at it. Sounds like a clever way to force-clear air passages, Greasy. Suspected as much but you never know. I've sprayed starter fluid all over the running engine and can't find any indication of a leak. Good call though. Thanks for confirming the lack of cosmicity in an '81 280.
I'll poke at everything y'all have suggested this weekend. Here's hoping. Too pretty a car to run so ugly. Thanks for your interest. Cheers, Clip