George993

Experts, I've just bought a 1976 450 SL which was running very well about 100 miles ago and passed CA smog without issues. But after that it has been sitting for a few years, and now it starts and idles easily, but if I press the accelerator, the engine dies/stops running immediately. If I start pressing accelerator VERY slowly, I can press it up to the floor and idle does not change. But at that point if I release accelerator rapidly, the engine revs up nicely to about 3000 rpm and dies. Fuel filter and pump were changed not long ago and I added more fresh gasoline so there should be enough fuel in the system.

Any ideas what the problem could be? thanks!!!

Smashausen

I've been having occasional flooding on start up. I noticed that some of the vacuum lines associated with the fuel system were dried out. Replaced those and it seemed to help my issue. I wonder if this could help you.

George993

Could be vacuum, I'll check the lines, thanks. But I have a feeling it's some sort of a fuel injection/emission control gadget, I just don't know which one...

George993

I pulled out the air filter and the engine runs well/revs up high if I press the big round throttle valve by hand. There are 2 round valves, a small one deeper inside the intake, which is controlled by the accelerator pedal, and a big one on the top - about 5 inch diameter. What controls (or blocks) the big round valve? What is supposed to be opening it? It seems that the engine suction is not sufficient to pull it down and give engine enough air. Engine has great compression so obviously the suction is sufficient if everything else works correctly. Thanks

fireman1073

big round one should pull open with engine vacuum and richen the mixture, if no then engine leans out and dies
spray it good with carb cleaner to loosen it up

hope this helps

Steve

George993

Thanks, I applied the carb cleaner, maybe the plate moves easier a bit when engine not turned on. But a surprise - there is something under the plate which pressurizes the system, so when engine is running (or the key turned without starting the engine) the plate becomes very hard to push down. There is a "pig -like" noise coming out as the air escapes. And it does not even idle any more, the plate is so hard to move. Any ideas what controls that pressurization system? thanks

fireman1073

sorry i don't, it has been a while since owning that type of fuel injection, maybe someone that currently owns one can look at theirs for comparison

Steve