1974 Mercedes 280C Idle Speed - Page 2 - PeachParts Mercedes-Benz Forum

Frank Reiner · #16 11-04-2016, 02:56 PM

Quote:

Originally Posted by grubby65

Thanks for the help. I will try these settings tonight. What is the device called between the fuel line and the carburetor, I think the third line is a return. I need to replace it because the brass tube between the body and the carburetor came apart and dumped fuel all over the engine.

That is a fuel return valve; hold off on replacing it if you can. The loose tube is common, use JB Weld, or other epoxy to secure it. The fixes to the problems of pressure and level control will delete that valve if you choose to go that route.

grubby65 · #17 11-04-2016, 04:45 PM

Quote:

Originally Posted by Frank Reiner

That is a fuel return valve; hold off on replacing it if you can. The loose tube is common, use JB Weld, or other epoxy to secure it. The fixes to the problems of pressure and level control will delete that valve if you choose to go that route.

OK, you have got my interest. What are the steps to eliminate the pressure and level control issues?

grubby65 · #18 11-05-2016, 08:13 AM

Thanks for the help on the adjustment for the idle speed. The rod from the vacuum pot was out of adjustment as well as the spring setting for when the car is in drive. It idles fine in and out of gear. I'm still interested in the float level and fuel pressure control though. I like this car it gives me something to "tinker" with.

Frank Reiner · #19 11-05-2016, 01:04 PM

Quote:

Originally Posted by grubby65

OK, you have got my interest. What are the steps to eliminate the pressure and level control issues?

Starting in 1976 Mother Benz made available for retrofit a combined fuel pressure regulator (fixed at ~ 3psi) and return valve with a fixed return orifice. The "valve" portion of the return valve was simply a check valve that closed when the pump stopped; the return metering was done entirely by the orifice of ~ .085-.090". The package was arranged so that the bleed orifice was upstream of the regulator section.
The regulator package was also used in production for cars going to Sweden in the same year.

The package can be functionally duplicated by assembling a tee of hose barbs, with the leg of the tee going to the return and fitted with the bleed orifice (solder & drill, or JB & drill, etc.). The run of the tee will have the hose from the pump entering on one side, and the exit on the other side going to a pressure regulator (see thumbnail), and then to the carb inlet.

Supposedly, starting with production as of January 1974, a new float was introduced for the Solex 4A1. The manual indicates that it was in 280 coupes from chassis # 101 671 and later. The only way to tell for sure is to open the carb, which is necessary anyway to reset the level to match the use of the regulator.

The screen shown in the thumbnail is located in the cylindrical section at the front of the carb. Many are missing, or broken, and most are somewhat clogged with rust from the tank. It is useful, when revising the fuel lines, to incorporate an inline filter between the pump and the tee.