It takes a looong time to start the engine - PeachParts Mercedes-Benz Forum

#1 08-17-2004, 11:11 AM

When I start my W114 ('72 250) I have to run the starter for about one minute before the engine starts. It does, however, start every time. Fortunately I have a good battery so I can wait patiently... The car makes NO attempt to start before I've run the starter for quite some time, then it gives a rumble and finally starts. It idles fine once it's running.

My guess is it has something to do with the fuel. I used to have a small fuel leak, but that's all taken care of. But it shouldn't take that long for the fuel pump to draw fuel all the way from the tank, even if the fuel lines are completely empty, right?

Any suggestions?

mzsmbs · #2 08-17-2004, 01:17 PM

do you press the gas pedal when cranking?? a minute sounds pretty long but if the lines drain dry it may take a while. I have a similar issue in my F150.

300SDog · #3 08-17-2004, 03:13 PM

Yep, like maybe one pedal push and release prior to starting somehow kicks the Zeniths into start mode.

#4 08-17-2004, 03:35 PM

Quote:

do you press the gas pedal when cranking??

Quote:

Yep, like maybe one pedal push and release prior to starting somehow kicks the Zeniths into start mode.

No, I'm afraid that won't do it. I've tried several rhythm patterns with my right foot

300SDog · #5 08-17-2004, 04:01 PM

Slow start can also be caused by valve clearances being off...... sort of creeping up on you over period of time.

Valve adjust nuts on that car are self-torquing and its common for self-torque threads to wear, allowing for valve clearances to slip. If this is the problem - they you have to replace loose valve adjust nuts and their retainers in the cylinder head....... notso bad and not expensive.

#6 08-21-2004, 12:28 PM

Nah...it's got to be the fuel. I filled it up to about 3/4 full yesterday, and today it took about 10 seconds of cranking to get it going. Yesterday I also looked at the see-through filter that I put on the fuel line, and it appeared as if no fuel had come through after the first attempt to start.

There is no sign of a leak under the car, so somehow the fuel must flow back into the gas tank. HOW?!?!

ctaylor738 · #7 08-21-2004, 02:07 PM

The US cars had a fuel return line to the tank and a vapor vent to a cannister in the trunk. Does your car have these?

I agree that this is a fuel problem. The Zenith's are famous for allowing fuel to evaporate and if any component in the fuel system is faulty, it can take a while cranking for them to fill back up enough the get fuel through the venturi and accelerator pump. But if it takes a minute of cranking, then you have a problem with fuel flow.

There is a strainer in the tank and small filters in each carb's inlet. Depending on the style of your pump. you may have a small brass filter on the inlet, or a larger cone filter under the cover. If any of these are plugged, you could have a fuel flow problem. Your pump may also be weak.

You can test this (except for the carb filters) by pulling the coil wire, disconnecting the fuel line at the carbs and sticking into a container, and having someone crank the engine while you watch. I have never seen a spec, but the Haynes manual says "well defined spurts" should be observed.

#8 08-21-2004, 04:24 PM

Well, there is only a problem when I start the car after it's been sitting for, say a couple of hours. Once it's running, it gets enough fuel alright. The fuel pump is new and the screen in the tank is clean, so no problem there.

It has the fuel return line, but I'm not sure how it works.

It would be weird if all the fuel in the lines would actually evaporate

300SDog · #9 08-21-2004, 04:48 PM

Then another thing I'd be wondering is if Zenith float valves have seized.... either cutting off flow from carb reservoirs to the jets or draining the reservoirs completely through the return lines when the car isnt being driven.

Nobody knows the exact fuel path within Zenith carburetors, but the return lines must be hooked up to the carb reservoirs somehow.

And it seems logical to me that fuel would flow downhill to its lowest point, draining the carbs if return line valves (float chamber valves?) were jammed.

ctaylor738 · #10 08-21-2004, 08:13 PM

Look on the front carb, directly below the fuel inlet. There should be a valve with a small rod on the bottom, and above it, a fitting with a return line. The valve is opened by the throttle arm closing and pressing on the rod, starting at 2000 RPM.

I still think you are not getting enough gas at cranking. Suggest you unhook the line, check for the "well-defined" spurt, and make sure the filters in the carb inlets are clean.

psfred · #11 08-21-2004, 09:41 PM

Also make sure the choke is closing on both carbs when cold and that the manifold heaters are OFF, preferably, but at least closing when hot, else the extra heat will boil the fuel out of the carbs when you shut the engine off.

Peter

wbain5280 · #12 08-22-2004, 01:17 AM

You're going to overheat the starter and damage it internally. The rotor laminations and the stator coils will overheat and contact each other causing wear. Try to find out the cause before too long otherwise it's new starter time.

I had a similar problem with my old 220SE that I fixed by adjusting a time delay relay. (not for your car though).

nachi11744 · #13 08-22-2004, 05:05 AM

Hello,
Block off the fuel return line and test, if it still persists, then the inlet valves(needle valves) in the carbs may be gummed up, needing inordinately high pressure to let fuel into the float chambers.
Have you changed the ignition condensor and points recently?
I cannot see the fuel boiling off to such an extent that the car will not start, even in the tropics where I have seen the fuel boiling in the float bowls of Weber DGAV/DCOE,Zenith INAT and Solex 4A1 carbs, the cars can still start, but the intial idle is slow, rough and the first acceleration is usually a series of stumbles.
Just my 0.2 cents.
Have a good week.
PS What kind of fuel consumption are you getting with this 250/8?

#14 08-22-2004, 09:50 AM

First, I'd like to thank everyone who's been helping me out.

Today the car started after just a few seconds. It could have something to do with being parked in a downhill slope all night. Anyway, after driving it I put a clamp on the fuel return, let's see what happens.

BTW, now it's parked uphill. Let's provoke the old bastard

nachi11744 · #15 08-22-2004, 10:23 AM

Hello,
I think your fuel pump is defective. It is letting the fuel drain back to the tank, it sounds crazy, but it happened to my friend's VW Type 2 Transporter with the 2 litre twin carb engine. There is a small valve in the fuel pump that should block off the pump completely when the engine is not running, it prevents *drain back* of the fuel lines.
Still, you should test with the blocked return line just to verify what happens.
Let us know what you find(or not!).
Have a good week.