Fuel Economy Still Dismal 10 KM/GALON

[gerardoparedes]

I just changed the mechanical pump in my car, it was leaking. I tought this was going to help my fuel economy by a lot.

My engine purrs like a kitten, carb is well setup, start fine, idles fine, runs fine at all stages, still i got 70 Km on 7 gallons of fuel. That's horrendous, considering what the australians here are extracting around 600 km from a tank. Combustion is good, no gas smelly smoke now.

I am going to check for leaks on this weekend, but can you give me any insight on what could be happening?. Car got a lockin gas cap, so take that down.

[koan]

That's a pretty poor MPG!

I can thing of a few things.

Obvious first is very rich mixture which would be evident as black exhaust smoke and a very black exhaust pipe. This is a vicious circle, rich mixture, down on power, more throttle needed, more fuel consumption. What is the car's performance like, is your foot often flat to the floor ?

Second, a leak somewhere, but you're onto that.

Third is some drag, either stuck brakes or maybe something wrong in the auto.

Are there any odd smells after a run, fuel, hot or burning?

koan

[gerardoparedes]

No black smoke, power is good, no drag the wheels move freely, that is the weird thing.

I will seriously review the fuel leak possibility.

[koan]

No black smoke, power is good, no drag the wheels move freely, that is the weird thing.

I will seriously review the fuel leak possibility.

Restricted exhaust system is another possibility.

Odd one.

koan

[gerardoparedes]

I might take a look at all that, but seriously, i believe i require a  CO Meter just to be sure the mix is ok.

[gerardoparedes]

Anyone on this forum has had to pass for an experience like this?

[Nutz]

Tire pressure correct?
Choke sticking?
Air filter dirty?
Ignition timing?
Old spark plugs and/or wires?

[WGB]

What model of car are we talking about - I don't know of a 116 with a mechanical fuel pump,

Over what period of time did you use the 7 gallons.

If it was all on one drive it is peculiar but if it was parked for several days you can have a fuel leak with no visible sign of a leak if it is evaporating before it hits the ground.

If it has only developed since you changed the pump I woudl check whatever you have done for leaks or faults.

Petrol can somtimes leak into the engine oil from a leaky diaphragm and be hard to spot.

Bill

[oscar]

What model of car are we talking about - I don't know of a 116 with a mechanical fuel pump,

Must be a 280S, it's got a mech pump.  I haven't taken one off mine but the racer presumably had a new one fitted before I got the car (shiniest bit in the engine bay).  I'm not sure of what seals are there but leaking into the sump like you say WGB could be a possibility though it would be really annoying if that happened on a new pump.

Another suggestion gerard, what's your ignition timing set at?  Your fuel economy suggests something worse like leak/s but assuming everything else is in good order, I'd dial the timing in at approx 5-8deg advanced and see how you go.   

Regarding no smoke out the tailpipe, have someone else drive behind you and check.  I've noticed retarded ignition produces less smoke which isn't visible whilst I'm driving.  With the Mrs following she'll confirm otherwise for me.  The f/a mix burns more completely but there's less power.  Advancing the ignition will increase power and economy and will be more likely to increase smoke in our older worn engines.

Considering the above and your other thread on starting the car and "no Brooooom"... advancing the ignition may help address this too but a carbed engine can be temperamental compared to an injected one.  Sometimes mine starts in less than a second. Other times not.  Sometimes it depends on the ambient temp, how long the car has sat round for without running, whether I've depressed the accelerator pedal too many times before starting.. a bunch of things.  During frosty conditions the car's always harder to start but does kick in within a couple of attempts.  Maintaining an idle whilst the engine warms up is more of an issue.  So long as the the starter turns the motor quickly and the engine generally runs fine I wouldn't worry too much about it unless you get to a point where you're flattening a battery trying to start it.  Then you should have a look at your startup procedure first then other causes.

[gerardoparedes]

Thanks guys for the input.

The case is, about six months a mercedes mechanic took care of the solex, the car used to run rough. No fuel consumption was measured at that time. Car have been in storage two years prior to that. At that time spark plugs, fuel filter, spark plug cables and brakes were done. The car have been used only on weekends and for small trips and errands.

Now i use the car as my daily driver, because i am againt at university, my drive is city only, with only three stops in a 10 km trip, i travel mostly in third and even in the fourth speed at around 40 km/h. The car  idles fines, accelerate fine, ALWAYS start at the first touch (even with no brooom ), about a week ago the same mechanica changed the fuel pump (albeit a Vaico from Germanstar) because i saw the fuel dripping and wetting the garage, it was a constant drip and i assumed that the faulty fuel pump was the cause of the sagging fuel consumption, but after changing the pump i am still getting the same fuel economy.

Tomorrow i am going to dissamble the fuel metering device and look if there is the problem, but i dont believe the reserve switch can be faulty. I am going to follow the fuel line and take a through look at why this is happening, if i cant find anything amiss i will step up the ignition timing a bit. If nothing of those helps i will have a long chat with the mercedes mechanic.

[gerardoparedes]

Guys, i checked for leaks and even removed the fuel metering device to take a look at inside the tank and.

No leaks.


But the acceleration pump had the screw all the down up, so it never stopped, i put a piece of white paper at the pipe, it went black in a few, i screwed the fuel acceleration stop screw , changed the piece of paper at the pipe, so far no blackening.

What i see is that the spray patter for the main carburetor circuit flows really uneven, its just a wide spray, not a nice spray patter but, something like a controlled leak.

I will drive for this week and if the consumption doesnt go well, i may have to talk to my mechanic again.

[koan]

What i see is that the spray patter for the main carburetor circuit flows really uneven, its just a wide spray, not a nice spray patter but, something like a controlled leak.

Might be wrong on this and please correct me if I am but at idle with the throttle closed there shouldn't be any fuel flow visible, flow will be from the idle jet under the butterfly.

koan

[gerardoparedes]

Koan, there NO FUEL visible at idle. But when i accelerate, the acceleration pump sends a shot and the main circuit catches in.

I will keep you guys posted and updated.

[koan]

Koan, there NO FUEL visible at idle. But when i accelerate, the acceleration pump sends a shot and the main circuit catches in.

OK, I misunderstood.

koan

[gerardoparedes]

There is something of which i am happy. When i was looking at the fuel metering device in the fuel tank, i took a good look inside the fuel tank with a powerful LED flashlight, guess what? NO RUST whatsoever, amazing, considering that this car have been parked for two years, and its 35°C and very Humid here in Central America