280c W114 Carb/Fuel Issues - Mercedes-Benz Forum

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post #1 of 20 (permalink) Old 06-19-2011, 12:12 AM Thread Starter
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280c W114 Carb/Fuel Issues

Hey Guys,

I've got a 1973 280c with some fuel issues. This car has been sitting off and on for a while before I got it. My uncle drove it for a time but stopped after it started leaking blue smoke. We eventually tracked it down the vacuum leak and fixed it. Since then the car has sat off and on while I stored it at my parent's house during college.

After fixing my vacuum leak problem and putting in new plugs, the car ran really well. I left in the car of my family for three weeks immediately after that. When it got back to me, it was running very wonky. Exhaust smells like fuel and I have to really pump the gas to get the car started. Also it idles rough after the car warms up and the choke goes off.

I'm pretty sure a lot of my issues are carb related. The idle and mixture screws were adjusted for poor vacuum. So I'm assuming with more air getting pulled in so it is now running lean. Does anybody with some experience in Solex 4A1 carbs want to give me a quick run down on adjusting the mixture? I've heard that you need to disable the egr valve to do this correctly. Is that true? I can just pop the vacuum line off the egr valve and plug that line closed to do that right?

On a somewhat unrelated note, I've heard they purposely put smaller jets on these carbs to make them pass emissions in the US. Some have said upgrading to larger jets meant more efficiency and power. Does anybody have any experience with this?

Please don't suggest a Holley conversion. I can't afford that right now and I'm trying to keep it as stock as possible. A mercedes tech a few years back said the carb head looked good with no warping and to torque the nuts to specification if I ever popped it off to rebuild it.

I'd also like to clean out the fuel system since it has been in storage so long. I crawled under the car today but the fuel filter doesn't seem to be in the usual position (American cars) next to the driver side door. I've also heard there is a fuel screen in the tank itself. I'd like to do this all in one go so I don't have deal with the mess/waste of gasoline twice. I couldn't find a stock fuel filter so I'm unsure what I'm looking for. What is the location of the fuel filter on this vehicle? Any advice on taking the tank off, what to use to flush the lines, and how to clean out the tank?

Thanks for all your help.
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post #2 of 20 (permalink) Old 06-19-2011, 03:04 AM
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If you smell fuel in the exhaust, it's burning too rich. You've already guessed what many of the folks here will say - get rid of the gas and clean out the old stuff.

Removal of the tank is actually really easy - after you remove the fuel lines (ensure the tank is empty), there are a few retaining bolts that hold it to the chassis. An empty tank doesn't weigh much, so taking it down on your own is a snap.

I'd recommend taking it to a specialist and having the thing steam cleaned, to get rid of any gunk, varnish or rust.

I'd also recommend you replace the fuel filter, and have the carb completely cleaned and readjusted.

Good luck!
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post #3 of 20 (permalink) Old 06-19-2011, 09:01 AM
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Spray some carb cleaner around the intake manifold, you may have a vacuum leak due to warping.

With best regards

Al

Check out the W114, W115 /8 enthusiast forum http://www.stroke8.org

My 280SL restoration
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post #4 of 20 (permalink) Old 06-19-2011, 04:30 PM Thread Starter
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Thanks Grubeguy,

Taking it to a specialist sounds like a great idea. I'm not sure of what I should be looking for though. I live in the Seattle area. Does you have some suggestions or even just what I should google to find a tank cleaner?

Thanks,
Albert
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post #5 of 20 (permalink) Old 06-20-2011, 10:48 PM
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Quote:
Originally Posted by youngishtari View Post
Thanks Grubeguy,

Taking it to a specialist sounds like a great idea. I'm not sure of what I should be looking for though. I live in the Seattle area.

Try radiator shops first - not the guys who install new ones, but folks who repair them. They should have the equipment to do the cleaning...
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post #6 of 20 (permalink) Old 06-20-2011, 11:45 PM
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The float has filled with gas. You need a rebuild. If the float is brass, just resolider it.
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post #7 of 20 (permalink) Old 04-03-2013, 11:26 PM Thread Starter
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Life finally gave me some time back. So I'm back to take on the beast again. Here's a list of what I've done so far.

I got the tank removed, cleaned out and restored. Felt really dumb because it was super clean inside but worth the money since they took the time to replace and reweld the rusted studs for the fuel sender. Everyone of those little buggers broke when I tried to take the damn thing off.

I took the carb off the body. Cleaned out and rebuilt the carb. Then I carefully torqued the nuts to right torque.

Now I'm back to trying to get the beast started. I tightened the mixture screws all the way and backed them off two turns. I used my trickle charger to get the battery recharged. The engine turns strong. It doesn't catch and start though.

When I pour a small quantity of gas into the carb, I get instant start and the engine turns for a couple cycles before starving off.

I'm thinking I'm not getting enough gas into the carburetor. So I pull off the fuel line right before the fuel return valve (in front of the carb). Whenever I crank the engine, this sprays a quantity of gas everywhere. However, it's not 100% full of gas like it was when I took the carburetor off in the first place.


I've tried to get an idea of what the fuel system looks from my factory manual and the parts catalogue but it's pretty terribly mapped out. They show the tank and they show the carb but nothing in between.

Also I've traced the fuel lines from the tank forward to a strange object with two dial shaped objects under car. This is located just under the back seat on the driver's side. One of the junctions to this object seems to be leaking fluid. Is this the pump? Do these cars have mechanical or electrical pumps?

What advice do you have for bleeding the fuel system of air? Should I continue to crank it like I am? Will that damage the pump? Do I need to remove some piece before the pump to remove air on the suction end?
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post #8 of 20 (permalink) Old 04-04-2013, 01:12 AM Thread Starter
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Okay, just found the mechanical pump. I'm going to try bleeding the suction end a bit to see if i can remove some air. Then I'm going to try cranking the engine until I get rid of the air. I'll probably crank a couple times and then rest for 30 secs or so the starter can get some rest.

Still have no idea what the thing under the car is. It looks like two dials from a combination lock. I'll try resealing this bad boy tomorrow. I'll take a picture to so maybe one of you can identify it.
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post #9 of 20 (permalink) Old 04-04-2013, 05:05 AM
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Originally Posted by youngishtari View Post
Still have no idea what the thing under the car is. It looks like two dials from a combination lock. I'll try resealing this bad boy tomorrow. I'll take a picture to so maybe one of you can identify it.
It's the valve package for the fuel evaporation system, full description can be seen here at main 47, sub 800, page 11.
Mercedes-Benz Model 116
Also section 7.2 for the solex 4A1.



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post #10 of 20 (permalink) Old 04-04-2013, 11:03 AM
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I had a cold start issue (had to pump the gas to get it going) with my car along with a hesitation upon acceleration. Replacing the accelerator pump fixed both.
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