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Sanity check please!

NutmegCT

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1960 Mercedes-Benz 190b (gasoline sedan).

Engine has "issues". Cranks fine, good spark, good fuel flow to carb, but tough to start and very rough idle.

So: carb rebuilt (cleaned, new washers, gaskets, etc.) new plugs, new wires, new rotor, new dist cap, new coil, new condenser.

But ... no fuel is getting to the plugs.

Fuel bowl is filled to correct height. Fuel squirts into throat with accelerator pump (and gas pedal). Linkage opens/closes butterflies. Checked but found no vacuum leaks.

Crank it with choke full on, fires once or twice, then just cranks merrily away without firing. Once this morning it idled roughly for about a minute, then just died. Crank it with choke off - doesn't fire at all.

Pull plugs. Completely dry.

I *want* to say a chipmunk built a nest in the intake manifold when I had the carb off - but that's too easy.

What am I missing? Jeez this is frustrating.

Thanks.
Tom
PS - classic M-B guys all say "rebuild the carb!" "change the fuel filter!". Did all that. grumble grumble
 

Keith_M

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Hi Tom,
The dry plugs are pretty diagnostic I think. It sounds like it's not getting enough gas. I can only think of two things to try.

1. make the mixture as rich as possible and see if that makes it run

2. check for vacuum leaks. check all vacuum lines including any that run to the brake booster (does it have one?). Tighten the nuts holding the carb to the intake manifold and tighten the nuts holding the intake manifold to the head. If you can get it running, you can check for vacuum leaks by spraying WD40 on suspected leak spots. If the engine slows down, there's a leak.

Hope this helps.
Keith
 

JPSmit

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Blockagein the tank or lines? Do you have a gas can you can run it from? And, FWIW getting this sorted does not make you sane! :smile:
 
D

Deleted member 8987

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I think I asked this before. This one have a Hydrax? Pinch off the hose to it with a set of visegrips. If there is a problem, it's a BIG vacuum leak.
The idle jet up on the side of the main body....have you checked that for clean with a small piece of wire? (I use a piece out of a wire brush held with needle nose).
Choke is not a plate on those, rather a bypass.
There is a choke jet in the side.
Tried a manual choking?
Dave
 
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NutmegCT

NutmegCT

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Thanks gents. Just rebuilt the carb, so I know all the jets and ports are clean.

Funny thing about testing vacuum: I squirted starter fluid all around the carb while it was lumping along, and no speed change.

BUT - this afternoon I removed the carb. I held it up to the (cloudy) sky and found I could actually see light between the carb body and flange; the flange goes between the body and base.

So I've just replaced that flange - a bakelite spacer - and now it seems to be a tight seal. Can't figure out why spraying starter fluid didn't detect that - it sure was open. The "bad" flange is part 31 on the diagram:

solex_type_32_paita_alternate.jpg


No Hydrak - simple four cylinder, four speed, one dual-throat carb.

When I removed the carb, I found some gas down in the manifold, so I know it was getting that far. As the compression of all four cylinders is *high* (spec is 125; actual is 150), I'd have thought it had a sufficient vacuum to pull fuel through the manifold despite the carb flange gap. Plenty of fuel going to carb; fuel bowl correctly filled.

Tomorrow I'll put it all back together, kill four chickens in the name of Zeus, and see what happens.

Thanks.
Tom
 
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NutmegCT

NutmegCT

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This is amazing. Failed again. Bolted the carb back on the manifold, attached the vacuum advance line, fuel line, throttle linkage. Primed the carb to fill the bowl.

Held the starter button - fired immediately, ran about two seconds, died completely. Now won't fire at all.

:wall:
 

Keith_M

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was the bowl still full after it ran for a few secs?
 
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NutmegCT

NutmegCT

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Keith - thanks for hanging in there.

I did *not* check the bowl this morning right after it ran for a few seconds. I did check that fuel was still coming from the accelerator pump jet afterward - no problem there. So I *assume* the bowl still had fuel, but can't be sure.

2pm EST. Now, just after lunch, I thought I'd repeat the whole morning cycle, to give you a firm answer about the bowl after firing. Just like this morning, right after re-installing the carb,I removed the coil wire, cranked it to fill the bowl (in case ...). Then removed the carb top and checked. Bowl was full.

Put the coil wire back in, cranked it - nothing. Didn't fire once. Removed carb top - bowl still full.

I've done this with full choke, half choke, no choke. No difference.

EDIT: 2:20pm EST. Dropped some fuel down into the throats. Cranked it again. Fired immediately a couple times, then nothing. Checked bowl - still full.

My goal of a cross country trip may turn out to be nothing more than pushing the car from one end of the driveway to the other. Jeez.

T.
 

TR3driver

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Part 31 is above the throttle plates, so there is very little vacuum at that point especially at idle. I'm guessing that's why you didn't detect the leak, it didn't leak very much.

My approach would be to hold the throttle and choke open and give it a healthy shot of carb cleaner (Gumout) down the throat (both of them if that's a mechanical secondary). Then immediately crank while holding the throttle open. If it doesn't fire at least once, I would suspect ignition instead of fuel.

The plugs aren't wet because the liquid fuel is puddling in the manifold rather than running into the ports. My Audi was like that too, it would never wet the plugs.

Might also be worthwhile going back to the parts that made it run badly. Sure wouldn't be the first time a new part was bad.

PS, if it is a fuel problem, I'll bet there was some crud in the lines that is now in the primary jet. It may even be moving around, sometimes falling back out of the jet orifice so it runs until the crud gets sucked back up against the orifice.
 
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NutmegCT

NutmegCT

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Thanks Randall. Didn't think about that "leak above the butterflies" factor.

I just tried again - gas down the throats; immediately crank with throttles open. Fired once or twice - then stopped.

Note - this problem is exactly the same as before I replaced the coil, wires, rotor, cap and rebuilt the carb. Now I've again removed the carb, cleaned it and the jets just last week. Very puzzling.

Tom
 
D

Deleted member 8987

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However. The fuel in the float bowl needs to go UP to the idle jets (if I recall), then DOWN to the mixture screw, out the port into the throttle body.
If there was a gap between main body and throttle body, there was no vacuum to suck fuel through the mixture port, the idle jet, and on to the bowl.
I'd have to go look again, but I think this carb is like most, where the idle fuel actually comes through the main jet. And gaps, gaskets, warped plates, etc, along the idle circuit path, and you get nothing.

The choke is not a choke like we may be used to. It is a fuel enrichment device on the side of the main body.
Works, but differently than a manual throat choke.

Doing a hard choke is your hand over the top and cranking.

Compression may be good, but what is your cranking vacuum?

Pouring raw fuel down the throat and it starts, but you cannot repeat, makes me want to know if vacuum for some reason is going away or spark is going away.

Dave
 
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NutmegCT

NutmegCT

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Thanks Dave. Here's a diagram of the PAITA:

attachment.php


You see the idle circuit in the picture on the right side; idle needle is in lower right of diagram.

Sure seems to me that dropping some fuel down into the throats should get more than a one second surge, followed by instant death. Plenty of pull if I put my hand over the carb top (air cleaner hasn't been on for over a month). And same "instant death" result, using full choke, half choke, no choke.

Tom
 
D

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See how the fuel has to go up to the idle jet?
That's what I was talking about.
I have two Solexes on my Jag, so I was somewhat familiar with them.
What I took off were two off a Ponton MB some yaywho had cobbled on in Singapore.
Interestingly, the throttle plates and centre section are one piece on these.
After it fires once, immediately pull the coil wire out of the cap, and see if you have spark still.
If more fuel won't do it, and you have good compression and vacuum, we're narrowing down the possibilities.
 
D

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Weak or no spark. Sometimes, all it takes is one start, and it quits. Why I said as soon as it quits, yank the coil wire out of the cap and have someone crank it while you check for spark.
Bosch.....condensor external or internal?
Corrosion when it bolts down. Bad, weak, loose, corroded connections on coil primary or at points.
Broken ground wire on breaker plate.
Try it with the vacuum advance disconnected.
 
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NutmegCT

NutmegCT

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hmmm - just replaced the condenser about a month ago, when I replaced the points and coil, rebuilt the carb, etc.

But ... the new coil was a Bosch coil which requires external 1.8 ohm ballast. I didn't have a resistor, so used it once (!) without the resistor. Then when there was no improvement, I put the old coil back on.

Maybe using that new coil without ballast fried the external condenser on the distributor?

I have to work this morning, but this afternoon will do more checking.

Thanks.
Tom
 
D

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No, would not have hurt the condensor. Maybe too much current and glazed the points.
Just remember, first rule of automotive repair:
Just because it's a new part doesn't mean it's a good part.

Got a dwell meter?
Crank it and read dwell. Should tell you if the points are breaking normally.
 

Keith_M

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Hi Tom,
This is starting to sound more and more like it's spark-related. It sounds like you've replaced most of the high tension stuff. Have you checked the low tension lead between the distributor and coil? If it's loose or partially broken it might be getting shaken when the car starts to run. Easy to check the tightness of the connections and the continuity of the wire.

Keith
 
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NutmegCT

NutmegCT

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Gentlemen - I don't know if this is the problem, but ...

THE CONDENSER ON THE DISTRIBUTOR IS DEAD.

Removed condenser from distributor. A good (old radio) condenser holds a charge (DVM set to resistance gradually drops). The questionable condenser doesn't budge when resistance is tested. That's the only test I know for a condenser.

Jeez - it's a $45 Mercedes-Benz (Beru) condenser, I've had for the sum total of 60 days. What the heck would make it die like that?

Now if I just had a replacement handy.

Tom
 

TR3driver

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Amazing how often new parts are defective, isn't it?

The condensor doesn't have to go inside the distributor. Grab the spare you kept last time you gave the TR3 a tune-up, and mount it on the side of the coil or distributor. That should do, temporarily, or even permanently if originality isn't important.

Hmm, that test might not work, depending on your DMM. Try selecting the 20Mohm scale (disable autoranging if your meter autoranges), then shorting the leads (with the meter attached) and see what happens when you remove the short. The reading should gradually increase as the capacitor charges to the supply voltage from the meter. With my Fluke, it takes several seconds to get even to 2 Mohm (and will go to infinity if you give it long enough).
 
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