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Solex PAITA carb

NutmegCT

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A puzzlement:

Car won't start. Good spark, points correct, strong starter, plugs and wires good. Strong fuel flow from pump to carb bowl. All carb jets cleaned, fuel bowl clean and no sediment.

Crank the engine, not a single plug fires.

Dump gas into carb throat, takes about five seconds of cranking to get it to fire - then it runs a bit but stops (like it just runs out of gas). Open carb top, the fuel bowl is full. Once it does run with a prime, engine runs strong and smooth ... then just dies.

Engine was hard to start since I got the car two weeks ago. Now that I cleaned the jets (!) it's worse.

Pump the gas pedal, linkage moves, accelerator pump works, butterflies open - but no go. When the engine runs after priming, pushing gas pedal does *not* increase engine speed. Instead, pushing gas pedal seems to "flood" the carb and kill the engine.

I *did* notice that fuel weeps from the gasket that joins the carb top to the carb base, and fills the pan under the carb. Would that be enough to prevent gas from getting to the manifold? Note: the gasket is the "insulation flange" between carb top and carb base - NOT the gasket between base and manifold.

arg
Tom
1960 Mercedes-Benz 190b

dis03_Front_Carb_Bench.jpg
 
Last edited:

aeronca65t

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Look for obvious vacuum leaks at the base of the carb.
Check for vacuum leaks at manifold to head (tighten all manifold bolts)
Check ignition timing.
Check valve adjustment.
If your car has an external ballast resistor for the ignition coil, you can temporarily "jump" across it to make sure it's not bad.
Is gas "good" and not contaminated? (disconnect fuel pump and plug it.....manually fill float bowl with good gas)
Sometimes, plugs will become partly fouled but will look OK. If unsure, replace them.

On occasion, I've had problems like this where I can't get things running and can't seem to figure out what's wrong:
So I'll start the thing on starter fluid and just keep "spritzing" it down the carb until the engine will run on it's own. I'm never quite sure if it's stuck valves, clogged jets or whatever........but as a last resort, it might help (be sure fire extinguisher is handy!)
 

Billm

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I just got thru bringing two VW bugs back from very long sleeps and found that I had to clean the jets several times since the crud from the lines kept plugging them up again and again (even with inline filters). Now they both run strong but you may check the jets again.
BillM
 
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NutmegCT

NutmegCT

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Thanks gentlemen. I had checked for vacuum leaks (spraying carb cleaner around the connections), but no evidence. All fresh gas. No external resistor at coil.

Today I completely rebuilt the carb. New jets, washers, nozzles, etc. Put it back in and cranked it up. Exactly the same thing. Never fired.

I checked a plug - slightly moist and smelled like gas. So ... I tried a spare 12v coil.

Sprayed carb cleaner in the throat, cranked it about ten seconds ... and it sputtered to life. While idling (rough but continual), I got out and slightly richened the idle mixture. Could actually give it gas and hear it rev up. Ran for about 2 minutes.

Then it died again.

Plenty of gas in the bowl.

I again put about 3 tablespoons gas in the throat, cranked it ... but no joy. Didn't fire once. Tried a third coil. Still won't fire.

This is so weird.

Possible new clue: after about ten tries of cranking for about 30 seconds each, battery is nearly dead. Three year old WalMart battery, I re-charge every night. Battery maintainer shows it's fully charged every morning - but it sure seems to run down fast to me. Could all this be due to a "weak" battery? (even tho' the maintainer shows fully charged after running overnight?)

Edit: just tried again using big battery eliminator in parallel with main battery. No change - still doesn't fire. Sheesh.

One strange thing to me - open butterfly, drop a couple tablespoons fuel straight down into throat - but engine still doesn't fire (except *very* rarely - when it races for about five seconds, then dies out). Seems even if the carb were totally screwed up, that fresh fuel directly in the manifold should fire until it runs out.

Thanks.
Tom
 
Last edited:

aeronca65t

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......One strange thing to me - open butterfly, drop a couple tablespoons fuel straight down into throat - but engine still doesn't fire (except *very* rarely - when it races for about five seconds, then dies out). Seems even if the carb were totally screwed up, that fresh fuel directly in the manifold should fire until it runs out.

Thanks.
Tom

Unless the plugs are partly fouled and "shorted". Clean gas can unfoul them for a moment and then they short again.
I'd clean the plugs really, really, really well (deep down into the cones where they can short across) and see if that helps.
Blow them out with compressed air or a least, starter fluid.
Or just replace them. This is an old car, so set gaps a little tighter than normal (around 0.025").

Sometimes, it's worth waiting until it's completely dark outside and cranking the car.......you might see a "tracer" indicating some errant electrical insulation wasting electrical current.
 
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NutmegCT

NutmegCT

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Now THAT is a good idea. I'd completely forgotten to pull the plugs, clean and check gap. For that matter, I don't know for sure they're the correct plugs (or gaps). While the plugs are out I'll also do a compression check.

Sure seems that if the spark is good (wire to block), and the fuel system is good, it might be the plugs themselves. Amazing how strong the engine feels/sounds ... when it actually runs.

Thanks Nial.
Tom
 
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"One strange thing to me - open butterfly, drop a couple tablespoons fuel straight down into throat - but engine still doesn't fire (except *very* rarely - when it races for about five seconds, then dies out)."

Okay, let's discuss that statement.
Are you saying you hold the butterfly open, drop fuel into the throat, and leave the butterfly open, so when you crank and it does catch, it races.....or do you let go the butterfly, and when it does catch it still races?
If the latter, it cannot race if the butterfly is closed. No air (or insufficient to cause it to race).
And, what do we mean by "race"?
This on the MB?
This one have a Hydrax?
 
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NutmegCT

NutmegCT

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"One strange thing to me - open butterfly, drop a couple tablespoons fuel straight down into throat - but engine still doesn't fire (except *very* rarely - when it races for about five seconds, then dies out)."

Okay, let's discuss that statement.
Are you saying you hold the butterfly open, drop fuel into the throat, and leave the butterfly open, so when you crank and it does catch, it races.....or do you let go the butterfly, and when it does catch it still races?
If the latter, it cannot race if the butterfly is closed. No air (or insufficient to cause it to race).
And, what do we mean by "race"?
This on the MB?
This one have a Hydrax?

Good points. Here's what I do: Hold butterfly open, drop fuel into throat, close butterfly. Engine usually doesn't fire at all. Crank it about 15 seconds, and it *may* fire - runs high rpm for a a second, then drops down to normal idle (600rpm).

This is the 1960 MB - no Hydrak.

UPDATE 2pm EST. I put in new, correct, NGK plugs. Correct gap, strong spark, timing, points, distributor set correctly. But there's no change at all. Even without priming the carb, if I crank for about 10-15 seconds, it may start and idle. When it starts, it idles for maybe 2 to 3 minutes, but then just dies, like fuel starved. But the float bowl is full (and I know the fuel pump is strong). Note: when it's idling, if I goose the throttle, speed doesn't increase. Goosing throttle actually seems to kill the engine.

One of the tough things about writing a description, is that you do several things (butterfly, prime, close, crank, etc.) and can't really remember the details of the results of each attempt. Need to dictate into a recorder during the whole process!

Thanks.
Tom
 
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JPSmit

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question: if it quits, will it restart? or do you have to wait? If it is running for 2-3 minutes, this is more than a "floats worth" of fuel. However, if you open the float and it is full, then it isn't between the tank and the float, it is more likely between the float and the carb. Is there a blockage? particularly a "floating one?" I'm not familiar with Solex carbs but, sounds like something is gumming up after a couple of minutes.
 
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NutmegCT

NutmegCT

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Thanks JP. When it quits, I crank it another 5 to 10 seconds, and it'll usually start up again. Then idle for a minute or two until it quits again.

As an experiment, I waited 'til it quit, then pulled off the carb top and checked the fuel bowl. Bowl was full.

Note - problem was the same before and after I rebuilt the carb.

As it has run (idled) for up to five minutes, I'm sure the bowl is emptying and refilling.

Still seems weird that it has plenty of fuel in the carb, and the fuel is being burned (and bowl refilled). Also interesting, you'd think that opening the butterfly, pouring in some fuel, closing butterfly, then cranking would start immediately. But instead it still takes 5 to 10 seconds before it ever fires.

And of course ... goose the throttle when it's idling, but no speed increase. And the choke is set for fast idle, but it's idling at warm rpm (700).

Nothing is simple!
Tom
 

JPSmit

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electric pump?

how is the timing?
 
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NutmegCT

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Mechanical pump with good flow. Also checked timing and it's spot on.

Right now I'm thinking the choke circuit is screwed up, and/or there's a choke or throttle linkage adjustment I haven't figured out.

It can idle for several minutes without problem - smooth, no exhaust smoke, bowl refills as it should. But the fact that the engine just dies, even with the bowl still full of fuel, is puzzling. And the choke is set for fast idle, but it's idling at warm idle speed (700rpm).

Plus, the fact that goosing the throttle linkage properly squirts gas from the accelerator jet into the throat, but doesn't increase rpm, is a mystery. So I'm wondering if I need to completely re-install the choke and/or accelerator linkages.

Wish I had my own Colossus bombe to decipher the German engineer's Lorenz Geheimschreiber codes. (I figure at least a few of us will know what I'm talking about ...)

:jester:

Onward through the fog!
Tom
 
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Billm

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To me it is beginning to sound like the coil is overheating during running.
Pull off one of the plug wires and hook it to a plug on top of the engine so that you can watch it and try again.
I will guess that the plug stops flashing just as it stops running and is winding down.
BillM
 

aeronca65t

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........Plus, the fact that goosing the throttle linkage properly squirts gas from the accelerator jet into the throat, but doesn't increase rpm, is a mystery. So I'm wondering if I need to completely re-install the choke and/or accelerator linkages.

Onward through the fog!
Tom

Are you sure the throttle plate is opening when you step on the gas pedal? (I realize the accelerator pump is working.....but is the actual throttle plate moving in the carb body?)

Good reference to "Colossus bombe". ;)
 
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NutmegCT

NutmegCT

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Thanks gentlemen. I've used three different known good coils; no change. Now using fresh coil and new plugs, points, etc.

Moving throttle linkage definitely opens the primary butterfly; full throttle starts to open the secondary, which is designed to open fully with engine vacuum.

I'd say the intake manifold is blocked ... but there are times when it idles just fine for several minutes. Today I actually got it to rev up when I opened the throttle, then slowed to normal idle when I let up on the gas pedal. Kept idling for another minute ... then died.

I just removed the carb again, and have it on my work bench. Any suggestions on what to look for?

T.
 
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NutmegCT

NutmegCT

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Nope - no anti-dieseling valve. (Sounds like the anti run-on valve on my old MGB.)

Carb is now on my bench. I manually pushed the linkage, and the primary butterfly began to open. Fully pushed linkage, primary fully open, and upper secondary began to open. Lower second is free to open, but as there's no vacuum it remains closed.

Main thing to me: if fuel bowl is full of fuel, and primary butterfly is opened by linkage, and pedal is tromped (and squirts fuel down toward open butterfly) ... why the heck doesn't the fuel get burned (other than about once in 20 seconds, when it then idles fine for a couple minutes)?

T.
 
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NutmegCT

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This *may* be the culprit: faulty mixture tube in primary throat.

I wanted to clean the air cap on the fuel/air mixture tube, and found the cap very difficult to remove. Had to twist the entire mixture tube holder and remove it all as a unit.

Inside the holder is a brass tube containing a ball valve. Ball should be free to close the valve unless suction pulls it open. I shook the tube but the ball didn't rattle.

Ball seemed stuck in the tube. If the ball can't move, then (I think!) manifold vacuum can't suck gas from bowl. I've now soaked the tube in carb cleaner, and blown it out. Ball now rattles when tube is shaken.

Fuel is supposed to flow from the bottom of the bowl, through the main jet, and into the bottom of the mixture tube. Manifold vacuum is supposed to pull that ball up, allowing fuel to be sucked into manifold. I'm betting the ball was stuck 90% of the time. Picture of the complete mixture tube unit attached.

View attachment 24427

Tomorrow will be the "acid test" - as my dad used to say.

Keeping fingers (and toes, and eyes, and ...) crossed.

T.
 
Last edited:

DrEntropy

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Was that it, Tom?
 
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