This is what l did for fuel supply. Orange lines are new. The right black one line is from the pump left one is the return. I was thinking to raise the float a bit to have a bit more fuel stored. What do you guys think?
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Does it happen when cranking up, or any time during driving?
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No it cranks right up but under driving it starts to lean, then go baack to rich and if it doesent l need to āresetā the fuel pump
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Maybe just a slight amount of restriction in the return line to force fuel to the carburetor and keep the fuel pump still thinking it is pushing against the injectors that it use to serve. Iām thinking that when the computer does not feel a back pressure, it might think something is wrong and shuts the fuel pump off. Even carburetors have some pressure coming to it from the old mechanical fuel pumps. TomC
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You might turn the tee to where the gas is going straight to the carb and the return is going off to the side.
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The T maybe causing a vacuum on the carb. at high demand. Kind of like an air suction gun.
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I would put a check valve, like this one, in the orange tubing to the left the carburetor in your picture. It will act as a pressure regulator. The ācracking pressureā of .5 psi will feed your carburetor better.
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Good Morning KristijanL.
Thinking about it I am not surprized you are having carburator fill problems.
On the FI fuel supply system you are only going to have return side flow IF the FI fuel system regulator allows flow.
Usually these regulators are intake manifold control referenced. This makes for FI system pressure boosting when the engine is under low manifold vacuum engine loading and acceleration. Easy proportional enriching.
Try removing this vacuum reference line from the FI fuel regulator.
Three possible changes then:
Works fine then. O.K. Go with that.
OR, too much fuel pressure all of the time. Need a carburetor-specific inline fuel pressure regulator added in.
OR, fuel starvation all of the time to the return-line/carburator. (figure out how to wedge the FI regulator orifice always slightly open to correct)
You should still have the FI fuel-side pressure for your re-purposed cold-starting āboostingā injector.
I am actually surprised doing has you have you have not ran into carburetor flooding.
You really should add a carburetor-spec inline fuel pressure regulator to be assured of never too much pressure supply.
Regards
Steve unruh
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Steve, there is no more fuel pressure regulator. Just tank - pump - filter- (carb) - return to tank.
Ha, your reply brings me bitter sweet memoryes from a not so distant history 
when l bought the carb the guy told me the carb pluggs in directly in a fuel pump, and the return to the tank is on the other side. I connected it like that, wife cranked the fuel pump and l got a majestic squirt of dino piss in my face from the carb. Turns out there is only one LOW pressure intake from the fuel pump and the other connection is just a crankcase breather connection. The fuel pump on the MB produces about 100psi so imagine that on a carbs floatā¦
This it where l decided for a T connection. But the more l look at it the more you guys make sence. I made a venturi ejector with the T! I wuld guess even a bit of resistance shuld help fill the carb instead if empty/barely fill it.
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Either that, or just a bigger T to slow down the venturi effect.
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Ok l found the T on the fuel line does provide pressure. But the problem is still there.
Interasting thing is when l rev in neutral it shows rich on the O2 sensor all the way from idle to wot. But under load strange things happen. Untill about 2200 rpm the engine is runs wery lean with bad power and stumbling no mather the throtle position. After that it shows rich. Why wuld that be???
The secondairy throat on the carb will open on intake pressure so only when there is real high demand so that might be the reason why it runs well after 2200rpm, but why does it not matter in neutral?? Is it normal a carb acts this way? Plese help, l am a newbie to carbs
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Hi KristijanL.,
Your primary barrel (bore) load-enrichment circuit is clogged; undersized-jetted; or has a blocked intake manifold signalling channel.
In neutral RPM revved up you will not create the continuous low manifold vacuum you do created with a worked loaded down engine.
The load enrichment circuit gets this low manifold signal and spring-action then valved in a circuit allowing for added emulsified (internal carb air and fuel mixed foamed-bubbled) mix to flow then below the throttle plate.
I do not know your actual carburetor so do not know the actual load-enrichment type it uses.
However many times on retrofit carb installations the special internally notched gasket mounting gets done with a solid gasket blocking carburetor base flange signally ports.
Check here first.
S.U.
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Thank you Steve! Took me a wile to digest all this.
Well this carb has a membrane pump and each time pedal is pushed it squirts some extra gas, thats all l know of any enrichment.
Ok. Yesterday l took a look at it again. I enlarged the main jet just a hair and things are MUCH better. Surprised how much of a difference such a small change makes. It now runs good down to 1400 rpm on load, then starts to go lean.
I think that all might be my fault. I set the carb jets originaly only on narrow band o2 sensor under load. I was hunting for stechiometric 500mv reading wich is hard on a narrow band, but l just looked at some graph and it seems in reality a richer reading is preffered, around 700mv. Mine runs at 800 now.
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Hi back KristijanL.
You describe the one-shot-squirt accelerator pump.
Load enrichment circuit is different.
The best carburetor education I had was American Holley Company sponsored. Not available since the late 1970ās.
As good was a decade long series of books by H.P.Books. One on Holley carburetors and intake manifolds. (carburetor can only be as good as the distribution intake manifold)
One book on GM Rochester carburetors.
One book on American brand Carter carburetors.
One book on european Weber, Solex and Zenith carburetor company.
Ha! Ha! British SUās; Ford Motorcraft; Stromberg and the Japanese carburetors and you were on your own.
No matter they all have to satisfy the same vehicle engine needs.
Carburetors work by pressure differential induced air flows.
You live by an accurate intake manifold vacuum guage.
The engine load enrichment circuit is enable by low intake vacuum from the wide open throttle. But with the running loaded engine actually flowing air. It then continuously allows in an additional rich āemulsifiedā carb internal air-fuel flow.
Mr. Italian Weber was a genius. Heās learned that air was quick responce low weight-mass. Gasoline fuel was a heavy dense slow response weight-mass. Bubble-mix together to even out these differneces.
This is done in the internal mixing-well with bubbling tubes. Air to these sucked in by the top of carburetor air-bleed holes.
Hard, hard lesson for me and others. Downdraft Weber designed carburetors Need Heated Carburetor air to function in the cool-wet. These air bleed in holes will air-moisture frost up and plug. This kills the effectiveness of their supplying circuits. Cough. Spit. And die. On demanded rpm and loads changes.
S.U.
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Some carburetors use a tapered needle inserted down the center of the main mixing well emulsification tube. High intake manifold vacumn by a diagram hols this needle inserted for normal flow. Intake manifold goes low and a spring then retracts this needle allowing for a richer fuel supply ratio.
Other carburetors use a āpower-valveā. This is intake vacuum closing off a supplying circuit. Intake vacuum goes low and again a spring opens up additional emulsified flow into the carburetor venturi.
Yeah. Carburetors tune for rich.
The try-to-stay stociometric carb types had additional electrical duty cycled air-bleed enleaners. Or duty cycled enricheners. Ha! Or dual-action both.
Sod this. Just go then to EFI.
S.U.
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Thank you Steve you clarified many thins! Specaly the emulsifier, l had no idea why its neaded.
Well this carb is ment for a 1.3 or 1.5l engine, mine is a 2.3l! And like you sayd, the intake manifold is not designed for a carb. I am amazed it runs as good as it does! Right now l am 90% pleased with the performance. I suspect a leak on my diy carb-tb conecting peace, idle sometimes goes lean.
Allso the accelerator cable comes short so the carb only opens the second big barrel maybee 20%. Still, the car does 105mph wich is as fast as it ever went with injection! If te second throat wuld open more it wuld be a monster. But the fuel consumption wuld be too athugh its an easy adjustment l will leave it like this for now.
By the way, with fuel injection l got 21mpg. With a carb l get 18mpg. Thats with the carb not tuned 100% and doing lots of test, idle, ā¦ thats acceptible.
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Since l modifyed the intake system to accept woodgas and carb, the woodgas part must seal 100% in order for 100% dino drive (and specialy idle!) Is possible. This means ordinary DIY butterfly valves are out of the question.
I have used ball valves for the air side before and it worked well. My question is what about the woodgas side? Soot and tar traces might make it stiff. Has anyone got any ideas what l culd use?
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I use ball valves. They are either on or off so they donāt meter the gas like the air side. No problem with my brass valves but the pvc ones are stiff anyway with or without soot.
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You might try RV sewer valves if you can find any over there. I used them on my latest truck and they seem to work well.
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Designed to work in dirty conditions. That totally makes sense.
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