So, how much fuel does a carburetor need? Stutter problem...

[StefanLee]

I just experienced a stutter or rather dying-on-me problem a few days ago.

Basically, the car (with a down draft Weber) stuttered and died as if it wasn´t recieving enough fuel. So, thinking there was a blockage I pinched the fuel return line to increase pressure and hey it ran again.

Still, that is not a proper fix (and I don´t wan´t the engine to run lean) so I began troubleshooting. I cleaned the fuel pressure valve I have next to the carb to make sure it was working. Then I unscrewed the fuel line at the carb, and despite the pump running there was very little fuel coming. A spurt at start but then it slowly stopped. Not good!

I checked if the fuel pump was working correctly, unscrewing the outgoing fuel line... It was, flowing fuel like crazy! Good. I went forward, unscrewing lines and checking as I went, and found a small blockage in the T-section of pipe where the fuel line connects with the return line and the carb. I blew it out, and the flow was dramatically increased in that last section of pipe. Whew! Problem solved! (I thought).

I screwed everything back together, and tested the flow at the carb with the line in a large coffee cup (remind me to wash that before the wife sees it! ).

With the pressure valve at the highest flow setting (it´s a knob, graded to six) the pump filled the 2,5dl (250cc´s, 0,25 liters) cup in say a little over ten seconds. A pour, but not streaming out if you understand. So, perhaps 20cc´s a second.

I hooked everything up, turned down the knob to setting four and started the engine, hesitant at first (died when throttled and backfired), but after a few tries she ran fine.

Drove perhaps three miles, no problems, but then she dies on me when driving along all of a sudden. When the car slows down with gear in she ignites and starts to run but then dies again... Hmmmm. I get her started after a few minutes, drive to a nearby street and turned the flow regulator to setting six, the highest. That should do it!

Everything works, I drive around doing some errands (five miles) and she dies for a couple of seconds on the way home (maybe two) but keeps running. Popping the hood I fiddle with the regulator but since it is already at the highest setting I do nothing. I drive home without trouble.

So, clearing the blockage helped a great deal, and the first stop was perhaps because I turned down the regulator (fearing the Weber would recieve to much pressure otherwise). How much fuel pressure does the Weber need?

What happens if the pressure is too high? I just assume it was too low because it worked better when I turned to the highest setting, maybe I´ve gotten everything backwards?

What could be the problem otherwise? I like to use the car to work but don´t want to break down on the highway with a non-starting engine so I want to get to the bottom of it.

I thought hey maybe it is because the battery is a little flat after winter (I have a spare battery with me and cables) but the battery started the car and I checked it, 12,2 Volts at off and 13,2 with the generator running at idle. So the generator works (or how much should it be with the engine running?)

Carburated engines are fiddly, but fun. I´ve only had injected cars before so the Weber is new to me.

Any tips would be greatly appreciated.

Stefan

[opelnut10]

The Weber will take more fuel pressure than the Solex, no more that 6PSI, between 5 &6 is fine. Vapor lock (boiling fuel in the bowl) will sometimes be the problem, yours sounds like it may be that problem. Place two clothes pins on the fuel line between the fuel pump and the carburator (Don't hang laundry on them ) and see if it runs better, the clothes pin will absorb some of the heat and reduce vapor lock. If that works then insulate the fuel line around the engine to the carburator.

[GTJIM]

Have a read of this Thread: http://www.opelgt.com/forums/fuel-ta...tank-sock.html

... and follow up the links to see more about fixing this problem.

Fit a couple of in-line fuel filters - one at the tank outlet to stop crud getting into the fuel pump and another before the carb to catch anything else ... and provide the line back to the tank that 1973 models have.

Webers don't like much more than 3 to 3 1/2 PSI of fuel pressure so you must concentrate on sufficient fuel flow volume rather than pressure.

HTH

[StefanLee]

Thanks for the replies guys! I tried to search for info before I posted but didn´t find anything. Sometimes it is difficult to know what to search for...

I think my sock is already removed, because my fuel outlet of the tank is on the top (as is the fuel return). I saw that today when I checked the fuel pump. It appears to be a modification done by a previous owner, perhaps he had the sock problem too! I noticed it because I could see that it wasn´t a factory weld around the outlet pipe. But the fuel outlet should be on the bottom off an original tank, is that correct? That´s what I can gather from the picture of the "sock" in the thread you link to.

My car has a large aluminum (and I mean LARGE, sodacan-ish) fuel filter before the pump, and a clear plastic filter after the pump (and it was clean, no crud). I disconnected the fuel line after the clear filter as I said, and the pump ran STRONG! It was like.... you know when you REALLY have to go to the toilet? Like that. I sure didn´t seem clogged, that´s for sure. There must be a pickup in there, and one possibility is that it is clogged, but it seems unlikely since it flowed so well. The car also has a fuel return line to avoid high pressure at the carb. How does the return work on the -73?

So I´m leaning towards fuel starvation due to the fuel cap or something... I have a racing gas cap and I´ll have to check how it seals. I´ll test the flow with the gas cap off next time I work on it.

Opelnut10, I have to honest and say I don´t completely understand where I should put the clothes pins. Won´t they compress the fuel line and restrict flow? How do they dissipate heat?

Stefan

[yellaopelgt]

Is it possible that when you got the crud out of the tee that it actually allowed more junk in? point being is that I would get the clear fuel filters (2) run it, and see just how much garbage is really floating around your fuel system. It sounds like starvation from one source or the other and i would start from the tank and work my way to the carb. Might even be the fuel sock in the tank. I dont know if the car was sitting for a long time or how extensive you have replaced things along the way. Just juicing up the pressure probly isnt the best idea.... could cause a fire, you should really have a shut off switch with a electric fuel pump.(unless you do already)
Joe

[StefanLee]

Could be YellaopelGT.

I don´t want to up the pressure without knowing the reason for the maladie, you are right about that. The car has sat since september

I just went out to the car and unhooked the fuel line at the carb and ran the pump with and without gas cap. No difference, and now it flows even less. A trickle at most! Gunk must be trapped somewhere. I blew a piece of pipe clean but new crud must have taken its place!

I´ll give the previous owner a call and ask what he knows. Since the tank pickup seems to be a custom thing he might be the only one who knows.

(and yes, I have a shut off switch. The battery is relocated behind the passenger seat, and an emergency cut off switch is located on the battery box in easy reach from the drivers seat)

Stefan

[StefanLee]

I am second guessing myself as to how my lines are connected. I don´t have the time to rip everything apart now to check, and when I did I didn´t know what to look for...

Let´s hypothesise that I have a -73 tank since I have a fuel return line. How many lines are exiting the TOP of such a tank (or any GT tank, for that matter) One or two? I know I have two lines.

I called the previous owner and he said he knew nothing, it was the owner before him who fixed the fuel system. But he said to check under the removable cover under the car (where the original fuel exit is) Maybe I´ll find something interesting... But I don´t really feel like draining the tank and removing the sock if there is one tomorrow, my wife won´t be happy if I´m gone for most of the day and then return smelling of petrol from every pore!!!

I know what to do next, I´ll remove the large aluminum filter between the tank and the pump tomorrow, and look inside... And bring a bigger bucket so I can check the flow from the pump for a longer duration of time. If it also slows down, albeit less than at the carb, the tank is the culprit. If the tank is rusty, I feel like throwing it away and replacing it with a fuel cell...in PLASTIC!

Stefan

[yellaopelgt]

if I'm not mistaken there is a drain plug of some sort on the tank (old fuel outlet ect.....I'm not familar with the 73)since the car will be sitting overnight, all the sediment or rust or??? will have settled to the bottom. Which might explain the odd timing on when the motor studders since when driving everything is being sloshed around. drain the tank...and get it over with. You may get lucky and just find water in the gas??? Then systematically move up the fuel system until you find the culprit. 7 months of old gas sitting can do some weird things.....next year,fill the tank up and add some preservative before the winter storage.
HTH
Joe

[soybean]

Stefan, there is an easier way to drain the tank rather than from the bottom. Get a 12 volt electric fuel pump (cheap Kind), a 10 ft piece of fuel line. Cut 4 ft off, enough to get the outlet of the pump to a 5 gal container. Use the other 6 ft to the inlet of the pump and stick the hose into the tank from the filler neck. Hook to a 12 volt source and start pumping. You'll be able to get most of the gas out. Or a cheaper solution is the same amount of hose and siphon it out. There will only be a little gas left to contend with after siphoning most of it out. That's why the gas tank tops are lockable. As far as replacing the tank do a search for relining the gas tank. I did mine with POR-15s product and it's worked well. Here's the Link Hth, Jarrell

[StefanLee]

I thought about siphoning it out, but I am a little worried that it will leave a lot of crud in the bottom of the tank. Maybe unscrewing the bottom plug will "clean" the tank better. I´ll decide after I open the first filter after the tank.

Now I just have to find a large enough bucket or something for the gas...I just filled it up!

Stefan

[soybean]

Originally Posted by StefanLee I thought about siphoning it out, but I am a little worried that it will leave a lot of crud in the bottom of the tank. Maybe unscrewing the bottom plug will "clean" the tank better. I´ll decide after I open the first filter after the tank. Now I just have to find a large enough bucket or something for the gas...I just filled it up! Stefan

Stefan, that would be 11 gal US. Your best bet might be after you get it siphoned/drained out, to take the sending unit out and shine a light inside and see how much "crud" is inside and go from there. I have a feeling you're going to end up in the long run pulling the tank and cleaning it. Keep us posted on what you find out. Jarrell

[StefanLee]

I´ve broken new ground today.

Because of unforseen events (the wife) I could only work on it for half an hour. I went and bought some supplies for the car, including 2 meters of fuel hose and two clear new fuel filters among other things.

I started by siphoning about half a gallon of fuel (i tried to get the hose as close to the bottom as possible through the tank hole), to see if there would be "irregularities" in it. No particles at all, but a very small amount of water collected on the bottom. Ok...

Next up, removing the back wall exposing the tank and pump. I took a few snapshots with my cell phone to illustrate what the connections look like.

The first one shows the large aluminium filter that was between the tank and pump, and the new one I replaced it with. The pump is underneath the metal plate and the fuel enters from the right.



I wanted to replace the old filters with new, to see if it made any difference. Also, clear filters have a definitive advantage when it comes to determining fuel levels in the filters under load (more on that later...)

You can in the next picture see the connections on top of the tank.



The left connection is the fuel outlet, the one that is custom. I haven´t seen a GT tank with the exit in that location anyway. My assumption is that there is some sort of pickup reaching down to the bottom of the tank, possibly with a metal filter on the end. I won´t know until I look... If anyone of you GT-wizzes have seen anything like this before let me know! The fuel return is on the right.

The last picture is with both filters replaced, and this is where I tried the pump. I disconnected the fuel line at the carb, and stuck it in a small fuel bucket.



I observed the fuel filters, and I could see that the first one between the tank and the pump filled up but then quickly emptied. When repeated, it filled up and then emptied again. So, I have concluded (as you all expected) that there is a blockage in the tank. The sucking action from the pump forces fuel into the filter, but then the blockage prevents more fuel from entering and the pump sucks the filter dry.

Hmmm...

So now I have to read up on how to remove the tank! What black arts are involved in that?! Should I call an exorcist?! It looks pretty easy to remove the tank, but I bet there is a catch somewhere. It is never easy....

Comments appreciated!

Stefan

[tomking]

Why are you not pumping from the BOTTOM of the tank? I am not sure your pump can handle the suction load from making it pull out the top of the tank!!
When you turned on your pump after installing the clear filters, did you see the filters plug up with crud or did the volume just go down on the pump? If the latter I think it is likely you need to plumb your outlet from the tank Bottom, the original location.

[StefanLee]

I don´t know really. It was like this when I bought it.

There is a hatch fastened with screws underneath between the dual exhausts, and I expect that is where the original location is. I didn´t have time to unscrew it and see what it looks like. Perhaps there is just a plug there?

It has been like this for several years, and the previous owner had no problems with it. He was mechanically very adept and worked on other parts of the car, and I am sure he would have noticed if there was a problem with the fuel supply. I spoke with him yesterday and he said he knew nothing about it.

I can imagine it was done when the electrical pump was installed, and that was not yesterday.... Seems to have worked fine, or atleast satisfactory.

Stefan

[tomking]

Take an air hose and blow back into the tank with gentle air pressure. I suspect you have some piece of crud plugging the intake line. You will blow gasoline all over the place if you inject high air pressure. But this is only a temporary fix. You will have to remove the fuel tank and clean it out. Then I would repair the bottom outlet and plumb the fuel pump from the bottom outlet.

[yellaopelgt]

Just an observation......... I would agree that pumping fuel from the bottom of the tank would make things easier. Also, I dont think Ive ever seen a fuel pump inside the passengers compartment before!! The very thought of that just makes me very nervous!!! The fuel lines,filters,pump,all inside of a car(and I think you also said the battery was relocated inside??) is a recipe for disaster. If there is ever a leak or a fuel line failure your toast!!!There are many better locations outside/under the car for these things. Call me a worry wort but....
Joe

[tomking]

AND, search this site for locations for an electric fuel pump. It isnt where yours is located!!

[namba209]

Stefan, looking at the rear of the car, to the left of the left exhaust stinger, there is a hole in the belly pan. That is where the original fuel outlet was/is. To remove the fuel tank, it's pretty straight forward, there are two bolts on the side flanges of the tank. Remove the bolts and the filler neck hose, disconnect the vent lines at the filler neck, remove the filler neck, then lift straight up and forward. That's all there is to it.

[StefanLee]

Thanks for the replies.

I can understand your concern for the pump location, but there is a firewall between the tank compartment and the passenger compartment. And the fuel lines are copper tubes underneath the car, so there are no lines in the passenger compartment at all.

Also, the battery is lowered and enclosed in a locked steel box, as per racing regulations. It is not "in the open". It is all approved by the department of transportation.

I´m glad to hear it is easy to remove the tank...whew!

I guess my next move is to siphon the entire thing, examine the state of the fuel and the try to examine the inside of the tank.

Stefan

[StefanLee]

Siphoned the tank today, or atleast most of it. I disconnected the outgoing hose and blew down it with my lungs, and there was something large in there that popped out. It felt like a solid object, but could be a mass of debris, I don´t know.

I peered down the inside of the tank through the fuel gauge transmitter hole, but I could see only slight rust on the bottom, and no floating debris. I can add that the gasoline that I siphoned was completely free of particles. I did see a piece of old gasket on the bottom however, most likely from the fuel gauge hole. The gasket under the transmitter was intact, but it must have been an old one dropped into the tank. Could be the thing blocking the tube.

I could see nothing more of interest since there is a splash wall obstructioning the view towards the center of the tank.

Pump flow was excellent after clearing the blockage... The pump has no problem at all sucking fuel from the top

The car ran fine, and I took it for a test spin around the block, but as I expected the object got stuck again and I almost didn´t make it home. Ah well, I knew it...

Didn´t get around to pull the tank today, but will tomorrow. I´ll get some long instrument to reach down and pick up any object that I see, and basically see the condition of the tank once it is out.

Stefan

[yellaopelgt]

yes, if you see somthing down inside the tank, it "could" very well mean that its been there and disinegrated over time and very could well mean that there are other things down with it as well. I'm one of those (might as well get this over with/do it once) kind of people, so I'd dig into this and figure out what going on. Its not going to leave you alone until you fix it. Look on the bright side: at least you havent been stranded....or it hasnt done any real damage yet. You can still start it up and see whats going on.
good luck,BTW....it seems that every time you clean somthing out...you find another blockage.... best to do some digging.
Joe

[StefanLee]

Indeed.

I´m trying to figure out the best way to clean the tank completely. It doesn´t look like it needs to be treated for rust (don´t know for sure) but I need to get everything out that should´t be there...

After emptying it, I´ll take it out and turn it upside down to drain and hopefully some crap will flow out with the last gas. Or perhaps slosh some gas around to dislodge everything and grab it with a long tool... I´ll se if that bottom hole is plugged, perhaps I can get it open and push stuff out that way.

I guess I´ll wing it tomorrow and see what I end up with.

One thing is sure though, I´ll smell of gas when I´m done!

[StefanLee]

Tank cleaned!

It was a pain to get out... The reason for that is because my tank is modified with a lower bottom (larger volume) so it is a little tight to get out.

Anyway, the tank does not need to be treated for rust, the reason for the plugged line was an old rubber gasket that had fallen in the tank, the one I saw when I first removed the fuel guage sensor. The rubber bits plugged the fuel pipe that is in the tank, so no fuel.

I took it out, sloshed fuel in it and cleaned it completely from debris, now the car runs like a dream. Phew! Basically an easy fix.

I can post a picture of my frankentank if it is of interest to anybody, I also have a large drain plug in the center bottom of the tank, handy for well...draining.

Thank you all for the comments and suggestions you have given me.

Stefan