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I took the story below from a list (with Kari's permission). It is not directly about Fulvia carbs, but it does give valuable information.
Sonny put a question on the list about putting different carbs on a 124 spider. Shaun read the question and passed it on to Kari, who then answered the question. When getting Kari's permission to put it on this website, I had to promise to correct his english grammer. We need more of those guys who know more about carburetors than about english.
Note, that the S1 Fulvia does not have a fuel return line. The S2 and 3 Fulvia's do have a fuel return line.
Let's hope that Kari does find some time to add some notes about the Fulvia carbs.
BTW, Kari lives in Phoenix, Arizona. I used to go to Phoenix often in the seventies. One of my favourite places.
Question asked by Sonny
I replaced the stock 28/36 DHSA carburetor with a 32/36 DFV carb on my (currently stinky) 124 Spider awhile back. I have a few that I hope you all can answer:
The original carb had what looked like a "pressure release" line that was T'd in almost right next to the inlet on the carb itself. A hose connected the outlet of the pump to the inlet of the carb. Then a hose went from this pressure release line to the metal return line back to the tank.
The DFV does not have this. It just has an inlet...but, I don't think I can just run the fuel pump straight in there, can I? I'm sure that under some conditions, the pump will pump too much fuel and that excess fuel has to go somewhere, right? This scenario was one of the more difficult problems
t o solve when shifter-kart racing (my other hobby) started getting popular. The excess fuel would force the float down, causing the engine to mometarily bog. This situation is often remedied using a 'Y' before the carb. One leg of the Y goes to the carb, the other goes back to the fuel tank (with appropriately sized restrictor).
The fuel filter I'm using has two outlets...a fat one that I send to the carb and a real skinny one that I send to the return to the tank. I'm wondering that if this filter is plugged, will that cause a problem? All of the fuel will go right to the carb, right?
Secondly, I'm looking to rebuild this carb this weekend and I have all of the parts. Reading through the Haynes Weber manual though, it looks like I need a special reamer and another special tool to remove the venturis? Can I get those at a local parts shop or are there other things I can use?
Answer from Kari (through Shaun)
I expect that this will answer most if not all of your questions:
"Okay.. tell him that the reason early non-emissions Webers only had an in line and not a return is that Webers require fuel pumps that only use 2 pounds of pressure. He needs to make sure he has a fuel pump made for European specs and will do this. A stock American after market fuel pump puts out up to 7 pounds. Facet makes two fuel pumps for example, they look them same except one has a red label and says it is American and is for 5-7 pounds and one has a blue label and says it is for European and does 2-3 pounds. I'm not sure about Purolator (though I actually think they are better after market pumps than the Facet).
Okay when Webers used a T system for fuel return, they used one way limiters on each line so that the fuel couldn't try to back down the wrong way and they used a pressure limiter on the in line to keep it low and a minimum pressure on the other line. These are innocuous little jobbers in the middle of the fuel line and they generally disappear on cars over the years. They might still be available new.
Rebuild: Assuming the carburetor isn't in really nasty shape, he wont need a reamer. He may not even need a rebuild kit, they often don't. He wont need a tool to remove the venturis either. To remove the venturis, use a wood handled screw driver and press gently from below (probably have to be a smaller electrical screw driver and he will have to open up the bottom butterflies to do this. If they aren't to stingy you can gently use pliers to pull them up from below. It is an aluminum piece though so if any forcing has to be done make sure its from below and with something that will distribute force evenly. They have little tiny wheels on them so once they are broken loose they will be fine. I always put a little dab of Teflon oil on the wheels when they are out and I've never had a problem pulling them out a second time, just push them with my finger from below. That's assuming he is referring to the little airplane winged round things in the middle of the venturi.
Never remove the bottom butterflies, if they have to be taken off it probably needs to be rebuilt by someone who specializes in Webers. If you remove the top butterfly, do it only under the most direst of circumstances.
There are two ways of cleaning up the carburetor for the non invasive way I take it to a sink and use gunk foaming engine cleaner (the least humanly toxic engine cleaner I've found and yet oddly one of the most effective) and soak it over and over again.. using a nylon brush to clean up the outside and the inside. Clean it out with water and then clean the water out with carburetor cleaner. Remove the all the different jets and emulsion tubes and whatnot one at a time (so they don't get mixed up) and use carburetor cleaner. To test the float, clean it gently and shake it to see if there is any fluid in there, then submerse it in water and rub it gently.. air leaks should in theory occur. Also try leaving it submerged for a half hour and repeating the shake test.
The other way is to remove all paper gaskets and anything rubber or brass (make sure you label where each jet, emulsion tube, etc. came from). Then put it in a can of carburetor dip for a while. Now be careful with the carburetor dip as it is the opposite of the recommended engine cleaner. It is so nasty I've had one droplet land on me and burn so badly I had to immediately run and wash it with soap and water. So be careful and gentle with the stuff. It should be about 12$ a can. Get a good nylon brush and use it to gently(!) clean the carburetor while dipping it. When done rinse it well in a dip of paint thinner or carburetor cleaner. I often do both several times. I only recommend using the carburetor dip if the carburetor is especially nasty and corroded and covered in cooked oil.
When you remove the top of the carburetor you will be able to see if the paper gasket is in good shape. When you fill the bowl with carburetor cleaner you should be able to depress the throttle and if fluid squirts out of the bottom, then you know you don't need a new pump diaphragm. If these are bad a new kit should be about 15$ and is probably available locally (though they may have to transfer it across town or something) it will include a new paper gasket, diaphragm gasket, schematics (id love to have a copy of those), float perhaps, and any other miscellaneous gaskets they thought might be needed.
There is an excellent chance you wont need a kit. I've pulled carburetors off of 30 year old cars that were so nasty and covered in cooked oil I had to use the dip that didn't need a kit. Only about 1 in 7 of the Webers I get in junkyards need them. I've also never got a carburetor that needed professional rebuilding.
When putting it back together, use Teflon oil and oil every moving part sparingly.. the throttle will be much smoother and everything easier to use. None of the gaskets require any silicone or anything, excepting the bottom one between the manifold and the carburetor and only then if its been put back on and is showing signs of air/fuel leakage. The carburetor is probably held on studs with 13mm nuts, don't be afraid to replace the flat washers with wave washers.
Shaun, which donor car did he get this carburetor from? Early 6 cylinder BMW's have two cousin carburetors on them, Opel GT's have one of them, VW Weber conversions usually have these on them, and early Pinto's and Mustang II's have them or Carter clones. Id love to find out what else has them. Also what list is this from?
Kari - email@example.com.
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