Leaking carburetors on a 1974 1.3s

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ThomasW
Posts: 36
Joined: 10 Jul 2017, 10:43

Re: Leaking carburetors on a 1974 1.3s

Unread post by ThomasW »

OK, thanks. All the pump casting parts I can take of, I will sand them lightly on a flat surface using very fine sandpaper to be sure they are flat, otherwise I will use a file as you suggest.

May be I reuse the old gaskets between the pump body and the carbs itself, they were pretty good and I slighty doubt the thickness and material of the new red ones as well. When I get the carbs of on the bench I will poor some fluid (spirit of some sort) into the chambers to see if the seals on the bottom are good.

I was checking this: http://www.viva-lancia.com/fulvia/qanda/carbs/leak.php and got into the last paragraph were Huib tells about the two plugs. I have checked these and blew them trough with air altought I did not check the steel balls, have to do that as well. Can you explain what the function of these plugs is? I understand the 'valve function' of the rod and ball below, but I am not sure if these plugs move or what the function is, when are they engaged of disengaged?

The attached image may come in handy to name and identify the parts.
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bmarler
Posts: 110
Joined: 22 Dec 2008, 17:33

Re: Leaking carburetors on a 1974 1.3s

Unread post by bmarler »

if you only got the red gaskets you may be stuck using them. getting the mating surfaces flat be be critical though.
the plugs you refer to are for sealing the output from the pump. they are held stationary by the top casting of the carb. under the plugs are the balls and weights of the check valve. if these don't seal well the output from the pump won't be as much as desired. if the o rings on the plugs don't seal well it may be possible for fuel to leak around them and possibly leak out of the carb. i think that's what huib is saying, but i'd have to pop the top off a carb to see the route the fuel would take.
when putting the carb back together, is is best to test it on the bench. i hold it in a vise and put fuel in the bowl either with gravity feed to the inlet, or with an electric low pressure pump. this enables you to check the float setting as well as check for leaks. you may also fit some tubes on the accelerator pump nozzles and route them into a graduated cylinder to measure the pump output. there is a special tool to fit on the carb to measure this, but i only do carbs for me, so i use the tubing intended for fuel hose to my weed whacker. it fits well and doesn't leak.
'67 fulvia sport, '61 appia vignale
ThomasW
Posts: 36
Joined: 10 Jul 2017, 10:43

Re: Leaking carburetors on a 1974 1.3s

Unread post by ThomasW »

Ok, thanks a lot for your answers! I got the Fulvia running again and the leaks are gone..

For future reference, here's what I did:

I got the carbs of the car again and removed the accelerator pump castings to check their flatness. I got a flat board, make sure its completely flat (a mate tipped me to use a piece of glass/mirror, didn't have it), on top of that I used fine 800 and 1000 sanding paper to smooth out the pump castings by just gently pushing down and sanding them on the paper in circular motion. Using the 800 first and then the 1000 paper.

Visible in picture 1 and 2 you can see the before and after results. In picture 3 you can see the bright part showing after the first sanding action and it is on the corner, showing that the darker bits that do not fully seal..

When it comes to the upper mating surface of the pump housing and the underside of the carb (picture 4) itself it becomes a bit more precise to sand this smoothly, here is how its done: use a piece of the same flat board and cut/saw this to a size slightly larger than the surface on picture 4. Put a piece of the sanding paper around it and use this are your sanding block, going again in circular motion over the surface on the carb bottom until it is shiny. For the upper side of the pump housing use the side of the sanding block you've made.

Important piece of advice is to watch the aluminum dust that is created by the sanding, best time to do this of course is before cleaning the carburetors. I used a can of computer duster to blow of the dust every once in a while.

In my case I decided to put the old gaskets between the carb body and pump back to be sure however I believe that the thin red ones would have made a good seal as well after sanding them.

So, the car runs again, now it is time for further tuning of the carbs..:)-D
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Huib
Site Admin
Posts: 1778
Joined: 17 Dec 2008, 10:12

Re: Leaking carburetors on a 1974 1.3s

Unread post by Huib »

Good job. Compliments.
bmarler
Posts: 110
Joined: 22 Dec 2008, 17:33

Re: Leaking carburetors on a 1974 1.3s

Unread post by bmarler »

excellent work thomas,
glad to have been some help to you. i recently received a great deal of advice regarding these carbs too, and this is my way to pay it back.(forward?)
now go drive the car...
'67 fulvia sport, '61 appia vignale
bmarler
Posts: 110
Joined: 22 Dec 2008, 17:33

Re: Leaking carburetors on a 1974 1.3s

Unread post by bmarler »

as an update to this thread, i've noticed that the new red accelerator pump membranes don't last as long as the originals. the carbs i went through about 5-6 years ago are both leaking at the accelerator pump. i've been careful to only use ethanol free fuel, but can't be 100% certain there's not been any ethanol, as i've not done any testing. these carbs have been sitting all winter, so maybe that comes into play as well.
'67 fulvia sport, '61 appia vignale
marnix
Posts: 53
Joined: 15 Dec 2015, 21:29

Re: Leaking carburetors on a 1974 1.3s

Unread post by marnix »

I didn't read all the replies to this, sorry. But a quite common other cause is the float being stuck inside in a low position (after the float chamber has dreiied out, and the fuel level dropped low). The float valve needle doesn't close then, and the carbs flood rather heavily.
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