Classic cars forum & vehicle restoration.

[vitesse]

I am rebuilding a Polish Built Fiat 650cc engine with a mind to either fit in my Fiat 500 or sell on but I came across a bit of a problem with the carb.

You can appreciate these are not the biggest of carbs around and this particular one is made by a company in Poland called FOS but is based on a Weber carb the 28IMB. Apparently made under license in Poland and rebadged.

Anyway I bought a rebuild kit from a company in Germany. It came with a new spindle and butterfly. So I tried to undo the screws on the carbs butterfly and both of them sheared off. In the end I had to drill them out to remove the butterfly, so that I could remove the spindle from the carb body. On taking the spindle out I discovered that the one inside the carb is a much larger diameter than the new one and will never fit.

As I had to drill the screws out it meant even the new screws supplied with the kit are now too small. I could drill out the old spindle a tiny bit more and tap it but the only screws I can find are massive in comparison to the old ones. I assume if the heads of the screws are too big it is going to affect the fuel and air supply to the cylinder???? You thoughts?????

I can't find any spares for this FOS carb despite searching the Internet because everything is in Polish, even searching for Gasnik Polish for carb finds nothing.

In the picture below the old spindle is the one at the bottom of the picture. The new one has a recess for the screw to sit in, so it has less resistance to the flow. The black screws came with the new spindle the brass one is that I have that I could tap the spindle out to take.

Tony

[ka]

Looking at the spindle/butterfly in the SU, I do not think there will be a major problem. In the SU, the head of the screw is butterfly side, with the threads protruding through the spindle, simply split in half, and levered part. These must provide a disturbance in the air flow, but a minor issue compared to the restriction from the spindle and butterfly itself.
I was told that the quoted size of the SU, is actually less than the measured size to account for this restriction, i.e. a 11/4" is quoted as being an 11/8".
But short answer is, I do not think you will notice any difference.
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KA

Better three than four.

[ukdave2002]

Have you considered fitting bushes to the carb body to allow the new spindle to fit?

Dave

[vitesse]

Ok thanks guys. I guess the only answer is try it and see.

I dont think I could fit bushes in there Dave as there are little plastic seals at each end to prevent fuel/air loss.

The other problem again is unless I can split the screws at their ends to prevent them coming out, there is always the risk of a 3p screw doing some engine damage if it works it's way loose. Mind you I did find the little screw on adaptor of a spark plug inside the cylinder on the 500 and it hadn't done any damage it was just very shiny.

Tony

[colwyn500]

I don't know about the 500 carb. but usually throttle butterfly screws are peened on the ends to make them secure and so that even if they get loose they can't fall out.

It's fiddly but perch the head of the screw on an old screwdriver or the shaft of one in a vice and using a fine tipped centre-punch, carefully deform the end to clench the screw in place.

[vitesse]

[Penguin45]

If it's a brass screw, slot the end, fit, then open the slot. No impact required.

P45.
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'67 Wolseley MkI 18/85, '70 Austin MkII 1800 The Landcrab Forum.