I got distracted this week looking for some carb jets and going through a box of Fiat 500 carbs I came across a 500N Weber 26IMB 1 which must have been in a job lot of parts I bought. As I believe these original carbs are quite rare I have fixed and rebuilt it. I thought I would mention it here in case any forum members were interested.
General Weber 26IMB 1 for 500 Nuova
- Thread starter Toshi 975
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General Weber 26IMB 1 for 500 Nuova
Whats the difference between that and a 500L 26IMB?
I am missing the carb on my D, but was looking at using the one from my original 500L.
I am missing the carb on my D, but was looking at using the one from my original 500L.
OK from the running point of view no difference at all as all the jets and internals are the same, as are the working dimensions , Venturi etc. The main differences are in the butterfly spindle which only has one return spring and the top cover and upper carb body as the stud holding the inlet elbow at the front end mounts into the top cover rather than passes through it into the body. Butterfly linkage lever is also a different design as well as the idle jet screw.
I guess that this is one for the purist who might want total originality but there are not that many people out there who would know the difference I think.
I guess that this is one for the purist who might want total originality but there are not that many people out there who would know the difference I think.
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Esteemed gentlemen,
From the Workshop manual.
Looks like the IMB 1 was used in limited numbers on the original 479cc engine and the IMB 3 on the 500cc Sports upgrade.
None listed on that commercial gold standard eBay, so possibly quite a rare find.
Chris
From the Workshop manual.
Looks like the IMB 1 was used in limited numbers on the original 479cc engine and the IMB 3 on the 500cc Sports upgrade.
None listed on that commercial gold standard eBay, so possibly quite a rare find.
Chris
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It was a fairly sad looking thing when I pulled it from the box of 500 carbs. Bowed bottom flange, bowed top cover, the two top elbow mounting studs had been stripped and ugly bits of studding glued in and a few bits were missing. However having rebuilt a quite a number of thes carbs in the past I checked a couple of things. There was no structural damage, there were no signs of wear on the butterfly spindle or on the pivot pin and support posts for the float. So I could so that whilst the carb had had some rough treatment it had not had that much use. Everything now cleaned up, bowed bits straightened, helicoils fitted to top cover and replacements found for missing parts. Checked out the other carbs this morning. I have a 26IMB 4 , a 6 and 5 IMB 10s. The IMB 4 has the same top cover arrangement as the 1 but double springs on the butterfly and the later type throttle arm. The IMB 6 looks pretty much like the 10 but a slightly different idle jet.
With all the chat about carbs and conversions going on at the moment I thought that I would mention some of my experiences with the original Weber 26IMB carbs and bringing them back to good working order. I have yet to find a used one that had a flat mounting flange and many have a deformed top cover. Stripped threads for the inlet elbow studs are common. With care and helicoils these problems can be fixed. The problem I had with the IMB 4 was the excessive wear on the butterfly spindle with an oval hole in the body. Seemed a shame to scrap an original 500D carb so I got some 8mm dural rod and made some bushes with a "just under" 6mms hole. Drilled out the body so that the bushes were a press fit then reamed out the body holes with a 6mms reamer. With a replacement spindle it is now back to being like new. So unless your carb is physically broken there is a lot that can be done to bring them back to scratch.
