No lurching noticed yet !
Smell of petrol also !
Will give it another few days and see how it goes.

In the words of Ferry Porsche---'if it aint broke, don't repair it' so if the car is running well, idling well with no smell of petrol, leave it alone and just keep a watching eye on it.

Hi there,

I am sorting out some issues with my freshly restored car.
The car idles beautifully but will stall when pressing the gas /accelerator.
The ignition timing looks to be set ok, so I suspect the carburator which is a weber 26 IMB.
Would any of you have an idea about what could cause this issue?
Looking forwards to your suggestions.

Check for vacuum leaks around base of carburetor. Spray some carburetor cleaner or starter fluid around the base of the carburetor while the engine is running. If the idle speed increases, you have a leak. You may have a plugged jet or passage inside the carburetor. The mixture may be adjusted too lean. The carburetor float may be set too low or is binding (not enough fuel in bowl).
Probably best to just take the carburetor off, clean, blow out all jets and passages, and replace all gaskets. Not that hard to do.
John

Thanks John,
I will take it apart and let you know what I find.

Rene

I took the carb apart and found that it was very dirty, seals were leaking and the float setting was way of. Needless to say that the car, after rebuilding the carb, runs much better now
Thanks again.

Quick question in the hope that somebody knows the answer.
What is the difference between a webber 26 IMB3 and 26 IMB1?

reneb said:

Quick question in the hope that somebody knows the answer.
What is the difference between a webber 26 IMB3 and 26 IMB1?

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The IMB1 is the original carb used on the 500N and early 500D models. Rare carbs to find in good condition these days. Tha IMB3 is the ultra rare carb which was fitted to the 500 Sport models. It had a slightly larger Venturi than all the other 500 carbs and ran with a larger main jet.

Would the larger Venturi and main jet of the IBM 3 fit in the body of an IBM 1?
My car has the IBM 3 but the body is badly warped. I can find an IBM 1 carb but nor a 3. Could I swap the parts?

reneb said:

Would the larger Venturi and main jet of the IBM 3 fit in the body of an IBM 1?
My car has the IBM 3 but the body is badly warped. I can find an IBM 1 carb but nor a 3. Could I swap the parts?

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Where is it warped, bottom flange? If so there are several postings on the forum explaining the procedure of how to recover from that. I think I'm right in saying Toshi is the go to guy for this. Hope this helps you.

Carb is indeed bend at the bottom flange and the top cover.
I saw the posting about straightening thing out but am just looking at other options too.
As mentioned, the car came with the 26 IBM 3 carb (have the 004 sport engine) What other carbs could I use. Can I use the 28 mill carb from the 126 for example?

I guess that it comes down to how much you want to retain the original parts and engine specification. You could fit any of the other 26IMB carbs from the 500 range which would be a slight detune on a 500 sport engine but look original. The 28IMB carbs from the 126 have a Venturi 1mm larger than the 500 Sport carb and with the right jetting may give a tune up but it is a straight bolt on and would probably benefit from a modified Bakelite spacer.
Personally I would do my utmost to revive the original carb as the bottom flange can be sorted with care. Top cover can be replaced if necessary. The Venturi size is machined into the main body so cannot be exchanged. Some standard size carbs have been refurbished and the body bored out to match the 500 Sport carb but I do not know if there are any available at the moment.

Thanks for the info. I am learning a lot about these weber carbs through this forum. I did not realize that these 26 IMB 3 are "rare" and as such I will try to repair this carb. and keep the car original.
If that fails I am considering the 28 IMB carb since I definitely do not want to reduce power by going to a standard 26 IMB 10 which are readily available! This car is new to me and I am finding out more about it every day. Compression for example is higher than original at about 125 PSI so I trust that a former owner did some work to the engine.
I guess it is therefore safe to assume that the car may benefit from a little more carb.
If you have more suggestion on jet sizing I would welcome the info or any other suggestions you may have.
Thanks again

I have never had the opportunity to work on a 500 Sport engine so they are a bit of an unknown to me. I did see in the manual that the engine had an 8.6-1 compression ratio compared with the 7.1-1 on the D models. The Fiat workshop manual only shows drawings of the standard engine but at a guess I would say that they ran high compression Pistons. I do not know if an illustrated parts book exists for the Sport as it would be most interesting.
The early 126 carbs shared a lot of the same jet sizes with the Weber 26IMB3.

Thanks Toshi,
So my plan is to revive the 26 IMB3 carb. If that fails I'll install the 28 IMB which is probably a better match to my engine than a standard 26 IMB 10.

I'll give you guys an update after I am done. Can't wait to have this Autobianchi Bianchina Transformabile back on the road.

I was able to sort out my Weber carb 26 IMB 3
The bottom flange was severely bend as was the to cover.
I was able to get most of that corrected by squeezing them in a vice between 2 smooth metal plates.
I ended machining the bottom flange to get it perfectly straight.
New gasket did the rest.

Glad you guys convinced me to save this carb which is irreplaceable and original to the car.

The information on this forum was very helpful in the process.

Thanks again

That is great news

Out of the blue, I have just (today!) been given a copy of the early 'Haynes' workshop manual for the 500--which includes the '500 Sport'. Would you like me to go through it and see if I can come up with any relevant info regarding the car, and particularly the carb?

JakeF said:

Any gasket or o-ring etc(red arrow)?

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Unfortunately my repair kit didn't include this little seal. So i have put epoxy glue all around to seal it. Is this part avail?

gordinir8 said:

Unfortunately my repair kit didn't include this little seal. So i have put epoxy glue all around to seal it. Is this part avail?

Click to expand...

You could use an 'o' ring from one of those inexpensive selection boxes but it's likely to be made from a type of rubber (Butyl?) that not Ethanol resistant. I think you ideally need the Viton type? But in this application, you might get away with the cheap type?

Another source of small rubber type 'o' rings is motorcycles, especially older Japanese ones, they supply lots of O rings in engine gaskets sets and carb kits

Al.