Just looking for a carb part on eBay I was stunned how many of the reproduction carbs are now flooding the market. So just a reminder that after my lockdown project I have reconditioned carbs to suit most 500 models. 26IMB 4 for the D models, 26IMB 6 for the F and 26IMB 10 for the L models. Proper Italian made carbs.

A guy not on this forum contacted me a week or so back. He had been running a nice 500F with what turned out to be a carb from a 500D but not happy with it he bought a brand new carb from eBay. Now it runs even worse

My Lusso came with a Polish licensed 28imb. It was a nightmare. I never did get it running right and finally bought a Spanish built Weber. Fired right up and purrs like a kitten now. I can’t say it was specifically the original build quality of the unit, but I cleaned and rebuilt every damn part of it more than once to no avail.

Veloman518 said:

My Lusso came with a Polish licensed 28imb. It was a nightmare. I never did get it running right and finally bought a Spanish built Weber. Fired right up and purrs like a kitten now. I can’t say it was specifically the original build quality of the unit, but I cleaned and rebuilt every damn part of it more than once to no avail.

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That is refreshing to hear and the first positive thing I have heard said about the repro carbs especially as many have been made under official license in Spain. I have never got my hands on any of these so have had to rely on what people tell me. I had a look through the eBay selection of 26 & 28IMB carbs. There are big variations in prices, one or two dubious listings and some that do not even claim to be Weber carbs as they are Chinese copies.

Toshi 975 said:

That is refreshing to hear and the first positive thing I have heard said about the repro carbs especially as many have been made under official license in Spain. I have never got my hands on any of these so have had to rely on what people tell me. I had a look through the eBay selection of 26 & 28IMB carbs. There are big variations in prices, one or two dubious listings and some that do not even claim to be Weber carbs as they are Chinese copies.

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The only real difference I see on the Spanish 28 is there is no fuel filter on top anymore. It's just a solid cap.

My Polish unit may have just been worn to death. The butterfly shaft was wonky and it's possible the mixture screw had been turned in too tightly at some point. Top and bottom were warped. I sanded them flat, replaced the spindle (thanks to Hobbler/Tom) soda blasted, ultra-sonic cleaning, all new jets and gaskets and still ran like crap. Couldn't ever get the mixture right and it created all sorts of issues. The new one has been flawless so far.

I had routed a fuel return into the fuel circuit on my previous one to deal with vapor locking in the hot weather, but I removed it during trouble shooting. With the new unit on I will wait and see if I have any issues driving this summer and hopefully can just keep it off.

For a small carb they do suffer from more than their fair share of problems and you seem to have had a number of them. Spindle wear is one of the worst problems especially as it is the carb body wears the most. I have rebushed a few carbs to overcome this making and pressing in a small duralumin bush. Bottom mounting flange bending is very common but can be sorted but it is important to use good gaskets and that the Bakelite spacer is in good condition. Probably the worst thing is the secondary venturi working loose and wearing away itself and the carb main body. Brass floats can develop hairline cracks, brass inlet ferrules can fall out, inlet valves can wear and stick, top covers warp, stripped threads is so common and so on and so forth.

Toshi 975 said:

For a small carb they do suffer from more than their fair share of problems and you seem to have had a number of them. Spindle wear is one of the worst problems especially as it is the carb body wears the most. I have rebushed a few carbs to overcome this making and pressing in a small duralumin bush. Bottom mounting flange bending is very common but can be sorted but it is important to use good gaskets and that the Bakelite spacer is in good condition. Probably the worst thing is the secondary venturi working loose and wearing away itself and the carb main body. Brass floats can develop hairline cracks, brass inlet ferrules can fall out, inlet valves can wear and stick, top covers warp, stripped threads is so common and so on and so forth.

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The maddening thing is it might be one of the simplest carbs I have ever worked on but so many gotchas. I've got a '52 MG TD with SU's that I haven't had to touch in years. My Honda CB750 has a quad carb setup that I completely rebuilt with no issue. This thing was making me bonkers.