VM26SS or VM28SS

[Greg65]

Hi all,

A new member from across the pond.

I have just acquired a eBay GS1000 1978. The bike has very poor running due to badly maintained carbs. I have stripped them, found two with the rear air metering screw snapped and blocked (the fine needle pointed one) and sourced two additional bodies. Now in theory the original carbs are assumed to be 28's however are they? The additional bodies are of eBay and physically the same size. The markings on the manifold flange are as follows.

Orignal carbs. B853/49C10
New! carbs. B827/45C30

What have I got?

Thanks, Greg

[hampshirehog]

The only way to tell is to measure the carb outlets. The internal diameter of the carb on the cylinder head side is 28mm (plus a bit) on VM28s and 26mm (plus a bit) on 26s.

[Greg65]

Thanks. Mine are 26 plus a bit, so that resolves one question. I'm looking at NRP kits. They are out of stock as far as 26's go are the 28's just a different jet size?

[hampshirehog]

I wouldn't buy carb kits, just the bits you need which in your case just sounds like the airscrew - or do you mean the fuel screw as those are the ones with the very fine tips that get broken? Plus renew all the o rings (google cycle o rings; the guy who runs it is a member here and is top drawer.

[Nessism]

Have you seen this information on removing broken pilot fuel screw tips? http://members.dslextreme.com/users/...ew_removal.pdf

[Greg65]

Thanks for the link Nessism, good reading. While looking for info on the 26/28 identification issue I found an opinion that says the 26 has only the one airscrew on the side whilst the 28 has two! In addition it's the internal size of the hole by the slide valve. The hole is in fact an oval and the 26/28 refers to the area covered by this oval in mm squared. Can anyone give an expert opinion on this. Oh the joys of caburation.

Thanks all

[Greg65]

The carbs have come out of the ultrasonic cleaner and I can now read some stamp marks on the manifold/engine side of the carb. They are as follows,

Original carb's B853 49C10
Replacement carb's B827 45C30 or 45O30

Are their any Mikuni decodes?

[hampshirehog]

Thanks for the link Nessism, good reading. While looking for info on the 26/28 identification issue I found an opinion that says the 26 has only the one airscrew on the side whilst the 28 has two! In addition it's the internal size of the hole by the slide valve. The hole is in fact an oval and the 26/28 refers to the area covered by this oval in mm squared. Can anyone give an expert opinion on this. Oh the joys of caburation.

Thanks all

The 26 / 28 spec comes from the diameter of the venture - and that's approximate. That's how Mikuni size their carbs. Both carbs are 'the same' (apart from size) plus the 28s, as fitted to the GS1000, have a different choke activation set up. Both carbs have one airscrew and one fuel screw per carb.

The codes stamped on the bodies are, I believe, to do with the batch run.

[Greg65]

Thank you for the wise words.