carb tuning on 28's

[speedfrk]

Greetings, I've been reading this forum for a long time and just registered because I need help from the carb gurus! I have 4 RZ350's and all 4 of them came to me in different configurations. All 4 have different pipes and carbs. One of them has a set of Bassani pipes I'd never seen before.
Anyways, the bike in question is an 85 US bike that has DG pipes, and a set of Mikuni 28's with oil ports. Also has a Toomey Y filter. The bike runs OK but has the nasty stumble from 4-6K and then goes like hell to 10K. I need to tune out the stumble so I took the carbs apart to see what was in them. Mains are 320, Pilots are 25, Needle is non-adjustable 5CK1, floats are at 21-22mm. The only number I could find on the body was 1EL00. I don't know what they came off of. Trying to decide how much time I want to spend playing with them or if I should just get a set of stock 26's and jet them like my Canadian R model which runs great but doesn't have the top end that this bike does. It is a street bike, so ridability is more important to me than top end.

[85RZwade]

1EL is the prefix for a California model RZ, but I don't think they had bigger carbs than 48-state bikes, so? A non-adjustable needle would seem to indicate an OEM fitment carb, which might make sourcing brass more difficult. If your budget allows, an aftermarket set of mixers might be easier to source replacement parts. Having said that, the carbs you have should be tunable with a little research. Maybe post a picture or two of them to help with identification.

[Srhiskx]

If they are OEM carbs, try a Dynojet jet kit. They are on eBay for less than 60.00 for the RZ.
Then you have adjustable needles and can tune that stumble out. Are the carbs linked together with push pull throttle cable system? They would be just like the std carbs from the other US RZ carbs.

[speedfrk]

Here's a couple of pics...

[Srhiskx]

Those look like std US carbs. Go with the Dynojet kit. They have great instructions on how to tune with the kit. You can look in my signature for the spec on what I’m running in my RZ.

[speedfrk]

But these are definitely 28's not 26's so I'm not sure the jets and needles/slides would be the same... I have another bike with the 26's and they have some differences like the vacuum port on the side (red cap). I'll try contacting Dynojet on Monday to see what they say.

[kpke]

Why do you say they are 28 not 26? That is a set of US 26's.

[tacky1]

I think Europe used some of the sane carbs, but they are 28s Ken. Take a look on the euro ebays and you will see these for sale.

[silverstrom]

Is it not better to simply bin them and buy a pair of Canadian carbs?

[speedfrk]

I measured them with calipers. They are 28's but the OD of the throats are apparently the same as the 26's since the filter and manifolds fit perfectly. The rt carb does have a large vacuum port on the side that the stock 26's don't have. Maybe they are from a marine application or something.

[speedfrk]

Is it not better to simply bin them and buy a pair of Canadian carbs?

Yeah, that is the question. How much time and effort will it take to get these right vs buying a set where the baseline jetting is already known. I'm certainly open to that if I can find the right carbs.

[speedfrk]

Another question... how much should I expect to spend on a set of good stock US or Canadian carbs?

[MK]

Take into account that there's no guarantee that you have unmodified stock carbs.
There's always people boring out carb bodies to a bigger size.

Up to my knowledge all RD350YPVS had 26mm carbs. Different jetting, but all 26mm.

[waltmil]

I think Martin nailed it, these are US California carbs that have been bored to 28mm. They look to be in pretty good shape except for the dent in the mouth of the right hand carb. Probably the cheapest solution would be the Dynojet kit.

[speedfrk]

I think Martin nailed it, these are US California carbs that have been bored to 28mm. They look to be in pretty good shape except for the dent in the mouth of the right hand carb. Probably the cheapest solution would be the Dynojet kit.

They are in great shape and super clean. The brackets did not have all the original screws, some were missing washers, etc. The reason I don't think these are stock carbs is the very obvious, very large vacuum port on the rt carb. I don't think this was added and it's hard to imagine why someone would add it since it would just need to be capped off like it is.