TOPIC:

36's are def too big for a 1075 street motor. it will run fine but u will sacrifice bottom end for top.
More main please.

Ok guys, did some more work on the carbs last night and found something out kind of interesting. I fibbed to everyone just slightly; I thought I had 115s in it but they were actually 120s... As I said, until just a few days ago I hadn't even messed with these carbs in over a year. I didn't remember changing the mains out but I did.

Now for the interesting part. I have 3 other sets of carbs for my bike. 2 are Mikuni VMs, one being a set of regular 26s, and one being the original set of 28 pumpers. Also have a set of Mikuni BS34s. Now, I popped the bowl off of my VM 26s to see what mains I had last left in there and I noticed something very odd... the mains' heads were very small in diameter compared to my RS's. Also smaller than what I remember as I'd played with the VMs many times in the past. So I popped a bowl off my 28 pumpers because I knew for a fact that I had left these carbs in their stock configuration since they are the correct carbs for my bike. It has the regular outer diameter head mains in it (their fuel size being 102.5s). So I popped the bowl back on the 28s and put them away and then it slowly cam back to me; I HAD changed the mains out when I first got these carbs (the RSs), a closer look at the small diameter mains revealed why; they're 145s!!

So my question for you guys on this is; do the RS carbs have their own special main jets or can I use any standard Mikuni mains that work in the VM series carbs??? A quick comparrison showed them to be identical in height and obviously the threads are the same as I wouldn't have force threaded them into my carbs. The only real difference I can see is the outer diameter of the head. Does this matter? Are you guys running standard Mikuni VM mains in your RSs?

All that being said, I re adjusted my pilot screws for an 1/8th turn out (instead of 1 full turn) after being told and reading that they can only usefully turn out a 1/2 turn anyway. I did a rough float height adjustment to 17mm as given in the RS manual vs. the 19mm that was in the other manual I was using (I will get to using the clear tube soon), and did rough sync using a couple ball bearings rolling through until they all dropped at the same time. I don't have a vacuum gauge so that may be the best that parts going to get for awhile. I also stuck the "original" 145 mains back in them and put the 120s back in my VM26s. I know, I know, those are GROSSLY too big for my bike but thoughts are that they won't prohibit the jet needle/needle jet in the overlap area of the throttle. Anyway, I want to get some 130s for them (since I was already running 120s) but I wanted to find out about this head diameter thing first. I didn't test the bike last night, just put it all back together and ready to test tonight. It was cold and rainly here last night as it has been for the better part of a month now...

Let me know on the main jets guys... I hope theres no difference and I can just use VM sytle mains as they're much easier to come by!

by changing the float level from 19 to 17mm u have enriched the mix. i would try the same 120's again and see what it feels like. 130's are tooo big.
i dont know the correlation between the dif mik jets but i would strongly suggest using the proper jets.
Dyno jets look the same to but they run richer than mik's.
bench float height and slide height's will be good enough to get u going. the slide height affects cruise speeds the mostly, the float height will affect everything.

Good news! The adjustments worked out. The bike is damn close to being right now and believe it or not runs MUCH better on those 145 mains! Its actually RIDEABLE now as long as you don't constantly full throttle it from low RPMs. Obviously not right, still some stuttering at the top end, but of a different nature and a quick look at the plugs after a little 2 mile jont shows what we would of course suspect; too rich. I think 130s are definitely the way to go, maybe even 135s.

Can ANYONE chim in on the mains of RSs vs VMs??? I'd really like to get some jets on order, but I'd like to know which to go with.

Thanks guys!

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Ok, after some serious studying (not really) of the Sudco Mikuni parts book I answered my own question. The small round head mains that I currently have in my carbs are WRONG for the RSs. They are refered to as "Small Round Head Mains" (go figure, huh?) and have a 6mm outer diameter head. The RS series are supposed to use the "Large Round Head Mains" and have an 8mm outer diameter head. These are the same that are in the regular VM style carbs that came on our bikes as is indicated both by the Mikuni Part Number and the given Application list for them in Sudco's book. Case closed.

Call Sudco and see what the small mains you're using now are equivalent to in the large mains and go from there. I can tell you my 34's that I bought new had 5 different mains in the box and had 125's from the factory installed and as said before I could probably drop to 122.5's and be okay.

Already ahead of you. Called them and left a message with Chad who called me back last night sometime after posting my last reply; he said that the RS's use the large round heads, but that the small round heads are the same flow ratings and he wasn't even sure why they (Mikuni)offered both types... They are interchangable with each other.

My buddy had an issue running the RS34's on his 1015 motor - he had a huge bog at WOT lower RPM... about 3000 RPM, twist the throttle and it almost dies... picked up on the upper rpms around 4500 and ran perfectly around 6000-9000.
He tried raising and lowering the needle and running huge pilot jets with no improvement.
He called Mikuni and found out all 34's come jetted for GPZ750 in the midrange - he tried 2 sizes richer needle jet and it cured his problem... it was way too lean in the midrange.

Overall that size of carb comes jetted way to lean for a 1000.

I believe he is running 25 pilots and 125 mains on his mostly stock motor.

I ran 33 flat slides on a 831cc 650 motor... a lot of people said they were too big for that motor but they ran perfectly for me on the street... ran 120 mains on that setup. They came off a GSXR750 so I guess the needle system was the correct size for the fuel the motor required in the midrange.

So he actually had to change out the needles instead of just moving them up a notch or two? Seems odd, but I'm not doubting anything at this point. Good info to have if after messing with a few more main sizes when they come in and I can't get them right. But I THINK the needle size is ok... I know when I pushed the needles up to their last (richest) position, it made my acceleration worse instead of better unlike moving it from the middle to the 4th position which helped IMMENSELY. Also the 34's and 36s come with the same needle sizes when bought new, I mention that because the 36s are what they recommend for the KZ1000, whereas the 34s are indeed recommended for the 750s.... Stay Tuned....

six862m6 wrote: So he actually had to change out the needles instead of just moving them up a notch or two? Seems odd, but I'm not doubting anything at this point. Good info to have if after messing with a few more main sizes when they come in and I can't get them right. But I THINK the needle size is ok... I know when I pushed the needles up to their last (richest) position, it made my acceleration worse instead of better unlike moving it from the middle to the 4th position which helped IMMENSELY. Also the 34's and 36s come with the same needle sizes when bought new, I mention that because the 36s are what they recommend for the KZ1000, whereas the 34s are indeed recommended for the 750s.... Stay Tuned....

Injected is right. They make different taper needles to adjust the fuel mix further than you can by just raising and lowering the needle. I believe I said this in my first post and I wish you would take it to heart, no two bikes will truly like the same jetting. What is perfect on one will, at best, merely be close on the next, even if everything is identical. I could copy your build down to the lenghts of wire that were replaced, hell even the stickers under the seat, and mine would more likely than not require different jetting than yours. The point is don't rule out something just because Mikuni uses the same one on two different carbs. Small things affect jetting like if your exhaust is open or baffled all the way down to if your air filters are dirty.

Injected wrote: ...He tried raising and lowering the needle and running huge pilot jets with no improvement... he tried 2 sizes richer needle jet and it cured his problem... it was way too lean in the midrange....

six862m6 wrote: So he actually had to change out the needles instead of just moving them up a notch or two?.. I THINK the needle size is ok....

For RS34 carb, am thinking there are available several different size needle jets as well as several different size jet needles.

Good Fortune!