2017 Beta 125 RR-S

Discussion in 'Thumpers' started by Bowhunter, Jul 10, 2016.

  1. senecawarrior

    senecawarrior Adventurer

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    Found this page. https://www.jetsrus.com/carburetor/carb_mikuni_VM_series.html It gives dimensions of the Mikuni carbs. The inlet and outlet of both the 28mm and 26mm are both 44mm and 35mm which is smaller than our carbs but may be able to be adapted. Jetsrus.com handles both Mikuni and Kehin carbs and jets for them.
  2. UtahGuido

    UtahGuido Long timer Supporter

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    Yeah, I've thought about tilting the carb. It would be nice to avoid that but if its a matter of a few degrees that would probably be okay.
    I've got to say this conversation has my juices flowing once again. I'm going to try and make some time in a couple weeks to pull the carb and make some careful measurments. If you beat me to it post up what you find.

    Here's another angle: I've had this same carb (more or less - without the accelerator pump) on a KLR650 and my current KLX351 (for sale!) and in both cases I drilled the hole in the slide to make it slightly bigger, the theory being that the slide can move quicker and get better response. I think I also remved a bit of the spring on the KLX with the same goal in mind. The KLX has decent throttle response, not much lag. I have considered doing the same on the Beta but am reluctant because I haven't identified a source for a new slide and spring should it not work and in fact screws things up further. And I wonder if with the smaller displacement and air flow if enlargng the slide hole would do the same as on the bigger bikes, in theory. Maybe it would work better! But I don't know, and without replacement parts I don't want to do the experiment.
  3. UtahGuido

    UtahGuido Long timer Supporter

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    Somewhere I found a site with a pretty good catalog of inlet adapters. That side would probably relatively easy to make work. The airbox side might take some creative fabrication.

    Edit: Same site: https://www.jetsrus.com/mounting_flanges/mounting_flanges.html
  4. Navin

    Navin Long timer

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    Less spring = stiffer spring everything else being equal. Ive got a YZ85 carb Im not using if you want it. I think its 28mm. Somebody shoulda taken up my offer long ago to try the Mikuni from my TSE250R GPX but thats down the road now.


  5. The Letter J

    The Letter J Long timer

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    Another pumper carb to consider would be the old Keihin PD series round slides. Specifically the PD03A which is "28mm" (the OEM versions are actually 30mm at their largest portion, but have a tapered bore that starts out closer to 22mm-ish.) The engine side spigot is 40mm, filter side is 45mm, total length front to rear is 98mm, total height is roughly 170mm, and height from the horizontal centerline of the engine side spigot to the top of the carb is roughly 85mm. They use a rotary/push-pull style linkage too, so nothing sticks out above that.

    You can pick up Chinese copies for around $60 (search for a 1978 Honda XL250 carb), but those don't have the taper bore... still worth a shot vs the cost of an OEM TM28-1 which are very hard to find anyway (non-California DRZ250's are the only bikes that I know of that used tm28-1's?)

    There are also knock-off 28mm slant body FCR's for around $150 that have a smaller 35mm engine side spigot but also include other size spigots.

    If you want cheap, you can get PZ27 or PZ30 pumper carbs for $35-$40. I'm not a fan for a few reasons: they're flange mount (which could be adapted) and they use a screwey "Y" cable to pull the slide and the pump instead of one actuating the other. The cable pulls directly on the slide, so it's also a top mounted cable. They are physically smaller than the other carbs listed, so the overall height might still be workable for you?

    I'm not real familiar with the Beta engines, but I've been following along with this thread since I have a soft spot in my heart for small displacement bikes. The topic of pumper carbs is timely as I've been building a different 125 4t engine (DRZ125, 13:1, 66.5mm/170cc, Megacycle cam, R&D valve springs, ported head, 2mm larger intake valve, etc.) and am just about to start playing with carb fitment. A VM26 would be a direct bolt on in my case, but I REALLY want to try something with an accelerator pump on this bike!
  6. UtahGuido

    UtahGuido Long timer Supporter

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    Oh... well, I suppose that make my life easier. Thanks for the heads-up.
    https://www.eatondetroitspring.com/cutting-coil-springs-calculations/
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  7. senecawarrior

    senecawarrior Adventurer

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    Opening up the bleed hole in the slide will, or at least should make it open faster. Measure it first with a drill then open it up like you said. A small increase in size makes a bigger difference than you may suspect. As for a replacement slide I will check at my Beta dealer for availability and cost. I bought my bike 100 miles away and six months later a local guy a mile down the road opened up. Sigh. If you do drill it and things don't go as hoped I can pick one up if available and ship it to you at cost. But there is something else you could try first if the bigger hole is not better and you want to go back. Clean it with brake cleaner or alcohol or naphtha (I would keep the brake cleaner off the diaphragm not knowing what might happen.) then fill the hole in with a bit of good epoxy and re-drill it back to original. In the shop where I worked we would check for a minimum fuel flow on all the 250 and bigger two stroke bikes that we ran on the dyno. (If you want to know why and a funny story about things going South fast on one dyno run let me know.) Japanese carbs seemed to flow fine through the float needle valve but the petcocks needed replaced. European petcocks were fine but some Bing and Amal carb float needle valve chambers needed opened up to let more fuel past. We would drill holes and ground out some metal in the proper place but twice someone went too far. We filled in the " Oh #*%<* " with epoxy as mentioned, drilled, filed or ground as necessary and it worked fine. A few years ago I was helping with a restoration of a CZ400 MXer and opening the carb up I saw it was one of the ones that was repaired and the epoxy was still in there and tight.

    As for making an adapter to fit a smaller carb opening to a larger air boot or intake manifold here is something I did when putting a Mikuni on my Ossa 250 Pioneer to replace the stock twin needle IRZ. I found a piece of smooth pipe with the inside dimension that I needed and cut it the length that I wanted. I put a light coat of grease inside the pipe then positioned the clean carb inlet in the center of the pipe which was now the mold. I filled in the gap with automotive body putty and let it set up. The pipe slid off and after filing off a few rough edges it was ready to go and worked fine. If for some reason you want to return it to normal simply use a wood rasp to remove it. If you want something that will drive you right into your state mental home for the criminally confused try jetting one of those IRZ twin needle carbs. They had two needles hanging from the bottom of the slide. One for low mid-range and the other for high mid range. Both needles had their own supply jet and the two jets worked together to make your "main jet." A change of just one clip notch on a needle or one size on a jet demanded a juggling act with the other three pieces. IF you got it right you had a good working mixer, BUT it was a big IF! Too many flew off and landed in the cuckoo's nest before they got it right.
  8. UtahGuido

    UtahGuido Long timer Supporter

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    Sounds like a man who knows his carbs! Which is always a good thing.

    Like I said this has got my juices flowing and I may follow up on that slide drilling - but I won't cut that spring!

    I'm also glad we have some folks here who are enamored by small displacement motors. I suppose if you weren't you wouldn't be on this thread.
  9. senecawarrior

    senecawarrior Adventurer

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    I tried to find a picture of the slide of a twin needle IRZ carb but came up empty, but found something even better. If you were reading Dirt Bike Magazine in its early years the name Rick Sieman, aka "Super Hunky" will be known to you. Here is an article he wrote about the ten worst dirt bikes of all time. The IRZ carb I mentioned is listed under "Oddities That Boggle The Mind." The article is a great read.

    I looked in my Beta owners manual disk for any info on the carburetor and they say is it is a 26mm Mikuni UCAL 5Nh 26-38. That is not what we have on our bikes as we all know. A search of the net for a Mikuni of that number turned up nothing. The only place I found it listed was in the specs. for older Beta 125s. I will have a talk with the dealer and see if he can shine any light on what that carb is or if it is some in house part number that Beta used for one of the Mikuni VM series carbs. The truth is out there. Maybe. Maybe not.
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  10. UtahGuido

    UtahGuido Long timer Supporter

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    ^^^ Nice sleuthing! :lurk
  11. senecawarrior

    senecawarrior Adventurer

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    In my last post I neglected to put in where to read the article on the 10 worst dirt bikes. I am truly sorry about that and can only claim the fact that I have made more trips around the sun than I care to think about. In short, I'm old! Old enough to remember every one of these bikes! Go ahead. Look this up and have a laugh and appreciate what we have today. http://www.off-road.com/dirtbike/voice/ten-worst-dirt-bikes-of-all-time-15569.html
  12. senecawarrior

    senecawarrior Adventurer

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    Ok. I got to my dealer down the road and talked to him about a replacement slide for our Kehim CV carbs and what Mikuni might have come on the bike in the beginning. I did not get far. He was as mystified as we are about the Mikuni UCAL 5Nh. The old air cooled 125 RR-S listed the same carb which Mikuni does not list. Moving on he told me that according to his info the carb we have is discontinued and replaced on the new bikes with a different number, ( Ours is, 021-120658-200 ) and the slide is stupid expensive at $209. I do not know if a decimal got in the wrong place, or he jacked the price up way out of line to pay for his new building, or if that is what Beta charges. I would check at another dealer first. Something really off here. As for our carb I can't find anything on it from Kehin. I do not have mine off to look at for some model number but even so there should be something somewhere.

    If you wanted to try drilling out the bleed hole in the carb you might consider this option. Drill one or two small holes beside the original hole. If they do not work out fill them in with epoxy as I said before. But at the price quoted to me I would be happy to deal with it until this gets sorted.

    Now onto better tidings. You mentioned Mikuni TM carb but felt that it was probably too high to fit. I agree. On it the throat bore center to top of the carb is 117mm. I looked up the Mikuni VM28-49 and the VM26-8074 carbs. They are only about 60mm from center of the throat bore to the top of the cap nut if their detailed drawing is correct. I do not know how that compares to the carb we have but someone who has their bike apart enough to measure should check this out. Both the 26 and 28mm carbs are the same outside dimensions. Total height 122mm. Intake bell OD. 44mm. Outlet spigot OD. 35 mm. Total length front to back 93mm. Enricher lever on left side. At least this carb has been around a long time and there are plenty of jets easily available. There should be a lot of them out there used and new they run from about $80 and up on ebay. If you go with ebay make sure it is a genuine Mikuni. I looked at a few of them that said Mikuni were a little too inexpensive and could find no name in the blow-up view. Probably Chinese copys and who knows if the Mikuni jets would fit or the overall quality.

    Finally my local dealer told me that Beta has their parts diagrams, service manuals, and owners manuals on their web site. https://betausa.com/street-legal-offroad-support/ That may be of help. I am going to keep digging and let you know what I find.

    Keep riding. Life is shorter than you think. I am 68 and have no idea how or when that happened.
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  13. UtahGuido

    UtahGuido Long timer Supporter

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    Yeah, that slide price is ridiculous. I think I'll just leave mine unmodified.

    With regards to the Mikuni TM series I haven't found a diagram that shows the bore center line to top measurement. I suppose you can put a tape measure on the drawing and guesstimate the number - that being the critical measurement.

    Also with regards to the TM26, which looks to be shaping up to be the likeliest candidate, there is also the VM26-606 which some reports say works better than the VM26-8074. Not really sure what the difference is except that the 606 is half again more expensive.

    On a side note I drove my Jeep around the White Rim Trail down in Canyonlands NP on Tuesday in support of a friend who was riding the whole 100 mile loop on a bicycle. He's a tough hombre and he made it in good shape. One thing I concluded is that a motorcycle is absolutely the best and fastest way to get around that thing. In the Jeep I was making about 12 mph, not really faster than Jim on the bicycle. My next time down there I'm taking the Beta. We'll see how it deals with the climbs up Hardscrabble Hill and Murphys Hogback. I think it will charge up both in first gear but the approach to Hardscrabble from the north has a significant sand pit in the next to last steep section before the top. That could be a challenge for the 125. On the plus side the Beta could probably do the whole 100 mile loop without carrying extra fuel.
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  14. senecawarrior

    senecawarrior Adventurer

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    Welcome to this Beta site. I should have said this earlier. I have always been a fan of small displacement bikes. I find them more fun than big inch ones because you must work together to get things done. With big ones you just twist the throttle a bit more. I climbed off a Husky 610 that I had for 10 years. It was time. It had enough power to hurt me real bad and it was no fun on tight single track here in the Pennsylvania woods. Too big. Too heavy. Too much power. Especially when the trees are sometimes closer together than your handlebars are wide. Then I got old. Not sure how that happened. Getting on the Husky I had to turn facing the back and act like I was kicking a football to get my leg over the 38.5 inch seat height. And I am 6'4". When you went down it was like falling off the garage roof. You had time to think about it on the way down. Then dismounting it was more like a controlled crash. Had trouble getting my leg back over the seat. It was time to down size. Having the time of my life on the Beta. Reasonable fit, feet touch the ground for a quick dab, 100 pounds lighter, and I make a fool of my friends on their DR 400 - 650s when it gets tight.

    You got me thinking and that is always a bad sign. I usually end up spending long hours in the garage, tracking dirt, oil or grease into the house, or setting my pants on fire. A flange mount is not out of the question and they are easily made. Flat steel plate drilled and the proper size tubing for the spigot welded - brazed on to match the intake. A quick file job to check for and correct trueness or trip on a surface grinder if available to prevent leaks. I do not know anything about the PZ carbs. I took a quick look at them and do not know their origin. One picture on Ebay showed the Mikuni tag and "Made in Japan" but write up on others said China origin. My question is do they take easily found Mikuni jets. Let us know any info that you have. I am going to do more looking in the future and see what I can find. Thank you for your input. If I suddenly disappear from here and never return it is probably because I tracked grease into the house and the wife did what she has threatened before. Sudden death in my sleep.
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  15. The Letter J

    The Letter J Long timer

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  16. senecawarrior

    senecawarrior Adventurer

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    A big thank you to "The Letter J" for the above info on the PZ 27 and PZ 30 carbs with accelerator pumps. I looked on ebay and they do take a special split throttle cable to operate both the slide and the pump. These cables seem to be readily available and reasonable. Some carry the Keihin logo and it is possible they are being made under license from Keihin. The standard carb with accelerator pump looks like it would be the way to go for log hopping. Quick air along with a shot of gas. The 27mm is about $33 and the cable is around $10.

    https://www.ebay.com/itm/Performanc...801910&hash=item4212deb4d4:g:mWUAAOSw2s1Ur4vT

    Here is the PZ30 with throttle assembly and cable included for $70 including shipping.

    https://www.ebay.com/itm/PZ30-30mm-...ttle-Cable-For-Keihin-200-250cc/283542383054?
    epid=8016584548&hash=item42047169ce:g:9VoAAOSw-NFaqclH

    Look around and I would go with the ones that say Keihin on them. Some do not from what I can see. I hope the jets are the same as Keihin for tuning but it will take someone diving in to know. If someone does let us all know what you find out.
  17. der

    der Adventurer

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    I have a crush on small displacement dual sport bikes and I just discovered this gem. Sadly, the dealbreaker may be the carb - after selling my DRZ400S, I vowed never to go back to a carb since riding season here is <6 months and I've gotten spoiled with the no-fuss nature of the FI WR250R. Not surprisingly, it seems that most of the post in this thread are about messing with the carb. I've gone from a KLR 650 to a DRZ 400S to a WR250R and still find myself dreaming of roaming the wilds on something lighter (and quieter).

    Despite the carb, the beta looks tempting. Anyone use this thing for (very) light backcountry touring? Or is it purely a play bike? I'm 155 lbs wet and about 180 with riding and camping gear. I'm not looking for speed, just something that will putter all day long and still be playful when things get technical. The WR250R is actually pretty good but at ~300 lbs (pre-farkle), it's not skipping across any lily ponds. I'm hoping 150-250cc street legal bikes become more of a thing. For a while, it seems more displacement was all Americans wanted but that may be (slowly) changing. This bike would make Lois proud!
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  18. UtahGuido

    UtahGuido Long timer Supporter

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    Okay, got some measurements. But first: the carb sits under the backbone of the frame. The backbone however has gussets running up the side creating a channel in the middle through which the throttle cable can run. See the next two pictures.

    Right over the carb:
    IMG_20201026_174000931.jpg

    Further up the frame:
    IMG_20201026_174047891_HDR.jpg

    Right above the center of the carb that gives approximately (as best as I can measure) 17 mm of extra room.

    The centerline of the bore to the gusset on the frame is about 71-72 mm.
    IMG_20201026_181740767.jpg

    So from the centerline of the bore till you hit the frame looks to be 88-89mm.

    Those measurements are taken approximately 2.5 inches (63.5mm) from the front spigot.
    IMG_20201026_182002424.jpg

    • So there you go. My thinking is a 26 mm round slide carb with either a 90° or, maybe better, a 45° adapter at the top with the cable routed up the channel in the frame may work, depending on dimensions. Then the trick will be to come up with connections to the motor (easier) and the airbox (harder though scenecawarrier offered up some ideas on that earlier). Another factor is the location of the choke. The downward sloping members of the frame may interfere with a choke located to the rear of the carb. A choke coming off the front of the carb may be better.

    If I missed something let me know. The bike is still apart and I can get more measurements and pictures.
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  19. UtahGuido

    UtahGuido Long timer Supporter

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    I think the bike has the makings of a great light backcountry touring bike. I find it comfortable to ride all day and that is really important to touring around, and that's remarkable since I'm almost 6' 2" and (ahem) pushing 200 lbs. With a couple 1.5 liter fuel bottles I figure the range might be 150 miles. 200 miles would be better but there is no big tank option that I'm aware of. I believe the rear rack available for the bigger bikes in the RRS line fit the 125 but I can't validate that. I can say that the Wolfman small tank bag works well and doesn't get in the way when standing. Add some rear bags, either frameless or with a (possible) rack and you've got your light tourer. The limitations will be anything over 60 mph on the road, less if there are hills, and deep sand climbs off the road.

    Kawasaki's small bore off-roaders look good but I suspect they are heavier and may not be street legal.
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  20. senecawarrior

    senecawarrior Adventurer

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    Thank you der for stopping by. I totally agree with UtahGuido that this bike has a lot of potential for your intended purpose. If you do spring for one here what I found on my own bike. Give it time to break in. At first I thought that I had made a mistake because it seemed to not have much power, but after after 500 miles it was definitely better and getting stronger. I am sure that this feeling was amplified because I had just climbed off a Husqvarna TE610 which had the potential to hurt me real bad, real fast, and at a high rate of speed. After 1000 miles the Beta was fully run in and I put a Scalvini exhaust and jetted the carb to match. It picked up noticeable power at the bottom and top of the RPM range with some also noted in the middle. The motor is stock other than that. For my purpose of a run about, dirt road and single track explorer it works great and am having the time of my life. Reliability has been brilliant. I adjusted the valves at 500 miles and a recheck at 2500 showed no change at all.

    155 pounds! My wife wishes!!!! Always looking at me with "the look" when I start eyeing up seconds at the table. I am 6'4" and weigh in at 218, and the 125 pulls me quite well even though I went up to a 15 tooth countershaft sprocket to drop RPM a bit on the road. (Seeing that 218 in print makes me think strongly that she has a point. Gota do something about that.) The Keihin carb actually works very well and is jetted spot on with the stock exhaust. All the chatter you see here is because any CV carb responds slowly compared to other designs making lofting the front wheel to clear a log more difficult in technical riding. For steep hills throttle up early to give it time to rev into the real meat of it's power. Keep the revs up and it will surprise you where it will go. (Even with my girth.) This bikes feels light, handles exceptional and turns like a Q ball hitting a bumper compared to the DR400s and DR650 that I ride with. They are so heavy that I sometimes rub it in by lifting my bike onto my trailer rather than using the loading ramp. Try that with the 650 and your hernias will have hernias! I know. I am evil. As with all small bore bikes you have to work together as a team to get the job done. I think everyone on this site would agree that when you do that, hitting the shift points, selecting the right gear and working with the power curve they will reward you with riding pleasure that no big bike can match. Small bikes are not for everyone, but if you can try one of these on for size I think you will like it. As a side note this bike in Europe comes with fuel injection. Why we did not get it is anyone's guess. There is also different cams and big bore kits from Yamaha and performance exhausts to be had. The motor is made by Minairelli which Yamaha owns or at least has a controlling interest in it. A number of manufactures use it and it has been around for some time.
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