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Post by hippo008 on Oct 4, 2022 11:44:42 GMT -5
I have been researching what carburetor I should run on my scooters for a while now. I generally run in the Dio circles now and within the Dio circles there's a lot of dogma around the Keihin PWK. New build? PWK. Upgrading? Pwk. Stock bore + mild pipe? Pwk.
I've been digging into other carburetor options out there and it's dizzying. Jetless designs like Tillotson, SmartCarb, Lectron. Round slides of every shape and size imaginable like Polini CPs or Dellorto PHBG. Flatslide options like PWK, Mikuni TM and oddball Italian designs. Hybrid designs like VHST and others.
What the hell are the differences? Why use one over another? With so many choices I'm not sure what's meant for what application.
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Post by Lucass2T on Oct 5, 2022 0:38:03 GMT -5
This is quire a rabbit hole you wanna venture into. Its almost like asking the scene what tires are best, how to break in an engine or what oil is best or how read plugs. Everyone has a different opinion.
I stick to Dellorto, Mikuni or Keihin. Dellorto PHBG range is a GREAT and afforbadle platform for carburetor upgrades. Fits in stock minarelli intake boot. 15 to 21mm sizes availabe. Supports 5-15hp builds (you can stretch it though). Are also used on as OEM 50-65cc ktm dirtbike equipment, says enough right.
PWK 28mm carbs are great for hyper race builds. 15-25hp builds. Pwk 28mm is the smallest size of the pwk range. All smaller pwk type carbs are copies or knockoffs of the original PWK. Come as OEM on 85cc dirtbikes.
Mikuni TM is a dinosaur and quite old technology. Also comes from the dirtbike world. Mainly used on suzuki's. The TM 24mm flatslide was a very popular carb for the early hyper race builds in Europe. Im talking early 2000's, Malossi MHR speed+Yasuni c20 era.
Dellorto also makes flatslide carbs. Those are just as a competitor for Keihin and Mikuni. If you like dellorto carbs and have a bunch of jets around, you buy one of those. Dellorto is also OEM on lots of older italian 2t bikes.
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Post by jackrides on Oct 5, 2022 15:13:01 GMT -5
Makes me wonder if there is a way to quantify quality (size) of fuel atomization to satisfy OCD builders?
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Post by hippo008 on Oct 5, 2022 21:42:50 GMT -5
What interests me most is the behavior of each design and not necessarily what's "best". You're right, everyone will have differing opinions on what is "best".
I am building a Malossi sport + MHR crank w/ stock oil injection for my project Dio 2. I instinctively went "I should use my genuine Keihin 28 for this" and sort of caught myself. Why use the PWK? Is there an option out there that is more suited to this application?
What really makes me scratch my head is what each carb design provides. What does a PWK style carb do that a round slide Dellorto doesn't do and vice versa? What about a Keihin PE? Is that the same as a PHGB model? I'm really hoping somebody has done some testing and can distinguish them.
If anybody is interested I think this could be an interesting forum-wide experiment. Pool together different model of carbs and test them on the same engine. Report on running characteristics, tunability and maybe fuel consumption. We could build a sort of database for tuning results.
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Post by repherence2 on Oct 6, 2022 0:36:19 GMT -5
I have been researching what carburetor I should run on my scooters for a while now. I generally run in the Dio circles now and within the Dio circles there's a lot of dogma around the Keihin PWK. New build? PWK. Upgrading? Pwk. Stock bore + mild pipe? Pwk.
the PWK fad in your area is not from the "do as the Hawaiians do" fever?
just put it this way, when OKO pwk's are $85 for 24mm-28mm carb, local moped shops here always had them in stock, who wouldn't buy one? very good bang for your buck carb as far as price and performance. i even bought a knock off OKO from a local shop too.
at one point, i ran a polini CP24. i ran it on the 70cc engine and i tried it on the 90cc engine. the CP is charm to tune and it runs very well. however, it was night and day between the OKO 28 and the CP24 when it came to all out WOT speeding, rippin' it for miles at 60+ at 1 a.m. in the morning to work. 62km round trip. PWK's are in my opinion 2/3 to Full throttle carbs. aren't they from the Motocross realm?
check out this video of a PWK in action. i am pretty sure this is mauibird of this forum. mean video. i think he was running a 103cc minarelli with a Dio PG Long. at 0:47 the pwk ACTION begins.
it just all boils down to preference and what suits your needs the best. but that also entails understanding how to get the carb in a good state of tune and what it can and cannot do. with some manipulation, the cheap OKO pwk 28mm carb is good enough on a minarelli to take down some fast Dio's. even the knock off fOKO 26mm with power jet carb that i ran was good enough to take down Honda's and SYM's. the horizontal minarelli just flows much better than the cross flow of the Dio.
in my experience, for city/street/sport, the Polini CP carb is the best. easy to tune, very fuel efficient, and it is good enough. if i did not have the 28mm pwk to compare it to, i would have never known any better. however, for street/highway racing that goes on here on Oahu, the OKO pwk for the win. $85, 60+ mph full throttle racing, you can't go wrong.
Venturi Divider on a PWK makes it a whole new world.
i also think that the stainless steel tea strainer fine mesh makes a difference in flow characteristics and fuel dispersion.
i just stick to what works. so far for me, OKO with tea strainer mesh and venturi divider has suited all my needs. but without research and testing and tuning, how would anyone really understand how "good" a carb is or how to overcome it's shortcomings? my success and understanding of the OKO came from the necessity for it run fast but be reliable as a daily rider. $85 for the carb, $45 for a rebuild kit. in essence, why buy a rebuild kit when you can get a new one for $40 more?
what is "Best" is relative. it can be debated forever. but bottom line is how well or how willing you are to tune that carb. emulsion tube makes a difference too with the pwk carbs. i think any carb that is mounted at an angle needs to be a pivot float. i think that if you are willing to put in some research and effort/mods, an $85 carb can be good enuff.
the PWK's are tried and true on the streets of Hawaii, just watch the cruise videos, Everyone pretty much running 28mm PWK's. just because Everyone runs in it Hawaii, it does not mean it is the "best". we just make the most of the opportunity, it suits our needs. a hundred+ mopeds rippin' it on a cruise at full throttle to see who has the best setup/tune.
if it came down to rippin' it around in the city, i think a CP24 would out perform a PWK. PWK in stock form is not so impressive at low throttle range. $140 for a CP24 as opposed to $85 for a 28mm Taiwan PWK. guarantee the PWK outruns the CP24 at wide open throttle. there has to be a reason polini makes CP's up to 24mm and then beyond that they have PWK's.
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Post by Lucass2T on Oct 6, 2022 7:51:04 GMT -5
What interests me most is the behavior of each design and not necessarily what's "best". You're right, everyone will have differing opinions on what is "best". My suggestion? Read articles written by people who know their stuff. Someone like Graham Bell or Frits Overmars or the literature from Dellorto.I am building a Malossi sport + MHR crank w/ stock oil injection for my project Dio 2. I instinctively went "I should use my genuine Keihin 28 for this" and sort of caught myself. Why use the PWK? Is there an option out there that is more suited to this application? You've almost been brainwashed by the Honda folks and their obsession with oversized PWK carbs. You're questioning the logic here which I like. Remember this: if a 50cc bike with a 16mm carb can put out 17hp, you don't need a PWK style carb on your cast iron Malossi Build. What exhaust are you planning on running anyway? Stick with a Dellorto PHBG. You don't need any more carb, trust me. What really makes me scratch my head is what each carb design provides. What does a PWK style carb do that a round slide Dellorto doesn't do and vice versa? Round slide design is mor suitable for street use.
D-slide (PWK), Flat-slide (Mikuni TM) are pure racing carbs. They have some trade-offs compared to round slides. You can google it.What about a Keihin PE? Is that the same as a PHGB model? I'm really hoping somebody has done some testing and can distinguish them. Keihin PE and Mikuni VM are both oldskool racing carbs used before there where D-slides and flat-slides. The dellorto PHBG is basically a small bore-2T focused, modernised version of these. Very very decent, affordable carbs whith a design that has proven itself over the last 50yrs.If anybody is interested I think this could be an interesting forum-wide experiment. Pool together different model of carbs and test them on the same engine. Report on running characteristics, tunability and maybe fuel consumption. We could build a sort of database for tuning results. What new info would you think would come out of this? This info is already readly available everywere. Tested by engineers with very expensive equipment. Do some research, read Bells's book, read the Dellorto tuning manual. There's millions of pages of literature on this exact topic. |
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Post by hippo008 on Oct 6, 2022 13:05:18 GMT -5
You've almost been brainwashed by the Honda folks and their obsession with oversized PWK carbs. You're questioning the logic here which I like. Remember this: if a 50cc bike with a 16mm carb can put out 17hp, you don't need a PWK style carb on your cast iron Malossi Build. What exhaust are you planning on running anyway? Stick with a Dellorto PHBG. You don't need any more carb, trust me. Ive built about 10 Dio and Elite motors now. There are some definite benefits to the large PWK carbs on these setups. I couldnt tell you why but for some reason carbs that seem way oversize (28mm PWKs for example) run awesome on the Honda platform. My guess is that the highly inefficient intake design of the AF18/AF16 motors benefit from a super high flow option. As an example on my Roughouse I ran a 21mm PHGB on a Polini Corsa + Yasuni R. Ran great and was plenty fast for me. On the exact same cylinder and a slower pipe but on a Dio I ran a 28mm PWK with absolutely no problems. Again I am not sure exactly whats going on there but I think its important to point out there is legitimacy to the oversized Honda carbs situation. I plan on running a Red Mole (Red Mall?) exhaust. Its a rare pipe, I have only found 1 photo of it online and no documentation. From what limited info I have from testing it produces more power at a higher RPM than a NCY pipe but less overall power than the Arrow. A sort of interesting middleground not really available in the Honda space. If anybody is interested I think this could be an interesting forum-wide experiment. Pool together different model of carbs and test them on the same engine. Report on running characteristics, tunability and maybe fuel consumption. We could build a sort of database for tuning results. I havent seen this data and I did some good looking. I am interested in a sort of "carbs for dummys" comparison, simple ass-dyno information for the regular tuner. I havent seen a apples to apples comparison of say five different carburetor designs on one common scooter motor and their results. That is what I would hope to achieve. [/quote] |
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Post by islandscrub on Oct 15, 2022 1:42:07 GMT -5
I like PWK for what seems to be a quicker throttle response, more on-off that round slide carbs. I haven’t tried d slide but i guess it’s similar to pwk.
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Post by hippo008 on Oct 20, 2022 18:32:49 GMT -5
It seems like the flat slide / D slide designs have a quicker throttle response than the round slide options. I assume the trade off is that PWK type designs will be more challenging to tune?
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Post by repherence2 on Oct 20, 2022 20:20:11 GMT -5
"challenging to tune" is Relative.
for someone like me, whose only option is to run a big pwk with the CT intake manifold that i have, you just learn to deal with it.
when i first got my license, i was cruising up Tantalus and i ran into 2 skateboarders. they were hitchhiking and i was stoned and didn't care so i asked them where they were going. they said, "however far someone was willing to take them." i took them to the top so that i could watch them ride skateboards downhill. i asked them what they did about the Speed-Wobbles and they simply said, "you just handle it, don't fight it." --Daryl Freeman.
that is the approach that i take with the OKO pwk, you just handle it. there is difficulties in tuning them, but the answers and remedies can be found on the internet.
for me, the pwk is pretty much all that i know right now. it is one of those things that, "you just handle it" if you want to run it. i love it's WOT performance. low-end solution is the venturi divider. from there, it is all Duck Soup.
-- an old timer submarine mechanic told me, "you know how make Duck Soup? you take a pot, fill it with water, put it on the stove on high to boil the water, when the water is boiling, you put the duck in the water. and there you go, Duck Soup!" simply said, keep it simple, and it Is Simple.
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Post by repherence2 on Oct 20, 2022 20:48:07 GMT -5
the PWK solution is something like this: rich's taylored porting venturi divider.  Boyesen's solution.  Thunder Products Quad Flow Torque Wing.  |
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