sinfull
Scoot Enthusiast
Posts: 413
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Post by sinfull on Jul 3, 2024 1:52:17 GMT -5
Get a scooter they said, really simple to work on and no maintenance 🙄 just twist and go they say 🙄
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Post by aeroxbud on Jul 3, 2024 3:13:07 GMT -5
Get a scooter they said, really simple to work on and no maintenance 🙄 just twist and go they say 🙄 They also said be happy with 30MPH top speed. 😂 |
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Post by 90GTVert on Jul 3, 2024 21:55:04 GMT -5
Off topic, but… The dude brought his GY6 scoot over with no spark. Stator working, CDI and coil quickly swapped, Torch plug replaced with NGK, grounds checked. Still no spark. I start checking each pin in the CDI connectors for continuity with their opposite ends. No continuity between coil + and the CDI. That’ll do it. He takes body panels off and immediately starts stripping the harness so it can be checked.  It’s a straight run, no additional splits or connectors and nothing is pinched or stripped. I check the terminal that connects to the coil. No connection. Looks fine to me. 30 second repair with an hour of swapping and checking to get there.  He didn’t have the rear panels and seat, but it’s a 2023 GY6 “200” Chinese scoot. He cut off and narrowed the rear frame, added brackets, moved the gas tank and made Yamaha Jog panels fit. Front and rear are lowered. Otherwise basically stock. Power wheelies because it’s so small. Neat scoot.  |
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Post by 90GTVert on Jul 4, 2024 5:45:36 GMT -5
I still don't know if I want 20 small holes or 30 large ones in the atomizer. I didn't notice any obvious difference when I broke the original 30 hole and swapped in a 20. Some like to say no holes on a 2T atomizer, but I don't have a 0 hole atomizer and I don't know that trying to fill with solder would be wise.
The atomizers are different IDs. About 2.71mm for the 20 and 40 hole and 2.76mm for the 30 hole. I don't have a really precise way to measure those, but somewhere in the ballpark and the 30 hole is definitely larger inside. I'm thinking go with the 30 as it came from Polini just for the larger ID.
That brings me to the needle tip and emulsion tube annulus that Wobbly mentioned. For others that don't know what an annulus is, it's the free space between the two parts. Basically the donut of emptiness around the needle in the tube. He said I should have 30% larger annulus than the main jet area. I've used JJK and HLJ needles.
20/40 Hole Atomizer with JJL leaves me at about 28% larger by the time I get up to a 220MJ. With the HLJ I'd have to stay around a 210MJ.
30 Hole Atomizer with JJL allows just above 220MJ to stay 30% larger annulus. With the HLJ, about a 215 would fall in the range.
Here's where it was confusing and odd to me. The nozzle/needle bushing/needle jet ID is 2.6-2.65mm. They make both of those sizes and I can't tell which, but I believe it's in that range. If the needle is going through there still at WOT, shouldn't that be a restriction? I need to check where the needle is for sure. If it's not in the nozzle, then I suppose the area is just fine and not a restriction so it's a false alarm. If it is in there, then at 2.6mm I'd need to stay 200-205MJ to keep that 30% margin. EDIT : The needle is out of that orifice and only behind the shrouded section at full throttle.
From Wobbly on KiwiBiker :
"Re the emulsion tubes.
Again that is super wierd as I have seen dozens of Keihin 2T - 34/35/38 PWK carbs and none of them even have an emulsion tube.
The transition/ mid jetting is changed by the needle parallel diameter , then the taper.
This is a Keihin design " thing ". As all other carbs have screw in tubes of incremental size variation.
All the other 2T carbs with a variable diameter emulsion tube have no side holes, and the shroud height changes the fuel curve flow rate with rpm/ air flow
The only two stroke carbs I know of that have holes in the emulsion tubes are only a couple of years of Mikuni - RD Yamaha I think.
That system of emulsion tube air correction is for 4 strokes - but having said that I have no previous experience with carbs designed for " scooters ".
But anyway , those holes admit air from a main air corrector jet/drilling that comes in thru the front of the floor of the bellmouth.
The tube is in a " well " with fuel entering at the bottom and air at the top, and the holes change the fuel curve, more/bigger holes = increasing leaness with rpm/air flow.
Then you say the tubes are differing inside diameter and have differing hole configurations.
So in my opinion what you have is a bunch of jet parts that make it impossible to apply any logic whatever to get the carb tuned , as everything has more than one variable changing at a time.
An absolute complete nightmare when not all the parts being changed are from the same " series " of jet type, they should be all exactly the same apart from one variable."
From Tim Ey on KiwiBiker :
"Regarding the aftermarket PWKs:
I fiddled a lot with the aftermarket stuff.
Stage6 anno 2006 gave my bike seizures.
OKO was fine.
Polini on an Aprilia RS125 did funny stuff in fast lefthand corners - it leaned out badly.
Apart from overflooding due do even the most microscopic debris, I never had an issue with original Keihin carbs.
Today, I would check every hole in the aftermarket carbs before mounting them. You'll never know what hits you."
Also had suggestion to put it on a dyno with a lambda sensor to see what's happening with AFR over the RPM range. I have a wideband, but I really don't want to put an 18mm bung in the pipe. I'd have to take it to a dyno to avoid that. Some people have said that real world load conditions can vary from a dyno scenario too when I've done past research or had conversations. The guy that tuned my Mustang said he always road tests after dyno tuning because of that. That makes me wonder if the way load changes when I'm at say 65-70MPH wide open when EGT is rising is any different than what it may experience on a dyno anyway.
An earlier comment from Wobbly :
"Lastly , something you have also tested it seems is that if the ignition curve is overly retarded past peak power , trying to generate overev , then you can end up having to fit a huge main to cool the engine as the rpm goes past peak power.
This means you are using fuel as a coolant and to control the egt , not to make power."
Past peak I've just been doing flat. No more retard than it has at 14k. I still don't know that my timing is where it needs to be for peak though. I also need to figure out what I want to put in it for the first runs. This is the same sort of thing I experienced at the beginning of this ride. I had to advance the MVT to lower EGT, but then high advance doesn't seem safe. Malossi says 16* so staying around there makes sense to me... just not the flat curve that I had because that fouls plugs incredibly fast.
F5 Dave has suggested swapping to the S6 pipe due to larger stinger to see if it lowers temps. Worst part is, if that winds up being the solution I'm stuck being slower. Then it would only make sense to go back to a 28mm VHST and go quicker with the MHR exhaust, making all of this mostly pointless expense and effort to wind up where I started.
It's ready to go once I figure out what carb setup and ignition timing I wanna start with. I still haven't put the pipe back on, but I don't think I want to start with the S6 and throw it out of tune (CVT at least) with all of the other variables already. I'm not stressed out at all having possibly the last AA piston on Earth. Honestly it looks like a BB would be fine, but I've been wondering if somehow I get larger clearance readings because thimble clicking on the piston measurement is different than just enough tension on a dial bore gauge to get the reading to match a micrometer. That's how it's generally done though and if I was wrong by much at all I would think it should have wanted to seize really easily when I first tried a C piston in the A kit that I had just prior to this.
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Post by oldgeek on Jul 4, 2024 7:13:20 GMT -5
.......The atomizers are different IDs. About 2.71mm for the 20 and 40 hole and 2.76mm for the 30 hole. I don't have a really precise way to measure those, but somewhere in the ballpark and the 30 hole is definitely larger inside. I'm thinking go with the 30 as it came from Polini just for the larger ID. Wow that is some interesting info! Glad those guys are trying to help. When I was swapping atomizers on the PHBG the difference between an x.71 and an x.72 atomizer ID made a big difference. A small change there made a big difference. |
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Post by 90GTVert on Jul 4, 2024 9:16:13 GMT -5
I was curious, so I ordered some atomizers on AliExpress. Wondering how the super cheap Chinese ones are. Holes look at least close to the same size on them instead of the huge variance in Polini. I'm kind of scared of them even without seeing them first hand and probably finding rough edges and such if I have to guess. Ordered 2 more clear bowls at $6 each. Looks like the same stuff I paid $12 each for on amazon, but I can get this without the power jet barb and one even has a drain screw. Then I really got curious and ordered a 34mm "Keihin" PWK. It's $22 so it's fake, but many claim they are very convincing clones, so if nothing else I'm interested in seeing how the "Keihin" setup compares to Polini. I don't know that it will ever go on the scoot... but then I don't know if it can be much worse than what I've gone through already. www.aliexpress.us/item/3256803887289765.htmlProbably just wasted at least $35 of the $49 paid with tax and all (bowls should be useful if I keep the PWK at least), but some part of me wanted to investigate. 🤷♂️ |
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Post by xtremrox on Jul 4, 2024 10:35:10 GMT -5
I was curious, so I ordered some atomizers on AliExpress. Wondering how the super cheap Chinese ones are. Holes look at least close to the same size on them instead of the huge variance in Polini. I'm kind of scared of them even without seeing them first hand and probably finding rough edges and such if I have to guess. Ordered 2 more clear bowls at $6 each. Looks like the same stuff I paid $12 each for on amazon, but I can get this without the power jet barb and one even has a drain screw. Then I really got curious and ordered a 34mm "Keihin" PWK. It's $22 so it's fake, but many claim they are very convincing clones, so if nothing else I'm interested in seeing how the "Keihin" setup compares to Polini. I don't know that it will ever go on the scoot... but then I don't know if it can be much worse than what I've gone through already. www.aliexpress.us/item/3256803887289765.htmlProbably just wasted at least $35 of the $49 paid with tax and all (bowls should be useful if I keep the PWK at least), but some part of me wanted to investigate. 🤷♂️ I would say try a hole free emulsion tube, it makes the tuning so much more lineary logical. But as many have suggested times ago like my countryman pewpew the bidalot aerox man just get a keihin or "keihin" 28pwk, it has been proven to be the easiest and most straigth forward carb to tune in 70-100cc engines. There was for some time a aliexpres 28pwk that was a real keihin with just the logos removed for 30$ dunno if it is still availible. The chinese pwk parts are actually decent quality 90% of the time actually. The best keihin china clones are the ones with no powerjet, mixture screw on the left size and idle on the rigth (looking from the intake) and one central fuel inlet over outlet of the carb. |
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Post by 90GTVert on Jul 4, 2024 11:18:29 GMT -5
I would say try a hole free emulsion tube, it makes the tuning so much more lineary logical. That's how I wound up on AliExpress. Best thing I can find is 8 hole. I ordered 2 of those from China. I'd either have to solder the holes up or make my own... but I don't know how precise that would wind up either way really. I guess OD doesn't matter so much, so I could trim it close on the the lathe if need be as long as I could keep solder out of the bore of the atomizer. It feels like every choice is wrong with what I have. 30 hole is larger ID, but Wobbly says more/larger holes lean it more with RPM... so less/smaller holes would make more sense there. |
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Post by xtremrox on Jul 4, 2024 11:29:45 GMT -5
I would say try a hole free emulsion tube, it makes the tuning so much more lineary logical. That's how I wound up on AliExpress. Best thing I can find is 8 hole. I ordered 2 of those from China. I'd either have to solder the holes up or make my own... but I don't know how precise that would wind up either way really. I guess OD doesn't matter so much, so I could trim it close on the the lathe if need be as long as I could keep solder out of the bore of the atomizer. It feels like every choice is wrong with what I have. 30 hole is larger ID, but Wobbly says more/larger holes lean it more with RPM... so less/smaller holes would make more sense there. oh i looked up seems like the oem keihins have The 8 hole needle jet holder/emulsion tube |
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sinfull
Scoot Enthusiast
Posts: 413
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Post by sinfull on Jul 4, 2024 18:34:54 GMT -5
Ali express is a gamble for sure, but at least 2 people I know of who ordered the Kehin, got genuine Kehin carbs. Complete with the Japanese papers and the kehin on the side of the carb body. 1 other got a clone with a kehin sticker. Never know what you are going to get lol. But for the price worth the risk
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Post by 90GTVert on Jul 5, 2024 7:15:22 GMT -5
The folks at KiwiBiker have said I should try the other pipe because the minimum should be 19mm at the restrictor ahead of the stinger pipe for an engine making 40HP. I told them this thing is rated at 31HP and dynos seem to be 25-30. For now, I'm going with the MHR exhaust because the S6 changes the CVT tune and RPM that it wants to operate at and I already have multiple variables since my last run.
I think I'm going to go to a more cautious 2 1/8 mile passes when I make changes instead of the usual 4 to cut risk a little. Not totally sure though. EGT is a little higher with more runs so it also changes the data that I have to compare with past results. Depends what I'm seeing I guess.
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Post by xtremrox on Jul 5, 2024 7:40:12 GMT -5
The folks at KiwiBiker have said I should try the other pipe because the minimum should be 19mm at the restrictor ahead of the stinger pipe for an engine making 40HP. I told them this thing is rated at 31HP and dynos seem to be 25-30. For now, I'm going with the MHR exhaust because the S6 changes the CVT tune and RPM that it wants to operate at and I already have multiple variables since my last run. I think I'm going to go to a more cautious 2 1/8 mile passes when I make changes instead of the usual 4 to cut risk a little. Not totally sure though. EGT is a little higher with more runs so it also changes the data that I have to compare with past results. Depends what I'm seeing I guess. The stinger pipe is usually changed in very small increments on race bikes becouse its very easy to melt about everything with too small stinger(speaking from personal experience lol) The stiger also causes other variables (effects cylinder fill/peak power rpm/egt/and timing has to be retarded as the smaller stinger rises pcp(peak cylinder pressure) and pct(peak cylinder tempature)=lot of potential for melting stuff. One thing you could do is measure the exhaust pipes and analyze wich is more suited for your needs. Also if you have the tools and skills i could caculate a matched exhaust pipe for you and you can make it from 0.7mm steel pretty easily (I aso have some exhaust pipe specs ready like bidalot ones and i think i have my most 90/100 exhaust ones too) |
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Post by 90GTVert on Jul 5, 2024 7:49:42 GMT -5
The stinger pipe is usually changed in very small increments on race bikes becouse its very easy to melt about everything with too small stinger(speaking from personal experience lol) The stiger also causes other variables (effects cylinder fill/peak power rpm/egt/and timing has to be retarded as the smaller stinger rises pcp(peak cylinder pressure) and pct(peak cylinder tempature)=lot of potential for melting stuff. One thing you could do is measure the exhaust pipes and analyze wich is more suited for your needs. Also if you have the tools and skills i could caculate a matched exhaust pipe for you and you can make it from 0.7mm steel pretty easily (I aso have some exhaust pipe specs ready like bidalot ones and i think i have my most 90/100 exhaust ones too) I probably should measure both pipes. There are measurements posted for the MHR 94cc exhaust on the forum, but my stinger doesn't match what that person recorded so the rest may not either. 13,500 peak power.   Had to average some of the dimensions due to the number of segments,but here is the results; Has up to date dimensions,tuned for around 11,250RPM,should be a strong pipe with the right cylinder porting! This is the curve that I think I'm gonna use for now. Didn't want to back it out too much at lower RPM due to fouling. Peak is 14.5*, so 1.5* less advance than Malossi's 16* spec. I have more advance than before after peak because I was cautioned about retarding it too much past peak. In the past, less advance at peak has meant higher EGT so this may be the wrong way.  |
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Post by xtremrox on Jul 5, 2024 8:26:57 GMT -5
The stinger pipe is usually changed in very small increments on race bikes becouse its very easy to melt about everything with too small stinger(speaking from personal experience lol) The stiger also causes other variables (effects cylinder fill/peak power rpm/egt/and timing has to be retarded as the smaller stinger rises pcp(peak cylinder pressure) and pct(peak cylinder tempature)=lot of potential for melting stuff. One thing you could do is measure the exhaust pipes and analyze wich is more suited for your needs. Also if you have the tools and skills i could caculate a matched exhaust pipe for you and you can make it from 0.7mm steel pretty easily (I aso have some exhaust pipe specs ready like bidalot ones and i think i have my most 90/100 exhaust ones too) I probably should measure both pipes. There are measurements posted for the MHR 94cc exhaust on the forum, but my stinger doesn't match what that person recorded so the rest may not either. This is the curve that I think I'm gonna use for now. Didn't want to back it out too much at lower RPM due to fouling. Peak is 14.5*, so 1.5* less advance than Malossi's 16* spec. I have more advance than before after peak because I was cautioned about retarding it too much past peak. In the past, less advance at peak has meant higher EGT so this may be the wrong way. Lol malossi has so many exhaust models and generations, like their 50cc mhr pipe had 12 diferent variations And yeah these non programmable cdis are pita to work, you want 12-16° btdc timing at peak power but if you get that right everything else is f upped |
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Post by 90GTVert on Jul 5, 2024 10:37:38 GMT -5
And yeah these non programmable cdis are pita to work, you want 12-16° btdc timing at peak power but if you get that right everything else is f upped The programmable PVL kit is great for this stuff at least. I can set it wherever. Trying to figure out what it wants right now is what's tough for me. |
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