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Post by fuzzyruttin on Mar 15, 2018 17:30:29 GMT -5
Engine is 1P57QMJ, Japanese carb.  Question 1What size jets are typically run for GY6 150? The engine came with a 35 idle, 102 main. I swapped them out for a 36 idle and 110 main, as it seemed incredibly lean. I'm trying to get the idle set up, since the roads are such crap that I don't really want to gunk everything up. Question 2Wondering why the new idle jet (top) is so much longer than the stock (bottom)? The new one is basically flush now with the mounting hole. No concern really, just curious.  Question 3I rode around the block a couple times to get the engine warm (200F or so according to head temp sensor). Ambient temp is 38F... chilly yes, but that can't possibly be the reason for the awful bog the bike has. Idle mixture screw all the way in with 36 jet runs about 1100-1300. Idle mixture screw turned out 4 times runs about 1500-1600. Getting on the gas any more than half throttle when idling, the bike will stall. How big of an idle you think is necessary? It would be nice to not have to buy a whole range of sizes. It's sunny out but we just got dumped on with another foot of snow. Dang I just wanna ride. Well, tune, then ride. |
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Post by lilpinny on Mar 15, 2018 19:14:51 GMT -5
All of this depends on your carb and air intake... Mine is a pwk carb and the intake looks like yours. It also depends on your weather and altitude. Humid air (I call it chunky air) makes it operate different than dry air.
Q1: I use a 35 pilot and a 115 main. Mine is a 170 but I think I used that for the 150. If not go one size lower on the main (110, I think)
Q2: that must just be a thing with your stock jet. Pilots I have seen (for the pwk at least) are all long.
Q3: shoot for 1700-1800 RPM at idle when it's good and warmed up.
Your engine is dying because it's getting too much air or too much gas. You have to monkey around with the air screw to give it more or less air. If you turn more that four turns out on the air screw, up your pilot jet a size and start with the screw 1/2 turn out. Adjust so idle screw so the engine won't die when you are doing this. Once you have the air right, then fine tune the idle screw. Remember when you change the pilot jet, it changes the way the main acts.
This is assuming you don't have an air leak that's messing things up.
Another thing that has an effect is the needle size and height in the carb. I'm not familiar enough with that carb to say if it's a problem though.
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Post by fuzzyruttin on Mar 16, 2018 19:26:53 GMT -5
Q1: I use a 35 pilot and a 115 main. Mine is a 170 but I think I used that for the 150. If not go one size lower on the main (110, I think) Okay will keep that in mind. Currently have 110. Next step up is 114, then 115. Q3: shoot for 1700-1800 RPM at idle when it's good and warmed up. Okay. The other issue: weather is not permitting me to ride. Any idea what "normal" or "good" operating temperature is for head temp sensor? Being a new engine and all, there are lots of variables all over the board. I haven't messed with a carb in years, and never messed with a brand new one inherently un-tuned to the engine it has been slapped onto. I feel like, "Be patient young Padawan." Aside dumb statement, correct me if I am wrong - carbs don't work well when the engine is cold started as a result of the intake air-fuel getting supercooled by the surrounding cold metal, causing the engine to run lean. That's just genius, right? haha This is assuming you don't have an air leak that's messing things up. Right. I think the only things to question here are the vacuum lines or the carb manifold. The vacuum lines are fresh sticky rubber. I don't have clamps on them, but I really don't think it's an issue. Not a bad idea to purchase some nice wide clamps tho, insurance for when the rubber does start to deteriorate. But I did buy a clocking flange and had it powder coated. It came with a gasket (instead of an o-ring) and I hand-torqued it as far as I felt safe, pretty tight in other words. Not sure if it's worth taking off and having a look. Perhaps tuning a properly warmed engine might tell me there's a leak somewhere if the RPMs have a funky fluctuation, then I'll re-visit. Right now it seems the RPMs vary by about 300 maybe 400 RPMs at idle. Heck my 50cc ruck did worse than that when cold. The forum response: "Come back and talk to us when the engine is warm." Another thing that has an effect is the needle size and height in the carb. I'm not familiar enough with that carb to say if it's a problem though. As an experiment this evening, I move the clip to max lean and max rich then did the vrum vrum test. Seemed to take better at the rich setting. Well of course, the engine is not properly warmed. Another aside, how much does exhaust affect tuning? The one I have is quite loud and I have to assume quite unrestrictive. Not sure to what extent that affects sizing the main jet. Whelp, not much to do with this until the weather turns. Thanks for the info in the meantime. |
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Post by lilpinny on Mar 16, 2018 20:45:04 GMT -5
I usually say ride it around the block a couple times to warm it up to where it's running nice. That's more by feel than a specific temp. I don't have a specific temp, but you gotta get it running. I don't think it can idle its way "warm".
My bike runs lean at idle and then in the rich power zone (12.4 on the wideband) at full throttle. You tune at WOT, Then whatever idle is, idle is.
If your bike wants to run better at the carbs richest settings (even with the choke on maybe), it's getting too much air and needs the fuel to make up for the air in the mix. Turn your airscrew in some.
A performance exhaust will clear the spent gas out quicker. Your trying to gobble as much fuel and air as you can but if you can't shoot the spent gasses out fast enough to keep up it'll back it up and lower performance.
Sounds like you want to get it close then wait for a day you can take it out and really tune it.
The reason I bring up air leaks is that the symptom you describe (giving it gas and it dying and it seems to idle better when the carb is in its richest position(s)) is something an air leak causes. Not uncommon either. But it can also be a carb that just needs to be tuned up.
A wideband helps _alot_ with this process, but you still tune it at WOT. You might have to wait for the weather either way.
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Post by 3strokeengine on Mar 16, 2018 22:58:06 GMT -5
I usually say ride it around the block a couple times to warm it up to where it's running nice. That's more by feel than a specific temp. I don't have a specific temp, but you gotta get it running. I don't think it can idle its way "warm". My bike runs lean at idle and then in the rich power zone (12.4 on the wideband) at full throttle. You tune at WOT, Then whatever idle is, idle is. If your bike wants to run better at the carbs richest settings (even with the choke on maybe), it's getting too much air and needs the fuel to make up for the air in the mix. Turn your airscrew in some. A performance exhaust will clear the spent gas out quicker. Your trying to gobble as much fuel and air as you can but if you can't shoot the spent gasses out fast enough to keep up it'll back it up and lower performance. Sounds like you want to get it close then wait for a day you can take it out and really tune it. The reason I bring up air leaks is that the symptom you describe (giving it gas and it dying and it seems to idle better when the carb is in its richest position(s)) is something an air leak causes. Not uncommon either. But it can also be a carb that just needs to be tuned up. A wideband helps _alot_ with this process, but you still tune it at WOT. You might have to wait for the weather either way. Well CVK carbs like these dont have air screws, they have a fuel screw which work the opposite of air screw (fuel screws lean as you tighten, air screws richen as you tighten them). Further these adjustments only really affect idle and off-idle mixtures and have minimal impact above 1/4 throttle. The needle and vacuum slide changes the mixture based on the mass air flow through the motor. The needle usally has atleast two different tapers on it. One for crusing and one for power enrichment for near WOT. Moving the clip down richens the overall mixture and and up leans the overall mixture. The vacuum spring controls how the carb responds to engine load and more importantly maintains venturi signal. A shorter spring opens up quicker, slightly leans the mixture and can sometimes gain power, too short however and you'll lose venturi signal and lean bog. Longer springs are better for colder climates and for lower RPM motors but too long and it will have sluggish throttle responce and lose power. Its important to note the small hole in the bottom of the slide also plays a role in this The main jet controls WOT high rpm mixture With CVK carbs 90% of your everyday riding you tune with needle positons and spring lengths until you find what your motor likes best. Once you get it right a CVK will maintain the desired air fuel ratio over a wide range of temperatures and elevations, its the next best thing to EFI |
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Post by lilpinny on Mar 16, 2018 23:38:14 GMT -5
Yeah... I'm not familiar with that carb. Thanks!
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Post by 3strokeengine on Mar 17, 2018 12:02:00 GMT -5
Engine is 1P57QMJ, Japanese carb. Question 1What size jets are typically run for GY6 150? The engine came with a 35 idle, 102 main. I swapped them out for a 36 idle and 110 main, as it seemed incredibly lean. I'm trying to get the idle set up, since the roads are such crap that I don't really want to gunk everything up. Question 2Wondering why the new idle jet (top) is so much longer than the stock (bottom)? The new one is basically flush now with the mounting hole. No concern really, just curious. Question 3I rode around the block a couple times to get the engine warm (200F or so according to head temp sensor). Ambient temp is 38F... chilly yes, but that can't possibly be the reason for the awful bog the bike has. Idle mixture screw all the way in with 36 jet runs about 1100-1300. Idle mixture screw turned out 4 times runs about 1500-1600. Getting on the gas any more than half throttle when idling, the bike will stall. How big of an idle you think is necessary? It would be nice to not have to buy a whole range of sizes. It's sunny out but we just got dumped on with another foot of snow. Dang I just wanna ride. Well, tune, then ride. The bike idleing higher with the screw turned all the way out tells me its way too lean, try a 40 idle jet and then adjust the idle mixture so your idle isnt pig rich but your transistion circuit will get more fuel with the bigger jet compensate for the lean spot. |
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Post by lilpinny on Mar 17, 2018 14:58:21 GMT -5
Yep. Too much air
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Post by fuzzyruttin on Mar 28, 2018 19:12:54 GMT -5
Update. I've taken notes on 6 different jet sizes and needle position combinations. They still all indicate "too lean at low end." I need to get bigger slow jet(s), but in the meantime, I have basically riched out the bottom as much as possible by riching out the top, needle in bottom rung, and unscrewing the idle mixture 4 turns. Tinkering cuz it's too damn cold for leisure riding.
Another interesting point though - I've been keeping the scoot inside, where it's a balmy 70F or so (easy to do with a wood stove). After first pulling it outside and starting, low end throttle response seems great. After riding around in 35-40F weather, the low end response returns back to horrible. Theory is, the carb seems very well thermally insulated from the engine, and is basically out in the open breeze while riding. After riding, the carb is colder than when I first pulled the bike out of the house, or at least I think that is what's going on, and thus runs too lean. Thought about blowing a heat gun at it after a ride to see if performance changes for the better... or, just wait for the weather to gets warm. waiting sucks.
I've worked with 4 cylinder carbs, but man, this little one cylinder sure seems finicky.
Anyway, where's a good place to order scoot parts that won't charge 3 times the purchase price for shipping? That's an exaggeration of course, but you get the point. I placed an order for 3 slow jets from Parts for Scooters because they charged $8.35 for shipping.
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Post by jbjhillbilly on Mar 28, 2018 23:51:10 GMT -5
Engine is 1P57QMJ, Japanese carb. Sorry to say, but if the above is a picture of your carb, it may never tune. That's a Keihin knockoff, and I don't think it's from Japan. The only markings on genuine Keihin carbs are "Keihin", "Japan", the series designation (VE, PE, PWK, etc), and a serial number. It's also why the jets don't match up. Here's a picture of one from eBay  |
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Post by fuzzyruttin on Mar 29, 2018 16:54:11 GMT -5
Engine is 1P57QMJ, Japanese carb. Sorry to say, but if the above is a picture of your carb, it may never tune. That's a Keihin knockoff, and I don't think it's from Japan. The only markings on genuine Keihin carbs are "Keihin", "Japan", the series designation (VE, PE, PWK, etc), and a serial number. It's also why the jets don't match up. Here's a picture of one from eBay Yeah I was sort of guessing that it was a knockoff, giving the Chinese a naive benefit of the doubt here. Pisses you off that they even put "Japan" into the molding. I was wondering what the symbol was on mine, now I see they made it just different enough to help avoid copyright infringement. Anyway, big slow jets should be on the way. I will do my best to get it tuned. If that fails, I will contact the guy I bought the kit from and see what kind of response he has. He's been good with everything so far. Noobie question: what do these stand for: CVK = Constant Velocity Keihin (?) PWK = P-something W-something Keihin ? |
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Post by pinkscoot on Mar 29, 2018 17:56:45 GMT -5
I'm in the middle of tuning a true Keihin NCV carb and all of this is helpful. fuzzyruttin a great place for jets is www.Jetsrus.com. They have a great assortment of jets. Pull your old jets out and measure then go to FAQ identify this jet to get the right one. They have flat rate shipping and the jets show up in an envelope. |
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Post by jbjhillbilly on Mar 29, 2018 22:27:59 GMT -5
Yeah I was sort of guessing that it was a knockoff, giving the Chinese a naive benefit of the doubt here. Pisses you off that they even put "Japan" into the molding. I was wondering what the symbol was on mine, now I see they made it just different enough to help avoid copyright infringement. Anyway, big slow jets should be on the way. I will do my best to get it tuned. If that fails, I will contact the guy I bought the kit from and see what kind of response he has. He's been good with everything so far. Noobie question: what do these stand for: CVK = Constant Velocity Keihin (?) PWK = P-something W-something Keihin ? The problem with the Chinese knockoffs is the same problem with Chinese scoots in general: there's little quality control. Some are awesome, and some are trash. I have one I got as a spare for my CH150, until I could rebuild the original. It's perfectly fine. The mechanic at the shop I just helped close wouldn't even pretend to deal with the things. If a scoot came in with carb symptoms, he'd do a quick cleaning. If that didn't fix it immediately, he'd throw them in a box, and grab a Keihin, Mikuni, or Delorto, and magically the bike would run! We used some of the knockoff's pieces to rebuild Japanese carbs, but mostly they went in the scrap bin. As for the designations, I don't know, but that sounds good enough  |
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Post by fuzzyruttin on Apr 27, 2018 8:51:03 GMT -5
This carb is tuned almost as good as it's gonna get before I fold and chuck the POS in the trash. 38 slow jet 3 turns out was decent. 39 slow jet 2 turns out is better. After going through four slow jet sizes up, I am out, and just ordered two more, 40 and 41. It is apparently very fuel hungry on the low end, not sure if that's good, bad, or indifferent. I have to blip the throttle 2 or 3 times to get it going off the start line. Once the RPMs are up, WOT is ok, but the throttle response is still not up to snuff. Performance is not real consistent from ride to ride either, which makes it a bit more frustrating.
I had a 114 main in it for a while, which seemed to run fairly well. Tried 115 yesterday, and it finally started to pop and gurgle. I say finally because:
stock main = 102, 114 runs well
stock slow = 35, 39 is best so far; I expect 40 will be the ultimate best
The top end actually seems ok for the most part, but no scientific tuning there yet, just going by feel. On the straight and level, no wind, speed tucked, it got up to 57 mph after a couple/three miles. The tranny is still bone stock. On a nice downhill it pushed 70 mph - I won't peg an exact number on the speed because I was having too much "fun" to stare at the speedo, in, uh, 35 mph zone.
Another note after tuning some yesterday. It was about 60F (yaaa heat wave). The top of the carb (the spring retainer) felt like it had been on ice after just coming back from about a 5 mile ride. It's not picking up any heat from the engine, which could partly be the reason why I need to run such big jets.
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