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Post by dmartin95 on Feb 7, 2015 9:37:03 GMT -5
The other 28, 30 and 32mm carb thread keeps going towards rollers, sliders and springs.... Can we have one that only addresses using a large carb for a BBK? When it comes to the electrical system of the GY6, I've got it covered. When it comes to up-jetting and using a larger carb to accommodate other upgrades, I have a lot of learning left.... Now, I know enough to know there's no crystal ball here... So what I'm looking for it the proper way to tune a carb using the "jet" method... =============== I purchased a HOCA 30mm carb to go with a 180cc power kit... I'm concerned it may be too large in it's current configuration.... It has a #128 main and a #40 pilot... What I guess I'm looking for is some good tutorial videos or perhaps a walk-through on how to up/down-jet a carb Here's the carb I'm using, It's a HOCA 30mm, K&N air filter and aluminum intake.   |
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Post by JoeyBee on Feb 7, 2015 10:16:40 GMT -5
Tuning my carburetor was a breeze for me, but I cheated by installing a wideband O2 sensor. That by far is the best modification someone can make. The installation was super easy. Only other modifications has been a Unifilter, 12gram weights, and PAIR removal. Stock carburetor and exhaust on 150cc. Started with a 115 jet, but saw I was running way too rich. My goal was the stay in the 13.5:1 fuel/air ratio. The 115 was reading in the low 12:1 from 1/4-WOT. 12.2:1 is the max rich, and 14.7:1 is the max lean. The 110 was an improvement, but I was still running rich in the 1/2-WOT. Right now I am running a 104 jet. I have found this one to run consistently in the mid 13s:1 from 1/4-3/4 throttle. Once I pass 3/4 throttle the mixture falls to the high 12s:1. For this setting I also dropped the clip on my needle one notch lower. Before I dropped the clip I was running slightly too lean. Without the sensor I'm sure it is a very difficult process to ensure all portions of the throttle is getting the right mixture ratio.   |
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Post by scooter on Feb 7, 2015 10:20:12 GMT -5
The other 28, 30 and 32mm carb thread keeps going towards rollers, sliders and springs.... Can we have one that only addresses using a large carb for a BBK? When it comes to the electrical system of the GY6, I've got it covered. When it comes to up-jetting and using a larger carb to accommodate other upgrades, I have a lot of learning left.... Now, I know enough to know there's no crystal ball here... So what I'm looking for it the proper way to tune a carb using the "jet" method... =============== I purchased a HOCA 30mm carb to go with a 180cc power kit... I'm concerned it may be too large in it's current configuration.... It has a #128 main and a #40 pilot... What I guess I'm looking for is some good tutorial videos or perhaps a walk-through on how to up/down-jet a carb Here's the carb I'm using, It's a HOCA 30mm, K&N air filter and aluminum intake. Take your scooter for a performance ride. Write down time to top speed, top speed WOT RPMs, and any other data that is relevant to what you want in a ride. Put in a bigger jet. Test it again. If you like the performance, upjet and test again. At some point you are going to find the jet that that gives you what you want. I upjetted my last scooter by 5, from a 110 to a 115. It went faster. I went to a 120. It went slower. 115 was my magic number. Took three whole tries, two really because I started with the 110 already installed. Obviously you want to look at your plug and note your engine heat to avoid running too lean and hot. There are so many variables in these scooters that I think anyone would be hard pressed to just call out a number unless they knew a whole lot about scooters and had actually tried dozens of configurations of rollers, springs, exhausts, intakes, etc. |
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Post by geh3333 on Feb 7, 2015 13:11:33 GMT -5
I'd start with a 125 main and the 40 pilot and go from there. You should have noticeable gains using the 30mm carb compared to the stock 24mm
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Post by rcq92130 on Feb 7, 2015 13:21:45 GMT -5
My experience is the same as GEHs.
Just make sure you FIRST get the new carb properly set up at idle. If idle is off you will not correctly get the main set up.
Alley has a good primer of symptoms when tuning your carb - a "how to" with the pilot, and then a "what to listen for" to diagnose lean or rich conditions under load. I'm sure a search will turn it up.
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Post by jerseyboy on Feb 7, 2015 13:28:09 GMT -5
After hearing how that 28mm carb ran on that BBK Alley posted,,Im just going to go with a 28,,it will match my intake better also...that thing was snappy!
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Post by JerryScript on Feb 7, 2015 14:19:34 GMT -5
The proper way to jet without an O2 sensor is by doing plug chops. Your goal is a nice chocolate brown to coffee brown color. White is too lean, dark brown to black is too rich. You go on a WOT ride for at least a couple of minutes, then pull over and look at your spark plug. If it's too white, you begin by adjusting the air/fuel mixture and needle. If you get to the point the needle has been adjusted as far as it can (or has three washers added as spacers), it's time to go up in jet size. Put in the new jet, and put the needle back to the middle position, then follow the carb tuning procedures, then go for another WOT ride, and check your plug. It's best to do each plug test with a new spark plug, but that is only necessary if you started from a too rich setting and the spark plug is already dark brown or black. Here is a chart you can use to compare colors, NOTE - DO NOT ACCEPT ANY OF THE "LEAN BUT OK" COLORS, GO FOR LIGHT BROWN ONLY:  |
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Post by rcq92130 on Feb 7, 2015 14:41:37 GMT -5
Hey JS - have a question:
It was my understanding that you should FIRST set idle up (a/f screw and pilot jet) and get the idle circuit working optimally.
THEN set up the main WITHOUT AGAIN TOUCHING THE PROPERLY SET IDLE A/F MIXTURE SCREW.
Is that correct?
ps: in case some do not know the difference ---
"needle" can refer to 2 different things in the carb
(1) the a/f mixture screw (a needle valve)
(2) the needle that rises and lowers in the main jet (connected to the diaphragm atop the carb).
So when you are raising or lowering the "needle", it refers to #2. When you are setting idle it refers to #1. "Adjusting the needle" means opening the diaphragm cover and adding or subtracting special made washers so that the rest position of the needle in the jet is either higher or lower. Since the needle is tapered, when resting higher it INCREASES the open space between the needle and the jet, allowing MORE fuel into the airstream; when resting lower it decreases the space and the fuel sucked into the airstream (making the mixture more lean).
pps: GREAT chart!
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Post by JerryScript on Feb 7, 2015 17:47:20 GMT -5
Generally speaking yes, but I'll defer to alleyoop's 4TS carb tuning guide, it has never steered me wrong. During testing, when you do your high speed runs, if you bog when you open the throttle you usually need to raise the needle (the diaphragm needle). If you have raised the needle as high as you can, and you still bog or your plug chop doesn't look good, you need a larger main jet. Here is a good article on jetting from a jet retailer: www.jetsrus.com/FAQs/FAQ_rejetting_101_how_to_rejet.htmAnd here is Mikuni's VM Carburetor Super Tuning Manual: www.mikuni.com/pdf/vmmanual.pdf |
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Post by dmartin95 on Feb 8, 2015 21:33:34 GMT -5
Wow gang! Thanks for the links and info, very informative..... I've considered the info that has been provided, read the links on jetting (thanks Jerry  ) ... When it comes to these carbs, the thing I'm still confused about, is this: When people mod their scoots with say, a BBK, UNI and a performance exhaust, they wind up "upjetting" or getting a slightly bigger carb,.... What I can't determine is what are the limits of "slightly bigger".... Actually, I would just like this explained: Is putting in smaller jets in a larger carb going to yield the same results as upjetting a smaller carb? If not why....====================== With all the info provided, one would think I could figure it out by now.... |
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Post by rcq92130 on Feb 8, 2015 21:50:03 GMT -5
Wow gang! Thanks for the links and info, very informative..... I've considered the info that has been provided, read the links on jetting (thanks Jerry ) ... When it comes to these carbs, the thing I'm still confused about, is this: When people mod their scoots with say, a BBK, UNI and a performance exhaust, they wind up "upjetting" or getting a slightly bigger carb,.... What I can't determine is what are the limits of "slightly bigger".... Actually, I would just like this explained: Is putting in smaller jets in a larger carb going to yield the same results as upjetting a smaller carb? If not why....====================== With all the info provided, one would think I could figure it out by now.... The opposite, Dan A larger carb has a larger AIR opening. It may come with a larger jet or not. But the larger AIR OPENING means a lower vacuum at the venturi (where fuel is sucked past the needle into the airstream). So, all other things being equal, you will need a LARGER jet in a larger carb than in a smaller carb to get the same mixture. |
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Post by dmartin95 on Feb 8, 2015 21:54:13 GMT -5
There are so many variables in these scooters that I think anyone would be hard pressed to just call out a number unless they knew a whole lot about scooters and had actually tried dozens of configurations of rollers, springs, exhausts, intakes, etc. Yeah, I get that there's no crystal ball here.... I'm just confused because I'm getting conflicting info here and there.... This specific carb will be installed on a 180cc GY6.... It was listed for a 125/150 and the jet size is 40 pilot and 125 main... Is what's weird is that it came with two extra pilots... Not mains... Seeing as how it's listed for a 150cc, maybe they include those pilots because that's what needs to be tweaked... Or I could just be reading way too much into the accessories  ...... But why did they include those pilots? I think I'm over thinking this... I may just need to get a main and pilot jet set and tune away till I get it... I do have an O2 sensor.... It wasn't going on this build but I can use it just to calibrate the scooter then seal up the bung...  |
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Post by dmartin95 on Feb 8, 2015 22:01:31 GMT -5
The opposite, Dan
A larger carb has a larger AIR opening. It may come with a larger jet or not.
But the larger AIR OPENING means a lower vacuum at the venturi (where fuel is sucked past the needle into the airstream). So, all other things being equal, you will need a LARGER jet in a larger carb than in a smaller carb to get the same mixture. You posted while I was posting..... That makes sense....... |
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Post by rcq92130 on Feb 8, 2015 23:00:21 GMT -5
I am seriously jealous of your O2 sensor. What a great tuning and diagnostics thing you have there!
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Post by dmartin95 on Feb 9, 2015 0:31:22 GMT -5
I am seriously jealous of your O2 sensor. What a great tuning and diagnostics thing you have there! Do you post on scooter.doc? The reason I ask is because earlier I posted a pic of my ecotrons on that site, not here.... Joeybee is the one that posted a pic of his installed O2 sensor, didn't know if you got us mixed up or not..... This is my setup. It's an ecotron's Wideband ALM-with gauge  Thing is, I wasn't planning on installing this o2 sensor on this particular scooter... But it won't hurt anything... More work, but better end result I suppose..... |
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