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Post by scooterpimp on Mar 24, 2019 15:34:01 GMT -5
This sounds kinda lame , has anyone used a 20mm replacement carb on a stock 139qmb? Have a friend with sealed carb with issues , was thinking of getting her a 20mm replacement using proper jetting . I used 20mm on my bbk setups & worked great. But curious on stocker Edit she wants to stay stock so I found a eBay special
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Post by FrankenMech on Mar 25, 2019 10:58:06 GMT -5
Personally I don't think it will make much difference. Jetting may be a little harder. The stock airbox and 50cc displacement are the main performance limitations. The stock airbox is like breathing through a drinking straw.
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Post by fugaziiv on Mar 25, 2019 11:04:47 GMT -5
The 20 is just a bit too much for most stock applications. It's a little difficult to tune unless you've got the engine breathing more air somehow.
Matt
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Post by scooterpimp on Mar 25, 2019 13:54:52 GMT -5
Decided to stick to 18/19 mm stocker thanks for the input was going to bbk her scoot ,that’s why I was thinking 20mm , but she wants it stock. So no sense in getting the 20. , but I will tune her cvt when She’s not lookin
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Post by walleye1963 on Mar 26, 2019 23:16:58 GMT -5
The 20 is just a bit too much for most stock applications. It's a little difficult to tune unless you've got the engine breathing more air somehow. Matt i got a 20mm carb form you guys and its not a 20 mmm carb.s0 how can i ge a refund .
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Post by fugaziiv on Mar 27, 2019 8:38:36 GMT -5
The 20 is just a bit too much for most stock applications. It's a little difficult to tune unless you've got the engine breathing more air somehow. Matt i got a 20mm carb form you guys and its not a 20 mmm carb.s0 how can i ge a refund . Can you shoot me a Sales Order number? This post made me go and check our inventory, and we do indeed have an issue with some of our stock. The bore is correct, but there's a notable step down at the venturi, and that's not right. We're going through our complete stock now (about 700 of these carbs), to determine how much of it is good. I'm more than happy to issue a refund to you, and you can throw away that carb or keep it for a stock application, or I can send you a good 20mm after we go through our stock. Thanks, Matt Edit: For the time being we've pulled all of our 20's out of stock.
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Post by fugaziiv on Mar 27, 2019 9:27:11 GMT -5
Further update.
So, on every single QMB139 CVK carb, there is a stepdown from the intake to the venturi, as there is on the 20mm carbs.
The 20's feature a stepdown similar in ratio to the 19's and 18's, and maintain a correspondingly larger venturi. The venturi in these carbs is ovoid, so it looks small, but that's the way they are shaped to work.
I'm still determining if these can go into stock or not, or even what constitutes as a "true 20mm" carb at this point.
Since we sell 100's of these without complaint and have not changed suppliers, I'm pretty sure they are good.
Matt
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Post by benji on Mar 27, 2019 10:22:05 GMT -5
Further update. So, on every single QMB139 CVK carb, there is a stepdown from the intake to the venturi, as there is on the 20mm carbs. The 20's feature a stepdown similar in ratio to the 19's and 18's, and maintain a correspondingly larger venturi. The venturi in these carbs is ovoid, so it looks small, but that's the way they are shaped to work. I'm still determining if these can go into stock or not, or even what constitutes as a "true 20mm" carb at this point. Since we sell 100's of these without complaint and have not changed suppliers, I'm pretty sure they are good. Matt btw, this the mark of a good supplier. Saw or heard about a problem, and addresses it immediately with a public explanation. This is the right way to do business IMO.
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Post by FrankenMech on Mar 27, 2019 15:43:57 GMT -5
I am just guessing but it may be that the venturi area is the same as a 20mm round opening. The carbs I have seen seem to have what is sometimes also called a 'double D' shape through the venturi. I suppose with the right tools and instruments the area could be calculated.
The throttle shaft reduces the flow area also. That is just the nature of the beast.
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Post by walleye1963 on Mar 28, 2019 16:08:20 GMT -5
i got a 20mm carb form you guys and its not a 20 mmm carb.s0 how can i ge a refund . Can you shoot me a Sales Order number? This post made me go and check our inventory, and we do indeed have an issue with some of our stock. The bore is correct, but there's a notable step down at the venturi, and that's not right. We're going through our complete stock now (about 700 of these carbs), to determine how much of it is good. I'm more than happy to issue a refund to you, and you can throw away that carb or keep it for a stock application, or I can send you a good 20mm after we go through our stock. Thanks, Matt Edit: For the time being we've pulled all of our 20's out of stock.
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Post by walleye1963 on Mar 28, 2019 16:11:25 GMT -5
not sure of the sales order number. i got it off ebay from your company.ill see if i can find it.
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Post by fugaziiv on Mar 28, 2019 16:34:55 GMT -5
not sure of the sales order number. i got it off ebay from your company.ill see if i can find it. We don't sell anything on eBay. If it's one of our Universal Parts brand carbs you must have purchased it from one of our resellers. I can't refund that directly unfortunately, you'll have to go through the company you purchased it from on eBay. Matt
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Post by fugaziiv on Mar 29, 2019 9:55:38 GMT -5
Okay, so final update.
We reached out to the manufacture of the carb, and long story short, this is how they're made to work. The bore is a true 20mm, while the venturi is smaller by design. A 19mm or a 18mm carb will have a smaller venturi even still.
To back this up, I went ahead and purchased a few of the other 20mm carbs on the market. Long story short, ours may be the truest 20mm out there as we have a true 20mm intake bore all the way to the venturi, while some others are 20mm stepped to 19mm (or even 18mm) before the venturi.
Anyway, I've put our supply of 20's back into stock and they are available for sale again. They're as true a 20 as any you can buy. As far as I'm concerned this concludes the saga of the Universal Parts 20mm carbs.
Matt
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Post by walleye1963 on Mar 29, 2019 19:16:11 GMT -5
sorry about that i got it from scooters to go.again sorry about the mix up.so i can get a true 20mm carb at parts for scooter?
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Post by benji on Mar 30, 2019 21:52:45 GMT -5
sorry about that i got it from scooters to go.again sorry about the mix up.so i can get a true 20mm carb at parts for scooter? this is a valuable learning experience. There are only a few reputable parts distributors in the scooter game, and you can usually tell who they are because many people try to copy-cat them and sell cheaper versions of their parts on eBay. I used to search eBay for the best deals, and I still do, but I know it's a Gamble. When I want something to be actually what it is, I spend extra money with the vendors that you find on this forum. If it's more expensive, I tell myself I'm tipping the guy for running a legitimate business. That's pretty valuable.
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