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Post by tr1ppyy4m4h4 on Jul 8, 2012 9:23:31 GMT -5
I was just wondering as far as 2-stroke performance goes, what bore size on a carb would give the most perfomance in speed? considering this scoot has multiple mods including 70cc bore kit and exhaust. this site sells them from 21-30mm
Thanks for any input!!
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Post by 90GTVert on Jul 8, 2012 9:54:35 GMT -5
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Post by johnnymac01 on Jul 8, 2012 9:56:42 GMT -5
In the Dellorto manual the graph specifies that if you're looking at about 10hp you need somewhere between a 17mm and 21mm carb. This link shows that the gain from a 17.5mm to a 19mm carb on a 70bbk is minimal, if not non-existent: www.pedparts.co.uk/blog/yamaha-aerox-carb-comparisonOf course, there's a lot of variables, but if you look at getting a minimum 17.5mm and a maximum 21mm carb, you should be cool. Too large a carb for your setup and you'll lose low revs intake speed and therefore torque - just like cars (note the graph shows more power down low for the 17.5mm). But if you wanna rev really high - like some bbk's and exhausts are setup for, you will need a carb more like 21mm. Hope that helps.  JM p.s. also remember that when you change the carb you may need to change the connection to the airbox or even get a new air-filter. ALSO, if you get a big carb and your venturi is larger than the largest section of your intake stream (my intake manifold is 19mm inner diameter) then you're wasting your time with a carb bigger than this diameter. The fastest part (i.e. the smallest inner diameter) should be the carb venturi. |
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Post by tr1ppyy4m4h4 on Jul 8, 2012 10:04:48 GMT -5
i have found enough information, i was measuring the intake bore on the carb not the actual bore inside, you dont think 24mm is too big do you??
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Post by felliott on Jul 8, 2012 14:21:32 GMT -5
24mm was to big for anything I have done. Engines seem to get very peaky with a 2 big of carburetor.
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Post by tr1ppyy4m4h4 on Jul 8, 2012 21:41:25 GMT -5
ive decided to run a 24mm carb with a 140 main jet and 38 pilot jet and work down from there. does anyone know about power jet and if its needed??
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Post by tr1ppyy4m4h4 on Jul 10, 2012 1:17:55 GMT -5
i did some calculations... stock Zuma carb is 80 main jet for 14mm carb not much increase jet size to 17.5mm due to upgrade to 70cc 85 main jet for 17.5mm carb 95 main jet for 19mm carb 110 main jet for 21mm carb 130 main jet for 24mm carb 155 main jet for 28mm carb 170 main jet for 30mm carb would recommend starting at these numbers then down sizing  im going to start with the 140 mj and 38 pilot and see how rich it runs. then i will put in 125 main jet and leave the pilot 38 which should run good at happy medium although might have to lower it and try 120 for performance. |
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Post by tr1ppyy4m4h4 on Jul 13, 2012 16:38:49 GMT -5
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Post by 90GTVert on Jul 13, 2012 16:53:49 GMT -5
A lot of us know about carbs and/or Zumas. It's just that will work and best choice are 2 different things. What other feedback are you looking for?
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Post by tr1ppyy4m4h4 on Jul 13, 2012 23:09:27 GMT -5
i mean what do you guys think about a 24mm carb on a 70cc zuma all modded out with the proper jets? No other scooter around will be able to touch it!
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Post by tygertung on Jul 14, 2012 1:29:02 GMT -5
I think it will have too bigger of a carburettor.
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Post by lshigham on Jul 14, 2012 5:10:36 GMT -5
i mean what do you guys think about a 24mm carb on a 70cc zuma all modded out with the proper jets? No other scooter around will be able to touch it! You don't get more power by sticking an excessively large carb on... |
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Post by 90GTVert on Jul 14, 2012 5:18:29 GMT -5
I wish you could just get a big carb and make big HP. Life would be simple in the scooter world.
It's gonna work. I've seen people use 28mm carbs on 70cc sport kits and be happy. I think if they tried a 19-21mm they'd be even happier though. The one thing I've seen with big carbs that I think makes some believe they are much faster with the larger carb is the difference in throttle opening. It often takes much less throttle opening to get moving or to cruise because the carb is so big. Unfortunately, just because it feels faster at 1/4 throttle doesn't mean it's faster WOT than a smaller carb.
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Post by jmkjr72 on Jul 14, 2012 17:16:55 GMT -5
im still sticking with the feed back i gave in the other thread and over on zf
unless you are running a race bore that 24mm is too big for your scoot
you will notice that it will be very hard to compare
also you cant realy compare jets the way you tried
as jets are numbered diffrently from diffrent manufactures
some use hole size
some use flow
and then others use sevral diffrent formulas that combine the hole and flow
bot to mention you skiped completly over needle tuning and that is going to be your most important spot to tune as you spend 90% of your time in your needle controled area
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Post by tr1ppyy4m4h4 on Jul 16, 2012 14:44:00 GMT -5
Now I talked to the mechanic he said he refused to work on it and be liable, "ticking time bomb". he said with all the performance parts its too risky and that I would blow it up and blame him. He told me that the jets in the 24mm carb were 107 main and 45 pilot. he had ordered a jet kit around that area. i told him that would be too small and would run too lean. he told me he had an 07 Zuma that he had installed a big bore kit and other parts on it. he blew it up twice then put stock parts on it and sold it. i asked him why he added those parts and he said "just to see what it could do". well i told him to just put the bore kit on and he agreed so i will go get it later today and do the carb myself. I still have a 140 and 125 main jet and the 38 pilot you recommended. If you could offer any advice on how you installed it or about the needle adjustment that would be great. the guy also didnt know how the manual choke carb would work when theres an auto choke plug in on the Zuma. i told him you just wouldnt plug in the auto choke cable and just use the manual when need be. im just afraid the 140 would run too rich but my dad said that wont hurt anything as long as it runs. any final advice? i will update you guys when done.  |
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