I believe the original carb came with a Mikuni main jet, but the replacement carb has a main jet other than Mikuni. The punch line is: Mikuni main jets flow about 10% more fuel than the same size (number) main jet of another manufacturer because Mikuni main jet sizes are based on actual fuel flow rather than the the hole diameter. This is the primary reason for the reduction in top-speed that many C70 owners experience when replacing the original carb with an aftermarket one. So, replace the main jet in the aftermarket carb with the Mikuni main jet found in your original carb, put the needle in the middle groove and work from there.
-----Original Message-----
>From: cayman2653 <cayman2653@yahoo.com>
>Sent: Oct 3, 2011 7:59 AM
>To: Honda-C70@yahoogroups.com
>Subject: [Honda-C70] After market carb
>
>Earlier this summer I replaced the Honda Carb on my 81 Passport with a after market carb from dratv. It runs good but is not completely right. The bike runs right up to 33-35 mph and seems to studder (?), like its running out of gas or out of time maybe. There are lots of instructions on how to set up a Honda carb on this site and they work very well. But I don't think the settings are the same for the dratv carb. Does anyone know what groove the needle should be set in? What should the main jet size be? The bike idles very smooth and slow; it will rev right up in first and second gear but seems to run out of power in third gear. Gearing is stock, 15-36, and the engine has about 200 miles on a upper end rebuild.
>
>
>
>------------------------------------
>
>C70 Passport Not Running Right?
>1970-73 C70 Honda Service Manual: http://tinyurl.com/6ebwtw
>1970-73 C70 Troubleshooting Guide:
>http://tinyurl.com/6ebwtw (scroll to sec.7.1 page 101.jpg)
>1980-83 C70 Honda Service Manual: http://tinyurl.com/hu42c
>1980-81 C70 Troubleshooting Guide:
>http://tinyurl.com/hu42c (scroll to sec.18-1 page 170.jpg)
>1982-83 C70 Troubleshooting Guide:
>http://tinyurl.com/hu42c (scroll to sec. 20-28 page 205.jpg)
>
>1980-81 C70 Maintenance Schedule: http://tinyurl.com/z4zn6
>1982-83 C70 Maintenance Schedule: http://tinyurl.com/hw35c
>
>More resources for C70 Passports and Cubs:
>http://www.shlaes.com/Vehicles/Scooter.htm
>http://www.velodrome.com/HondaC70/HondaC70.htmlYahoo! Groups Links
>
>
>
TC
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1970-73 C70 Honda Service Manual: http://tinyurl.com/6ebwtw
1970-73 C70 Troubleshooting Guide:
http://tinyurl.com/6ebwtw (scroll to sec.7.1 page 101.jpg)
1980-83 C70 Honda Service Manual: http://tinyurl.com/hu42c
1980-81 C70 Troubleshooting Guide:
http://tinyurl.com/hu42c (scroll to sec.18-1 page 170.jpg)
1982-83 C70 Troubleshooting Guide:
http://tinyurl.com/hu42c (scroll to sec. 20-28 page 205.jpg)
1980-81 C70 Maintenance Schedule: http://tinyurl.com/z4zn6
1982-83 C70 Maintenance Schedule: http://tinyurl.com/hw35c
More resources for C70 Passports and Cubs:
http://www.shlaes.com/Vehicles/Scooter.htm
http://www.velodrome.com/HondaC70/HondaC70.html
