A friend needs some urgent help PLEASE

[gonebiking-2]

A friend that I have made on the forum has emailed me in Australia with a problem concerning his motor not performing at high RPM. Here is what he sent me, and I have copied and pasted his post on the forum on his behalf This is the contents of his email to me: " I run a 76 Supersport on a rigid frame I've made, I run the four into one exhaust wide open at the collector with no muffler after it, and I run the individual cone filters for the carbs, I have installed # 120 main jets on all four carbs.  She runs awesome until I give her more to get in the higher rpm's and speeds, she hesitates and won't make it up to speeds that I am accustomed to with these bikes.  I believe she is running lean and needs more fuel, but at what point do the main jets not help.  I have not been able to find a set of needles that are adjustable so that I can let more fuel through, but I have been looking at jets up to # 140's. What do you think?  And do you know anywhere to get aftermarket needles for these carbs?"   Please email me back at [e-mail]

[CB750Winger]

  I have a 4 into 1 header with muffler and stock air box. I'm not sure about the jet selection but mine stumbled coming off idle so I dropped the needles a couple notches and helped. I have them in the middle notch right now and may need to go one more. I got the full carb rebuild kits from oldbikebarn.com which included adjustable needles. You can also try www.hdlparts.com (honda direct line) phone [phone]. It may take a couple trys to get the needles where they need to be.  Paul