Need some Advice on problem

[CB750SC_Screwed_Up]

Hello,
To give you a run down on what I'm working on:
1982 Honda CB750SC, 9,898 miles. Engine has been rebuilt by a shop by pervious owner. He says it's been bored +.030 and has had 10:1 comp pistons. Stock carbs that have been completely rebuilt as well with stage 1 jet kit. The exhaust has been replaced with a MAC 4 into 1 headder. Air box and everything else is stock.

The Problem:

When I got the bike, it did not run. The owner told me shortly after the rebuild, it lost all power out of nowhere and never ran right after. Even the bike shop could not figure it out. So it sat for 2 years, and he gave it to me free thinking it was no good other than for parts. After a few hours I had it running, the OKI or some call it a CDI for the 2 inside cylinders was junk. I replaced it and did a few other adjustments and it ran well accept for this current issue that I can't figure out.

The bike runs fine just going around town and at normal highway speed. But, if you get on it, it pulls very hard through 6,000 RPM. At 6k R's it starts to break up and by the time you reach 7k it just flat lines. It will not pull past 7,000 RPM no matter what you do. According To the preve owner, the bike would pull good clear through it's red line (9,500) until he started having his problem.

I Replaced:
Both OKI's, Both Coils, Pulse Generator, New NGK's, New Wires, Rebuilt the carbs (again), Regulator/rectifire, Checked for good fuel flow, Hell I even coated the inside of the fuel tank wondering if I was getting rust in the fuel. These changes ESP changing the coils did make some improvement as it used to die at 5000 r's.

So does anyone have anymore ideas for me that I may have overlooked. I'm really stumped on this on.

Thanks,
Jay

[blackhawkrider]

sounds like to me you have gone over the ignition system pretty well. So did you clean the carbs out too?
If you did maybe the main jet isn't big enough and you are leaning out in the top end.

[CB750SC_Screwed_Up]

blackhawkrider wrote

sounds like to me you have gone over the ignition system pretty well. So did you clean the carbs out too?
If you did maybe the main jet isn't big enough and you are leaning out in the top end.

Well, I went out and gave it a good hard running came back and pulled the spark plugs. They have a off white color on the ground, and the core and porcelain (if I spelled that right) are a very, and I do mean very light tan color, Looks like white with just a light hint of tan. Think I should go a step bigger on the jets?

Thanks,
Jay

[blackhawkrider]

what main jets are in there now? Also are the needles adjustable? If it is white most likely it would not hurt to bump up a jet size or adjust the needles a few clicks further to richen the mix

[freek-3]

Hi I had the same problem, openend my carbs top, cleaned and streched the neadle jet springs and shuffled the units arount until they moved freely.

Another problem I had was the bike would run fine up to 4000 refs byt no futher,
after extensive cleaning and checking I found one needle jet broke of and got stuck.

also make sure all extra pipes from the carb, is sealed.