I've just got my CB450 back together after a rebore and top-end overhaul. It starts and idles just fine but as it warms up it start to get rough - this is with no filters fitted for the time being. The mixture screws are turned right in as far as they'll go and both sides are still too rich. The bike was like this before I dismantled it. I have new float valves and the float height has been set on the bench with a credit-card gauge and fuel flowing. When I go the bike the carbs were exceptionally clean but I stripped and checked them anyhow and replaced the gaskets. One of the main jets was originally 145 but I've borrowed a 130 so both carbs have 130 mains. I checked the rest of the components and they're all the right parts.
Off-idle the engine runs cleanly with a crisp throttle response. I've been very careful to set the ignition timing as well as valve clearances.
I wonder if anyone has any specific pointers to assist in getting this sorted out? I've spent a good deal of time researching this and reading through the factory manual, but nothing I've tried has made any difference. The air and fuel passageways look good but someone with more experience of these bikes may suggest something I've overlooked.