Ksgfx
Member
I’m hoping this group can help as I’m just about at wits end with my 72 cb450. I’ve done a complete restoration, including a full engine tear down. My problem is while it will run it does not run well. I think I’ve narrowed it down to a carb problem, but I’ve been wrong before.
Here is the issue:
- Starts good and will idle but then starts to accelerate on its own once warm, stops around 4000 rpm and holds
- Also hangs when revved
- Have determine the right cylinder by itself will hang but must be revved. Will then hold at 3000rpm and will not fall
- Left cylinder will also hang on rev but will slowly drop on its own.
Here is what I tried:
- Carbs vapor blasted and cleaned in an ultrasonic multiple times. Also cleaned each passageway with small brushes and drills.
- Cleaned and swapped advancer twice, no change
- Checked and rechecked static timing, all seems good
- Checked and tightened valves to OEM spec, one was a little loose, no change
- Swapped to a spare right carb I had but kept the same jets, no change.
- Removed airboxes, no change
- Set fuel screw at every half turn from .5 to 3 turns out. Issue improves slightly
- Sprayed carb clean all around the intake boots and carb, no change at idle
General Specs:
- main jets:140, pilot:38, both Klein originals
- Fuel screw: 1.5 turns out with new OEM oring
- Using OEM airboxes with old filters. They are a little yellow but still seem to pass air just fine.
Let me know if you need any further information and thanks in advance for your help.
Kevin
Here is the issue:
- Starts good and will idle but then starts to accelerate on its own once warm, stops around 4000 rpm and holds
- Also hangs when revved
- Have determine the right cylinder by itself will hang but must be revved. Will then hold at 3000rpm and will not fall
- Left cylinder will also hang on rev but will slowly drop on its own.
Here is what I tried:
- Carbs vapor blasted and cleaned in an ultrasonic multiple times. Also cleaned each passageway with small brushes and drills.
- Cleaned and swapped advancer twice, no change
- Checked and rechecked static timing, all seems good
- Checked and tightened valves to OEM spec, one was a little loose, no change
- Swapped to a spare right carb I had but kept the same jets, no change.
- Removed airboxes, no change
- Set fuel screw at every half turn from .5 to 3 turns out. Issue improves slightly
- Sprayed carb clean all around the intake boots and carb, no change at idle
General Specs:
- main jets:140, pilot:38, both Klein originals
- Fuel screw: 1.5 turns out with new OEM oring
- Using OEM airboxes with old filters. They are a little yellow but still seem to pass air just fine.
Let me know if you need any further information and thanks in advance for your help.
Kevin