Maybe you guys can help me diagnose an issue I have had with my CB750 motor for going on 4 years now. It's why I shelved this motor, before I got the bright idea to put it in a chopper. I've gone through all the checks. I've done everything I know to do and nothing seems to work. It's nothing I've ever dealt with, and it has me baffled.
It's a 77 motor with PD carbs. The carbs have been rebuilt and cleaned. I've synced the carbs and I've adjusted air mixes. I can turn them all the way in until they start to backfire through the carb and turn them out in 8th increments until they stop, and they still foul the plugs on 1,2,4. #3 stays somewhat lean. I've run this motor and these carbs with a stock airbox and currently with a breadbox. The mouth of the carbs are saturated with fuel on all four carbs. They have new boots. Pumper sprays well into all four carbs and appears even. Maybe too much?
The motor has a fresh top end. All new valves and machined seats. Tappets are set for both intake and exhaust. Timing has been set and checked and rechecked ad nauseum. I've run Dyna and points and get the same result. I've run Dyna ignition with Accel coils and two different plug wires. When I put the motor in the chopper I went back to points, Dyna coils and new plug wires. It gets spark on all four. Brand new, fresh built wiring harness for juice with a well charged LiFePO4 battery.
Compression is 152 across all four cylinders. Pretty much on the money. I've sprayed everywhere looking for leaks and I have found zero. Fresh head gasket doesn't show any leakage- oil or air. 750f exhaust with my own custom mufflers with fresh gaskets. No white smoke out of the exhaust, though it definitely is showing signs of unburnt fuel. I suspect somewhere somehow I'm getting way too much fuel. The float are set per the manual- 14.5mm.
I figure it's something to do with these carbs, but I can't figure out what else to look for. The internet really doesn't show a search for another bike that has had the same thing going on. I'm comfortable with the condition of the motor and every setting I have, but I'm also open to the possibility that I'm an idiot. I still think it's these PD carbs. Any help is appreciated.
It's a 77 motor with PD carbs. The carbs have been rebuilt and cleaned. I've synced the carbs and I've adjusted air mixes. I can turn them all the way in until they start to backfire through the carb and turn them out in 8th increments until they stop, and they still foul the plugs on 1,2,4. #3 stays somewhat lean. I've run this motor and these carbs with a stock airbox and currently with a breadbox. The mouth of the carbs are saturated with fuel on all four carbs. They have new boots. Pumper sprays well into all four carbs and appears even. Maybe too much?
The motor has a fresh top end. All new valves and machined seats. Tappets are set for both intake and exhaust. Timing has been set and checked and rechecked ad nauseum. I've run Dyna and points and get the same result. I've run Dyna ignition with Accel coils and two different plug wires. When I put the motor in the chopper I went back to points, Dyna coils and new plug wires. It gets spark on all four. Brand new, fresh built wiring harness for juice with a well charged LiFePO4 battery.
Compression is 152 across all four cylinders. Pretty much on the money. I've sprayed everywhere looking for leaks and I have found zero. Fresh head gasket doesn't show any leakage- oil or air. 750f exhaust with my own custom mufflers with fresh gaskets. No white smoke out of the exhaust, though it definitely is showing signs of unburnt fuel. I suspect somewhere somehow I'm getting way too much fuel. The float are set per the manual- 14.5mm.
I figure it's something to do with these carbs, but I can't figure out what else to look for. The internet really doesn't show a search for another bike that has had the same thing going on. I'm comfortable with the condition of the motor and every setting I have, but I'm also open to the possibility that I'm an idiot. I still think it's these PD carbs. Any help is appreciated.