norton
Unregistered user
We’re trying to get a ’77 R100/7 with 18 K miles sorted and are running out of ideas. The owner has had the bike for several years and in the past it had run well. Motor was reconditioned about 10K miles ago. The current issue is a high speed stumble. Accelerates through the gears fine, and at a steady speed of 65-70 mph 4500 RPM’s, while rolling on the throttle it stumbles, and recovers in a few seconds. The carburetors have been rebuilt a while back and appear to be clean and OK. During the investigation of the carbs they have been disassembled inspected, cleaned and appear fine. Over three years the stumbling has become slightly worse, and gas milage is in the 30 mpg range, despite the efforts to resolve this. (or is it because of the efforts?)
The following is what has been done in response to the issue
Fuel flow at the petcock 700ml/minute
Fuel to the bottom of the bowl 350ml/minute
Fuel in the bowl is at 32 mm
Air leak test showed no leak. Ran bike and sprayed starter fluid on the outside with no increase in RPMs
New gas cap that was drilled for venting purposes
Diaphragms look fine
Tank and petcocks are clean
150 main jet (stock) have tried 160 and 145 no help
Stock needle jet
Stock needle
Needle clip is in position 3 (1 up from bottom) stock position
Valves adjusted and are dead on
Does not smoke at all
Boyer electronic ignition
Timing is a degree off as measured by a strobe
Starts right up from cold
Carbs 64/32 19-20
The following is what has been done in response to the issue
Fuel flow at the petcock 700ml/minute
Fuel to the bottom of the bowl 350ml/minute
Fuel in the bowl is at 32 mm
Air leak test showed no leak. Ran bike and sprayed starter fluid on the outside with no increase in RPMs
New gas cap that was drilled for venting purposes
Diaphragms look fine
Tank and petcocks are clean
150 main jet (stock) have tried 160 and 145 no help
Stock needle jet
Stock needle
Needle clip is in position 3 (1 up from bottom) stock position
Valves adjusted and are dead on
Does not smoke at all
Boyer electronic ignition
Timing is a degree off as measured by a strobe
Starts right up from cold
Carbs 64/32 19-20