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My Chief gets about 35+MPG with a flat head motor. Timing, manifold seal(Cotton has written quite a bit about this subject), and carb setting make all the difference. Setting these old bikes up is not simple. It's an art form that is slowly dying.
A tuned motor also can wear slower than a badly tuned unit mainly because of overheating. One of the easiest ways to tell if you are out of tune is to observe the amount of heat coming off the motor. The motor can actually smell like it's cooking if it's lean. The exhaust smells like un-burnt hydrocarbons when it is too rich. You can also measure cylinder heat with an infra-red thermometer. After-burning or back-fires when you close the throttle fast at speed is another simple lean test.
Valve adjustment is really important with an old motor. You can't really time a motor correctly until the valve lash is completed. If a valve does not fully return to it's seat because there is no gap between the stem and the lifting device, you could be burning up your valve seats and over heat the motor.
Too much advance on the timing is also a very common problem in poor running motors. Don't time a motor "By Ear".
If you been around these bikes long enough you can hear a badly tuned bike as it passes you and unleashes noises that sound like a fork in the garbage disposal. We have all witnessed this.
This does not necessarily mean that your engine is out of tune but it just something to be aware of.
DSCN2688.JPG DSCN2686.JPG DSCN2687.JPG DSCN2684.JPG DSCN2689.JPG
A tuned motor also can wear slower than a badly tuned unit mainly because of overheating. One of the easiest ways to tell if you are out of tune is to observe the amount of heat coming off the motor. The motor can actually smell like it's cooking if it's lean. The exhaust smells like un-burnt hydrocarbons when it is too rich. You can also measure cylinder heat with an infra-red thermometer. After-burning or back-fires when you close the throttle fast at speed is another simple lean test.
Valve adjustment is really important with an old motor. You can't really time a motor correctly until the valve lash is completed. If a valve does not fully return to it's seat because there is no gap between the stem and the lifting device, you could be burning up your valve seats and over heat the motor.
Too much advance on the timing is also a very common problem in poor running motors. Don't time a motor "By Ear".
If you been around these bikes long enough you can hear a badly tuned bike as it passes you and unleashes noises that sound like a fork in the garbage disposal. We have all witnessed this.
This does not necessarily mean that your engine is out of tune but it just something to be aware of.
DSCN2688.JPG DSCN2686.JPG DSCN2687.JPG DSCN2684.JPG DSCN2689.JPG
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