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Old 08-12-2012, 10:22 AM   #66
BadBMWBrad
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Joined: Aug 2007
Oddometer: 13
Dachary/Kay - I enjoyed reading your travel adventure blog. Being a mechanical systems engineer and having spent a lot of time learning and practicing the Kepner-Tregoe problem analysis method, root cause analysis and other failure modes analyses methodologies, I'm compelled to gain an understanding as to why your engine's power output changes dramatically and why your fuel economy is so poor. In addition, I'm still not convinced the plastic breather elbow melted because somehow it was defective...

I submit that your electronic ignition's spark-advance function is unreliable. This would explain engine overheating, poor fuel economy and sudden increase/decrease in engine power. If the spark timing does not advance at high RPM then the spark occurs too late for efficient fuel:air combustion. Much of the fuel:air combustion occurs late in the power stroke and the engine will over-heat. Fuel economy will also be poor. If the spark timing advanced intermittently then sudden increased/decreased engine performance would be manifest.

There are quite a few design changes in the evolution of Ural's electronic ignition system. Significantly, problems occurred with heat affecting the ignition advance curve. One solution is to retrofit a set of contact breaker points and a flyweight spark-advance mechanism. There may be more maintenance associated with this design but it is field servicable which would be an important advantage on your RTW trip. Another (more expensive) solution is to upgrade the Patrol's Ducati ignition system with a Power Arc (aftermarket) ignition system available from Raceway Services.The Power Arc employs an optically triggered ignition spark. Read this thread for some direct operating experience with the Power Arc system. If you take this route, make sure to water-seal the sparkplug cable penetrations and any gasketed flanges (to exclude water/moisture) which cover the Power Arc electronics.

If you have an ignition timing strobe lamp then you can see when the voltage pulse (spark) in the sparkplug cable occurs in relation to the engine crank position (while the engine is operating). To see the ignition timing in action (on a BMW boxer engine), there is a little rubber plug on the engine crankcase which is removed to see the flywheel's perimeter surface (timing hole). The timing strobe lamp is powered by a 12v battery (such as the motorcycle battery or a separate 12v battery). An inductive sensor lead is spring-clamped around one of the sparkplug cables.

Start the engine, point the strobe lamp into the timing hole and pull the strobe lamp's trigger. Every voltage pulse sensed by the inductive sensor will fire the strobe light. Stroboscopic-effect allows you to see the flywheel timing marks through the timing hole. The timing marks appear motionless at constant RPM. You can rev up the engine and see the timing mark's position change in relation to engine RPM. The BMW engine has marks for crankshaft piston at top-dead-center, a mark for the low-RPM spark timing and another mark for the high-RPM spark timing (full spark advance).

Perhaps engine heat affects the spark-advance circuitry on the electronic ignition module or maybe it's simply defective. A heat-affected spark-advance function might be revealed by using a hair dryer to blow hot air on the ignition module to see if it has an affect on spark-advance.

BadBMWBrad screwed with this post 08-13-2012 at 06:11 AM
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