![]() ![]() There was some clear information by Bosch when J and K Jetronic systems were first around and they had some good block diagrams explaining the function and also how to test for faults. Since many people are learning to ride on one of these, they are also learning to maintain and. I feel that this makes a good instructable since the XR80 and XR100 is extremely common as a first dirtbike. 4 hours ago XJet (XJET) announces downsized 1,600,000. The bike used in this example was a 1998 Honda XR80R but will also apply to the Honda XR100 as well. Ignition Timing (BTDC or Mark) Valve Lash. NOS also has a very informative new timing chart, that is included with all the new jetting charts. The injection timing, not only the start time but the duration of injection is controlled by the ecu (engine control unit) based on the parameters listed above which are compared to a characteristic map held in memory. Timing Marks On Spark PlugsBy measuring these two factors, you can get a good. The ignition timimg and fuel timing are controlled by the position of the crank, cam and various sensors measuring the engine load, speed, temperature etc valve timing diagram is a representation of the positions of the crank when the various operations as inlet valve opening, closing, exhaust valve opening and closing and also the beginning and end of various strokes. For crank position, Hall effect sensors can often be used, but the trick is that there are two or three magnets a specific distance apart on the flywheel so the ecu can have a rapid update on crankshaft speed changes. Valve Clearance Comments VA Series.020. Once you have electronic control then there can be several sensors involved: crank position sensors, cam position sensors, throttle position etc. Model: Point Gap: Spark Plug Gap Timing Mark On Spark Occurs Firing Order Int. Then all you have to do is set the timing so that cylinder 1 fires at approximately 5 degrees before top dead centre. Once you have the camshaft correctly timed and it is driven at half the crankshaft speed then that will be the correct speed for the distributor. The distributor is usually driven from the camshaft and is often also the drive to the oil pump, so the shaft comes up from the gear driven off the camshaft and descends down to the oil pump, usually to save cost and weight. Keep in mind that this timing diagram is only used to explain the principles of operation and the general timing of these events in relationship to the position of the crankshaft.First I will assume older engines with no electronic systems. Although each point on the timing diagram is just an example, all four-stroke events generally occur somewhat near the points shown. The exhaust stroke continues to about 10 degrees BTDC at which time the cycle starts all over again. The power stroke goes to about 12 degrees BBDC. The compression stroke then continues to the ignition point, about 15 degrees BTDC. To begin, the intake valves open about 10 degrees BTDC. During the four cycles of operation, the crankshaft revolves two complete revolutions or 720 degrees of rotation. ![]() Two circles are shown to represent two complete revolutions of the crankshaft. Tramming, an old but accurate method of setting valve and ignition timing, can be a great way to set basic timing. The mark at the bottom of the graph would illustrate the position of the piston at BDC. Any event that happens after top dead center is called ATDC or after top dead center. Any event that happens before TDC is referred to as BTDC or before top dead center. ![]() For example, at the top of the diagram, the piston would be located exactly at TDC (Top Dead Center). One way to look at this diagram is to think of these events in terms of the position of the crankshaft and 360 degrees rotation. The diagram is set on a vertical and horizontal axis. Move the flywheel until the mark after TDC is lined up with the tram and adjust the rocker arm screw so that there is a slight pressure on the screw. Any variance that may exist then will occur.at the low idle end of the advance curve. Therefore, the distributor should be set to give the exact timing at high idle. This establishes the timing marks for ignition and exhaust valve closure. NOTE 1: Proper ignition timing at high idle is essential for best performance and engine life. Describing the Principle: A timing diagram is a method used to identify the time at which all of the four stroke events occur on a typical four-stroke engine. Now measure out five degrees in each direction, again scribing a mark. ![]()
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