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FJR Motorcycle Forums
Technical & Mechanical Problems
Fast Idle unit on throttle bodies
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<blockquote data-quote="RadioHowie" data-source="post: 629772" data-attributes="member: 426"><p>You are correct. One of the control plunger lines runs directly to the radiator, the other goes to the coolant pipe atop the valve cover, BELOW the thermostat, so there's pressure on both lines when the motor is running, whether the thermostat is open or closed. The thermostat only allows maximum coolant flow to the radiator when the coolant in the motor heats up the thermostat enough to open, allowing "bypass' to the radiator for further cooling, so the fast idle will get hot coolant long before the thermostat opens, making the unit actually more effective, since the "un-radiatored" coolant in the mtor will heat up a lot quicker than all the coolant in the entire system.</p><p></p><p>Good catch!!</p><p></p><p>Although I still think 1500rpm is too low for a "fast" idle on a motor with no flywheel. Hell, even my 15 year old Honda Del Sol fast idles at 2200rpm, and it's got plenty of flywheel to prevent "clunking", which I think is the motor stopping for a fraction of a second because a piston hits a "dead hole" that isn't firing because the motor's cold, so the cylinder basically becomes an air spring, forcing the motor to come to a momentary halt that makes the entire bike shudder and all the attached mechanical bits "clunk". The increased idle helps to overcome the relatively low inertia of the piston and crank assembly, essentially creating a virtual flywheel effect.</p><p></p><p>Basically, a motor spinning at 2500rpm is much harder to stop than one spinning at 1500rpm.</p></blockquote><p></p>
[QUOTE="RadioHowie, post: 629772, member: 426"] You are correct. One of the control plunger lines runs directly to the radiator, the other goes to the coolant pipe atop the valve cover, BELOW the thermostat, so there's pressure on both lines when the motor is running, whether the thermostat is open or closed. The thermostat only allows maximum coolant flow to the radiator when the coolant in the motor heats up the thermostat enough to open, allowing "bypass' to the radiator for further cooling, so the fast idle will get hot coolant long before the thermostat opens, making the unit actually more effective, since the "un-radiatored" coolant in the mtor will heat up a lot quicker than all the coolant in the entire system. Good catch!! Although I still think 1500rpm is too low for a "fast" idle on a motor with no flywheel. Hell, even my 15 year old Honda Del Sol fast idles at 2200rpm, and it's got plenty of flywheel to prevent "clunking", which I think is the motor stopping for a fraction of a second because a piston hits a "dead hole" that isn't firing because the motor's cold, so the cylinder basically becomes an air spring, forcing the motor to come to a momentary halt that makes the entire bike shudder and all the attached mechanical bits "clunk". The increased idle helps to overcome the relatively low inertia of the piston and crank assembly, essentially creating a virtual flywheel effect. Basically, a motor spinning at 2500rpm is much harder to stop than one spinning at 1500rpm. [/QUOTE]
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FJR Motorcycle Forums
Technical & Mechanical Problems
Fast Idle unit on throttle bodies
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