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Other Honda Mini Trails
CT90, CT110, ST70, ST90 Discussion
ST50 Shifting issue + leak
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<blockquote data-quote="69ST" data-source="post: 182785" data-attributes="member: 5"><p>It takes practice and time, to coordinate the throttle/rpm/shift lever movements. If you've never mastered shifting with a manual clutch, this is going to be more difficult...because...what needs to be done is translating & replicating manual clutch shifting. You see, when the lever is moved to either travel limit, the clutch is being disengaged the same as if you were squeezing a hand lever to work the clutch. That's why it's a "semi automatic". It uses a centrifugal assembly to engage above a certain rpm, beyond that, centrifugal assembly fully engaged, it becomes a fully manual clutch. You're unaware of that, since there's a cam plate assembly, as part of the shift linkage, inside the engine.</p><p></p><p>You must coordinate engine rpm & torque load to shift gears, same as with a manual. Any of these transmissions will fight you, if the load, throttle application and rpm are not properly coordinated. The gears are constant-mesh. When you shift, the gears move in pairs...it's their drive dogs (fitting into their respect pockets on the next gear) that engage and disengage. Those drive dogs have a "reverse taper" (bigger toward the ends) that mechanically lock them together. Without those, the tranny would jump out of gear, while riding...a symptom of worn gears.</p><p></p><p>I'm guessing that you gear changes are rough, with an audible "snap". That's a bad sign...telling you that you're not shifting correctly. Seriously, it is possible to execute smooth, seamless, gear changes with a semi-auto. It's just not intuitive, you have to think about what you're doing, then practice refining your technique, long enough until it becomes almost second-nature.</p><p></p><p>If the head nuts are backing-out as the engine runs, something isn't right. There aren't many parts involved: 3 acorn nuts, 1 hex nut, 3 flat washers, 1 sealing washer, 4 studs, head gasket. If it were mine, I'd probably replace the head gasket, nuts & washers. That's less than $10 worth of parts and not much work, either.</p><p></p><p>As for why it dies at idle, that diagnosis could be more complicated...along with the correction. If carb adjustments (pilot airbleed, a.k.a. "idle mixture" and idle speed) won't do the job then, based on the info you've provided, I'd suspect a leaky intake valve. Take a look inside the intake port; if it's blackened, the intake valve is leaking. That's a very common malady with heads of this vintage and, it can persist for a long time before manifesting as poor performance or, ultimately, a non-running engine due to sever compression loss. </p><p></p><p>For now, is the insulator where it should be...between the intake & carburetor? The manifold should only have a gasket between it & the intake port flange on the head. I've seen guys move these between the head & intake, which results in an over-cooled intake...or omit it altogether, causing fuel percolation inside the carb a.k.a. "vapor lock", especially at idle or during the heat soak period immediately following engine shutdown.</p></blockquote><p></p>
[QUOTE="69ST, post: 182785, member: 5"] It takes practice and time, to coordinate the throttle/rpm/shift lever movements. If you've never mastered shifting with a manual clutch, this is going to be more difficult...because...what needs to be done is translating & replicating manual clutch shifting. You see, when the lever is moved to either travel limit, the clutch is being disengaged the same as if you were squeezing a hand lever to work the clutch. That's why it's a "semi automatic". It uses a centrifugal assembly to engage above a certain rpm, beyond that, centrifugal assembly fully engaged, it becomes a fully manual clutch. You're unaware of that, since there's a cam plate assembly, as part of the shift linkage, inside the engine. You must coordinate engine rpm & torque load to shift gears, same as with a manual. Any of these transmissions will fight you, if the load, throttle application and rpm are not properly coordinated. The gears are constant-mesh. When you shift, the gears move in pairs...it's their drive dogs (fitting into their respect pockets on the next gear) that engage and disengage. Those drive dogs have a "reverse taper" (bigger toward the ends) that mechanically lock them together. Without those, the tranny would jump out of gear, while riding...a symptom of worn gears. I'm guessing that you gear changes are rough, with an audible "snap". That's a bad sign...telling you that you're not shifting correctly. Seriously, it is possible to execute smooth, seamless, gear changes with a semi-auto. It's just not intuitive, you have to think about what you're doing, then practice refining your technique, long enough until it becomes almost second-nature. If the head nuts are backing-out as the engine runs, something isn't right. There aren't many parts involved: 3 acorn nuts, 1 hex nut, 3 flat washers, 1 sealing washer, 4 studs, head gasket. If it were mine, I'd probably replace the head gasket, nuts & washers. That's less than $10 worth of parts and not much work, either. As for why it dies at idle, that diagnosis could be more complicated...along with the correction. If carb adjustments (pilot airbleed, a.k.a. "idle mixture" and idle speed) won't do the job then, based on the info you've provided, I'd suspect a leaky intake valve. Take a look inside the intake port; if it's blackened, the intake valve is leaking. That's a very common malady with heads of this vintage and, it can persist for a long time before manifesting as poor performance or, ultimately, a non-running engine due to sever compression loss. For now, is the insulator where it should be...between the intake & carburetor? The manifold should only have a gasket between it & the intake port flange on the head. I've seen guys move these between the head & intake, which results in an over-cooled intake...or omit it altogether, causing fuel percolation inside the carb a.k.a. "vapor lock", especially at idle or during the heat soak period immediately following engine shutdown. [/QUOTE]
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CT90, CT110, ST70, ST90 Discussion
ST50 Shifting issue + leak
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