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My GS750 (8valve) started making a scratching noise at certain RPMs on a recent trip and has noticeably less power/response. I rode out ~130 miles and back and it happened sometime right in the middle and has been like that since.
The noise will go away in certain gear/RPM combinations. For example, if I'm going ~55 in 4th and then shift up into 5th, there's the noise and a lack of power. Everything at idle and low speeds <15 mph feels normal.
Pulling the plugs, the 1 & 2 cylinders were carbon fowled whereas 3 & 4 look fine.
Just for fun, I pulled the valve cover since I couldn't remember how many miles since my last valve adjustment. Everything's in spec. there, but I did notice some unevenness on the exhaust cam in cylinder one. The actual face looks fine, but the edge looks almost cerrated. Looking at the other cam lobes, this is present on a couple of others, but it's not as noticeable (see cam C for reference). The shims and buckets look normal and I don't think this would affect performance in any way but it was my first time noticing it.
I've also gone ahead and pulled the carbs and done a preliminary spray through with compressed air and carb cleaner. Everything also looks fine from that perspective. Yes, I've done a full disassembly and thorough cleanup with new O-rings, intake boots, etc. and have been riding the bike regularly since. I tore one of the adjustment screw O-rings and totally mangled the float bowl gaskets so am waiting on replacements right now.
Ignition is a Dyna with the green coils installed the year before last and also have been working well. I reset the CCT at some point last summer so don't suspect that's at fault, either.
Any help would be appreciated!
The noise will go away in certain gear/RPM combinations. For example, if I'm going ~55 in 4th and then shift up into 5th, there's the noise and a lack of power. Everything at idle and low speeds <15 mph feels normal.
Pulling the plugs, the 1 & 2 cylinders were carbon fowled whereas 3 & 4 look fine.
Just for fun, I pulled the valve cover since I couldn't remember how many miles since my last valve adjustment. Everything's in spec. there, but I did notice some unevenness on the exhaust cam in cylinder one. The actual face looks fine, but the edge looks almost cerrated. Looking at the other cam lobes, this is present on a couple of others, but it's not as noticeable (see cam C for reference). The shims and buckets look normal and I don't think this would affect performance in any way but it was my first time noticing it.
I've also gone ahead and pulled the carbs and done a preliminary spray through with compressed air and carb cleaner. Everything also looks fine from that perspective. Yes, I've done a full disassembly and thorough cleanup with new O-rings, intake boots, etc. and have been riding the bike regularly since. I tore one of the adjustment screw O-rings and totally mangled the float bowl gaskets so am waiting on replacements right now.
Ignition is a Dyna with the green coils installed the year before last and also have been working well. I reset the CCT at some point last summer so don't suspect that's at fault, either.
Any help would be appreciated!
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