Hello All,
New member here, just got myself a '80 CB750K for a winter project, goal is to make it my daily next year. (just moved to Wisconsin and it seems like EVERYBODY rides up here) My other ride is a 78 Yamaha XS400, it did great around town for college, but it is pretty taxed on the highway. It can do highway, but the parallel twin vibes are not fun for more than 15-20 min on the highway at 5500-6000 rpm.
Here is the Dragon as found.
Since I have purchased the "purple dragon" ,as I'm calling it, (probably should be called the "purple money pit") I have focused my attention on the engine, since I'm pretty sure the P.O. never checked the valves, adjusted the cam chains or any of that, and with 32K miles I'm hoping no valves are burnt.
First order of business was a complete carburetor disassembly. They were "rebuilt" when I got it. I had to remove the several shims under the slide needles and block off the aircut valves. It was running VERY rich when I got it, and just barely running at that. I can't believe I was able to ride it across town (1 mile, ) to get it home. All the aircut valve diaphragms had holes, so that's the reason for blocking them.
Next, I balanced the carburetors on the bike, with a nice home-made manometer. It does pretty well. (I did it the first time w/o the airbox, will do them again later with the airbox, and after valve lash adjustment)
And now I have been working on the top end of the engine, with the carbs decently cleaned/balanced, new plugs and plug caps (the original plugs were so fouled that it wasn't idling on all cylinders) I warmed up the bike and took some compression readings. From 1 to 4 I got: 150, 150, 155, 150. I thought this was pretty surprising for the bike's mileage and the valve clearances I found next.
The valve clearances were next, I measured using the service manual's instructions
Exhaust were 1 to 4: .004, .003, .0025, .003, .004, .003, .0025, .002 (inches)
Intakes were 1 to 4: .004, .004, .003, .003, .004, .005, .003, .003
Cylinder 4 had some firing issues at idle and from the exhaust valves I can see maybe why, hopefully not burnt, fingers crossed there.
A shim kit and shim change tool is now on the way...... at least one was at .005
Hopefully once the valve clearances are set, I'll be able to get my idle smoothed out and further set the carburetors. I haven't been able to set the idle screws currently, they don't move the idle speed unless I take the screws several turns in or out. I get some primary chain noise at 1000RPM idle, goes away and smooths out at 1500 RPM, so it's fairly close currently. (I can feel the cylinder "hits" in the clutch lever at 1000, but not at 1500)
Other things I have noticed in my adventures, the cam chains are adjusted fine and do not make noise, surprising. From what I can see of the tensioners, they look to be decent.
While checking valves, I noticed that, on the valves with low clearance, the cam lobes looked like they had taken some wear. So I took my China slide caliper and took some rough measurements. I only had a few at the service limit for the cams but they were within the "accuracy" of my china slider. So I'm not too worried about them yet, if need be I'll get some CB900 cams.
Other than the engine, here are some interesting things I found on the bike:
The "custom" rear lowering option from the PO
Needless to say, new shock/spring assemblies are on the way....
Other than the springs, a front fork rebuild with new seals is in order.
For the bike, the chrome is fubared, a local place specializes in powdercoating small jobs so I'm currently thinking of going that route. Disassembling the wheels, powdercoating the rims and spokes. Also powdercoating the fenders. As for the body, hell maybe just re-paint it with plum crazy purple!
Anyways, and let me know what you think of my new mess!
New member here, just got myself a '80 CB750K for a winter project, goal is to make it my daily next year. (just moved to Wisconsin and it seems like EVERYBODY rides up here) My other ride is a 78 Yamaha XS400, it did great around town for college, but it is pretty taxed on the highway. It can do highway, but the parallel twin vibes are not fun for more than 15-20 min on the highway at 5500-6000 rpm.
Here is the Dragon as found.
Since I have purchased the "purple dragon" ,as I'm calling it, (probably should be called the "purple money pit") I have focused my attention on the engine, since I'm pretty sure the P.O. never checked the valves, adjusted the cam chains or any of that, and with 32K miles I'm hoping no valves are burnt.
First order of business was a complete carburetor disassembly. They were "rebuilt" when I got it. I had to remove the several shims under the slide needles and block off the aircut valves. It was running VERY rich when I got it, and just barely running at that. I can't believe I was able to ride it across town (1 mile, ) to get it home. All the aircut valve diaphragms had holes, so that's the reason for blocking them.
Next, I balanced the carburetors on the bike, with a nice home-made manometer. It does pretty well. (I did it the first time w/o the airbox, will do them again later with the airbox, and after valve lash adjustment)
And now I have been working on the top end of the engine, with the carbs decently cleaned/balanced, new plugs and plug caps (the original plugs were so fouled that it wasn't idling on all cylinders) I warmed up the bike and took some compression readings. From 1 to 4 I got: 150, 150, 155, 150. I thought this was pretty surprising for the bike's mileage and the valve clearances I found next.
The valve clearances were next, I measured using the service manual's instructions
Exhaust were 1 to 4: .004, .003, .0025, .003, .004, .003, .0025, .002 (inches)
Intakes were 1 to 4: .004, .004, .003, .003, .004, .005, .003, .003
Cylinder 4 had some firing issues at idle and from the exhaust valves I can see maybe why, hopefully not burnt, fingers crossed there.
A shim kit and shim change tool is now on the way...... at least one was at .005
Hopefully once the valve clearances are set, I'll be able to get my idle smoothed out and further set the carburetors. I haven't been able to set the idle screws currently, they don't move the idle speed unless I take the screws several turns in or out. I get some primary chain noise at 1000RPM idle, goes away and smooths out at 1500 RPM, so it's fairly close currently. (I can feel the cylinder "hits" in the clutch lever at 1000, but not at 1500)
Other things I have noticed in my adventures, the cam chains are adjusted fine and do not make noise, surprising. From what I can see of the tensioners, they look to be decent.
While checking valves, I noticed that, on the valves with low clearance, the cam lobes looked like they had taken some wear. So I took my China slide caliper and took some rough measurements. I only had a few at the service limit for the cams but they were within the "accuracy" of my china slider. So I'm not too worried about them yet, if need be I'll get some CB900 cams.
Other than the engine, here are some interesting things I found on the bike:
The "custom" rear lowering option from the PO
Needless to say, new shock/spring assemblies are on the way....
Other than the springs, a front fork rebuild with new seals is in order.
For the bike, the chrome is fubared, a local place specializes in powdercoating small jobs so I'm currently thinking of going that route. Disassembling the wheels, powdercoating the rims and spokes. Also powdercoating the fenders. As for the body, hell maybe just re-paint it with plum crazy purple!
Anyways, and let me know what you think of my new mess!