Please forgive me if I am too basic with the following. You have propably considered ALL of this already:
1.) Zen, if your pipes/baffles are shot, the plug colors are going to give you misleading results. However, it is a good idea to look at the plugs, replace them with new, color the new ones and look again.
There is some sore of reverse pulse resonance (echo?) the occurs, with bad exhaust systems, at certain matching rpms that destroys the "scavenging" of exhaust from the combustion chamber. This can cause very hot running at certain rpms and can foul plugs at other rpms. This caused bad "running compression" and you simply can't catch the affect with a regular compression test.
2.) If your pickup coil wires are bad, the wire's insulation at higher temperatures might be "relaxing" and you will be dropping 2 cylinders if the wires are broken. Take off the left case cover, run the bike, and manually move the advance plate to see if she cuts out completely.
You can also try a quick thing where you pull the vacuum hose from the No. 2 carb, plug the nipple, and run the bike to see if the prevention of motion of the timing plate stops the problem. If it does, it is indicative of a coil wire problem. This is a quick and dirty test...very easy to do.
3.) Your fuel delivery might be deficient. Did you try running the bike on prime to see if the vacuum control (octopus on special or petcock on standard) is messing up? Did you check inline fuel filter? Did you try running with the gas cap ajar? The tower filters on the petcocks may be plugged.
4.) Carbs. There are some tiny inlet screens on the fuel valves that can get clogged. This can slow down the fuel rate and will result in the bike idling fine (once the bowls are full) but can cause the bike to cut out at speed.
I really think that your bike is suffering from fuel starvation from the sound of it. But I would have to tinker with it :-)
1.) Zen, if your pipes/baffles are shot, the plug colors are going to give you misleading results. However, it is a good idea to look at the plugs, replace them with new, color the new ones and look again.
There is some sore of reverse pulse resonance (echo?) the occurs, with bad exhaust systems, at certain matching rpms that destroys the "scavenging" of exhaust from the combustion chamber. This can cause very hot running at certain rpms and can foul plugs at other rpms. This caused bad "running compression" and you simply can't catch the affect with a regular compression test.
2.) If your pickup coil wires are bad, the wire's insulation at higher temperatures might be "relaxing" and you will be dropping 2 cylinders if the wires are broken. Take off the left case cover, run the bike, and manually move the advance plate to see if she cuts out completely.
You can also try a quick thing where you pull the vacuum hose from the No. 2 carb, plug the nipple, and run the bike to see if the prevention of motion of the timing plate stops the problem. If it does, it is indicative of a coil wire problem. This is a quick and dirty test...very easy to do.
3.) Your fuel delivery might be deficient. Did you try running the bike on prime to see if the vacuum control (octopus on special or petcock on standard) is messing up? Did you check inline fuel filter? Did you try running with the gas cap ajar? The tower filters on the petcocks may be plugged.
4.) Carbs. There are some tiny inlet screens on the fuel valves that can get clogged. This can slow down the fuel rate and will result in the bike idling fine (once the bowls are full) but can cause the bike to cut out at speed.
I really think that your bike is suffering from fuel starvation from the sound of it. But I would have to tinker with it :-)
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