Loss of low end torque, 3rd cylinder pooped?

[mluk1]

I finally got my 77' CB750F running good for a couple of months and I even took on the highway on a 3 hour trip twice and everything was fine. My speed was about 140 km/h on average on those trips and I was riding like that for about an hour and half at a time. But the other night I took a friend out of my bike and was doing 100 mph, the ride home was fine but the next morning it my bike felt like it lost a lot of torque. At red lights I started to touch each exhaust head and figured out that the 3rd head was not as hot as the other three.

I don't feel much pull on my bike any more and it takes a really long time to accelerate, it sounds different now too. It has a lower pinch to it and I'm struggling to get up to 120 km/h. Does this mean I'm running on three cylinders?

Could any of these factors have anything to do with it:

- It's freezing in the morning when I take it to work, it's about 10 degrees Celsius
- The oil that I'm running is 15W- 40 topped up with probably about a litre of 10W-40
- The oil pressure light sometimes comes on for a bit but then turns off

Any help would be great, thanks.

[Re-run]

Hmm well I wouldnt say 10C is freezing but a 15 weight oil might be too thick. I would consider moving to a 10-40 or maybe a 5-40 synth suchs as rotella. That might also solve the oil light flickering on and off.

I would initially pull out the plugs and compare them. See if #3 is darker than the others. A couple things that may have happened is that either the jets got plugged somehow or maybe a jet fell out and is sitting in the bowl.

Another thing to try is to swap the #2 & 3 plug wires as they fire off the same coil and see if the problem stays or moves. If it moves, then it is wire related, if it stays, it is fuel. When you move the wire, maybe move the plug too.

[free2ride]

10C is OK . . . 7 is where it gets dicey.

[mluk1]

I rode my bike home from work with the 2 & 3 plug wires switched up and the bike was still running like shit. When I was parking it in my garage I was so happy to see that the run off tube from Carb 3 was leaking gas! I pulled the Carbs and found a tiny piece of debris stuck in the jet, everything works fine now.

Thanks for all the help.

[Re-run]

It is so irritating and yet nice that it was something so simple.
Almost drives you to drink!

[LukeM]

Congrats on the fix.  As I've seen on so many forums, you can't keep the carbs too clean. I pulled mine off my 1979, and they didn't look very dirty at all.  Still, I took them as apart as I could and cleaned them as best I could.

Luke M