Since I have gotten my CB750K4 project back on the road, cylinders 1 and 2 have always sounded weird coming out of the left pipe. When idling, I can crouch down behind the bike and the right pipe sounds strong and consistent while the left sounds stuttery. When you give it throttle, they both sound fine. This is also been evident when cruising at a consistent speed, more at lower speeds and RPMs. Again, when you load the engine it goes away. Also been noticing after the bike is warm that it will hesitate when getting underway from a stop. Just right as you are letting the clutch out, it acts like it misses a beat and almost dies unless you give it more juice.
I won't take credit for this, It was this post from jimbojangles that led me down this path.
http://forums.sohc4.net/index.php?topic=108701.0I had some keyster carb kit brass leftover from my carb refurbishment, so I decided to try what Jimbo did and swap out the needle jet with the aftermarket ones. Since cylinders 1 and 2 seem to be the problem, and cylinder 1 always ran a little bit cooler, I decided to swap that one out first and see if I could tell any difference.
I was able to do this with the carburetor still on the bike. Removed the air box and air box rubber. Remove the tank. Opened the throttle all the way and fixed it there with the throttle stop. Unscrew the top cap on carb one And after taking the rubber boot off of the top of the rod was able to get the top of the rod out of the throttle arm thingy. This allowed me to lift the needle all the way out of the needle jet by about half an inch. Then I removed the main jet and slow jet in order to make room for my improvised tool. I modified a clamp. The fixed part of the clamp was inserted into the carburetor on top of the needle jet, the movable part of the clamp with the threads was laid to rest on the part of the car that houses the main jet. I had to cut the clamp shorter so it would fit down in there. Then I used it to press the needle jet out. I think I could do this on all of the carbs and leave them in place.
Anyway, put everything back together fired it up And let it warm up at 2K RPM for a minute or so. Let it fall back to 1100 RPM and crash down behind the bike. The left pipe sounded approximately 80% better than it did before. Almost as consistent as the right one. I took it for 7 mi spin or so. While cruising along, the gurgling was nearly gone and after the bike had warmed up I never once experienced a hesitation when getting underway.
I'm very happy about this and I think I will go ahead and swap the rest of the needle jets out when I get time. Just wanted to share this even though the solution has already been posted in the past. It seems it worked for me too!
