When im riding my bike and I hold the throttle it wants to fluctuate. As in at 4000 rpm it will go fast and slow, fast and slow. I just had the carbs synced and cleaned. What's it sound like to you guys?

 

Ok, here is my initial thought. I don't know how extreme of a change it is when you say change from fast and slow, but- There could be any number of things wrong, from the chain, maybe even the cush drive, to tuning carbs, and to syncing them. First, find out what throttle position this happens at. RPM can help you distinguish what is going on, but throttle position will reveal a lot about how your throttle is being delivered. Rev your bike in neutral (with a fan in front) and go through rpm/ throttle ranges, and hold it at certain areas. See if you notice any fluctuation when trying to hold a steady throttle.

If nothing, then you (sort of) know it is happening when under load. I had this problem for a while. I couldn't figure it out. But I tried syncing my carbs to right around my cruising rpm ~4.5k rpm, rather than idle rpm. I really did notice a difference.

Obviously without feeling your bike, it could be anything. But if I understand you correctly, I think my bike did the same you described yours does.

 

If you are holding it at 4000 rpm - flat ground on one gear, the bike's speed shouldn't change.

So are you holding throttle steady, not changing throttle position and the RPMs are increasing and decreasing their own? If that's the case it could be carbs, or an air leak in the carb boots, maybe even the vacuum line supplying the petcock. Check the carb boots for cracks/leaks, and make sure they're tight.

Also - check your chain - make sure its got about an inch of play up and down measured at the middle of the bottom stretch. A too tight chain could bind up (sprockets aren't 100% round) and at the tightest spot it might be binding up the final drive a little.

 

If you are at a constant RPM and Throttle Position and your bike's speed seems to change, my educated guess is youre getting a "lean surge". This is caused by a lean fuel condition in one or more of your cylinders. Richen your mixture screws about 1/4 - 1/2 turn and see if it goes away. If this is in fact the problem, you may also notice your spark plug electrodes are white as opposed to a nice creamy biege colour that they would be in a properly running engine.