My bike "grumbles" (best way I can explain it) when I'm riding. It eventually clears out tho. I thought it was bad gas, I drained it and put fresh gas in and it still does it. It happens after I cut the bike off and run in the house. When I return (sometimes not all the time), the muffler has a funny sound to it (the gurgling I described), like its under water or something. Power is greatly reduced during this time. But when it clears out, all power comes back as well.

 

Just a funny thought... but could it be possible that there actually is water in the chambers of the muffler which then settles enough to allow a passage? Or do you have a straight-thru woolpack can?

Another possibility a bad ground somewhere?

 

No water in the tail pipe but I will check the ground. Bike starts up fine and runs, just gurgling sound and and reduction in power.

 

I changed the spark plugs and all that stopped. However my plugs wasn't even close to a year old. After I change the plugs, about a month later it started again. Taking it to the shop over the winter to have carbs redone!

 

Misfiring. Some bikes just go through plugs more quickly than others. Now it's not a Honda and it's a triple, but my bike tends to wear out about 1,5 sets a season. Last time I changed them at the start of autumn the cyl 1 plug actually broke and I had to fish out the threaded pipe part that snapped off into the threads.

 

If you changed the spark plugs you might have incorrectly installed the hoses from the breather to the air box. Happened with me and had the same gurgling sound. Might be worth a look.