Could be a partially clogged pilot jet.
After riding for a few hours today, I noticed that when in gear, didn't matter which one, at the bottom of the RPMs when the throttle was completely loose,the engine would stutter right before acceleration. I need help diagnosing this. Thanks for any help.
You might first try to clean it with 1-2 oz Berryman's B12 Chemtool or Seafoam/gal of fuel in the tank and run it through and see if that helps.
This ^^, but I think it best to remove the jets and clean with carb cleaner or similar.
It takes about 5 minutes to pull a carb off of these bikes with a #2 phillips screwdriver. Then you need a small flathead screwdriver to remove the pilot jet. And then you need an appropriately sized stiff wire to poke through the hole in the pilot without gauling or enlarging it.
Mine was plugged up when I got the bike. I ran wire through it and carb cleaner to flush it out.
You need to be able to see daylight through it.. The hole is pretty tiny.
.4mm I am guessing given the #40.
This one item in tandem with the adjustable mixture screw under the carburetor is responsible for idle and up to about 1/4 throttle. (Also the enricher/choke if the bike is cold is usually involved.)
Thanks for all the great help. I followed your advice and ran a wire thru the pilot jet. Didnt seem clogged at all. Ill put it back together and run it tomorrow and see whats up. Is it possible it is running too rich now that the temps are getting warmer? I have been running it all winter in sub freezing temps and this problem arose once I ran it all day in warmer temps.
With the factory pilot jet, I find it hard to believe the bike will ever idle rich at 1000 feet above sea level, where I live, haha They send these things to the USA so lean that they hardly run right. But maybe in your case. If it started and ran easily in really cold temps and now it doesn't want to run, my guess is that it's getting too rich on you. The simplest check is to make sure there's not a mouse nest in your airbox or something restricting airflow into the carburetor.
The pilot jet screws in tight. The pilot screw on the outside of the carb on the bottom will lean up the mix the more you screw it in.
I believe they come from the factory turned out 1.5 turns from seated. Most people are running them 2-3 turns out just to make their bike idle though. Maybe yours is turned out too far. A black plug would definitely be too rich or mean oil is getting past the piston rings.
You might just change the plug out since they're cheap and see if the bike runs better just from that. I think I bought all five D8HA sparkplugs my store had in stock when I got my TW200, haha.