Hello everyone, I finally finished my Timberwolf 4x4 crankcase swap / top end rebuild. Bike starts and idles perfectly and runs good while warming up. The problem I have is when the engine warms up over 220F (on my spark plug washer temp gauge), it hesitates and / or stalls if I give it gas too quickly off idle. This happens in neutral or in gear. I have to feather the throttle to get it going but after that, it runs fine. Valves were set in the middle of the range, carb was cleaned in the ultrasonic cleaner and rebuilt with a new carb kit. Clip on the needle is 4th position from the top. Floats are set perfectly; I did the fuel line on the drain plug test. Pilot was initially set at 1.5 turns out but I hooked up a tachometer and adjusted it with the idle screw per Yamaha's service manual until I had the idle steady at 1400RPM. No intake leaks, intake is clear, air filter is brand new and oiled. Compression is 129 p.s.i. cold. Spark plug is correct range, gapped and looks perfect with a nice coffee color. Stator is brand new and I've got 14.1volts at the battery. What am I missing? Once I am moving, it's fine. It's just off idle, if I throttle it too fast, it stalls. I'm stumped!

 

You mention pilot 1.5 turns out, then adjusted it to 1400RPM, The mixture screw may well be 1.5 turns to start with, but you set the idle speed screw to get the right RPM, not the mixture screw, which is set to give the max speed it will give, on a warm engine, then adjust the idle speed screw to that 1400 RPM (which seems a bit high to me, but what do I know). I avoid altering the mixture screw like the plague, but if I have to, I always set it slightly on the rich side, as engines like a slightly rich mixture when accelerating (hence accelerator pumps on more expensive carbs).

 

Thanks for the response. Doing some more thinking about this, I’m thinking I’m too rich on idle circuit. Bike starts easily with no choke and stalls if I choke it. I’m going to try turning in the idle mixture tonight and see if that helps

 

As I wrote above, with a warm engine, the mixture screw is screwed in or out until the revs stop rising and start to fall, then back until they start to fall again, then to half way between those points. Give the throttle a blip occasionally when doing this, to clear the carb's throat.

 

Update: turns out the choke cable was too tight and slightly pulling up on the plunger. Adjusted and now she’s running perfect