390xp tuning or chain set up issue?

[FlyingDutchman]

Recently got a big saw. 390xp and running Stihl RS on a 20" bar. Cuts killer with the spikes buried but doesn't seem to like it too much cutting small (less than 12") logs in the bucking pile. Its 4 stroking and I lose a lot of chain speed. I don't really want to touch the carb because it performs well for ripping and cutting.
With this kind of power I feel like I could set the depth gauges stupid low or move to .404 chain.
But even with Stihl RS I'm struggling to keep the chain sharp enough in the conditions I'm cutting in.

 

[huskihl]

Carburetors were made to be adjusted, that’s why the screws are there. 1/4 turn in on the H screw and you will be good to go. You could take a couple swipes off the rakers and/or run an 8 tooth sprocket when you’re cutting smaller stuff as well

 

[3000 FPS]

Yep Huskskihl is correct. The carb is just a little to rich.
As long as you can still hear the 4 stroking when not in the cut at wide open throttle then you are good.

 

[Jonny Quest]

+1
4-stroking at full throttle NOT in the cut. When in the cut, under load, 4-stroking should go away. If not, turn H-needle in by 1/8th increments until 4-stroking smooths out. Good to go. Or you could tune it with a tachometer…

JQ

 

[Huntaholic]

+1
4-stroking at full throttle NOT in the cut. When in the cut, under load, 4-stroking should go away. If not, turn H-needle in by 1/8th increments until 4-stroking smooths out. Good to go. Or you could tune it with a tachometer…

JQ

I always tend to run my 390s a tad on the rich side, the torque is so strong that I will give up a few RPMs to make sure my babies keep running fat and happy.

 

[FlyingDutchman]

Because the chain isn't perfect through the whole tank and the logs are piled, unless I can set the spikes it won't put enough load on the engine to 2 stroke. But if I switch to a bigger log pulled from the pile I can set the spikes in, or a longways rip, it seems like I need that fuel. Will play with pulling back the fuel but trying to get some semi chisel chains made because the real problem is dirty wood forcing me to use the spikes within a few cuts to get good cutting speed.