hello all, I have done the mod to stock petcock (found here) and for a year there has been no issues.. Now at full throttle the the power surges like it does if I need to switch to reserve (low fuel).. I have disassembled the carb and cleaned all orifices (looked fine).. Pulling out the enrich knob makes no difference while problem develops.. this happens 50% of the time when at full throttle.. It is not a misfire like a fouling plug.. MY THOUGHTS are petcock dribbling fuel too slow for full throttle, or float needle misbehaving, or that TEV diaphram sticking, I could not get the screws out that secure TEV cover

What JOG said. The petcocks fail in one of two ways.
1) The diaphram leaks and fuel does not shut off.
2) The diaphram gets stiff and in low vacuum situations, will not pass enough fuel.

You sound like problem 2. That's what happened to me. I first noticed stalling when slowing to idle in cold weather. Then on a 300 mi trip with some buddies, we rode faster (65mph) then I normally do and on the return trip was bucking a 25mph headwind. The result was a low vacuum event. After a couple of minutes under these conditions, my Savage would begin stumbling like I was running out of gas. Flipping to PRIME would result in the engine picking back up like normal. After this happened about 5 or 6 times I left it on prime. I had no reserve, but I kept close track of how many miles I had travelled.

The next day, I ordered a Raptor petcock.

thanks  

the mod to stock petcock, eliminates the vacuum diaphragm, on-off-reserve like the old style.. just plug the vacuum port on carb