i have average player base and this server can't handle it... 

Current CPU Usage: 244% of single core a single core is all we get?

1) Considering 100% is a single core, you're using 100% of two cores, and 44% of a third core, based upon the reported 244%.

2) The Fun Pimps (TFP) have the game coded to Halt-and-catch-Fire when a full 2 cores are maxed. Most likely the third core being utilized in your server charts is OS based features and functions, as 7Days also offloads a portion of what would normally be CPU driven to the GPU. As the servers here are headless, they're using onboard video. To date, the only thing so far that they've pushed onto the GPU is dynamic RNG construction. 

3) What do you consider an average player base? The Fun Pimps considers the maximum player base to be 8 on their server code, but admit their architecture can handle more. They just don't garauntee it.

Even with those above caveats, there are a number of things recommended for performance management all throughout TFPs forums. The most common suggestions by Mad Mole himself (Outside of playing single player, as he's on record for hating multiplayer, and only added it  "if it will shut you guys up, we'll make the game multiplayer.") is to reduce entity spawn across the board, except for horde night.

In general, the system handles upwards of 60 AI entitites at a time without causing any instructional deteriation, and is heavily recommended not exceeding the threshold of 80 advanced AI entities (Zeds and vehilces) and 20 simple AI entities (animals) active on the map at any given time.

All that mentioned though, to re-iterate 7DaysToDie is coded to a Halt-and-Catch-Fire usage of CPU, when it approaches maxing out 2 cores, it won't offload additional information or instruction to a third CPU core, only to the GPU, and only those things that are RNG related. Even on a consumer PC, this will only delay a halt-and-catch-fire situation, as the server code isn't built for a safety valve point, and as the game is in Alpha still (not beta) it's probably going to be addressed in Beta. Along with Workshop Support, RNG World creation improvement, Enhanced AI, and the return of a entity based loot system.

14 players during bloodmoon if thats the case why on server list i see 40 people on a server at one time like the walking zed server they have a large player base ?

decided to do whitelist only however when i add people to whitelist and restart the server the names gets removed from whitelist it's empty i been doing it through console  command whitelist add but when server restarts the list is cleared

Any configuration files that are built from the Basic, Advanced, or Expert tabs need to be changed via those tabs. Otherwise when they're built from those tabs on restart they'll be reverted to the version created by the tabs.

As for the Walking Zed server, they most likely have made other concessions to allow for the performance difference. You might want to check wtih their admin team and see what tweaks they've made to obtain that balance.