<max_ncpus>N</max_ncpus>
An upper bound on NCPUS (default: 64)
(which is why during the test I never got past 64 threads)

http://boinc.berkeley.edu/trac/wiki/ProjectOptions


read N from
On multiprocessors, use at most 2 processors

from

When and how BOINC uses your computer Computing preferences

N=setting
in this case the on multipro.... use at most 2 processor

therefor N is replaced with 2.

yafujobmt_0.04.xml


<job_desc>
<task>
<application>yafu</application>
<stdout_filename>out</stdout_filename>
<command_line>-threads "2" -batchfile in</command_line>
<multi_process/>
<checkpoint_filename>nfs.dat</checkpoint_filename>
</task>
</job_desc>



or however you change a dynamic argument to a static

$NTHREADS=2


client_state.xml would look like

app_version>
<app_name>yafu</app_name>
<version_num>13401</version_num>
<platform>windows_x86_64</platform>
<avg_ncpus>8.000000</avg_ncpus>
<max_ncpus>2.000000</max_ncpus>
<flops>21017886472.298004</flops>
<plan_class>mt</plan_class>
<api_version>7.1.0</api_version>
<cmdline>--nthreads 2</cmdline>
<file_ref>
<file_name>yafuwrapper_26002_windows_x86_64.exe</file_name>
<main_program/>
</file_ref>
<file_ref>
<file_name>yafujobmt_0.04.xml</file_name>
<open_name>job.xml</open_name>
</file_ref>
<file_ref>
<file_name>yafu-x64-13401.exe</file_name>
<open_name>yafu</open_name>
<copy_file/>
</file_ref>
<file_ref>
<file_name>yafu_w64mt_02.ini</file_name>
<open_name>yafu.ini</open_name>
<copy_file/>
</file_ref>
<file_ref>
<file_name>ecm63mpir230core2-64.exe</file_name>
<open_name>ecm.exe</open_name>
<copy_file/>
</file_ref>
<file_ref>
<file_name>gnfs-lasieve4I11e_w64_01.exe</file_name>
<open_name>gnfs-lasieve4I11e.exe</open_name>
<copy_file/>
</file_ref>
<file_ref>
<file_name>gnfs-lasieve4I12e_w64_01.exe</file_name>
<open_name>gnfs-lasieve4I12e.exe</open_name>
<copy_file/>
</file_ref>
<file_ref>
<file_name>gnfs-lasieve4I13e_w64_01.exe</file_name>
<open_name>gnfs-lasieve4I13e.exe</open_name>
<copy_file/>
</file_ref>
<file_ref>
<file_name>gnfs-lasieve4I14e_w64_01.exe</file_name>
<open_name>gnfs-lasieve4I14e.exe</open_name>
<copy_file/>
</file_ref>
<file_ref>
<file_name>gnfs-lasieve4I15e_w64_01.exe</file_name>
<open_name>gnfs-lasieve4I15e.exe</open_name>
<copy_file/>
</file_ref>
<file_ref>
<file_name>gnfs-lasieve4I16e_w64_01.exe</file_name>
<open_name>gnfs-lasieve4I16e.exe</open_name>
<copy_file/>
</file_ref>
</app_version>




sounds easy but, then I'm not a programmer. :)

also
<avg_ncpus>8.000000</avg_ncpus>
will need to be changed to
<avg_ncpus>2.000000</avg_ncpus>