I figured it out.  I used a utility that comes with Plop that allows you 
to customize plop so you don't have to go through menus each time you 
want to use it.  I used that to chose the options I want and replace the 
copy of plpbt.bin that's in /boot.

On 4/10/19 2:52 PM, Todd Cole wrote:
> there may be a way I can check tonight normally I burn Plop to a cd 
> boot the cd and the plop menu will offer up usb options to install
> I also suspect your bios can boot to usb directly but usb options will 
> only be shown if the usb is plugged in and and sometimes shows up as a 
> harddrive not a usb
> also check as usb devices are often disabled by bios as a boot option 
> by default sometimes are well hidden in menus and hard to find
>
> On Wed, Apr 10, 2019 at 2:33 PM Jim <azanorak@gmail.com 
> <mailto:azanorak@gmail.com>> wrote:
>
>     My system normally boots from /dev/sdd1.  I've installed Plop to
>     /dev/sda1. If I switch on the machine and press F12 to select a boot
>     device, then pick /dev/sda1, Plop loads.   When I installed Plop, I
>     chose the MBR of /dev/sda1.
>
>
>     Is there a way to put a menu entry in Grub2 that would tell the
>     system
>     to boot from /dev/sda1?
>
>
>     I did manage to create a menu entry in /etc/grub.d/40_custom that
>     lets
>     me load plop, but when I do, it gives me a warning that I can't save
>     changes.  Is there a way to fix it so I can save changes? Here is my
>     40_custom file.
>
>
>     #!/bin/sh
>     exec tail -n +3 $0
>     # This file provides an easy way to add custom menu entries.
>     Simply type the
>     # menu entries you want to add after this comment.  Be careful not
>     to change
>     # the 'exec tail' line above.
>
>
>     menuentry "Plop bootloader" {
>     insmod ext2
>              set root='hd3,msdos1'
>              if [ x$feature_platform_search_hint = xy ]; then
>                search --no-floppy --fs-uuid --set=root
>     --hint-bios=hd3,msdos1 --hint-efi=hd3,msdos1
>     --hint-baremetal=ahci3,msdos1 15d4e39e-2e6c-4ee4-9a24-67fd9ccab8f9
>              else
>                search --no-floppy --fs-uuid --set=root
>     15d4e39e-2e6c-4ee4-9a24-67fd9ccab8f9
>              fi
>              linux   /boot/vmlinuz-4.15.0-47-generic
>     root=UUID=15d4e39e-2e6c-4ee4-9a24-67fd9ccab8f9
>              linux16 /boot/plpbt.bin
>     }
>
>     thanks
>
>     ---------------------------------------------------
>     PLUG-discuss mailing list - PLUG-discuss@lists.phxlinux.org
>     <mailto:PLUG-discuss@lists.phxlinux.org>
>     To subscribe, unsubscribe, or to change your mail settings:
>     https://lists.phxlinux.org/mailman/listinfo/plug-discuss
>
>
>
> -- 
> Todd Cole
> Ubuntu Arizona Team
> 2928 W El Caminito
> Phoenix AZ  85051-3957
> toddc@azloco.com <mailto:toddc@azloco.com>
> 602-677-9402
>
> ---------------------------------------------------
> PLUG-discuss mailing list - PLUG-discuss@lists.phxlinux.org
> To subscribe, unsubscribe, or to change your mail settings:
> https://lists.phxlinux.org/mailman/listinfo/plug-discuss