I have been getting horrible lag in minecraft and when i look in f3 i get spikes. Multimc keeps saying root and root.render taking to long. Also see linked picture.
Define "lag spikes". 30fps is quite a reasonable speed to run at. Also, what are your system specs? If you have a really old/under powered system, that would explain your lag spikes.
http://i1364.photobucket.com/albums/r725/magmaslime/Screenshotfrom2014-02-13164116_zps2d719208.png
At least 86% of what I say is always correct.