First off, I would look again at task manager and see what else is using the CPU. Boinc runs at the lowest piority so anything else you have running will pre-empt the BOINC job.
Cheers

Thanks for your reply. The issue I experience only pertains to one of my four BOINC projects, which suddenly drops to 1% CPU usage. The other three projects continue to run at 19-20%, as normal. I can never predict when one of the four projects will suddenly drop to 1%. Do you think it's because I'm running other programs or is it a BOINC problem? Thanks again.

Supposition and guesswork, but maybe something to check out:

If you're running four BOINC tasks, and they each normally run at around 20% CPU utilisation, then that suggests that either other tasks on your machine are taking up 20% of your CPU all the time, or you've told BOINC to restrict its usage to 80% of total CPU. If you need to restrict usage because of thermal issues, then fine, do that. But if you don't get thermal issues then why not let it go flat out? -- task priority should make sure that everything else gets preference and you shouldn't notice that BOINC is running.

You don't say for how long a period of time you see a BOINC task running at just 1%. If it's periods of a few seconds, then I would say that BOINC is restricting those tasks because of your usage settings. If it's for minutes on end, then I would want to know what else is running on your machine that is taking up 20% or more of CPU time for such long periods, or else I'd want to know more about what tasks BOINC is running in parallel (because I wouldn't expect WCG's tasks to interfere with each other as your post suggests they do).

Thanks again. I have an Intel i5 with four cores, and I prefer to dedicate all four cores to BOINC. When one of the four cores suddenly drops to 1% usage, it does so for many minutes, if not hours, on end. I am then forced to abort that particular project since it never returns to regular CPU usage. I usually have my browser open at the same time, with many tabs open, so that likely restricts what I'm able to use for BOINC. The only 'solution' that I have found so far is to change the BOINC settings to only use 75% of CPUs, which thus only uses 3 out of my 4 cores, but again I'd prefer to find some solution that allows all four cores to be used reliably. Thanks, guys.

Not all all WCG projects have the same requirements. You might want to check out the help page at https://www.worldcommunitygrid.org/help/viewTopic.do?shortName=minimumreq for further information.