I had the same problem.  I added a brake line banjo bolt crush washer under the impeller bolt along with a dab of silicone sealer.  That was the fix posted on the old site and it fixed the problem for me.

Jerry recommends this fix, not sure if the problem being solved by these two methods is the same...

http://www.suzukiquadracerhq.com/engine-13/couple-of-trouble-shooting-items-for-1987-zilla/msg22232/#msg22232