I am having problems with the VST system on my '96 502 Mag MPI motors. At the end of last season, when we would get above 4000 RPM the engines would stumble if we hit the slightest wake. The problem was found in the screen filter in the VST tank. This problem happened with one engine first and was repaired with the other engine to follow with in days. Now, after about 10-12 hours of run time I am having the same problem again.

Has anyone else had this problem? I know that Merc discontinued this system, is this why? Is there an easy way to upgrade this system or eliminate this problem?

Thanks, Todd

I've experienced problems with VST screens many, many times. But no more.This topic has been discussed in several threads here before but I'll give you a quick answer. It sounds like you may have a little debris in your fuel system.

Improve your fuel filtering. The standard Merc fuel/water separator filter is 70 microns. Replace it with a RACOR with metal water drain bowl and you will not have VST screen clog problems. I use a standard Merc first then the RACOR @ 10 microns so the Merc catches anything 70 and larger and the RACOR anything else. This also keeps the RACOR clean longer. Yes, I have two filters on each engine. This will stop VST clogging fuel problems immediately.

Just a note from experience. Buy yourself a new VST screen for a spare and keep it in your boat tool stash for emergencies. They are pretty scarce on Saturday or Sunday afternoon's. They are also reasonable to replace if you take care and have reasonable tool skills. The O ring CAN be re-used if you are careful removing it. You may want just a little bit of superglue to hold it in place when re-assembling.

Good luck.