pn for 1997 502 mag MPI's fuel pressure regulator
 

I am going to order new regulators for my 1997 502's with VST's. Anybody have a part number handy. The "resident mechanic" at our marina let me use his pressure gauge at the end of the season as he stated with around 500hrs, he would bet they were reading low. Well he was right as Port was 34psi and SB was 38PSI.

Would everyone agree that the regulators are bad, or is there something else to look at in the VST system to alleviate the low PSI?

There are a ton of threads on here if you search vst, vaporlock, 502. Hope this helps

There is nothing wrong with your readings if they were taken at idle. According to the manual (Merc Manual 16) the pressure should be between 34 and 38 psi at idle. To test further you will need another tester and block off the fuel return to see if it goes to 60 psi. The fuel pressure regulator part number is 805227A1

If you experiencing vapor lock the do to things; Stop using ethanol fuel and make sure you let the engine cool down on hot days before you turn it off.

Engines run fine. Yes, I have an occasional vapor lock issue if I forget to let her idle with the hatch cracked for a few minutes.

Reason I ask is because he said they should be at 43psi.

The pressure can get to 60psi but 43 is not correct according to the manual. If you pull the vacuum line off the regulator the pressure will go up. Book says 34 to 38 at idle with vacuum line connected. Click on the "Merc Manual 16" in my above post and go though the test. I don't think you have an issue.

I have the same setup as you with the VST in my cruiser and I would not be worried

I have found this site VERY helpful with both the part numbers and matching engine serial numbers to what they actually are.

http://www.perfprotech.com/mercruise.../04/mercruiser

Thanks.