brody1

I have a 1996 502 MPI that "surges" above 4,500 RPM, almost like it's hitting the Rev limiter. It seems the problem is less when the motor is cold and gets worse after running for awhile. The distributor cap, rotor, plugs, wires, ect have been changed recently. I have also checked the fuel pressure at idle and it is right on. All fuel lines have been replaced and the filters outside of the tanks replaced as well. The boat is a Nordic Scandia with duel tanks, the switching valve seemed to be fine and the problem seem the same when running off either tank. The motor has the mechanical fuel pump along with a vapor separator and high pressure pump on the back of the motor. The problem did seem to go away for awhile after changing the fuel line / filters but seems to be back again? I have also checked the condition of the fuel in the spin on filter and it has no signs of water or debris... Any help would be greatly appreciated.

F-2 Speedy

iTrader: (6)

Have you had it scanned, what ECM is on it, could be a bad sensor, its the VST system ??

Hook'em

The VST has a screen/filter in it as well, have you had it open? I think it's a 300 hour part (recommended replacement) It's kinda pricey, but mine was nasty. Not too many of those out there as they were only used a couple of years. Hopefully you can find an "old schooler" who is familiar with the VST system and motors. Good Luck.

ballon78

its the vst filter, just take it apart and clean filter, real easy, happened to mine at 500 hours a few years back. cleaned and it was fixed. reused gasket and filter just cleaned. if the oring get swollen from the gas then just cut it and super glue it back and reinstall. mine never leaked.

brody1

Thanks!! I'll check the screen / filter this weekend. Assuming it is easy to track down somewhere under the VST cover?

Hook'em

I've heard guys having hell with the VST o ring as mentioned above. I wouldn't assume you're going to be able to reuse it. Thats the LAST PLACE you want a leak for sure. I'd replace the filter too if it were mine (I did).

ballon78

the filter is easily cleaned. its the secondary filter after the fuel water separated. as for the oring, the fuel only goes have way up in the vat tank, its basically like a float bowl in a carb. i reused mine and they have never leaked. the oring gets larger when it hits air with the gas on it it so it stays soft. the orings are very expensive if i remember right and nobody stocks them. just cut and super glue very easy. I've done it too a bunch

92nsx

I have done the same thing that Ballon78 posted several times. Once that oring moves you can not get it back in and I will not give Merc $100 for there "kit". Cut, lay it back in, and cut off the extra. Then super glue the ends it back together. I have no leaks.

Here are a couple photos from when I took mine apart so you know what is in there.



Here is what was on my screen for the elec pump

thinksomuch

that right,. Once that oring moves you can not get it back in and I will not give Merc $100 for there "kit". Cut, lay it back in, and cut off the extra. Then super glue the ends it back together. I have no leaks.