200 ox 66 drive slipping?

[GW267000]

Three trips off shore. First trip, starboard motor would pick up ~4000 RPM when hitting waves that would require turning under load, no speed pick up, but would settle back down, this seemed to happen only when turning or plowing into a wave. Second trip, same thing, but seemed to be more often. Third trip, after about 1 hour it was more frequent. On way back, boat had problem getting on plane, Starboard motor would not pick up RPM until what seemed that the Port motor would take enough load off and then the motor would pick up and go. From there it was the same, hit wave or turn and pick up RPM. Only thing on the third trip home was when plowing into a wave that would "stuff" the bow. The Starboard motor would lose RPM, then come back to normal RPM, or the ~ 4000 high RPM. The crew on the third trip said that when this happened they could see the motor raise up. Running on smooth water, past inlet, seemed to have no problem. This seemed to me to be a prop hub as you could hear what sounded like cavitations. Had prop checked at Bay Propeller for slip, prop was good. So where do I go from here? Can lower unit slip, as this sounds and feels like an automatic transmission would on low fluid coming in and out of gear for a short time? I am lost and need some help.

[jb123]

i would suggest you monitor fuel pressure while running,sounds like a dirty VST filter

[99yam40]

Sounds like fuel (lean) problems and if you keep running it that way you will lose pistons

[rodbolt17]

gotta agree, go fix the fuel system.
preferably before replacing pistons.
good thing I read this in the AM and not the PM.
might get banned again.
2 other trips knowing the motor is dying?
might get a darwin award.

[GW267000]

I know three trips, After first trip we changed the 10 micron filter and on board filter. Second trip just ran out the inlet down the beach. We then cleaned out the VST tank checked and cleaned the VST filter and checked the pressure regulator screen. Thrid out the inlet up the beach same thing. As it only seems to act up under load, as you said I dont want to blow it out by running it any more, but I have gone over all fuel things I know to check-clean. Can the pressure regulator be tested?

[rodbolt17]

yep.
simply attach the fuel pressure test guage and run it at the problem RPM and load.
it either stays at 35 PSI plus or minus 3 PSI or something is broke.
if pressure goes low find the air leak or restriction.
if pressure is high clean the filter in the regulator.
but your describing a classic loss of fuel rail pressure.

[GW267000]

Thanks Rodbolt, I was so sure it was a prop after last trip, but have always read posts to try to have an idea of what to try if I should have a problem and at least 90% of problems seem to be fuel. Will run the boat and check pressure, If low, would it be safe to run fuel hose from tank pick up to first low pressure pump, or should I not bypass the filters, I do not have an aux tank to use. Would like to check all that I can when out.

[GW267000]

Had time to go over the fuel system. Problem pointed to the tank, pulled the anti-siphon valve and found it to stuck in-between open and closed. Pressed out the check ball and ran boat with no problems. Question is to replaced with anti-siphon, or not. Alot of threads on issue some being that new ones do not open easy enough and still restrict flow. Of course this pick up was under floor so we had to remove center console and floor to get to it and dont want to be doing that again. Thanks for the help.

[99yam40]

I believe they are installed to keep the fuel from siphoning out of the tank and filling the bilge of boat with very flammable fuel if there is a line break or leak. It is up to you, but probably would not pass and inspection if ever there was a fire loss, if there was still enough to inspect.
Just my thoughts

[Tucker]

Replace the anti-syphin valve. In the event of an accident, if an insurance surveyor determines damages were because of someone tampering with a safety device, you're toast. Looking at your sig, looks like you have a Grady. I thought they would put inspection ports at a spot like this.

[GW267000]

Yes Tucker it is a Grady. The port is over the sender and the Starboard pickup. The Port pickup is just on the edge of the inspection port pointing away from the inspection port thus you can not touch the anti-siphon or hose as they route to the Port side. If there is enough slack in the fuel hose, I may be able to turn the 90deg elbow inorder to bring the anti-siphon around to where I can get to it thur the inspection port.