OX66 225 "stumbling" when running over 3500 rpm

[SkunkBoat]

I started getting an occasional "stumbling" feeling on the way in one trip ago. It seemed it would happen when we thumped an odd wave. we could not figure out what motor it was or if it was both.
We tightened up all battery connections.
This last trip it did it more and finally we saw the port tach actually show an rpm drop.
It seems to be getting worse. Now I can make it do it when accelerating hard. I need to fix it before another trip for sure.
I'm guessing a fuel pump is not keeping up?
Suggestions on what to look at?

 

[Andrew93]

Sounds like the filter in the VST tank. Make sure to get a VST gasket also, they stretch easily and make it hard to get back in place. If it was real dirty might be worth send injectors out to be cleaned also, most places have a quick turn around time.

 

[deepdesire]

How old are the low pressure fuel pumps?

 

[seasick]

Ditto on the VST filter. The drop in revs when hitting waves is a common symptom even though I don't fully understand why

 

[SkunkBoat]

Yep, haven't done anything with VST yet, guess I'm gonna learn something new.
I'll post when I get chance to look at things

 

[seasick]

It is fairly easy to drop a screw when removing the cover so take care when unscrewing. You can place a rag under the VST tank to stop falling screws from dropping into the lower cowl. The gasket is an odd shaped rubber ring and if relatively new, can be reused. It is overly expensive You need to apply some grease to the groove to hold it in place. IT has a habit of expanding when removed and can be a pain to get back n place. Even new rings can be a pain. Some folks put tge o-ring in the freezer for a while to shrink it so that it fits better. I can't say it that really helps.
The VST filter/screen can usually be cleaned if not too bad. You can buy a new one if you don't now how bad it is.
Often a clogged screen looks OK but isn't. If you look into the hole than connects to the pump pickup tube and point towards light like a sunny background, place you hand behind the filter. You should be able to make out your fingers. When the screen is clogged, all you see is a white blurry image.

 

[deepdesire]

Electric fuel pump is located in the VST tank. Vst tank is filled by the lp fuel pumps. Pump cant pump fuel if its not in the tank. Start at the beginning.

 

[SkunkBoat]

good comments. Thanks.
The LP pumps look new. I've had the boat since Oct 2017. I'll take a close look.

So the other little o-rings in the VST don't usually need to be replaced due to taking it apart?

I'm thinking I'll buy 2 tank gaskets and 2 filters. I'll do the trouble motor and see how it goes, then do the other motor once I've solved my problem.

Boat's in water so it'll be tricky....

Is it easier to drop the tank cover on the motor or to remove the whole VST and do it on the bench???

 

[seasick]

good comments. Thanks.
The LP pumps look new. I've had the boat since Oct 2017. I'll take a close look.

So the other little o-rings in the VST don't usually need to be replaced due to taking it apart?

I'm thinking I'll buy 2 tank gaskets and 2 filters. I'll do the trouble motor and see how it goes, then do the other motor once I've solved my problem.

Boat's in water so it'll be tricky....

Is it easier to drop the tank cover on the motor or to remove the whole VST and do it on the bench???

It is more work to remove the assembly since you have to cut hose clamps for low and high pressure fuel in addition to the oil line and vent lines. The high pressure lines need special pinch clamps and the pinch clamp tool to install them. The hoses may not come off easily either. You have tie wraps and cable to remove also.
There are no little o-rings, There is one odd shaped rubber ring that has the same shape as the VST cover. If relatively new, it can be reused but they tend to expand and often just can't be set correctly in the groove.
Use caution when pulling the cover off since the height pressure pump comes out with it. Be careful with the internal pump wires.

Check the VST bowl for gunk or particles. Hopefully you don't find any whitish crystals.

 

[SkunkBoat]

VST filter appears to have fixed the problem. gave it a good run this morning, no stumbling. will do the other motor when i get a chance

 

[seasick]

Nice job.

 

[Andrew93]

With the filter that dirty it may be worth sending the injectors out to be serviced if you have time to have the boat OOS or after the season. I have used fuelinjectorman.com in the past and his turnaround time was pretty quick, but there are others out there too.

 

[SkunkBoat]

With the filter that dirty it may be worth sending the injectors out to be serviced if you have time to have the boat OOS or after the season. I have used fuelinjectorman.com in the past and his turnaround time was pretty quick, but there are others out there too.

Will definitely look into that.

 

[SkunkBoat]

A follow-on to this... I did end up getting injectors cleaned...awesome! In combo with VST filter and pressure reg screen filter it was the fix to this problem.
https://www.greatgrady.com/threads/ox66-fuel-injector-man.28234/