VP2003 variable RPM while throttle unchanged

[cam11585]

I'm having a weird issue with my VP2003 where the RPM of the engine can change dramatically, plus/minus 1000 RPM, without me touching the throttle. It doesn't matter if the engine is hot or cold. When running at low RPM this can sometimes cause the engine to stall altogether. The only other symptom I see is a small amount of diesel coming out with the exhaust water. Any ideas?

[Engine man]

Sounds like a fuel supply problem. How many hours on this engine?

I'm assuming that the fuel tank has sufficient fuel to cover the pickup tube, and that it's not a simple problem of very low fuel in the tank.

You can do the following simple test - get a FRESH, CLEAN container of diesel fuel. Remove the fuel hose from the boat's fuel tank, and submerge it into the portable container of fuel. Now change ALL fuel filters and bleed the system. If the problem is now gone, investigate the fuel tank pickup tube for restrictions [such as a screen installed] or cracks that would allow air into the system.

If the problem remains, temporarily bypass the engine's mechanical fuel pump and install an electric pump. Now bleed the system and see how the engine runs. If the problem is gone, replace the mechanical fuel pump, or permanently install an electric fuel pump. Joe

Originally Posted by cam11585

I'm having a weird issue with my VP2003 where the RPM of the engine can change dramatically, plus/minus 1000 RPM, without me touching the throttle. It doesn't matter if the engine is hot or cold. When running at low RPM this can sometimes cause the engine to stall altogether. The only other symptom I see is a small amount of diesel coming out with the exhaust water. Any ideas?

[Cheechako]

Fuel issue. But may very well be a clogged tank vent, or obstructed vent hose! Little bugs build a nest in the vent outlet sometimes blocking them. Been there, done that.
When you engine starts doing that, remove the fuel fill cap on deck... is there vacuum there? If there is.... that's your problem.

[cam11585]

Thanks for the advice. I'll check that out.

Engine has about 1800 hours.

[capt jgw]

Originally Posted by Cheechako

Fuel issue. But may very well be a clogged tank vent, or obstructed vent hose! Little bugs build a nest in the vent outlet sometimes blocking them. Been there, done that.
When you engine starts doing that, remove the fuel fill cap on deck... is there vacuum there? If there is.... that's your problem.

And further verification if it runs normally with the cap off.

[capt jgw]

If the above doesn't work, pull the fuel line pick up tube out of the tank. It's probably just screwed into the top. If there's a screen at the bottom of the tube, cut it off. You don't need it and all the filtering should be done in the primary and secondary filters where you can change them. Don't know why they put those in there, it's a very bad idea.