DF20A rpm's drop and surges

[AndrewVal]

I have a 2019 DF20A which is 1 year old and about 75 hours on it. The motor starts and runs perfectly at low speeds. When I fully open the throttle it runs perfectly for about 10 - 11 minutes and then the rpm's drop from 5900 to around 52-5400. If I pick up on the throttle lever 1/16" it picks back up to 5900. If I do not pick up on the throttle it will take about 30 seconds surging to get back to 5900 rpm.
Every single time it does it the same place on the river within about 200 yards.
The low pressure filter was changed. I pulled the hoses off of everything and did find a few small black particles in them. I have no idea how they would have got past the filter or were they there when built? All fuel hoses are tight. Plugs are burning perfect and there are no alarm codes. Engine was winterized with sea foam.


I tried a clear filter after the primer bulb and at idle there are no bubbles. When it is at full throttle bubbles appear and at idle they go away. The bulb also feels sort of soft.

To me since it is doing it at the same place on the river every time, I am wondering if it is running on the fuel that was primed into the engine at the dock?
I see there are screens in the high pressure pump, but it says do not take apart.
It doesn’t say if there is a screen in the fuel vapor separator. It is a black plastic canister.
Is there a spec on what the low pressure pump puts out? I am thinking it may be the low pressure pump, but I am not sure. Any advice would be greatly appreciated

[2014DF25ARS]

Do you have a gauge/display that will show error messages from the engine? The surging sounds to me like over-rev protection. This is what my DF25A does if I exceed the rev limit. But I don't know why you would over-rev at a particular spot on the river. My DF25A has an in-line fuel filter located between the fuel vapor separator (VST) and the high-pressure fuel pump. This is a fairly simple plastic disk with a screen in it. I replaced this filter when my engine had around 175 hrs on it, because overnight the motor wouldn't run above "limp mode" idle speed.

[AndrewVal]

Thanks for the reply. I do not have a gauge that shows the error codes. It is definitely not the over rev protection. Nothing beeps to tell me there is a code. Before it surges the rpm's go down like it is running out of fuel, almost like a partial vapor lock. There is no filter on mine between the high pressure pump and Vapor separator.

I have a very low pressure inline electric fuel pump for a carbed generator that I am half tempted to try and see if it clears it up. My gut tells me it is the low pressure pump, but not sure how to test it.

Can the vapor separator be taken off and flushed out to see if there is anything in it? The screens in the high pressure pump also are suspect. They say do not take either apart.

[Moonlighter]

If you saw bubbles in the lines at revs, then there is an air leak in your boat’s fuel system somewhere. Need to find it and fix.

I would also recommend you install a water separating fuel filter between tank and engine. Racor style, they make a smaller one to suit smaller engines. Keeping dirt and water out is important.

[AndrewVal]

If you saw bubbles in the lines at revs, then there is an air leak in your boat’s fuel system somewhere. Need to find it and fix.

I would also recommend you install a water separating fuel filter between tank and engine. Racor style, they make a smaller one to suit smaller engines. Keeping dirt and water out is important.

I tried a portable fuel tank and it did the same thing as the onboard tank, so it must be somewhere in the engine.I am going to go over the hoses again and see if any are sucking air. Do you know of a good way to test them?

[AndrewVal]

Since I a not getting any alarms could there still be a fault code stored in the ecm? I think that I will order a diagnostic kit for my laptop to see what is going on and maybe it will help solve the problem. The engine runs perfect for 10 minutes of wide open throttle and then it starts surging, idle is always perfect. I hate intermittent problems.

[Moonlighter]

Did you eliminate the bubbles in the fuel lines yet?

[AndrewVal]

Did you eliminate the bubbles in the fuel lines yet?

Yes. I even put a small 3# electric pump on temporarily between the tank and motor to help rule out a fuel issue. I am thinking it has to be something electrical. I ordered the diagnostic kit in hopes that I can get some useful information for a dealer to make repairs.

[rackbid]

"The bulb also feels sort of soft."

I have a 2016 DF20A and about a year into owning it and light use I had very similar symptoms. Mine would idle or at low speed (not on plane) run fine all day long, but at full throttle it would only run for a few minutes and then die completely. Turned out to be my fuel bulb was losing prime at higher RPMs. After (like you) thinking I had some deeper problem, I realized that I could re-prime the bulb after this would occur and it would run fine for a few minutes before dying. Replaced with an OEM bulb and problem solved. Don't know if this is your problem, but I was surprised that the factory fuel bulb would be a problem after barely a year.

Fast forward to last year and my quick connect would leak fuel on the tank side of the hose. The leak would happen when priming the bulb, OR when just connected to the tank while in the sun (tank was pressurized). Replaced the tank side quick connect and problem solved again.

Great little motor, but the fuel delivery system has surprised me to be problematic so soon and with such light use. I have maybe 30 hours on it and the tank and fuel hose are always stored inside.

[AndrewVal]

I started off today pumping up the primer bulb with the fuel line attacked directly to the engine fuel filter/ water separator, eliminating the fuel connection at the engine. I would pump the filter full and immediately some of it would drain back to the onboard tank. I switched to my portable tank with the same results.

I then put a clear line from the outlet of the engine fuel filter/Water separator and while running, the line would develop a big air pocket.
I then changed the primer bulb with the same results. With all tests there was a good stream of small air bubbles at full throttle coming out of the filter / water separator.

I then took the low pressure pump hose outlet off of the VST and it would pump out the bubbles and make the clear line full, only to start putting air bubbles back in the clear line that is coming out of the filter / water separator. The low pressure pump was spurting out fuel when taken off of the outlet of pump.

I did pull the line from the high pressure pump to the vst and there was hardly anything coming out of it. From what I know there should be only fuel coming out of the high pressure pump to the vst when the regulator in the high pressure pump sends it there.

I am at a loss, any ideas what the heck is going on? Thank you for the replies.

[redlowrey]

What do you mean by, if I pick up the throttle leaver it runs good. Does your engine have a battery or is it pull start. For obvious reasons it will have different flywheel and control units.
If you mean you move the throttle leaver a bit more and it runs good, tells me that the throttle position signal voltage it not going to maximum and and the fuel pump is not outputting max pressure.

On larger engines the computer controls the fuel pump ground depending on load, it is duty cycled, your little toy engine might use the throttle position out put for max fuel pump output..

[AndrewVal]

What do you mean by, if I pick up the throttle leaver it runs good. Does your engine have a battery or is it pull start. For obvious reasons it will have different flywheel and control units.
If you mean you move the throttle leaver a bit more and it runs good, tells me that the throttle position signal voltage it not going to maximum and and the fuel pump is not outputting max pressure.

On larger engines the computer controls the fuel pump ground depending on load, it is duty cycled, your little toy engine might use the throttle position out put for max fuel pump output..

It has a battery. When is starts to lose rpm and surges, I pick up on the throttle lever about 1/16" and the rpms pick up but eventually it will bog down again, but changing the position does affect it. I would think moving the throttle would make the computer control change the mixture and thus tricking it to run better?

Today, I checked the oil and to my surprise it was about 1.25" high and had a gas smell to it. I think with the air bubbles and no explanation for them and the oil level would it be safe to assume that the low pressure pump is going bad? Thanks for the reply.

[AndrewVal]

Tried out the diagnostic software and have some readings. On the graphs when it was running good they were all pretty much flat lines. When it started surging (only at full throttle) the timing, throttle position sensor voltage and throttle position angle were erratic on the graph. The low pressure pump was changed due to gas getting in oil. There are still some air bubbles in the line going to the low pressure pump , but out of it to the vst it is solid fuel. Does anything pop out to anyone what is going on?

These readings were when it was running good
Engine speed 6031rpm
Ign timing btdc 19 degrees
Manifold absolute pressure 28.95
Barometric pressure 29.53
Cylinder temp 133 degrees
Intake air temp 97 degrees
Battery 12.82 v
Fuel inj pulse width 7436 us
Injected fuel amount 18 mcc
High fuel pump duty 69.2%
Iac valve duty 100%
Throttle position angle 65.92
Throttle position sensor output 3.40v

These readings were when it started to surge
Engine speed 5781rpm
Ign timing btdc 13 degrees
Manifold absolute pressure 28.95
Barometric pressure 29.53
Cylinder temp 135 degrees
Intake air temp 99 degrees
Battery 12.82 v
Fuel inj pulse width 7144 us
Injected fuel amount 17 mcc
High fuel pump duty 68.4%
Iac valve duty 100%
Throttle position angle 56.64
Throttle position sensor output 3.09v

[AndrewVal]

I forgot to mention that it did have 1 code stored. #21 and said tps failed 3 times. The motor had 113 hours and there was a failure time and it said it was 101 hours. Does that mean it really hasn't run right except for the 1st 11 hours? I am going to make an appointment for the dealer to repair and am trying to gather info for them. Any suggestions are welcome on what to log.

Is there anything I can read that tells what normal readings should be?

[AndrewVal]

Got it fixed , thanks for all the help