Suzuki DF300 - running rough-stumbling

[jeffro22]

Boat sat for a little longer than usual over the winter

the first time I tried to use it this season it started fine and seemed to run ok for a few minutes but then started to stumble and surge. then it started running really rough under load.


I did drain same cloudy fuel/ water out of racor and emptied the filter mounted on motor

took vst apart thinking that was the issue and it was really clean.
going to try new plugs and maybe a portable fuel tank to eliminate the fuel

is the high pressure filter something to look into changing or could the -hp pump be failing ?

any other thoughts. Engine starts up fine and revs fine but starts stumbling really bad as soon as it goes in gear and obviously won’t get on plane

is the high pressure canister filter need to be replaced or is it something that would be causing this issue?

[Murray]

I assume it ran fine when you parked it for winter. You drained some cloudy fuel/water from the Racor, this was after it was running rough? If so then you might have introduced water into fuel system. If you haven’t introduced too much water try adding some methyl hydrate to the gas tank. Siphon some fuel from the tank and check for old stale fuel. The fuel should be clear, if the fuel is an amber colour then it’s old and has lost some of it’s octane. If the methyl hydrate trick doesn’t work then you will have to drain the fuel system and replace with fresh fuel including new filters

[jeffro22]

Yes. Motor was fine before sitting

after motor started running rough first time I did drain filter and got cloudy fuel/ water contamination

[Murray]

What’s the condition of the fuel in your tank? Ethanol blended fuels will attract water over time and separate in your tank. You can drain filters but if your tank has contaminated/old stale fuel you’ll never get the engine to run properly. Water is heavier than gas so water will sink to the bottom of your tank and continue to contaminate your entire fuel system. I would suggest you siphon fuel from the tank collecting the first 3-4 litres in a clear container so you can evaluate the condition of your fuel. In my case with the boat on a trailer I was able to siphon the old fuel through the fuel gauge sending unit. Trying to route the siphon hose though the fuel fill hose wouldn’t work in my case. Another option that might work for you is to disconnect the fuel line before the Suzuki low pressure filter, shove a slightly diameter hose over your fuel line and siphon the fuel that way.

[jeffro22]

Changed plugs, ran off remote fuel tank with no change

guessing either a bad fuel pump or clogged injectors?

is the hp filter something i should change?

Fuel does have slight yellow color and smell but no change with fresh fuel

[Murray]

I would check your fuel pressure with a gauge. There is a fuel filter before the HP pump, I think it is a screen but not sure. Go to the “ Buy Suzuki Outboard Parts” and you will see the filters used in your engine.

Have you considered a sensor failure? Fuel line kinked? Are you sure you have zero moisture remaining in the system?

[jeffro22]

I did get a fuel pressure tester. Will be trying out today. What is the recommended pressure?

also - i did clean the screen in the vst for the hp pump. It was actually very clean when I took it apart

whT sensor would you look at?

[Murray]

My service manual (2009 DF90A) fuel pressure specification is 36 psi, I’m ASSUMING your much larger engine would be the same. Again from my service manual sensors that determine the optimum fuel injection time duration (fuel amount) are MAP, CKP, Cylinder temperature sensor, Exhaust manifold temperature sensor, IAT sensor, TPS, battery voltage, CMP and Shift position sensor. Battery voltage and condition of your battery is very important, Suzuki’s need a strong fully charged battery, a weak battery would make sense in your case, sat all winter. A weak battery will cause all kinds of grief. I would suggest you get a genuine Suzuki Service manual, the manual lays out the test procedures for the entire fuel system and all the mentioned sensors.

[jeffro22]

Ok. Thanks

So took boat out and had 40psi after high pressure pump, and that seemed pretty steady when trying to accelerate

checked it it before and after hp filter also

ran on test tank also. No stumbling this time but didn’t seem to want to go on plane and I didn’t want to keep trying

batteries are only a couple months old at this pointe and have a full charge

wondering if the injectors need to pulled and cleaned ?

[Murray]

Are you sure all the water is gone? If it is slowly getting better then perhaps you are working through the moisture? Did you try gas line antifreeze(methyl hydrate)? If your problems are moisture related then methyl hydrate will speed up the process.

[jeffro22]

I haven’t added any yet. I’ll pick some up.

Guess I got to figure something out with my fuel. Have about 80 gallons in boat now

Might try hookjng up portable tank again and then opening the top of fuel rail and letting fuel “cycle” through system until fresh fuel is coming out of top rail?

then try running again and see what happens?

[Murray]

Since your engine is running you are chasing very small amounts of moisture, if that is your problem. Old stale fuel will also cause an octane drop, symptoms are usually idles fine than bogs down under load. As fuel ages it will turn a yellow to amber colour depending upon how old it is. You mention a slight yellow colour to your fuel, an indication that you have old fuel. I do know that you can burn old fuel in your vehicle, I believe that automobile’s can compensate for low octane fuel better than a Suzuki outboard can. When I come across fuel that isn’t crystal clear then I drain it all and replace with fresh non ethanol fuel. We purchased a cottage a few years back all contents including 80 litres of fuel in jerrycans. None of the engines ran right (chain saw, water pump, ATV and a weed wacker) Dumped all the fuel replaced with fresh plus a shot of methyl hydrate and haven’t had an issue since.

[jeffro22]

It’s definitely yellow and not fresh.

I am am thinking of hooking test tank back up and then flushing all fuel out of fuel rails and seeing how it does. Assuming it runs fine then I will drain the 80gallons and start fresh

Any thoughts on the injectors? Do they need to be pulled and cleaned? Vst was spotless when I pulled it apart so hoping injectors wouldn’t have gummed up from sitting?

[Murray]

Don’t know much about injectors, some people claim that they should be cleaned by a professional shop that specializes in injectors others claim that it’s a DIY job. Couldn’t hurt to clean them. Perhaps someone with more experience will chime in. If it was me I’d deal with the old/moisture fuel and see how the engine runs. My Suzuki I bought used sat for 3 years, the fuel in the VST was a dark amber colour, drained all the fuel added fresh and I’ve had no issues with the injectors.

[jeffro22]

Thanks. I appreciate it. I am going to start draining fuel and see how it does. If problems persist then will probably pull injectors. Doesn’t look to hard to clean them

since vst was clean I hoping injectors are also.

appreciate the help. I think you are right that moisture and stale fuel is the issue. Will keep you updated on progress