NS3.5B2 dies after a few minutes of running

[Sybarite999]

I've got a Nissan 3.5hp with F-N. It runs well, but occasionally it will just die after running fine for several minutes. The vent is open, fuel turned on, new plug, fresh hi-test gasoline with Stabil added. It will usually restart immediately, but sometimes it takes 10+ pulls. After restarting it will run fine or it might quit again after a few more minutes. Eventually it will continue to run without stopping.

I have completely disassembled the carb and cleaned all passages with carb cleaner and pipe cleaners. The float moves freely, the float valve visually looks fine and it is connected to the float actuator hinge.

It certainly acts like the fuel supply is being interrupted, but a sticking float valve doesn't seem likely.

Any ideas as to the cause?

 

[pvanv]

Re: NS3.5B2 dies after a few minutes of running

Did you inspect the in-tank filter? Is the motor trimmed correctly so that the gravity flow feeds fuel well? You cannot properly clean a carb with spray and pipe cleaners. If needed, you must completely disassemble it, soak it for 4 hours in real carb dip, and then you can blow out any softened organic varnishing with generic carb spray.

 

[Sybarite999]

Re: NS3.5B2 dies after a few minutes of running

Thanks for the suggestions. I wasn't aware that there was an in-tank filter, and this year I have added an in-line filter. The fuel flows freely from the open fuel line and the engine will quit with a full fuel tank so I don't think fuel delivery to the carb is an issue.

I wasn't aware of the proper carb cleaning method, but I will get a pail of carb dip to use at my next opportunity. Even though just carb spray and pipe cleaners are not 100% effective, is it really possible that there is some spot of a deposit that would bring the engine to a complete stop? I will say that after my spray and pipe cleaning exercise, the engine has been running much, much better. It has stopped once since this cleaning, but only once in 15 uses. In prior years the engine would stop several times almost every use.

Any other possibilities that you can think of? This shouldn't be rocket science- if the engine has clean fuel in a proper mix, good spark, and compression, it should run.

 

[Sea Rider]

Re: NS3.5B2 dies after a few minutes of running

The. 3.5 has inside fuel **** a small round mesh filter, if you have not removed **** to clean it, probably could be the culprit. A mesh filter will suffice, no need to add a second in line filter, being flow fed by gravity, could be being restricted by adding another in line filter.

If carb and mesh filter are cleaned to immaculate condition and engine keeps with issues, could be experimenting electrical issues due to components overheating ?

Happy Boating

 

[TOHATSU GURU]

Re: NS3.5B2 dies after a few minutes of running

Fuel-Fire-Fun

If the engine is getting fuel to the spark plug and the plug is firing and if you have any compression the engine will start. So, Look at the fuel system again and test for fire...Change the sparkplug before you do anything else and make sure you do not have to much oil in the gas.

 

[Sybarite999]

Re: NS3.5B2 dies after a few minutes of running

I will check and clean the screen in the fuel petcock. But for now I have a steady stream of fuel from the disconnected fuel hose, so I think that regardless of the state of the petcock screen, the carb is getting plenty of fuel to run.

I am very careful to add the correct amount of oil for the 50:1 mix. Unless I am starting with an empty tank, I add gasoline first and note the amount and then add the proper oil quantity.

I have considered some sort of heat problem or ignition issue, but since the engine immediately re-starts after a quit (usually just a couple of pulls), I have discounted heat or an intermittent spark issue. Is this a valid conclusion?

The problem is that both fuel and spark seem to be OK, and clearly one of them isn't OK. As I mentioned in a previous post, this engine has quit just once in the last 15 uses, and for that last 14 uses it has run just fine. Maybe all I need is another very through carb cleaning?

I considered that there could be some drops of water in the fuel, but with all the alcohol (10%) it seems like any small amount of water would be absorbed and burned- pretty much like dry gas additive would do. And besides, I completely emptied and cleaned out the tank a couple weeks ago.

I just hate intermittent problems. Much easier to find the cause of a complete death.

 

[TOHATSU GURU]

Re: NS3.5B2 dies after a few minutes of running

No

Maybe

 

[Sybarite999]

Re: NS3.5B2 dies after a few minutes of running

No

Maybe

Please enlighten me. Why doesn't an immediate restart after a quit eliminate a bad spark from the possibilities?

 

[jrs_diesel]

Re: NS3.5B2 dies after a few minutes of running

When I had a 3.5 (forward only, no neutral), I had an issue with it stalling. It would run fine at lower speed, when I ran it faster sometimes it would sputter and eventually stall out. If I dropped the throttle to idle when it was still sputtering I could keep it running. Mine was a dirty carb, and something was getting sucked against the main jet when running, partially blocking the main jet.

Yours sounds more electrical, in that it just stops with no sputtering. Pull both cowls off and closely inspect your wiring. You might have a loose (or bad) kill switch. The timing is fixed on these motors, so the stuff under the flywheel should be fine (no movement of the plug wire or anything like on a motor with spark advance).

 

[TOHATSU GURU]

Re: NS3.5B2 dies after a few minutes of running

"I have considered some sort of heat problem or ignition issue, but since the engine immediately re-starts after a quit (usually just a couple of pulls), I have discounted heat or an intermittent spark issue. Is this a valid conclusion?"

No, because intermittent spark is...Intermittent. A bad ground, internal failure of a coil or trigger, electrode on a spark plug, etc can all fail due to vibration. The engine stops, no vibration, the engine starts again. Sometimes it's heat build up in the part itself. Other than random parts replacement, you have to run the electrical tests, as found in the service manual, to eliminate those parts.

As simple as these engines are it is possible that you are looking at something that is freaky. I've seen a bad carb on one that looked perfect in every respect...It just wouldn't work. So, you eliminate what you can through the tests and then start on the rare problems next.

 

[Sea Rider]

Re: NS3.5B2 dies after a few minutes of running

If engine stops and restarts with no issues, suspecting vibration issues, could have a internal broken or corroded wire that spreads when engine vibrates, and joins after the engine has stopped. Check all grounds to be inmaculate clean and adjusted tigh to engine body to attain proper ground on all related electrical parts. Wile engine is on at idle, move back and forth all visible cables and check if engine stops, if so bingo, you already found the culprit...

Happy Boating