Nissan 8hp four stroke fuel problem

[Wiggs]

I have a Nissan four stroke 8 hp, it is about 7 years old with very low hours. After it runs for about 20 minutes it dies. Sometimes it will restart right away, sometimes not. Borrowed a neighbors fuel tank and hose, no change, replaced fuel filter, no change. Carb replaced a year ago, less than 5 hours on it. Any guesses? Any help would be much appreciated.

Wiggs

[MacGyver]

Wiggs,
Did you also replace the plug?

I will look in my book tomorrow sometime and see what if any modules it has and see if any service stuff on it.

Mac

[Shawn]

Is it cutting out after 20 minutes of idling or 20 minutes of actual load on the engine?

Are you opening the vent on the gas tank?

Is the bulb still hard when the engine is cutting out? Have you tried squeezing the bulb every couple of minutes and seeing if that keeps the engine running?

Why was the carb replaced?

Shawn

[Wiggs]

It fails after idling as well as under load. The vent is open and the bulb is full but not rock hard. If I squeeze the bulb is tries to choke out. Carb was replaced because it was busted up during hurricane Charlie. I read my original post and see I called it an 8 horse, I lied, it is a 6 horse.

Hey guys thanks for all the help.

Wiggs

[Wiggs]

I have not replaced the plug. Could it be that simple?

Wiggs

[MacGyver]

Possible that it is that simple, I am surprised sometimes by the ease of issues.

Got interrupted several times on my lunch break and didnt get a chance to check it out.

Mac

[Wiggs]

I have the amazing ability to make things more complicated than they need to be. I will try that tomorrow.

Thanks again to all.

Wiggs

[skip1930]

It runs; so the engine is happy. For 20 minutes. Boy have I been there!
The engine has:
~Compression
~Spark
~Timing
~Fuel [for 20 minutes]


Fuel for twenty minutes.
Fuel delivery unreliable.
Air in fuel system. [She won't run on air bubbles, won't create a suction either].

I had this problem with my 5 hp 2 stroke Mercury O/B. I had to wiggle the fuel line connection between fuel tank to fuel line adapter inlet at the engine when it started to sputter. Some times it kept running, some times not. Some times it would start right up. Some times not.

I wiggled it so darn much that I cracked the plastic fuel line adaptor that a long screw goes through to hold the adaptor steady and to the engine proper.
Changed that still no good. And that seals with yet another ''O' ring.
Tried new 'O' rings, goop, epoxy putty, and every other thing I could think of.

Here is my answer; Let it leak! Kind of...The only thing that has worked, and I would still be fighting this problem if not for a silicone tape called "Rescue Tape".
It's a silicone tape that sticks to itself, is fuel proof, stretches like crazy, is clear and creates a liquid tight, even under a 'squeeze ball' pressure, it seals.
Basically the tape creates a tunnel from the outside of the fuel line going over the connector, and over into the fuel line adapter. NO AIR CAN ENTER.
It's kind of a screwy setup but all these Jap outboards follow the same crazy fuel delivery paths. [All because people want to have a external fuel tank that is removable.]

The only other problems I have had was gasohol that leaves a sticky green gelatinous gunk in the main metering jet, typical with two cycles, but I dare say gasohol becomes a problem with four cycles because the hole in the jet is so small, darn near anything will plug it up. I use premium no gasohol gas. Even my new 2013 Areins Snowblower recommends no gasohol gas. No one buys premium so it's pretty old by the time it's purchased by me. Water sinks, hopfully they pump from above the bottom of the tank.

Two more causes of concern. Gasohol will fag out the crankshaft pulse driven fuel pump rubbers, leaving you with Mr. Mean'O Gravity to deliver fuel to the churn. That green gunk also gets between the flapper valves that open and close on pulse pressure causing a 'none seal', 'no pump' condition.

Last; if your engine is fitted with an internal fuel tank of a few quarts as well as the three gallon external tank, then there will be a selector valve AND two one way fuel check valves that are placed in the fuel lines. Yep one sticks open and one sticks closed...basically allowing the fuel from the internal tank to flow into the fuel line 'Y' junction and together both fuel tanks will feed the carburetor's pulse controlled fuel pump. And in this case Mr.Gravity will help with the flow of fuel until the top tank is empty. At that point a empty internal fuel tank may or may not contribute to the ingress of air. Boy do I hate the EPA for mandating ethanol. Fooling Mother Nature is always a bad idea.

A simple system correct?

skip.

[Ted]

Skip,

A couple questions. When you say gasohol, I take you mean gas with ethanol.

When you suggest that premium is at least part of the answer, are you implying that premium has no ethanol?

I am asking because I just cleaned the carb on my 6hp mercury and I am pretty sure old gas was part if the problem. I have to drive a long way to get ethanol free gas.

I would also be curious to know how well stabilizer works for y'all. I know a lot of folks use it but since I haven't I am curious what it might do the the motor, how long the gas will last with it, etc.

[nies]

The premium around here does not have ethanol in it..................I only use premium w/o ethanol, the small amount I use in a season would be worth the drive, maybe 10 gallons..................have used stabilizer and feel it gums up motor and makes the motor  run like a old John Deere tractor,..........end of season, end of gas for me , start fresh every spring, trying to save a few gallons of gas causes more trouble than its worth....................nies

[skip1930]

A couple questions. When you say gasohol, I take you mean gas with ethanol. Yes. The % of ethanol is set to increase year by year to 15++%. All that 'Flex Fuel' stuff. Problem is cutting down forests to make fields to grow corn [which is really sun power]. Germany tried it. They went broke and made fuel that the majority of their cars can't burn since they are diesel. My 1930 Ford Model 'A' will start on gas and run poorly on alcohol with a 4:1 compression, making 40 hp on gas with 202 cubic inch displacement.

When you suggest that premium is at least part of the answer, are you implying that premium has no ethanol? B.P./Standard oil Premium has no ethanol in it.

I would also be curious to know how well stabilizer works. Have not a clew. I don't use it. My gas never gets that old before I dump it into my Ford Expedition.

I always untape and unplug the fuel line and run the engine till it dies from lack of fuel at end of my season. Then she sits for 6 months dry so nothing in the fuel bowel fouls up the float or the needle.

skip.

And by the way, Gasohol and Ethanol have fewer btu's per gallon in it then gasoline, so tell me how the heck does it save fuel? You burn fuel to make heat. The more btu/gallon the less you burn to go the same distance. Tell the EPA and Obama to suck an egg,

Shawn "Ethanol in gasoline is the result of the "Energy Independence and Security Act" of 2007."[/i] And it was way before that that president Jimmy Carter came up with that half baked idea called The Department of Energy. Suppose to make America energy independent...He's so full of poop his eyes are brown. That D of E has not saved us one btu. Stupid idea. Growing corn to feed cars instead of people. Want to save Federal tax money? Close it down. When I worked at Funk Seed International the industry switched to a plant population of 80,000 corn plants per acre. That way the growers know how many 80,000 kernels to a bag to purchase.

brackish "...So far it is working.  I do have some low speed problems in the winter, but I think that is thermostat related.  I have to run a little rich to offset." You have a thermostat on an out board engine? Water is cold in the winter and that hinders the vaporization of the fuel. If the fuel is not vaporized, liquids don't burn.

It's amazing to think that on the water jacket side of the cylinder it's ambient water temperature and just 3/16 of an inch away on the combustion side of things it's 1,750 degrees + [1,300 degrees on a Model 'A' because it's only 4:1 compression]. And the temperature differential happens the instant the engine fires. Every firing, 1,750 degrees +...

skip.

[Shawn]

Ethanol in gasoline is the result of the "Energy Independence and Security Act" of 2007.

Shawn

[Shawn]

"I would also be curious to know how well stabilizer works for y'all."

I use Seafoam in each tank ans also have a racor fuel filter installed and have not had an issue with gas yet.

Squeezing your bulb should not cause the engine to bog/choke down. Sounds like your float may be sticking.

Also, how full is your crankcase?  Too much oil can cause running problems as oil will foam and make its way up the Pcv and foul the spark plug.

Shawn

[Bob23]

Hi Wiggs:
   I'm looking forward to seeing you try the suggestions as noted by the distinguished authors above. I'll add my own 2 cents: Premium fuel only. I use Stabil and have had no problems with it. Like Skip, I never carry gas over to the next season. What ever is left at the end of my sailing season, goes to the county recycling place. My motor is an old Nissan 8hp 2 stroke so she may be a bit more forgiving than your 4 stroke.
   Always remember to close the vent on your external tank at the end of the day. Ethanol, if any is present in my premium gas, absorbs water and as the outside temperature cools off, if the vent is left open, outside air which is moist will be drawn into the tank thus increasing your chances of contaminated fuel.
   I'm no outboard mechanic but it seems the 4 strokes are more prone to fuel related problems than the old 2 strokes. My Nissan starts first pull, every time...I'll never part with my Miss Nissan, size 8.
   Lotsa good advice from the guys here...you're well on your way to problem solved.
Bob23

[brackish]

I tend to agree with Shawn, sounds like a sticking float.  Runs fine until the fuel in the bowl is used up then stalls.  If you jostle it enough to drop the stuck float it starts back up, if not it won't.  I replaced a carb on a Nissan truck once and the brand new carb had a sticking float.  The pin would "set" in the cone if it sat overnight, then the next morning start fine, run the bowl empty then stall.  A sharp pop to the carb would drop it down, then fine all day until it sat overnight again.  I'm not sure that outboard carbs have the same design but your problems certainly sounds like it.

I do my fuel differently than most.  Only use regular non alcohol gasoline, which I can get a mile from the house.  Never run my engine dry.  Always keep the tank, line, carb hooked up and full so that there is little room for condensation due to surfaces that are not covered with gasoline.  Run my motor at least every two weeks all through the winter (boat stays in the water).  Switch tanks periodically and use up the old in my lawn and garden machines.  So far it is working.  I do have some low speed problems in the winter, but I think that is thermostat related.  I have to run a little rich to offset.