Losing Fuel / Prime 500cc

[Buddee]

2010 Hisun 500 - Carbed'.  She sat for about 3 weeks since last use.  Couldn't get it started.... has spark but plug was not wet.  Bought new plug, cleaned the carb, confirmed fuel pump (pulse type) is working.  Still nothing.  Put gas in the plug hole.... started right up and idled as normal and drove perfect.  Used it for the rest of the day without issue.  Tried to start again next morning.... same problem.  Poured gas in plug hole again.... started up and best kind again.

Anyone have any insight to what's going on?

[Joe Breaux]

My money is on the carb needle/seat

[that guy from Canada]

Either needle seat sticking or fuel pump weak.

Long shot is intake leak or a vacuum loss effects starting, carb flange/boot or improper valve clearance, worse when cold.

[that guy from Canada]

Also, most carbs with choke, have a passage on the side of the float bowl shaped like an L that had a little jet, it needs to be clean, see if I can post a picture...

[Joe Breaux]

Is the choke working? These things run lean to pass emission standards. They must have a little extra fuel for cold starts. Some have tradition flap in inlet but some have " fuel enrichment" jet..it could be clogged. Or just not engaging

[Ben1098]

First, you need to confirm that the fuel level in the carb is low and/or the gas has "cooked off" the good stuff and won't start on what dead fuel is left. 

Simple test:  Fuel bleed down problem OR having to look at possible carb issues.

Disconnect the fuel line at the carb and cap (you don't want a pumped fuel leak here if it fires off and starts running).   Your machine "should" have the mini fuel tank that is mounted on the heat shield behind the seat.  If the tank has indeed bled down, no fuel will run out.  There is a post from   "DOC"   that had the hose diagram hook up connections.  Buy or make a hanging test tank to now supply the good/new fuel to the the carb.  Let bowl fill for say 10 sec.  Crank over engine.  If the engine fires right up, you have a drain down problem.  Also, while running, check if the fuel pump is indeed pulsing fuel to the mini tank and has refilled it.  From your description, it is working AFTER it gets running.  Fuel will flow out when un-capped if it is working AOK.  Catch can and rag use here for safety.

FIX  OPTIONS:  BE SURE THERE IS NO WATER OR PHASE SEPARATED OH FUEL IN TANK BOTTOM.

Cheapest (but not the best) is to buy a "foot valve" type intake fuel pick up "gumdrop" with a screen and install on the bottom of the in-tank pick up line.  Check the NEW dip tube length because you DO NOT want the gum drop rubbing a hole in the bottom of the plastic fuel tank.  Found a major mower OEM had this condition from the factory.....BAD.  Your machine may have already been fitted with a fuel tank bottom dip tube intake filter.....they sometimes get choked off.  The foot valve gumdrop pick up filter includes a spring loaded check valve ball to make it a one-way valve (check or foot using the water well plumbing term).  Fuel cannot now bleed down back into the fuel tank with gravity.....only evaporate from the carb bowl.

MY FAVORITE FIX:

Electric fuel pump.....low pressure version NOT FI.  WHY????  Many reasons!!!! 

1.     Ultimate fix for gas golf carts,...gas pedal to start cranking.  Grasshopper (Kubota 3 banger w\ mechanical fuel pump---COST to replace OEM, and other machines with the cheaper pulse type fuel pump (run one dry and then you have to puff up the fuel tank and fuel lines to get fuel back up to the stock cheaper pulse pump again-----THEY DON'T PUMP AIR.                                                                                                                                                                                                                             Example...My neighbor was mowing and run out of gas on his mega buck GREEN mower.....even filling the fender fuel tank was not enough to prime...portable air tank/detach fuel line to pump/ to the rescue.

2.     Switch off the electric fuel pump when finished mowing/riding and "run down" carb bowl fuel level to a "fast idle up"---lean mix---the carb bowl fuel now is almost empty.  When used the next time, turn on the IGN and the added fuel pump switch.....wait for the pump hum/thump to change sound and by golly, the carb bowl is full of new fuel (not cooked off crap) and ready to run.

3.     This dates me some, but 50's GM 6 banger/1 bbl Rochester  had a flooding problem in the Spring time.  Cold fuel in gas tank from overnight.  Drive to town (couple miles).  Load some feed.  Come back out to go back home and the winter blended gas cooked off and expanded and overflowed into the intake manifold.  Reason was the cold carb from fuel tank and it's normal damp cold icing problem....fuel now warms up because it is also sitting above the adjacent HOT exhaust manifold runners.  You would have to lift off the carb and soak up the liquid gas with a rag inside the intake manifold.  Drain the carb by dumping over and out the atmospheric vent.  Reinstall and cap the fuel filter inlet and do a WOT and pray the plugs weren't TOO WET for your 6 Volt system.......Oh! the good old days.  I have had "enclosed motor" mowers do the same thing by wetting down a less than clean burning plug.  Not good when there is only one plug.

AS for the mini fuel tank mounted behind the seat, it has problems supplying fuel to the carb IF you are climbing a steep bank or long hill.  Not enough head pressure for the increased fuel demand for the hard pull.  Electric fuel pump helps here also as the "over pressure" is vented back to the intake side and the mini tank is no longer required.