9.9T ELRV Fuel problem (4 stroke)

[grump]

When under a load of half throttle or more the engine will stall for lack of fuel. If you pump up the primmer bulb when it begins to stall it will fill the float bowl and run until that fuel is used up.Wil run at idle just fine. The float is set at 25.5 mm. Tested the fuel line with hand vaccum pump and there is no leakage.Installed new 3/8 primmer bulb and fuel lines. Installed new style water cooled fuel pump. Checked fuel pump volume at idle seems to be OK. engine valve appears to be actuating the pump OK and the is no wear to the top of the valve where it contacts the fuel pump push rod.The fuel is drawn threw about 12'of 3/8 fuel hose. Could the fuel line diameter be to large? I am going to try hooking up a electric fuel pump and see if this problem goes away.Looking at previos posts it seems the fuel pumps for this engine are weak. Any suggestions?

 

[rodbolt]

Re: 9.9T ELRV Fuel problem (4 stroke)

check for excessive fuel system vacum, attach a vacum guage at the fuel pump inlet at run it at the problem RPM under a load, system vacum should be between 1 and 3" Hg. any more and its restricted someplace and any less and its leaking air someplace.<br /> is this an F or T 9.9 ?<br />mostly it does not matter but without the F or T prefix it indicates a two stroke.

 

[grump]

Re: 9.9T ELRV Fuel problem (4 stroke)

I conected a electric fuel pump into the fuel system and engine did not stall. I isolated the fuel pump and ran the engine with the electric pump strait to the carb inlet. Output of the new pump was very minimal. with 2' of line to draw from a container at the same level as the engine it had almost 0 output at idle and at WOT the pressure and volume was very low. New fuel pump must be bad.Conected a vacuum guage and reading was less than 1" HG. Is it common for these pumps to fail? One other note : when I had the electric pump in the circut the back pressure created quieted the ticking noise made by the valve to fuel pump clearance.

 

[rodbolt]

Re: 9.9T ELRV Fuel problem (4 stroke)

with no fuel pressure that mechanical pump is very noisy.<br /> I rarely see manu problems with that mechanical pump other tan debris in the check valves.<br /> but the tests I described above will find it.