G2 not getting enough fuel?

[dyates69]

Hi,

So I have a G2 which has needed choke to achieve higher revs for many months. It also backfires occasionally when stopping after heavy use. A while back it was running as per usual then on the way back home started struggling to achieve revs essentially just plodding back home at idle, at which point I parked it up for what ended up being several months.

There may have been water in the fuel as I noticed some after draining the tank once I finally got to it. I did some troubleshooting and decided it was starving for fuel so suspected a bad fuel pump. I disassembled the pump and noticed some whiteish sludge but the pump otherwise seemed in decent order. Regardless I ordered a replacement online, however it arrived with a smaller fuel inlet than the Mikuni it replaced.

The pump seemed otherwise the same so I swapped the seals and diaphragm from the new one onto the old and tried again. Still not sufficiently pumping fuel. When I lower the location of the pump it will pump fuel, but in it's standard mounting position it struggles to syphon it.

So my question is, how do I know if there's enough vacuum coming from the crankcase? I can hear and feel it sucking if I put my finger against the hose, but can't find any obvious leaks. If I lower the fuel pump and run the cart in neutral with the choke maxed it achieves what seems to be max rpm. However if I drive it similarly under load it just puts along.

Is a faulty fuel pump still a possible candidate or do I maybe have an insufficent vacuum issue? Any way to narrow it down further? I checked the airbox and the lid seems pretty well sealed.

Could something else be wrong? Any advice appreciated.

Thanks

[sparkyc4]

Might be choking down at the carb. Have you tried cleaning the carb?

[sho305]

There is a valve in the line you should clean, its above the pump next to the engine. Put it back on the same direction, its like a one way valve, like a pcv valve on a car.

The fuel/vacuum hoses for pump crack on these and leak air, check them carefully or replace if they look old. The pumps may not prime if the fuel level is low, they tell you to fill them before starting if you run out of fuel. That is normal, but if they don't get air in them they should pump fuel at any level. Take hose off carb it should spurt fuel every revolution on starter. Any leak can cause problems. In reality this engine needs very little fuel to run so if near any amount comes out it will run, if not enough it will run fine and cut out after heavy throttle use then run again at low throttle.

If not that check the usual things like dirt in carb, junk in tank. The tank has a huge filter in the bottom but most do not mess with it. Its easy to check take line off pump and fuel should come out gravity if lower than fuel level.

You could also have issue with the airbox that will make them run lean, the airbox has to be sealed up perfectly or it wont work right. You can hog the main jet out in the carb a little if you mod the airbox for more flow or can't make it seal. They can also get a crack in the spacer behind the carb on the head. They can get old and crack, or someone tightened it up too far.