1993 Suzuki 250 quad runner new fuel pump issue

[Pumpkinray]

Recently purchased an aftermarket fuel pump was defective, right out of the box would not pump any fuel. The old one worked fine. It was just leaking fuel. They sent me a replacement free only to find out that one didn’t work either after several hours of troubleshooting replacing fuel lines, checking fuel petcock only to discover that the small spring in the fuel pump was too tall, not allowing the diaphragm to pulsate the spring, measured 9/16 of an inch tall by placing it in a vice and shutting it down to half inch and reinstalling it back in the pump. it worked perfect this might help someone with the same issue in the future .

[kp3004x4]

Yes sir have ran across the same thing,with some having pin holes in the pump itself,you never know these days what you will get when you order parts.  Anyways have a good one .

[Jd101506]

Sounds silly, but how exactly do these pumps work? I’ve got one in my LT300 that’s bad. It won’t delivery any fuel to the carb but I can push air through the lines, and I can blow bubbles into the tank from the fuel pump as well so I know it’s the pump that’s not working. Is there a better way to test it? I don’t know enough about it to say yay or nay. Thanks! 

[Jd101506]

After digging in a bit. 
 

realize that these are all controlled by vacuum created by the engine cranking. My pump still won’t pump fuel but I know I can get fuel from the tank. I ended up ordering a new fuel pump to test out and see if that immediately fixes the issue. 

[Pumpkinray]

Vacuum from the engine to the fuel pump, causes the diaphragm to pulsate in and out, pulling fuel from the gas tank and pushing it to the motor

[Mech]

 

If it runs ok when the bowl is full then you need to figure why the bowl isn't staying full..

When the tank is full the fuel will/should flow out the carbs fuel hose if you pull it off.. You should check that happens first.

If there is fuel getting to the carb then use the drain bung to check it's flowing through the float needle and into the carb fast enough.

If there was no fuel to the carb then check for restrictions somewhere, or vacuum in the tank. That new pump might restrict the fuel when it's not getting vacuum. The tank vent could be blocked.

To test the fuel pump you lay the fuel hose to the carb into a bottle. Lay it on it's side with the hose laying flat. If the hose is dangling down you won't see the fuel pumping out properly. Then suck hard two or three times on the vacuum hose going to the pump, and then let the vacuum off suddenly. You should see a single slug of fuel come out of the fuel hose. The slug should be full diameter of the hose and about ten mills long. If that works then your pump is ok and will work if it's getting good pulsating vacuuum.

To test the vacuum you reattach the vacuum hose and start the motor and let it idle. It should pump fuel out of the fuel hose into the bottle at full diameter of the hose and slugs about eight mills long. If that works then the pump is working and it should start and idle at east.

Then you need to check the vacuum is still strong enough when the motor is under load. To check that you leave it all as is but sit on the bike, put the brakes on hard, engage first gear and open the throttle until the motor starts straining against the centrifugal clutch. As the motor starts to labour the pump will likely slow down it's delivery of fuel, but it should keep pumping some. If it stops pumping then you have weak vacuum or a malfunctioning pump.

The vacuum has to be strong, and pulsating when it gets to the pump. If the vacuum hose has been swapped with some soft thin walled stuff the pulsations can get lost as they suck the vacuum hose flat and then let it out again. Low vacuum can be caused by low compression, tight valves, or air leaks. Low vacuum at high revs can be caused by a blocked exhaust.

 

Oops. That was for someone else so the first few lines are not too relevant.