Owan fuel flow test on a 4,000

CJW8 wrote:
You haven't really stated the problem yet.
Gen wont run?
Gen runs but quits?
What?
Recently on two different RV's where Gen would run but quit. Both belong so sons in laws. First Travel trailer toy hauler. The fuel tank was about 25 feet from the generator and the fuel pump is located at the generator. A second fuel pump was added near the fuel tank. Second is a class C MH. Same issue. Gen would quit if the motorhome was going up hill or of it was parked slightly up hill. In this case, the installed fuel pump was relocated to near the tank. Both now run flawlessly. I believe on the MH, it was actually vapor locking because if the long suction line to the tank, high heat and 3 high points in the fuel line.

Correct, I did not explain the problem. Was trying to see if there was any type of fuel flow test. Apparently not, but good response to check if fuel is being pushed through hose. Mine is running rough after about 2 min under load. If it were an old 60's car, sounds like maybe spark plug wire.

This weekend going to borrow the neighbors carb (same model) to see his does the same thing.


On yours, just a thought...make certain fuel cap didn't get some road grime in vent hole on gas cap. Testing... First I would use without gas cap being on, just to see if yours is a venting problem. Second test would be new fuel line hose if your hose now is old or getting weak and in hot weather hose might be collapsing.

You haven't really stated the problem yet.
Gen wont run?
Gen runs but quits?
What?
Recently on two different RV's where Gen would run but quit. Both belong so sons in laws. First Travel trailer toy hauler. The fuel tank was about 25 feet from the generator and the fuel pump is located at the generator. A second fuel pump was added near the fuel tank. Second is a class C MH. Same issue. Gen would quit if the motorhome was going up hill or of it was parked slightly up hill. In this case, the installed fuel pump was relocated to near the tank. Both now run flawlessly. I believe on the MH, it was actually vapor locking because if the long suction line to the tank, high heat and 3 high points in the fuel line.

The Onan facet is more than likely 4-5psi max. Realistically a 3-4 psi pump is all that is needed to supply the carb.

The normal Onan/Facet pump operates at 4-5psi. With an 8ft lift. To find any information on fuel flow. You will need to know the pump number and check with the pump OEM.

Wuwee kudos on your answer Gdetrailer! I lift the hose 2' higher than the carb inlet and if fuel still comes out then it should be plenty.

path1 wrote:
Op here...OK thanks folks. I was under impression (probably wrong?) that the fuel pump would pump so much gas in 30 sec or 1 min. A trouble shooting test to see if fuel pump is my problem.

Small engine manufacturers do not very often include such type of specifications.

In reality the pump MUST be able to lift the fuel from the tank up to the carb and keep the carb bowl FULL at all times.

On carbed engines typically a fuel pump will supply about 7 PSI MAX to the carb float valve.

In a nutshell, that onan pump needs to be able to lift the gas from the tank, up to the carb..

I would try seeing IF the pump is able to at least supply MORE than a small trickle at the same height as the carb bowl..

If you barely get any fuel at that height the pump is bad (although any damaged fuel line IE rusted with even a pin hole can introduce enough air in the line to stop the pump from pulling fuel from the tank)..

If the fuel pump is more than 4-5 yrs old I would suspect the pump diaphragm and/or the valves are shot..

You could lookup onan fuel pumps with the model you have and see what kind of pump you have.. They have several different versions that have been used from vacuum type to d direct drive lever to electric..

Found one source HERE that might be helpful.

Op here...OK thanks folks. I was under impression (probably wrong?) that the fuel pump would pump so much gas in 30 sec or 1 min. A trouble shooting test to see if fuel pump is my problem.

3/4 of gallon is only 1.6 oz per min. So maybe a flow test is not accurate for trouble shooting?

The Onan fuel pumps (typically) are spring loaded solenoid plungers where the solenoid is pulsed (cocked) a couple of times per second. It is the spring that provides the pressure and there is a check valve involved somewhere. This info could be obsolete as it is the way it used to be circa 2000.

The 4kw Onan uses 1/2 to 3/4 gallons of gas/hour depending on the load, so the pump should move more than that.