Honda BF50 - Runs out of Fuel - What's Going On??

2008 BF50 - I cleaned and replaced all gaskets on the three carburetors two months ago. Since then, I've run the motor several times and motor runs smooth at idle and strong at higher rpms. No issues a all until last week.

Motor still runs strong but after 4-5 minutes of running at 3500rpm,she runs out of gas. If I manually pump the fuel bulb, she runs fine again. But I need to force fuel into the primary filter. Please note, that I have a large-canister Racor primary filter (30 micron) in front of the motor as well as the secondary filter inside the motor. Both filters are new and I have run both for several years without any problems. Also, at a fast idle (1500-1800rpm), she willrun out of fuel in 5-8 minutes.


The fuel pump is actively “sucking” and developing pressure. That doesn’t seem to be the problem.



Maybe the anti-siphon valve in the bulb is bad? I suppose that I will install a new bulb tonight and see what impact this might have.


What concerns me is the vacuum lines. When I have thecarbs off, I failed to reinstall the black vacuum lines for the top 2carbs. But the motor seemed to run justfine without them. And I’m not certainwhat these vacuum lines do. See attachedpictures. Might my problem be related tothese lines? And if so, why have I beenable to run the motor for 5 hours at high rpm since the carb rebuild with noproblem until now?

Pictures of carb Not the missing vacuum lines in the top two carbs

Are you sure your tank breather is open? Double check that the tank is getting air in to replace the fuel, try running with the fuel tank screw lid off. Are all the fuel line connections in good order and sealing? Try a different fuel line, bulb, connections. No cracks and splits in hose?

The vacuum tubes you refer to are not vacuum. They connect to a diaphragm that has a linkage to the throttle. It serves the dual purpose of pressurising the carb bowls (forcing more fuel in) when you accelerate as well as slowing down the closing throttle when you decelerate quickly. Not connecting this should not have caused any great issues but should have been noticeable if you quickly accelerate or decelerate (stalls, lags).

Is the primer bulb sucking flat when you run out of fuel? One common cause of this type of issue would be an air leak at your Racor (doubled up seals etc). Is your Racor between the tank and primer bulb or between the engine and primer bulb?

Thanks SKRONKMAN and ALIBOY. A few things to update - The Racor is located between the primer bulb and the engine. And the primer bulb is not going "flat". But the primer bulb is loosing all the gasoline as the engine is running. I installed a new primer bulb today (and verified that the anti-siphon valve was working) ....... made no difference in motor performance ..... motor still ran out of gas after a few minutes of fast idle.

I performed a few more tests today. With the motor running, I disconnected the fuel line at the suction (motor) side of the Racor and lots of gasoline came gushing out. So I assume that I have good suction to the Racor. Then I bypassed the Racor altogether (I used a barb to connect the two fuel hoses). Made no difference. I then bypassed the Racor and the quick-disconnect fuel fitting at the motor cowling and ran the fuel hose directly from the tank to the secondary filter inside the motor ...... this made no difference. Motor still runs out of fuel in 5 minutes at fast idle.

So all of this is telling me that I have good suction and no air leaks at least to the Racor (as far as I can tell anyway). Could the tank be bad? Maybe there is a bunch of small air in the fuel hose between the tank and the RACOR? Seems strange because I'm not seeing any fuel leaks from the same hose?

What sort of tank do you have? Is it a topside red tank?

If so, I would want to check:
1) that the tank vent is open and air is moving freely in
2) that there is no problem with the plastic feed hose connection that goes into tank
3) that there is no obstruction blocking the mesh filter on the end of the feed hose in the tank

Check as never summer says above then, If you disconnect the fuel line from the motor and press the end of the fitting down with something and squeeze the bulb you should get fuel squirting out easily and not sucking back air when you let the bulb reflate. If that works then I'd be looking to the fuel pump next as it sounds as though your motor runs till the carby bowls are empty then stalls. The fuel pump should keep trying to fill the bowls when the floats drop as long as there is free flowing fuel to it.

Try using a portable tank and hold it above the height of the engine. If that works, lower it to the deck and try again. If it then fails, check your fuel pump.

UPDATE - Fixed!!

The problem was related to an air leak at the fuel tank. The motor was sucking air into the fuel system. Thanks for the help guys!!