Honda CBR - carberator keeps flooding.....

[byez]

Brand new owner of a 99 CBR F4 with 45km (not miles) that had been sitting for the last 3 years. Gas had all but evaporated.

It was running but very rough and would die out after a min of idling so I decided to clean the carbs and change the spark plugs.

I was very careful with the carbs and did only one bowl at a time, the float pin & seat were in excellent shape. The needle jet was rusty/tarnished and I took care to gently polish before replacing. The floats was tested in a bowl of gasoline and were measured for proper height. Floats are non-adjustable and no modifications were made to the carbs.

Now when I try and start it, the engine completely floods, gas in spark plug wells, gas in cylinder head, won't fire at all unless I turn the gas line to off at which point it will run until the gas runs dry.

At the moment the plugs are out and drying, battery charger is hooked up & the gas soaked oil has been changed. I just don't get it, the floats are perfect, i even tried installing a shim in the floats so they would choke the gas off earlier, the float needles are spotless, its an oem fuel pump so there is no change in fuel pressure. I'm at a loss as to my next step. Why would it not flood before the carb cleaning and start to flood after cleaning?

 

[byez]

Additionally I did try bench testing the carbs by flipping the carbs over and blowing into the fuel lines to test for proper sealing. No air got through.

 

[spasm3]

Does this bike have a vacuum petcock? That could be the problem, not the carb

 

[JimPghPA]

Just a guess, did you use the old fuel tubing?

All it takes is one small speck of rubber to flow into the pin seal, and it is time to build an ark.

I had it once happen with a outboard motor that was less than one year old.

I hate black fuel tubing. It causes sooooooo many carbs to flood because it will thorw off small pieces of rubber.

Probably the best fuel tubing is Tygon fuel tubing. You can get it from McMaster-Carr. There are several kinds of Tygon tubing. The kind you want is Tygon F-4040-A , and McMaster-Carr sells it in just about any ID you could use.

McMaster-Carr has a special deal with UPS. Expect you package to arive at your door in one day, two days tops. And the shipping charge will be low.

The bad news is you will have to pull the carb apart again to get the rubber out of the pin seat.

Adding an extra inline filter is also a good idea.

 

[JimPghPA]

PS. The Tygon fuel tubing is translucent yellow, so you can see the fuel level in it.

 

[byez]

Petcock is gravity fed.

Fuel line was replaced post-filter and float needle bowls are spotless.

 

[Trav]

Check the little filters under the needle seat. They can be discarded if you use an inline filter, make sure the seats are tight in the carb body.
IIRC these F4's used an electric fuel pump, it may have some dirt issues also that can over pressure the fuel and blow the needles right off their seats.

Try a line from the tank only and bypass the pump and see if the flooding stops.

The OEM dark grey Honda fuel line is fine, its not normal black rubber hose and doesn't shed.

 

[CBR.worm]

I some cases, if the vent lines get plugged they will pour gas down the intakes, but that is usually when moving at speed. Aside from that, I would replace the float valves. the rubber is probably not very pliable anymore. I thought those had a fuel pump. Thump.thump.thump...thump...thump..... If so it doesn't take much of a leak to move a lot of fuel.

Are all 4 cylinders flooding? You should be able to see the fuel running down the throat of the offending carb first, unfortunately the float vents can let fuel from one overfull bowl flood into the other carbs as well. I don't remember if 1&2 vents were isolated from 3&4. I think they had separate fuel feeds.

Be aware that some of the fuel is probably running past the rings into the oil.

 

[byez]

Tried running without the fuel pump and it still flooded. Starts up for a few seconds then dies off.

When I took the carbs apart, the jet needles were rusted, it seemed like they were the dirtiest of any of the components. Would a worn jet needle cause flooding or should I look elsewhere?

Does the bench test of flipping the carbs over and blowing into the fuel lines really work? It passed this test and I aready eliminated the need for new floats and float needles.

I'm about ready to purchase a new set of carbs with 15k on them for $300. Do carbs really wear out with mileage or should I just replace the float needles in mine?

 

[mechtech2]

I still smell a faulty float system problem.

Older Hondas had notorious heavy float problems, and leaking floats.

 

[CBR.worm]

Carbs can wear out with mileage, whether you will notice or not is a different story. The slides get worn, the throttle shafts become loose, etc. All adding up to a less accurate air fuel mixture.

When you say 'Jet Needle' you are referring to the needle that sticks down through the slide and into the main jet orifice? I am not sure how this would get rusty unless water was in there which would lead me to a complete teardown and cleaning.

That needle being rusty should not be able to cause flooding as in gas pouring out. About the only thing that can cause that is bad float needles/seats. In some cases the seat itself can pull out and has an o-ring behind it that can leak. I don't remember if the Keihin's on the F4's had that. I don't even think missing main jets would cause flooding at idle.

And yes, they can pass the air test on the bench and then not work when flipped over with fuel - especially if they have been moved around. And the tabs on the floats can be bent to adjust fuel level, but it sounds like you are far from a minor level adjustment. On the other hand you could lower the float level a bit and see if it gets better. Bend the tab up if the float is hanging down.

Are all the other passages clear? low speed air mixture screws have been removed and had passage and tips cleaned - rubber orings and washers are still on the ends of the springs? Choke is off and all choke components (little o-rings and plungers) are in their places.