Bike dies when I put the airbox on

[Garrett]

Bike is a 94 CBR900RR that was running fine when parked ( did the stah-bil thing and all that). It was running iffy and I realized it had very little fuel. Put some fuel in it and that didn't help much. I pulled the tank and airbox off, fired it up and set the idle to ~1100. It will idle there all day until I put the airbox on then it will die and only refires when you hold the throttle open and dies if you don't rev it. I pulled the airbox apart and the filter is good and there are no restrictions.
I'm at a loss here.

Any help or ides would be appreciated.

[TTD]

On the 95 cbr 600's, there was a tube attached to the airbox... without that attached I recall having some issues. Not sure if the same for the 900 but figured I would throw it out there.

[Garrett]

There's a tube that runs up to the right of the head and connects to the airbox. With the bike running, the air coming from the tube is hot and smells of combustion.
Even when I just lay the fuel tank on top, it dies.

[TTD]

Sounds like a pinched hose if it runs with the tank up, but then dies when you lay it on top?

[Garrett]

I don't hook the fuel up to the tank.

[myzx6]

Just leave the air box off lol.

In all seriousness it sounds like dirty carbs or just plain bad fuel to me. Stabil doesn't do as good of a job with the ethanol fuel as it used to with straight gasoline. Seems how it runs better with no air box I'd suspect a stuck float causing it to flood out.

[myzx6]

Even better if you can't figure it out ill trade you for a strong running 95 zx6 that is pretty much all new, including paint.

it was worth a shot...right???? Lol

[TTD]

I don't hook the fuel up to the tank.

Not sure I understand what you mean here? You said this earlier... Even when I just lay the fuel tank on top, it dies.

[TTD]

I'm off to watch the Moto GP I recorded... be super specific with exactly how the bike runs and how it dies and I'm sure someone will have the answer.

[Garrett]

Darn. Was hoping to avoid a carb clean. I'll order some float needles and gaskets.

[Garrett]

Not sure I understand what you mean here? You said this earlier... Even when I just lay the fuel tank on top, it dies.

I'm running an aux fuel pump to the carbs. The tank is 10 feet away on a bench, air box next to it.
If I bring the air box 10 feet closer and put try to put it on with the bike running, it will bog and die out. If I put the airbox on and try to refire it, it won't refire unless I hold the throttle open and then it won't idle.
If I remove the air box and bring it 10 feet to the bench and start the bike up and take the gas tank and bring it 10 feet over to the bike and just lay it where it goes with out bolting the one 8mm bolt and one 10mm bolt, it will die.
If I try to refire it with the tank just laying on the frame, it will not start unless I hold the throttle open and then it won't idle

[myzx6]

Well an easy way to test the needle and seat is to pull the carbs off and hook your slave tank up to fill the bowls with fuel. Next let them sit for a little while and usually you will start to see fuel leaking out, also try keeping the carbs sitting in the position they would be when they are installed on the bike.

Does any amount of choke help or make things worse with air box on? Also is the bike on its kickstand, and have you tried holding the bike up while sitting on it with it running.

Defiantly check for Kinked hoses or vacuum lines (if any not sure on Honda)

[Garrett]

Welp I cleaned the carbs (thoroughly) and put new float needles and gaskets in. Bike ran fine for just under 10 minutes then died and wouldn't refire til I held it wide open. I took it for a very short ride and it died on me. Had to crank it for 30-45 seconds and hold the throttle open for it to come back.
I'm stumped.

[R7]

Welp I cleaned the carbs (thoroughly) and put new float needles and gaskets in. Bike ran fine for just under 10 minutes then died and wouldn't refire til I held it wide open. I took it for a very short ride and it died on me. Had to crank it for 30-45 seconds and hold the throttle open for it to come back.
I'm stumped.

Did you check the float level after replacing the needles and seats? Typically when you have to hold the throttle wide open to restart, it's usually because the engine got flooded with gas. Stuck floats, float level set to high, or even to much fuel pressure can be the cause

[Garrett]

Float level is not adjustable on these particular carbs, strangely enough.

Prior to the rebuild, the engine would lock up if it sat over night because it had bad needles and would get loaded with gas.

[R7]

Do you have a service manual for the bike? While there isn't a mechanical adjustment for the the floats, the float height is adjusted by bending the the little tab that pushes in the needle to the seat..or the arms that support the floats. I just did this to my 98 R1, mine were in spec, but there is a spec on what the level should be at, and steps to take to get them to that spec

[myzx6]

100% agree with r7, also did you replace your fuel filter too

[Garrett]

I have a service manual. I'll double check.
But the entire float is plastic. Its held into the carb body with a metal dowel on two posts

[Rada]

Not to ask something really stupid but.... Is the air filter in the airbox when you put it on? If so is it clean?

Hate to overlook the obvious...

[Garrett]

Yes airfilter is in the box and it's clean.

Heres a bad ebay pic of the floats.




As you can see, the entire float is plastic and the two "towers" that the dowel pin slide into are cast into the carb body.


The manual I have doesn't cover my year, it's for a 95 but it still says the float height cannot be adjusted.

[Garrett]

Boom head shot

[R7]

Surprising to see them all plastic. Is it possible you may need to replace the floats then? Italian bike owners know all to well what ethenal does to plastic

[myzx6]

I hope that was a pic from before you cleaned them carbs cause they are nasty did you soak them overnight cause if you didn't I can guarantee that there's gonna still be plugged passages especially the air passages, those almost always get overlooked during a carb clean and would cause your exact symptoms. Fuel would not be able to fill the float bowl as fast as its removed and eventually the engine will cut out usually in under 10 mins. After which it takes a while to restart because the bowls have to refill with fuel

[Garrett]

That was a pic from ebay.

I'll measure the float height tomorrow. I let the bike sit overnight last night and it started up and ran for 10 minutes then bogged out and had the same symptoms.

[Garrett]

I blew every air passage out thoroughly, with compressed air.