CBR1000F cuts out at half throttle. Please help!

[imdying]

saw this...

I am scared that I might end up like this guy.. hehe:

http://cbrforum.com/forum/archive/in...p/t-38450.html

Why would taht scare you? His fix was free, and his problem sounded very much like your own one.

I'd definitely be checking the same thing as he found, that would only be logical.

[Matt Bleck]

It may even be water in the petrol tank, drain it and check.

[MSTRS:Me]

Carburation 101..
When an engine is going, a vacuum is created in the engine-side of the carb throat/s.
Since nature abhors a vacuum, the carb's job is to ensure that air and fuel are constantly fed into that vacuum - in the right ratios.
Opening the throttle allows greater airflow through the carb, which in turn 'pulls' more fuel through as well.
Throttle fully open means maximum air/fuel flow.

Now - here is my thinking. Since you say the engine goes ok at lower throttle settings, it is obviously getting enough air and fuel, the spark plugs are working ok and you've got 'enough' compression. Gradual acceleration works 'fine'. BUT opening the throttle fully is exposing a weakness in one of the three things that your engine needs. It could be poor spark, but unlikely. It could be poor compression, but again unlikely. Bikes don't run vacuum advance timing, so that's out as well.
Which leaves air or petrol.
If your air filter was blocked, wide open would be bad but your engine wouldn't go well at any throttle setting. If your bike has CV carbs, there may be a problem with the diaphragm/s. Fully open throttle opens the butterflies all the way, which should mean the slides automatically fully lift for max air and fuel. But I suspect that if there was a problem with the slides, it would not show up just at full-open throttle.
So that leaves fuel.
The problem won't be in the system before the carb/s, because the carb bowls hold enough for there to be a delay before insufficient fuel is available. Therefore the problem must be in the fuel bowls. It could be dirt, but usually that partially blocks jets ALL the time and/or settles to the bottom of the bowls. Which leaves water. It sits on top of petrol, and will be in globule form, so it can get sucked against the mainjet. Since the surface tension of the water is quite strong, it won't go through the jet. And neither can the fuel.
This is a very common cause of 'dead' throttle when cracked wide open.
If I'm right, you will need to drain the bowls, fuel lines and tank. If you can, fit a (new) inline filter. Put a small amount of meths or IPA (google to get the amount) in your new fuel to flush any remaining water in the system.
Test.
Fingers crossed...

[Katman]

Which leaves water. It sits on top of petrol,

Really?????

[98tls]

Nope, water will rather happily settle in the lowest part of your tank,Hence this.

[AllanB]

I presume you have fresh fuel? if not change it pronto and pop a cap of meths in there to get rid of any moisture.

1. Check the air filter, it may be filthy or have a panty pad it previously ingested restricting it (hey - it could in theory happen!). Always beware of rogue panty pads.

2. Tank breather - is it blocked? Not sure? do this with a half empty tank, open the filler and rest it on the opening - ie it will not be seated and have a gap - duct tape in on so it will not flap about but leave a air gap. Go for a ride and see if it is fixed - if so the breather is blocked.

[MSTRS:Me]

Really?????

Nope, water will rather happily settle in the lowest part of your tank,Hence this.

Oooops.
I note that no-one disagreed with the rest of my theory...
People..his problem only shows up when the throttle is cracked wide open. That suggests most strongly that fuel or air is being denied in the appropriate amount.
Air is most unlikely, because it will be restricted at any throttle setting. Which leaves fuel...but not because of vacuum lock...that would also be happening at any throttle setting, and would not occur before the engine had been running awhile.

[Max Preload]

My money's on water in the float bowls and emulsion tubes and jets, originating from the tank. Meths won't make the slightest bit of difference - they'll need to be disasssembled and cleaned.

[Katman]

My money's on water in the float bowls and emulsion tubes and jets, originating from the tank. Meths won't make the slightest bit of difference - they'll need to be disasssembled and cleaned.

+1 on the meths. It doesn't work.

Do the job properly.

[notme]

Alcohol absolutely WILL remove water from fuel systems - but that may not be the problem here.

There may be water in areas that the fuel/meths mixture doesn't get to or you may have wrong/bad alcohol or summat like that, so it may have not worked for some in the past, or for the OP in this case. But in general, it's a good trick to know and worth trying if you suspect water in the tank.

Just wanted to have that fact recorded in case of others coming across this thread in future :-)

[MSTRS:Me]

Alcohol absolutely WILL remove water from fuel systems - but that may not be the problem here.

Don't know about 'alcohol' as such, but Isopropyl Alcohol (IPA) and meths will work.
What it does is weaken the surface tension of the water, so it breaks into ever smaller droplets. Small enough to pass through jets etc.

[Katman]

You guys can believe it all you like.

I have drained water out of enough tanks that people have put meths in to safely call it an old wives tale.

[notme]

Don't know about 'alcohol' as such, but Isopropyl Alcohol (IPA) and meths will work.
What it does is weaken the surface tension of the water, so it breaks into ever smaller droplets. Small enough to pass through jets etc.

Meths and iso are alcohols.... :-)

Just don't try Jim Beam or Johnnie Walker in there.

Iso is actually better but meths is cheap and easily available. The alcohol acts as a go-between for the petrol and water, and allows the three to mix by reducing the water molecule surface tension (i.e. the solvent (alcohol) solubilizes the solute (water) so that is is in solution (the mix of water/alcohol/petrol).
Thus the mixture can go into the engine and be used until the tank is empty and the water is gone.

[notme]

You guys can believe it all you like.

Thanks for that - cos I'd have been really miffed if I had to stop believing basic chemistry....I'd be doubting the laws of thermodynamics next, and wondering why an engine doesn't fill the petrol tank when you run it backwards!

I have drained water out of enough tanks that people have put meths in to safely call it an old wives tale.

Seriously though, the fact that you have seen it NOT work only means that ... you have seen it not work. It doesn't prove that the process will not work.

[Katman]

As I said before - do the job properly.