Trying to get my head around an annoying problem I have with the fuelling of the 919 Fireblade engine in my Westfield.
Spec is standard blade airbox and paper filter, some form of jet kit is fitted as the needles are adjustable, currently clip in third groove from top and seating and half thickness washers are in place. Main Jets are 132 and air screw is 2 turns out. Exhaust wise normal megablade headers to a modified straight through R1 end can.
My problem is a massive flat spot/hesitation from 4 to 5K car physically jerks and holds back then once past this point it will fly up to the red line with no problem. It only seems to happen when you plonk your foot down wanting the power, it will cruise at these revs with no problem. If the loud pedal is used less vigorously then you can nurse it through this rev range without the same pronounced effect.
I have read after numerous searches that the middle air correction jet needs to be blanked off next to the intake trumpets as part of a jet kit, mine are not blanked so wondered what the effect of this was. I dropped the needles one notch yesterday to see if things improved or worsened but it then rained so not managed a test drive yet.
Any other advise or pointers appreciated as to which way to go.

Cheers

Ian

I've used raced with this engine a fair bit. Below is what I would check, in no particular order.

You've got all the vacuum hoses correctly connected?
The little breather filter under the airbox is clean?
Air Filter is clean? Why are you not running a K&N BTW?
Fuel filter clean?
Fuel pump priming and working OK?
Cleaned the bowls out in the carbs?
Blown through the jets with some air?
Got genuine plugs in? I used Iridium ones, but make sure your not getting supplied the crappy counterfeit ones off eBay?
Balanced the carbs?

I'd check everything on the list above.

Thanks for the reply,

Few answers,
Air Filter is clean, I thought it had a K&N in it from the sticker on the air box but found a standard one when I looked inside
Not sure what you mean by the little breather filter under the airbox, is that the small matchbox size thing with the 20mm ish pipe conected to it?
Bowls are spotless, all cleaned out and blown out with compressed air
Fuel pump seems fine, primes and runs with no problem
Genuine normal NGK plugs fitted from a reputable source
Carbs balanced

I think its more of a set up problem than a particular faulty item as it runs well otherwise?

U2U sent. Geoff

Replied

Give Andy Bates a call at AB Performance, always helped me out with these sort of questions.

Iain

quote:

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Originally posted by IanG1
Trying to get my head around an annoying problem I have with the fuelling of the 919 Fireblade engine in my Westfield.
Spec is standard blade airbox and paper filter, some form of jet kit is fitted as the needles are adjustable, currently clip in third groove from top and seating and half thickness washers are in place. Main Jets are 132 and air screw is 2 turns out. Exhaust wise normal megablade headers to a modified straight through R1 end can.
My problem is a massive flat spot/hesitation from 4 to 5K car physically jerks and holds back then once past this point it will fly up to the red line with no problem. It only seems to happen when you plonk your foot down wanting the power, it will cruise at these revs with no problem. If the loud pedal is used less vigorously then you can nurse it through this rev range without the same pronounced effect.
I have read after numerous searches that the middle air correction jet needs to be blanked off next to the intake trumpets as part of a jet kit, mine are not blanked so wondered what the effect of this was. I dropped the needles one notch yesterday to see if things improved or worsened but it then rained so not managed a test drive yet.
Any other advise or pointers appreciated as to which way to go.

Cheers

Ian

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Bit of an update, spoke to Andy Bates, great bloke and very helpful.
He says that the main cause of my problem is the facet fuel pump and regulator I have fitted, basically they are crap for a BEC and overwhelme the bike carbs with pressure which causes the fluctuation as the mixture is then all aver the place. He says firstly to fit a pump from a bike which regulates the pressure to a level suited to the carbs. He gave me some other pointers regarding filters, jets and needles which I will try out after the pump is changed.

Ian, what pressure have you got the facet pump set to...

1.5 will be fine anymore will cause issues.

People buy the wrong pumps which causes

Not a clue mate as no way of measuring it, just picked up a pump for £25 so gonna try that when it arrives

The facet pumps work fine if setup right just remember the later 919 had no fuel pump so it's all about setting it up right.

I use a facet pump as they ar new and don't have issues if setup we'll. the reg should allow you to get it working fine.

Check the oil if it's not been running right you may find a lot of fuel in the sump


[Edited on 4/3/14 by jossey]

It is a good idea to soak all the jets in carb cleaner. Blowing through does not get out the 'varnish' that can build up. Blew mine out 4 or 5 times with limited effect, soaked them in carb cleaner and it transformed them.

Or sonic clean them....

Thought I would try and put the fireblade fuel supply issue into context.
The blade carbs require a very low fuel pressure to operate effectively in fact the pump should be viewed purely as a means of keeping the float bowls full at all times.
Now if we think of the bowls as the reservoir from which fuel is pushed up the main jet by atmospheric pressure as a depression is created by airspeed in the main throat, we can immediately see the huge problems that can be caused by over pressuring the float bowls. Bearing in mind that a single circlip position on the needle makes a huge difference to the fuelling of the mid-range just by lifting the taper slightly, imagine the effect of pushing fuel under pressure up the main jet, which is what happens all the time when using the facet pump. A 122 main jet can be made to function just like a 132 because of the pressure behind it.
In an ideal world you would use a regulator to control the pressure but unfortunately these regulators are far from reliable, a simple bump in the road can send fuel pressure soaring or drop it to almost zero. This is mainly due to the fact that inside it is purely a diaphragm and spring.
Experience has shown that no matter how you set the regulator up it will cause issues. The problem is that bike engines seem really fast even when they are off song and I have lost count of the number of people who we have transformed the power delivery for just by junking the facet and regulator and jetting correctly.
To demonstrate this at its extreme, a racer at Donnington left his ignition on at lunch time, the facet pump pressure forced the floats down sending fuel up the emulsion tubes and down the cylinders. On his return the engine hydraulically locked and having taken out the plugs he cleared the lock and went on to race....... for 1 lap. After the engine went bang we drained nearly 7 litres of fuel and oil from the sump The same car used to use nearly double the fuel load during a race of its nearest competitor using a self regulating bike pump.
My advice would be to always use a bike pump and do not use the facet and regulator - it does not work
Hope that helps
If anyone needs more info just call me on 01449736633
Andy

Good reply Andy, more usefull advice. One for cutting and pasting into the fireblade technical folder!!

I set-up the carbs on my 919 fury with different needles etc from Andys advice and it went very well. Im sure there was a point of blocking something off?! cant remember exactly now, it was in each carb.....as it wasnt using an airbox?! memorys not that great these days although it was 6 years ago!

quote:

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Originally posted by Andy B
Thought I would try and put the fireblade fuel supply issue into context.
The blade carbs require a very low fuel pressure to operate effectively in fact the pump should be viewed purely as a means of keeping the float bowls full at all times.
Now if we think of the bowls as the reservoir from which fuel is pushed up the main jet by atmospheric pressure as a depression is created by airspeed in the main throat, we can immediately see the huge problems that can be caused by over pressuring the float bowls. Bearing in mind that a single circlip position on the needle makes a huge difference to the fuelling of the mid-range just by lifting the taper slightly, imagine the effect of pushing fuel under pressure up the main jet, which is what happens all the time when using the facet pump. A 122 main jet can be made to function just like a 132 because of the pressure behind it.
In an ideal world you would use a regulator to control the pressure but unfortunately these regulators are far from reliable, a simple bump in the road can send fuel pressure soaring or drop it to almost zero. This is mainly due to the fact that inside it is purely a diaphragm and spring.
Experience has shown that no matter how you set the regulator up it will cause issues. The problem is that bike engines seem really fast even when they are off song and I have lost count of the number of people who we have transformed the power delivery for just by junking the facet and regulator and jetting correctly.
To demonstrate this at its extreme, a racer at Donnington left his ignition on at lunch time, the facet pump pressure forced the floats down sending fuel up the emulsion tubes and down the cylinders. On his return the engine hydraulically locked and having taken out the plugs he cleared the lock and went on to race....... for 1 lap. After the engine went bang we drained nearly 7 litres of fuel and oil from the sump The same car used to use nearly double the fuel load during a race of its nearest competitor using a self regulating bike pump.
My advice would be to always use a bike pump and do not use the facet and regulator - it does not work
Hope that helps
If anyone needs more info just call me on 01449736633
Andy

---

quote:

---

Originally posted by Andy B
Thought I would try and put the fireblade fuel supply issue into context.
The blade carbs require a very low fuel pressure to operate effectively in fact the pump should be viewed purely as a means of keeping the float bowls full at all times.
Now if we think of the bowls as the reservoir from which fuel is pushed up the main jet by atmospheric pressure as a depression is created by airspeed in the main throat, we can immediately see the huge problems that can be caused by over pressuring the float bowls. Bearing in mind that a single circlip position on the needle makes a huge difference to the fuelling of the mid-range just by lifting the taper slightly, imagine the effect of pushing fuel under pressure up the main jet, which is what happens all the time when using the facet pump. A 122 main jet can be made to function just like a 132 because of the pressure behind it.
In an ideal world you would use a regulator to control the pressure but unfortunately these regulators are far from reliable, a simple bump in the road can send fuel pressure soaring or drop it to almost zero. This is mainly due to the fact that inside it is purely a diaphragm and spring.
Experience has shown that no matter how you set the regulator up it will cause issues. The problem is that bike engines seem really fast even when they are off song and I have lost count of the number of people who we have transformed the power delivery for just by junking the facet and regulator and jetting correctly.
To demonstrate this at its extreme, a racer at Donnington left his ignition on at lunch time, the facet pump pressure forced the floats down sending fuel up the emulsion tubes and down the cylinders. On his return the engine hydraulically locked and having taken out the plugs he cleared the lock and went on to race....... for 1 lap. After the engine went bang we drained nearly 7 litres of fuel and oil from the sump The same car used to use nearly double the fuel load during a race of its nearest competitor using a self regulating bike pump.
My advice would be to always use a bike pump and do not use the facet and regulator - it does not work
Hope that helps
If anyone needs more info just call me on 01449736633
Andy

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Looks similar to the bike one I have bought, if it is self regulating i.e it cuts off when the float bowls are full with the car not running then think it is fine for the job, the trouble with the facet pump is it just keeps pumping and relies on the regulator to sort the pressure out .( which it does a poor job of at very low pressures suited to the bike carbs)

How can I verify in an easy way if it's self regulating?

Switch on the ignition and the pump if a separate switch. The pump will run for a short time to fill the float bowls then stop if self regulating. If it just runs and runs it's not. All this without the engine running.