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Discussion Starter #1
Hello,

my f4 750 doens't go any further than 11.000 revs.
At the moment I'm thinking about a problem with the fuel pump
To confirm this I have to know what the function of the small hole is which you can see in the picture:


The pump spills out a lot of fuel from that hole while idling which makes it drop pressure. My feeling says it ain't right but I can't find the exact purpose of the hole.

Hopefully someone can help me out! :king:
 

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I think it gift have something to do with an internal valve that stops fuel from draining back out the feed when the pump is stopped, but I don't know how it works. I did a lot of diagnostics on my 750 recently and don't recall seeing any flow from that hole when it idled.

Si
 

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11k only?

all Bosch pumps have that and work....

'T' an pressure gauge into the fuel line, you should see 3 bar 43.5 psi
if you don't;
when was your fuel filter changed last?
then check the fuel pressure regulator
 

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That hole is to bleed off Fuel to keep and hold a set PSI of fuel to the motor. Found this bit of info from my Mitsu EVO8 Days.
 

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wtf?

That hole is to bleed off Fuel to keep and hold a set PSI of fuel to the motor. Found this bit of info from my Mitsu EVO8 Days.
really?

so what does the Weber fuel pressure regulator in the fuel pump plate do????

:drummer:
 

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really?

so what does the Weber fuel pressure regulator in the fuel pump plate do????

:drummer:
Pump PSI and Inj. PSI are not the same The pump is set at one psi and that hole Reg. it so it dose not ever go over the red zone and over pressure the fuil lines. and the Weber Reg oversees that the Injectors get less of what the pump puts out and is at that psi at all times. And the pump psi will go up and down many times but the Injectors need a set pressure to supply fuel to the motor.
 

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Discussion Starter #11
I've refitted a new one 5000 km's ago. Took it out yesterday and the fuel drained easily from both sides.
The points I'll take a look at first will be the filter and the pressure regulator.
 

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A fuel pump is cheep you may buy one off Ebay that type of pump can be bought for $50 the EVO8 and most of the Honda pumps are the same and I had one here new in box for 2 plus years up till last month when many of my parts got put out with the trash by the wife or I would have given it to you to try.
 

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Have you ever asked a dealer how much a new Bosch unit is? Shocking!

Si
Hell yea Got it when I was looking to buy a pump for my First Duc a 916 SPS at the time Ducati wanted $365 for just the pump. When you can buy them for 50 to 100 other places. Same pump just not in a box with a Ducati part number.
 

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Discussion Starter #15
Just checked the fuel pump, seems to work properly. When it runs without resistance no fuel is coming out of the little gap but when I press the end of the hose against the bottom of the bucket I used, fuel was starting to get out of the gap. So the pump shoudn't be the problem.

Next thing to do is give it a try after swapping the fuel filter for a new one.
 

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?

Pump PSI and Inj. PSI are not the same The pump is set at one psi and that hole Reg. it so it dose not ever go over the red zone and over pressure the fuil lines. and the Weber Reg oversees that the Injectors get less of what the pump puts out and is at that psi at all times. And the pump psi will go up and down many times but the Injectors need a set pressure to supply fuel to the motor.
what 'red zone'? the pumps usually put out ~ 5+ bar the lines are good for ~17-20bar.
the Weber fuel pressure controls the pressure the injectors see, it varies with atmospheric pressure because of the open port on the bottom of the FPR.....which should be referencing manifold pressure instead

http://www.boschautoparts.com/FuelInjection/PublishingImages/FuelPumps.jpg

its a turbine pump so the output is fairly steady, the Weber is holding it at ~3bar, 43.5psi.....
the white fitting is the return port on the fuel pump plate and it goes to the FPR and it doesn't matter which way you connect the lines either
 

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Discussion Starter #17
Back inside again from an evening in the garage. Swapped the fuel filter, no positive result.
The problem eventually, after some testing, became even worse. At the beginning he woudn't rev further than about 11k rpm with full throttle. Right now that became 8-9k. When I close the throttle a bit, the engine picks up again.

At this point I haven't got a clue what it can be. Maybe still the fuel pump but it's quite hard to test. When I take a look in the tank I can see some fuel getting in the tank from the retour hose. This must mean that the pressure gets up to 3 bar, because at that point the pressure regulator opens.
(this is just my way of thinking)

Is it possible that the pump just delivers a to low flow but eventually gets up to pressure?

Thanks in advance for thinking
 

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That doesn't discount the possibility that your regulator is faulty and opening at too low pressure.

Have you checked that the injectors are balanced? Perhaps if one cylinder is slightly out of whack it might effect peak revs? Does it fell like it accelerates and runs cleanly below 11k?

This is a long shot and I don't know if it even ever applied to the F4, but do you live in, or does the bike come from a country that might have imposed max horsepower limits when it was made? Could there be an artificial restriction in the chip to limit the bhp by limiting the revs?

Si
 

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Have you checked the o-rings on the quick connect fittings for swelling mate, both ends. They are known to react to your great E-type fuel by swelling up. It makes sence to me as you said it ran well at first and then started going backwards.
Just and idea.
 
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