Fuel flow issue

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Seattle400
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Fuel flow issue

Post by Seattle400 » Fri May 06, 2016 3:34 pm

This is my second ZXR400 and both bikes have had the same problem. I have taken them both to a dyno shop and they are properly jetted showing a slightly rich condition.
While riding on the street though both bikes have suffered from what I think is a fuel flow issue. If you start in 1st gear, accelerate to redline, then do the same in Second gear and then the same in 3rd gear at some point the bike starts to cut out like it's running out of fuel.

My theory is that the engine is using fuel faster than the fuel can enter the carbs. What would cause that?
I checked the fuel pump an it is working, the fuel line is new and clear, the filter is new and clear. What else could it be? Does putting an exhaust system on and then having to put in larger main jets make for a situation that the stock fuel pump can not keep up with?

The bike runs fine under normal acceleration and riding. It's only when I set out to have fun does it have the problem.
https://youtu.be/sPyiOG8LUTY

Most recent bike came up with 57.70hp last one was 2hp less.

dobbslc
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Re: Fuel flow issue

Post by dobbslc » Fri May 06, 2016 9:07 pm

Try it with the tank cap slightly open, it could be a blocked vent in there.

Are the carb float heights correct? If they are wrong you could be low on fuel in the bowls that then runs out after a long draw on full throttle.

You can measure the pump output, put the output pipe in a measuring jug and see how much you get in 1 minute. You can find the correct amounts in the service manual.

Check the fuel tap filter if it has one as they can block up from fine rust particles in the tank.

Did the dyno place give you a print out of the fuel to air mix as that would show if it actually is running massively lean after a good full throttle run and not just at max revs.

Seattle400
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Re: Fuel flow issue

Post by Seattle400 » Sat May 07, 2016 2:59 pm

Try it with the tank cap slightly open, it could be a blocked vent in there. I'll give it a try

Are the carb float heights correct? If they are wrong you could be low on fuel in the bowls that then runs out after a long draw on full throttle. They haven't been messed with that I know but I'll check them

You can measure the pump output, put the output pipe in a measuring jug and see how much you get in 1 minute. You can find the correct amounts in the service manual. I'll give this a try

Check the fuel tap filter if it has one as they can block up from fine rust particles in the tank. Already checked that.

Did the dyno place give you a print out of the fuel to air mix as that would show if it actually is running massively lean after a good full throttle run and not just at max revs. Yes, it is actually a little rich with an average of 12.9% from 6,000 raps to 14,500 rpms

richyrd5
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Re: Fuel flow issue

Post by richyrd5 » Mon May 30, 2016 4:37 pm

Hi,I had the same with mine,it was the fuel pump.cant keep carbs full at high rpm's...(well the standard one anyway)easy enough to get a uprated one(or one from a cbr400 nc29)...

Seattle400
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Re: Fuel flow issue

Post by Seattle400 » Tue May 31, 2016 12:56 pm

richyrd5 wrote:Hi,I had the same with mine,it was the fuel pump.cant keep carbs full at high rpm's...(well the standard one anyway)easy enough to get a uprated one(or one from a cbr400 nc29)...

Are you using one from a NC29?

richyrd5
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Re: Fuel flow issue

Post by richyrd5 » Tue May 31, 2016 1:09 pm

No,I don't have bike no more,but was useless on the standard one..i used a tourmax one and that was just as bad!!!.ive heard nc29 ones flow a bit more and is a mod I've seen,hth.. :grin:

Seattle400
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Re: Fuel flow issue

Post by Seattle400 » Tue May 31, 2016 1:15 pm

richyrd5 wrote:No,I don't have bike no more,but was useless on the standard one..i used a tourmax one and that was just as bad!!!.ive heard nc29 ones flow a bit more and is a mod I've seen,hth.. :grin:

ok thanks

fstarocka
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Re: Fuel flow issue

Post by fstarocka » Tue May 31, 2016 7:44 pm

Mine is running ridiculously rich, out of ideas:( nice vid!

Sent from my SM-G900M using Tapatalk

jamesgoodfella
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Re: Fuel flow issue

Post by jamesgoodfella » Wed Jun 01, 2016 3:34 pm

I had this issue,
After fucking around with fuel pumps I diagnosed mine being a faulty fuel pump relay, wouldn't run right (never ran right) but after using a new relay it sorted out the fueling issue so check that.
If you go on the ZXRWorld Fourm you'll find the complete workshop manual so if you look at chapter 15 page 29 onwards, it will tell you how to diagnose if your fuel pump relay is gone or not(page 30).
http://www.zxrworld.co.uk/Manuals/H%20M ... r%2015.pdf
Here's the link if you're lazy 8-)

Seattle400
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Re: Fuel flow issue

Post by Seattle400 » Thu Jun 02, 2016 5:20 am

jamesgoodfella wrote:I had this issue,
After fucking around with fuel pumps I diagnosed mine being a faulty fuel pump relay, wouldn't run right (never ran right) but after using a new relay it sorted out the fueling issue so check that.
If you go on the ZXRWorld Fourm you'll find the complete workshop manual so if you look at chapter 15 page 29 onwards, it will tell you how to diagnose if your fuel pump relay is gone or not(page 30).
http://www.zxrworld.co.uk/Manuals/H%20M ... r%2015.pdf
Here's the link if you're lazy 8-)

Thank you so much, this is the best info I have gotten so far.


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