power lose at high rpms

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SeattleZXR
Posts: 33
Joined: Wed Jun 24, 2015 2:38 pm
My Bike: Kawasaki ZXR400

power lose at high rpms

Post by SeattleZXR »

When I'm in 5th or 6th gear at about 12,000rpms the bike starts to cut out. I think it might be the carb bowls are running dry. Is it common for the fuel pump or something to not function properly at high revs?
rccaulfield
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Re: power lose at high rpms

Post by rccaulfield »

probably need a bigger main jet, put choke in the on position next few times and see is she any better at wide open throttle. If better then need bigger main jet!
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Tirpitz
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My Bike: Kawasaki ZXR400L4
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Re: power lose at high rpms

Post by Tirpitz »

No it isn't. Check the inline fuel filter to see if it is partially blocked. Check to see how much fuel is coming from the tank outlet in case the intank filter is blocked. What does it look like inside? The fuel pump may be on its way out. Try running the bike with the tank fuel cap open - if the problem stops you have a blocked tank breather. Does it happen if you are running with the tap in reserve - if not that suggests you have a partial blockage of the main tank part of the filter / tap.

Do not start pissing about with changing jets on the carbs, that is just about the least likely source of the problem :ffs Try the simple things first and work through methodically.
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SeattleZXR
Posts: 33
Joined: Wed Jun 24, 2015 2:38 pm
My Bike: Kawasaki ZXR400

Re: power lose at high rpms

Post by SeattleZXR »

I'm sorry, I pulled rookie move and didn't mention all the things Ive done so far.

When I got the bike it was obviously lean so I took it to a dyno shop and after a few runs and some jet changes it is pretty much spot on. I can't remember what sizes I put in there. It has a Wr's pipe on it.

Here's a list of things I've done besides properly jetting it.

Cleaned and sealed the gas tank it was rusty when I got it.
Changed the fuel lines and full filter.
Cleaned and rebuilt the carbs

How I got the bike. Somebody had put a different petcock on it so it no longer has a reserve. I suspect the replacement petcock might have to small of a outlet on it. I am going to put a high-flow one on there.

Since the gas tank was rusty and the fuel filter was pretty gunked is it possible the fuel pump got dunked up and needs replaced?
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Tirpitz
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My Bike: Kawasaki ZXR400L4
Location: Doncaster, South Yorkshire

Re: power lose at high rpms

Post by Tirpitz »

I suspect you could test the fuel pump by disconnecting the outlet to the carbs and feeding it into a jar and turning everything on and seeing how much fuel is pumped through. If it's more than a trickle I guess there's nothing much wrong with the pump. Seeing as you had a fuel filter inline which should have caught any crap from the tank it shouldn't really have got through.

I'd be suspecting the petcock but again, easy to check. Just take it off and turn the tap on into a container and see how it's running. It's only a 400, it shouldn't be drinking the stuff neat, so providing you have a decent flow I can't see the engine getting topside of what's coming out.

I would have thought that if you had the thing set up on a dyno the jetting can be discounted, assuming the AF was correct. So it has to be a fuel starvation issue - on the dyno they don't hold it on max revs for that long. Just a matter of tracing the cause. As I said before, do check the tank breather isn't blocked as this will restrict fuel flow as a vacuum will be created in the tank.
ZXR400 L4, purple / black / pink
Hel braided hoses
Pirelli Diablos
Ohlins steering damper
A16 carbon fibre exhaust can
Nitron Sport shock
SeattleZXR
Posts: 33
Joined: Wed Jun 24, 2015 2:38 pm
My Bike: Kawasaki ZXR400

Re: power lose at high rpms

Post by SeattleZXR »

I'll check the tank breather first. That's a good call. My brother once had a dirt bike that would only run for a few minutes. Turned out a spider built nest in the tank breather tube over there winter and the gas was't flowing. If that does't work, I'll most likely change the petcock. I really don't think it's bog enough.
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