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Discussion Starter #1
I have a road race bike that I am having a mystery problem with. The bike normally has 160hp on my sponsors shop dyno. I was racing a national event this weekend and the bike dynoed 143hp

I can see in the graph that the bike looks to have a flat spot from 9500-12000 and it just levels out at aprox 140hp

I have swapped fuel pumps, dyno was the same.

I have done a leak down test and there is less than 1% loss per cylinder

I am hoping that someone may have some thoughts on where to begin.

ANY INFO WOULD BE APPRECIATED.

thanks guys

Justin
 

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Dynos vary a lot, does it feel down on power on the track? What does the air/fuel look like during this late 'flat spot'?

Have you ever degreed the cams? Did you locktite the cam sprocket bolts? A slipped cam could cut power, especially if it is worse at high RPM.

Swap your spark plugs, coils, injectors.

1% leakdown is very little, a typical tight motor is more like 3-5%. Did you do the leakdown? Is it your gauge?

good luck,
Dean
 

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Discussion Starter #3
I was unable to pull top gear fr more than a moment while accelerating down the straight during my last race. It is more than just the dyno #

While doing the leak down, at 100psi there was about 1 psi differential.

I have swapped plugs tonight, coils will be done as well. I do not have injectors though.
 

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you could have a bum fuel injector, especially if you have been running race fuel in it for a long time. Do all of the spark plugs look like they are burning the same? i would also be suspicious of the cam sprocket slipping as mentioned before.
 

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Discussion Starter #5
I will look at the cam sprocket tonight. I will have to see if I can get another set of injectors if the cam is ok.

Someone suggested to me the tps might be screwed. Is that a possibility?
 

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Discussion Starter #6
Cam timing, leakdown, and valve clearances are all OK. New coils , fuel, and plugs added.

I will be doing a dyno pull tomorrow with the Power commander installed and if the problem persists, one with it removed.

Any other thoughts?
 

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Discussion Starter #8
I will bring another TPS with me when I go to the dyno Room. I will have to see if the process of elimination works for me.
 

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Do you still have your secondary butterflies in? I have seen where they won't open all the way. If they are still in take out the secondaries and see if that helps.
 

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Do you loose power in all gears between 9500 and 12k? Might be worth checking each gear for a similar flat spot, even if you don't have baseline data for each gear. If it's a particular gear, I'd be thinking the trans has something wacked.

Trans slippage can cause power loss in autos, but I don't know M/C trans very well. Does it buck or surge during the flat spot, even slightly?

Just a WAG, but might the KIMS be kicking in from a false (not necessarily faulty, mind you - could be operating out of normal range, but still acceptable; don't know the parms and values involved) TP reading? Likely not, since KIMS doesn't operate at full throttle (assuming the throttle assembly can reach that point, as referenced in the ECU), however it's a thought IF you haven't already disabled it.

Since it's high in the rev range, vibration induced anomalies can occur, like the dreaded grounding problem. If you can monitor your voltage at those rpms, that might help (watch if it fluctuates). Your charging system and battery can also cause all kinds of strange behaviour, so ensuring they're up to snuff - terminals that are corroded and vibrate when loose may cause the injectors and fuel pump to loose some power, not to mention the coil packs.

I've done some work with autos and I've modified my own bikes, but I'm no pro. Just some things to think about. G/L.
 

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Ok, now newb questions - chain is in top working order? Sprockets in good shape? Engine temps are in the expected range? Fuel line is in top shape - no kinks, pinholes, ...? Air filter is good (assuming you run one)? Airway is clear?

Spark plug conditions can tell you a lot about what's happening in the combustion chamber - what did they look like? White, grey, oily, cracked, ...?

I agree - knowing whether you're running lean or rich at that time could help.
 

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Discussion Starter #13
I have the stock ECU/harness, and run the stock rev limit. fuel line is good. Engine temps good. electrical connections good as well. Battery, is 100%.

Dynoed the bike yesterday and it made 155hp on the shop dyno.

It is looking like a bad batch of fuel is the culprit.
 

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Discussion Starter #15
Lol. That ended up being slot of work for a simple problem. At least my motor is still good. That was my biggest concern.

Thanks for all the help

Justin
 

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Run a bit of Toluene or Xylene in your gas (even if race gas), which will do two things - raise your octane and help clean everything out. I'd add no more than a litre in a full tank, and use some mineral spirits or (my choice) some Lucas upper cyclinder lube. Once yer done that, I'd also flush out the oil (not the filter, unless it's time). If you don't already know, stay away from Naptha-based injector cleaners - it is hard on seals and such.

I'm sure you know you can get T or X at any home improvement store - also dedicated paint stores sell them by the 5 gallon drum for cheaper (ask if there's City or Prov pricing and it gets even cheaper). Lots of guys run that stuff to make race gas and is MUCH cheaper.

G/L!
 
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