Pushed to the limit

**Mikkel** · 26th February 2008, 16:20

I think I've now managed to push my ZXR250A to the limit... And needless to say - I want to go faster still!

Today I started getting a funky fluctuation in the power delivery while pushing hard at the track. Exhaust note changed and in the mid-range it started feeling as if it was running out of petrol (switched to reserve, made no difference and there was heaps of petrol in the tank).

I cruised off the track and after having had it sit for a while I took it back out again. Was absolutely sweet for ~3 laps and then the fluctuation came back.

Went of the track packed my stuff together and decided to go home... and the bike was riding like a dream, no issues whatsoever.

Anyone got an idea about what might be causing this? I've had one person say "maybe the air filter needs cleaning" another went "perhaps sparkplugs are getting too hot" and another suggested that there might be some sort of leakage at one of the manifolds. Any clever suggestions would be appreciated.
Dunno if it's just because it's a very hot day and I was going hard on it...

Anyway, I might consider looking for a bigger trackbike (I was thinking 400-600 ccm) - perhaps even a road legal thing that I could use on the track until I get my full in ~4 months. Any suggestions for a suitable bike for such a purpose?

Oh - and there's a nice song to go with the post btw:
[YOUTUBE]http://www.youtube.com/watch?v=cN0auZtm2tg[/YOUTUBE]

**FROSTY:Me** · 26th February 2008, 16:28

I'd like to make a suggestion--Flick the tap to PRIME --not on or reserve.
Im thinking your fuel flow for one reason or another aint enough to keep up with constant full or nearly full throttle riding.
That kinda lines up with the simptoms too.
That then leads me to think--Fuel pump is a bit old or maybee part blocked fuel filter -either the intank one or inline somewheres.
the other possibility worth looking at is the vac line having a kinkor split in it-Not allowing the fuel tap to flow enough fuel
Id like to bet too that if ya keep the tank topped up its not such a problem
sparkplug suggestion clearly nonsense
Airfilter suggestion--yep but would be a constant rather than a come and go issue

**Mikkel** · 26th February 2008, 16:38

Originally Posted by FROSTY

I'd like to make a suggestion--Flick the tap to PRIME --not on or reserve.
Im thinking your fuel flow for one reason or another aint enough to keep up with constant full or nearly full throttle riding.
That kinda lines up with the simptoms too.
That then leads me to think--Fuel pump is a bit old or maybee part blocked fuel filter -either the intank one or inline somewheres.
the other possibility worth looking at is the vac line having a kinkor split in it-Not allowing the fuel tap to flow enough fuel
Id like to bet too that if ya keep the tank topped up its not such a problem
sparkplug suggestion clearly nonsense
Airfilter suggestion--yep but would be a constant rather than a come and go issue

That sounds very plausible - and if there is a bit of crap sitting on the filter in the tank it won't move away when it first has been sucked in. When I turn the engine of it'll flow away with the fuel around in the tank. Perhaps time to give the tank a thorough look over, then fuel filters and perhaps the fuel pump.

**FROSTY:Me** · 26th February 2008, 16:45

SORTA. What I'm saying is that as long as ya give it short bursts of fullish throttle the bowls still have enough juice to keep the plot rolling. When ya back off the carbs refill and all is good
You could be right with the floating thing but more likely its a coating just not letting enough gas through. -or fuel pump too old n worn to keep up.
Given its 3 laps that suggests only a partial blockage.
HMNMM--Hang on it could be the filters IN the carbs too--or even just one for that matter.
In fact the more I think about it the more likely it is just that

**Mikkel** · 26th February 2008, 16:51

Hmmm, so how do I check (and fix) this problem? I am fairly new at the art of motorcycle maintainence and that stuff.

**FROSTY:Me** · 26th February 2008, 17:18

Just went to send ya a fairly indepth description--frigging broadband dumped me

**dipshit** · 26th February 2008, 17:19

First cheek there isn't any twists or kinks in the fuel lines.

**FROSTY:Me** · 26th February 2008, 17:20

Just to 100% qualify--you aint bouncing off the speed limiter at 190k are ya?

**FROSTY:Me** · 26th February 2008, 17:25

Originally Posted by dipshit

First cheek there isn't any twists or kinks in the fuel lines.

Yep--good point--kink = reduced fuel flow

**Mikkel** · 26th February 2008, 17:35

Aww, sucks when the connection slips. Occassionally I've had the odd big post or email disappear because I've managed to get the browser to go backwards on page...

Hmmm, it's a 250 4-stroke I'm quite stoked to hit 175-180 km/h at the end of the straight

So yeah, definately not a 190 km/h limiter...

I'll have a look at the fuel lines at an appropriate time.

Anyone got good advice on how to clean out the tank if there should be some crap in there?

**Morcs** · 26th February 2008, 17:39

Im sure skidmark would have something to say about pushing a zxr250 to the limits. He would be able to lean it so far It goes through the road, do wheelies on the front wheel and 300kph.

**Mikkel** · 26th February 2008, 17:48

Oh, btw. it might be worthwhile mentioning that this is my fourth time out at the track. All the other times I have also been pushing quite hard and the bike has taken that in stride.

Today there was nothing of note until the 4th 30 min session - and then it occurred about 15-20 mins into the session.

**headlesschicken** · 26th February 2008, 18:55

I had a similar problem before my bike totally cut out. It was running too rich. The bike shop tuned it and it ran sweet since. Just another idea to consider..