Lower top speed in hot weather??

LoneRonin

LoneRonin

Well-known member
I've noticed my Ninja has a harder time getting to top speed as of late. The fastest I've gotten was 162km/h on the GPS and I wasn't fully tucking or anything.
Recently the weather has been hot, and on a flat it seems to be stuck at about 145km/h with the bike in 6th gear at 11-11.5rpms. I find that to be a pretty significant difference, because when I hit 162 I wasn't fully tucked and didn't have nearly as much road to accelerate.
Also I've noticed a tick-tick-tick noise, its not the typical consistent valve tick I don't think, sometimes I hear it sometimes I don't...I used the screwdriver stethoscope method to listen to the engine and there doesn't seem to be any unusual internal noise..
I wonder if its still contributing to the problem, or if I even have a problem... Its Sunday and all the neighbours have their lawn mowers out, but when its quieter I will try and make a video of the noise. I still have warranty til next season so I'm going to keep riding until anything serious happens, if it does then off to the dealer, but right now I'd rather ride and have it in my garage than theirs...
 
How many Kms check that the valves are not too tight this will burn your head and cause power loss.
 
Scuba Steve said:
How many Kms check that the valves are not too tight this will burn your head and cause power loss.
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44.5k, just had valves done a little over 10k ago. Acceleration and mid-range seems fine just the top end is a bit lacking. I'm going to ride my cousins bike and see how fast I can get that to go...
 
Hot weather and humdity affect performance. Many different variables. This is why trying to "measure" fuel economy is a bunch of crap. Weather plays a measurable role in mileage and performance.
 
Hot and humid air is less dense than cold air so it will affect your performance; it will especially be noticeable on a 250cc engine. You'll see a performance difference if you take your bike out at 6am vs 2pm.
 
Basically cold air contains more oxygen than hot air.
This will cause a perfectly jetted bike to run a bit rich when it's hot out.
Ninja 250's run very lean at idle/low RPM and are miserable in cold weather!
But WFO jetting seems not so lean.
Therefore a stock Ninja 250, in very hot weather, becomes perfectly jetted at idle/low RPM but runs a bit sweet at WFO throttle.
I grew up in a world of air-cooled bikes, and very noticable in cold temps or middle-of-the-night etc. that bike would run like a rocket!
Way faster in October vs. July, y'know?
But although this effect is partially disguised and not so dramatic with modern liquid cooling, it will still occur on any carbed bikes.
Also (as mentioned) valves generally tighten up over time - so hearing no ticking doesn't mean everything is okay.
Always have them inspected religiously according to the manufacturer's schedule,
Regards
 
Thanks guys, I wonder if other 250s are experiencing the same thing, then again they're probably not riding the way I do...
I have my carbs shimmed and according to Gryphon's explanation, I think that is what is also causing the backfire...
What does WFO mean?
 
LoneRonin said:
What does WFO mean?
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That's ten-tenths; in other words wide open throttle.
Your bike gets on the main jets only at WFO.
(Even at 90% throttle it's still mostly on the needles.)
 
may be you got a bad tank of gas? try a tank of shell v power (gold) no ethinal. regular gas has 10%, that crap has 1/3 the energy of straight gasoline. i notice a big difference in over all milage.
 
I have a 2011 Ninja 250 and I hear a noise too. It's almost like a beep beep beep sound. That's the best way I could describe it.
 
TheNewDude said:
I have a 2011 Ninja 250 and I hear a noise too. It's almost like a beep beep beep sound. That's the best way I could describe it.
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we should meet up sometime and compare...you ever go to Burrito Boyz on Tuesdays?
 
TheNewDude said:
I have a 2011 Ninja 250 and I hear a noise too. It's almost like a beep beep beep sound. That's the best way I could describe it.
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That's the pressure in the gas tank being released, nothing to worry about.
 
Gryphon said:
Basically cold air contains more oxygen than hot air...
...Way faster in October vs. July, y'know?
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This is true but interesting to note that most speed tests are done in scorching hot deserts because the hot air is less dense and provides lower resistance to moving objects. Not that this matters to us on the street... these guys are moving at landspeed record vicinity where aerodynamic drag becomes much more important.
 
LoneRonin said:
we should meet up sometime and compare...you ever go to Burrito Boyz on Tuesdays?
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I've also got a Ninja 250 with 30K kms and had the valves done at about 24k kms. I also have a tapping noise which used to be a lot louder before I reset the cam chain tensioner, now I think it's just a regular valve tap though i'm also a little unsure if this is normal.
 
Gryphon said:
Basically cold air contains more oxygen than hot air.
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Please don't take up teaching physics... or Chemistry lol.

What you meant (I believe) is that air density is impacted by temperature.. colder air is more dense which typically means you can jam more fuel in with your air to produce power. Since most bikes don't constantly update their fuel maps with temp, the amount of fuel will be relatively consistent with varying temperatures. This causes the bike to run leaner at colder temps and richer at hotter temps, though sometimes insignificantly it's enough to notice a difference at higher temperatures.
 
Wait till cooler weather before going to Bonneville Salt Flats,LOL
 
Twoth said:
Please don't take up teaching physics... or Chemistry lol.

What you meant (I believe) is that air density is impacted by temperature.. colder air is more dense which typically means you can jam more fuel in with your air to produce power. Since most bikes don't constantly update their fuel maps with temp, the amount of fuel will be relatively consistent with varying temperatures. This causes the bike to run leaner at colder temps and richer at hotter temps, though sometimes insignificantly it's enough to notice a difference at higher temperatures.
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I believe he is technically correct. For a given volume of "air"..there are less oxygen molecules..
 
thanks for all this knowledge...I guess the theories hold true. Last night was 20 degrees with windy conditions but I had her screaming back up at 161
still have to figure out this ticking though, or if its worth getting checked out...
 
Stewart said:
may be you got a bad tank of gas? try a tank of shell v power (gold) no ethinal. regular gas has 10%, that crap has 1/3 the energy of straight gasoline. i notice a big difference in over all milage.
Click to expand...

Depends, if its a late model ninja the 91 octane won't run as smooth as 87. The comperession ratio on the new gen isn't as high as the old, you'd be dumping more unused fuel into the exhaust.

Also slightly offtopic, i noticed that the newer shell pumps no longer say v-power contains no ethanol. can anyone confirm?
 
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