Bike pulling more revs to go 100 km/h

Have you done ANYTHING to the bike recently? Changed air filter, changed oil, changed brake pads, changed fuel type (or changed your normal fuel provider), changed tires... Any minor change can have large impacts on the overall (perceived) performance of the bike.

Assuming that you have not (I had to ask just in case) then I would be saying that the bike may have been in 'top tuning' originally and it is gradually becoming out of tune. How many k's since the last complete check-up? How many k's overall?

My hypothesis: The needles on 250 sports bikes will wear, and once the wear starts to become noticable it increases dramatically. If you are sitting up at 30 000 k's plus then this may be a possibility. Essentially a worn needle will allow more fuel / unit of air and therefore be running slightly rich. This would cause the increased RPM's at a certain speed, and would also result in fewer k's per tank. Check your spark plugs to make sure they are still a nice clean colour - see this link

** Note: could be many other things, but having had teh same problem with the needles on my fzr running rich and needles is always my first hypothesis. Could be air filter problems etc. too... Could be anything really.. but still check the spark plugs!

 

Boz, my bike is at about the 36k km mark and I am in the market to get the needles replaced. What did you pay to get your needles replaced? Are the emulsion tubes the same thing as the needles? Any pitfalls or related conditions that should be taken into consideration when replacing the needles? Ok that is all for now.

Cheers.

 

yes emulsion tubes are same as needles. I never knew that until FZRDude told me. Cost - I sold my bike instead. <!-- s --><img src="{SMILIES_PATH}/icon_biggrin.gif" alt="" title="Very Happy" /><!-- s --> However, before I sold it, I got a quote for $400-$450 for the needles installed (as it was an import the dealer could not find a part number, so would need to take it apart before he found out what part was actually required and based his quote on his experience with cbr imports). They were also going to do a basic carby cleaning/tuning for me - no dyno or anything. Cost for the needles (no installation) would have been between 330-380.

I do not know of any pitfalls with it as I never dealt wtih them - I have successfully steered clear of any carby work on all bikes i have dealt with. I am sure others could shed more light on carby work...

 

190 kms when it hits reserve? If so thats very normal. Also, im pretty sure mine would sit at around 9k at 100km/h, I dont think you have anything to worry about.

 

I do 9.5k rpm at 100km/h. I get about 180km to about 8ltrs or 190 or so until i hit reserve. This is normal, i've asked several people with FZR's. You have nothing to worry about. You'll only have a problem if this gets worse...

I can get up to 160 no worries but RPM gets a bit high..

 

Hmm.. now im almost positive that im running non standard sprockets (undertoothed on the rear). I sit at 8300rpm @ 100km/h. I'm positive of this because at 10k, im running at just over 120km/h.

Im definitely going to have to get a new set of needles for my bike (or fix the carbies first). I'm not getting near that sort of economy. <!-- s --><img src="{SMILIES_PATH}/icon_sad.gif" alt="" title="Sad" /><!-- s --> I was stoked the other day when i got 150km out of ~8 litres.

Anyone recommend a place where i can get new needles?
And when replacing the needles... am i right in saying that the emulsion tube (the bit the needle goes into & slides through) may also be worn out? If so, how much are they gonna cost?

 

Yes, you are correct and you should replace both the needle's and the needle jets/emulsion tubes if any signs of wear.

 

Chain and sprockets could have a large change on the bike characteristics. I am guessing that you are probably good - when I had my problems I was lucky to hit 140 k's (city riding) before reserve on a 2kr. I should have been able to get to at least 160-180...

So sounds like you are in luck and no problems really!

My regular place (central motorcycles) could not find the appropriate parts on their books and wanted to take my carbies apart, then figure out what to order (though I keep going back because their service and pricing is excellent, even if they had minimal experience with the fzr). As such, if you can find a place that has experience with fzr's that would be ideal.

One place (it is actually a guy's backyard workshop) that specialises in yamaha's and has worked on MANY fzr's is yamwreck - located in ashwood on Yooralla street. The guy's name is Bruce, and his number is 9807 8376. He will have the parts available (probably immediately if you want them). He is extremely good, though when you go around there he will want to keep talking. He has numerous interesting bikes - usually a few fzr250's, and lots of classic bikes as well. His business may seem a little on the 'dodgy' side of things, but his prices are excellent, his service is good, etc. When I need an expensive part or lots of parts I will go to him, otherwise if it is something simple I go to Central Motorcycles...

 

I think your problem might be the fact ur running larger tires. Because speedo is measured at the front wheel nd ur tacho at the engine. Your speedo will be running slow. when your speedo reads say 100, you will be actully going ~103 give or take etc. So ur tacho will be reading higher rev cuz ur actually going faster

 

He is only running a larger rear, whcih won't effect the speedo... I initially thought the same until I re-read his post.

Edit: though it will effect the number of revs for the speed (should actually lower the number of revs / speed because it is a bigger tire)

 

its would b variable.
from the ambient temperature affecting the pressure in the tires changing the rolling diamter...even only a lil....
but wind direction would b the most contributing factor....
strong head wind would see more power (hence revs) to travel at the same speed as with a tailwind. of course u can prove this with velocity vectors n such but i cbf doin all that....


dave

 

and also size of the person on the bike (or carrying a pillion) would affect it. Just like a car - if you want to stay at a constant speed and are going up a hill or have a heavy load you will need to press the accelerator a bit more.

With greater torque though this variability is reduced to a degree. The fzr250 has bugger all torque though...

On a side note (but related to your comment) there is power lost between the engine and the wheel - this is why you will hear dyno's being run from the engine and also rear-wheel dyno's. Rear-wheel dyno's can be anywhere between 5-15 hp lower (sometimes more) than engine dyno's for a bike that has about 100 hp.

 

Ha ha Boz yeah I got stuck around there one day for about an hour (I was just buying a battery) - the dude certainly loves a chat - but i did get the battery for $50 which i gather is pretty good and he did have a few 'interesting' stories about some grey import dealers..

 

You mean someone else knew about Bruce? Wow!

 

I don't know if this is allready said but,

There is a direct linear relationship between road speed(km/h) and engine speed(rpm), each gear has a different ratio, but each WILL be linear relationships. So unless either the rolling circumference of the rear wheel has changed (become smaller in your case) or sprokets have been changed to give a higher ratio. There should be no reason for your problem other than clutch slip which i would think is very unlikley.

I would seriously doubt it the tuning of you bike would cause this problem. But if it is then you better explain it to me. Throttle Postion does not have a liniear relationship with engine speed. It does have a positive relationship but not linear.

A flat tyre can cause a decrease in radius and thus circumference, but i doubt if it would make that kinda difference

A larger front tyre rolling diameter may also produce the same symptoms, but you would still be travelling at the same speed, It would just cause a reading inaccuracy.