Rejet yet retain fuel economy?

[galahs]

I have a 2005 model so my carbs have three jets.

A pilot  (17.5), a mid main (60) and a main (130).


But I've been wondering as I am soon to add a lunch box air filter and a Jardine exhaust.

Tradtionally I should be looking to add a 22.5 (pilot), 65 (mid) and 145-150 (main) setup....

but if I want to retain low down fuel economy whilst adding up high power, could I just increase my MAIN jet to say 150 and leave the others as stock?

[rangerbrown]

not if you dont want it to run like crap.
i was geting about 65 or so i now get
60mpg after the rejet and i wnet to a 14T front sprocket this was all hwy too, at 85-90

it not like the mpg will drop to 20 or somehting

[galahs]

My theory was that at lower RPMs, the improved air flow offered by the lunch box and exhaust would have minimal effect, so why does it effect the air/fuel ratio?

But at higher RPM's the reduced restriction would allow the engine to breathe more, meaning it requires more fuel in high revs. I'm interested in learning why this theory incorrect? 

[rangerbrown]

because all engines are more efechent at higher rpm, not when there under load. when under load they use more fuel. so

the lower rpm would make it work harder (not much mind you) but would require more fuel per air
as to the other.



what would you rather do, lift a 1 ton block by hand in 10 sec or take 30sec and use somthign that wound make you brake a sweet same rules apply

[rangerbrown]

but i should add, if i do around town romping on it yea it will drop, the othe mpg was nothing but hwy

[hmmmnz]

i would leave the jets as they are and not put on the new filter at all, just change the exhaust. exhausts don't really make the bike run any leaner (mabee a tiny bit)

[galahs]

but I want to have my cake and eat it too! 


Its so hard to believe that an erxhaust system won't make it run any leaner. surely a sports exhaust has a huge reduction in pumping losses so there for allows the exhaust to escape the cylinder easier, allowing more frewsh air to be drawn in on the next stroke, ie making it leaner?

I think I'll try running it for a short while with just the K&N on the see how that effects down low rpm. might even do some Air/Fuel ratio  tests and If I'm satisfied its ok, will re evaluate the steps I'll take after that.

[hmmmnz]

exhausts don't really make it leaner as the engine can't suck any more air through the restrictive nature of the air filter,
if you change the filter on the other hand it can suck more air, so making it lean, which makes it run hot.
i wouldn't change the filter with out rejetting it,
but if your hell bent on doing it, you'll find out very quickly it runs like crap
enjoy:D

[Gisser]

My theory was that at lower RPMs, the improved air flow offered by the lunch box and exhaust would have minimal effect, so why does it effect the air/fuel ratio?

The K&N lunchbox doesn't seem to affect the pilot circuit as badly as the main circuit.  Jet kits don't even bother with the pilot jet--or the mid-main in your Mikuni.  You can control fuel economy through the mixture screws.  As long as the motor will cruise without surging, you're good.  You can fiddle around with pilot jets if you want instant response to the throttle.    

[galahs]

OK, I temporarily installed the Lunchbox.

Firstly, pretty easy to install.

Remove the seat,
remove the two bolts holding the tank
close the tank valve
remove three pipes attatched to tank
remove the tank
reove the two screws holding the air box to the fram
remove the two clamps holding the airbox to the carbs
wiggle and jiggle it till it comes free (remove two hoses attatched to airbox)
put K&N filter in place, tighten clamps
clover the enbds of the hoses that used to go into the airbox with some material to stop dirt getting in there (makeshift filter)
replace tank (don't forget to reopen valve)



Anyways, my first impression was it sounded normal during idle.
But when you rev it you get a nice deep thraoty roar 

Drive impression.

Well for just cruising the bike ran as normal. Not much louder than stock. Seemed to pull pretty good too.

When you open the throttle you get a nice induction roar but its not too loud to be intrusive.

But, here's the findings.... it pulls hard to about 5500rpm then gets bogged down dramatically. So ayt higher rpm it is obviously running very lean.

Conclusion: I think its safe to say if your after an ecomonical cruiser but with more top end you:
- could easily keep your stock pilot jets (no quicker warm up though, sorry guys)
- could possibly good to go up one size for your mid range main jet
- definately will require a much bigger main jet


the tough part will be to see how just increasing the Main jet effects the power delivery curve.

I need to get my mates Air/Fuel monitor out and do some more tests me thinks.

[galahs]

Just put my stock air box back on and geez, it seemed to go so much better.

After all the trouble required, I sure hope a jetted and lunchbox filtered bike is better than the stock setup 

[yamahonkawazuki]

it is, the drop is not that bad to worry about, and besides if it (to you) feels like it is, you can always put the stock parts back on

[galahs]

Being quiet happy with how the bike idled and cruised at low revs I think I'm going start by leaving my pilot jet stock (17.5) to help maintain decent slow speed fuel economy and emmisions but will upgrade my :

- Mid Main Jet to 65
- Main Jet to 145

Bike upgrades include a K&N lunchbox Airfilter and a full Jardine exhaust.

Will post a review of how this works out once I get all the parts installed.