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Message started by Stimpy on 09/14/09 at 16:08:45

Title: MPG main jet experiment
Post by Stimpy on 09/14/09 at 16:08:45

|| QUICK RESULTS ||

- .140 "undersized" main jet = 56mpg (@ 7,000ft elevation)
- .140 "undersized" main jet = 60+mpg? (@ seal level+dry climate) *cannot test here

- .162 "oversize" main jet = 41mpg (@ 7,000ft elevation)
- .162 "oversize" main jet = 45mpg (@ seal level+dry climate)

|| STORY & SIDEEFFECTS ||
Recently I got my hands on a .140 main jet and replaced my
.162 oversize jet with it, here are the whys and the side effects:

Exhibit A: my "since-for-ever" trusty .160ish main jet that I made myself
- look here, this is how I made it :)
http://p1.bikepics.com/pics/2007%5C06%5C20%5Cbikepics-937953-full.jpg
http://p1.bikepics.com/pics/2007%5C06%5C20%5Cbikepics-937959-full.jpg

WHY I made it? cause I needed to re-jet for a free flowing exhaust system
and I live in the 3rd world right now where it's sometimes impossible to
get even the simplest of things so one learns to macGyver everything.
The results were great: nice generous top end torque and a lots of backfire! 8-)

WHY I decided to change it? basically cause I moved from living in the
desert at sea level to living in the mountains at 7,000 feet and suddenly I
was barely getting 100miles per tank.

* the .160 jet at sea level+dry conditions was a bit rich but perfect cause of
all that oxygen ...but not away from sea level though, at 7,000 feet elevation
the mix was way too rich and the bike understandably lost some torque and
top speed; lack of oxygen supply at higher elevations makes the combustion
unefficient therefore a lot of the gas goes directly out the tailpipe untouched.

** after installing the .140 main jet mileage was much better BUT some
of the TORQUE WAS GONE :-/ ...while response is still "sufficient" the
top speed went from 90-92ish mph to about 82mph which is no big deal
but it now takes longer to get there and that is no fun, I don't drive like
a lunatic but my driving style does requires "passing power", I'm SURE
that anyone with a gentler/constant driving style gets much better
millage than I do, guarantied.

***conclusion: the .140 main jet is GREAT for driving within the city
all day long on chores, commute or short roadtrips where you do not
intend of going over 65mph and even though this jet feels like it robs
the savage of about 150cc's, 56+mpg is just unbeatable nowadays.
However, after this little experiment the trend shows that either the
.150 or 152.5 main jet will be the ideal balance between torque and
mpg's at this altitude and maybe the .155 or .157.5 at sea level.

- Additional info: 1) at all times the bike ran w/stock air element
but w/o the airbox's plastic side cover 2) at all times the air/gas
mix screw was adjusted in a range between 2 and 2 3/4 turns out
3) at all times all other carb and engine components were stock
4) at all times bike ran w/free flowing exhaust 5) I use regular
6) very important: during this experiment the total load of my
bike was about 340lbs (me 165lbs + my GF 155 + backpack
w/water, rain jackets and tools 20lb.)

Hope this info helps those of you interested in getting higher MPGs.
C'ya!

Title: Re: MPG main jet experiment
Post by T Mack 1 - FSO on 09/14/09 at 19:40:58

Did you adjust the low speed/idle mixture setting too? And, did you adj the needle "white-spacer" setting? Most normal driving conditions are in the Mid-range or less, which are affected by these 2 things.

Also, I suggest taking some temp readings too. When I was jetting the Savage I did the "go-back" to starting point and noticed the engine was noticeably hotter.

Jetting sometimes can be a compromise. :-?

Title: Re: MPG main jet experiment
Post by Stimpy on 09/14/09 at 20:24:02

- The idle mixing screw is fine, in an air cooled savage
highish idle revs are not a bad thing as one might think
because the oil pump works a bit faster so it lubes well.

- The white spacer mod didn't really work for me, bike
lost low-end response somehow, so I put it back the way
it was w/small washers, I don't mind the backfire at all.

- Temperature is fine, I have a meat thermometer stuck
to the head that works like a charm and always informs
me well on my engine's operating temperature (try it, $5) ;D

** These bikes were made to run as hot as a coal chamber ;)
just always, ALWAYS mind your oil's level and quality, C'ya

http://p1.bikepics.com/pics/2007%5C10%5C21%5Cbikepics-1062008-full.jpg

Title: Re: MPG main jet experiment
Post by Charon on 09/15/09 at 06:45:27

You already seem to know it, but the move from sea level to 7000 feet altitude will cost you about 20% of the power, even with a perfect mixture. It is interesting that your estimated "loss of 150 cc" is pretty close to the 20% loss due to altitude.