Date: Sun, 28 Mar 1999 09:21:40 -0500
Subject: Fuel/Oil Ratios plus Burnout Thotz
From: Chris L Johnson 

>According to what I have heard the best ratio for POWER is 
>some where between 26/1 to 33/1. 

Nice write-up on oil/fuel ratios, Bruce.  It goes in the permanent file!

Call me a skeptic.  Here are a couple of opinions based on experience.

RATIOS

I have wondered about oil ratios for optimum power.  I remember a
motocross star (can't remember his name) in the `80s whose family was
part owner in a motorcycle pre-mix oil business.  He used to recommend
these really rich ratios saying it increased power.  The guy was also a
dick with no integrity and a really arrogant "Valley Boy" attitude.  I
suspected he was an oil pusher to increase usage and profit?  Who knows,
but ever since that observation, I've wondered where these
recommendations come from and under what conditions the tests were made. 
If fully loaded under a dyno at very high RPMs it may make sense.  For
trials, I think 100:1 is nothing to be afraid of.  I even ran 125:1 for a
year on all my bikes because I was reading the chart wrong!  Oh well. 
Nothing scientific here, but I've found more problems running oil richer
than 75:1 than running it leaner than 100:1.  As you said:

>For Trials, this may not be an optimum 
>fuel/oil ratio, because at lower engine speeds, oil tends to condense,
and 
>collect in the crankcase, then when high throttle settings are used,
this excess 
>oil may cause the engine to run poorly until it is burned out.  This may

>be why you used to see World riders revs their engines up high when at a
dead 
>stop in front of an obstacle that they could not afford the engine to 
>hesitate on.

Really, the oil ratio thing is very flexible.  All kinds of ratios will
work, so it's hard to be dogmatic.  My stand on leaner ratios comes from
having no problems with 100:1, but realizing benefits like less pollution
and less muffler fouling...a significant problem in the flat midwest.

BURN-OUT

I have often puzzled on this burnout thing.  It is a habit that I think
is not necessary.  A properly jetted bike simply will not need burn-out
after the initial warm-up burnout.  I NEVER "clean out" a bike once I
start an event.  And I NEVER have had even one stumble before an
obstacle.

What most people don't know is that when you open the throttle wide when
the bike is unloaded (not hooked up to the ground) you create a rich
condition as there isn't enough load to use the fuel being run through
the motor.  A little known fact of jetting is that rich/lean is a
function of engine load as much as it is jetting.  So, wick the throttle
open and you raise the needle and slide high and run a burst of fuel
through, causing a temporary rich condition.  The blubbery sound that
emirates with smoke gives one the false feeling of a clean-out.  It's a
wash and may do more psychologically than anything.  The best way to
clean a bike out is to head up a hill in the middle gears, load the bike
as much as possible, and use high RPM to scavenge the spooge from the
crank case.

You may ask, "why do these top riders do this, then?"  Answer: not all of
them do.  Just because someone is a great rider does not mean they
understand all the technical nuances.

On this clean-out issue I am open to differing opinions and will listen
to any intelligent case presented.

Chris Johnson, Director of Engineering
College Park Industries, Inc.
papazit "at" juno.com
www.college-park.com