Any Small engine guru's out here.

Being in the land down under - Australia the lawn is a tad dry and
dusty at the moment, so I thought it would be wise to invest in a
remote air kit to draw fresher air.

(It's a Honda 21" HRU217D Buffalo Bull Muching mower fitted with x2 low
lift & x2 highlift swing blades). It does a fanatastic mulching job on
the new local breed of "sir water" buffalo summer grass. The grass is
coping well with the water restrictions at the moment.

Back to the topic:
The idea was I would spend less time / money on airfilter maintence and
replacement and more on the garden........

So my mowers which ran spot on was in for the above accessory & the
carburettor had to be re jeted to a larger one a number# 72Jet. - Well
thats 20% increase in rich mixture size from a #68!
Instructions to only refit main filter, not pre filter or spacer as
there is another filter at the top of the snorkel - hence double
filtration.

Well when up to operating temperture it nearly stalled under load at
full speed, Accelerated with black smoke and back fire slowing back to
idle. The spark plug said it all - completely sooted up.
Had to change it back to the stock #68 myself so I could finish mowing
- still stuttered a bit at full speed and backfire on slowing down.

So went shopping and got a #65 lean jet for those 1000Ft altitude
contions I was experiencing at near sea level. It ran a lot better but
still had a trace of stumble at high speed and very small back fire on
slowing.
The EPA sealed idle mixture screw has a reasonably wide sweet spot,
where as the main jet size is very critical.

In the end it all went back to the standard#68 Jet & standard
aircleaner & it was perfect again.

Question is why would the local Honda Manufacturer get it so wrong with
the jet sizes?
Ie why did they fit a jet x2 sizes richer when it appears it should be
x2 sizes leaner.

So practically a small engine with a long air intake requires a lean
jet and theoretically speaking one with no intake of filter would
require a richer one am I on the right path ?

Any way it's got me so worried as running an air cooled engine too lean
can damage it I reverted back to the standard set up which is really
perfect - the standard air cleaner setup.
The other thing is you loose 3.5% HP's for every 1000Ft elevation.
So two jet sizes down is 7% less power to run a remote airfilter -
negating their claim of no power loss ?
It's seems to me the Japanese have done an excellent job, while locally
in OZ the accessory department blew it completly with their factory
accesory calibration. It may be a case of the marketing deparment
insiting on accessory that wasn't feasable for this configuration - I
can only speculate.


Anyway at least the grass looks nice now that it's cut.

All the best

Martin