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From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: Champion Generator review
Date: Sun, 05 Nov 2006 05:06:35 -0500
Message-ID: <65glk2lo6drhhv57uj62tf4do66q1li2ji@4ax.com>

On Thu, 02 Nov 2006 17:12:13 GMT, "Victor V" <slackamn@aaahawk.com>
wrote:

>
><boondocky@no.spam> wrote in message
>news:3d6kk291i2kt2qr6eqfhf143lej65ssep3@4ax.com...
>> "Victor V" <slackamn@aaahawk.com> wrote:
>>
>> I'm not sure what the "coming from you" part means, but I'm taking it
>> to mean "coming from a guy who has been dry-camping for going on 4
>> years straight in high-altitude cold-weather conditions". <g>
>>
>
>Yeah, that and I find that smart-ass guy to be too over the top. Never
>listen to him for anything.

Good idea.  Won't go wrong there.

>All good stuff. You reckon my gen will run OK at altitude? Say 9K?

At 9K?  Probably not.  From the US Standard Atmosphere chart,
http://www.sworld.com.au/steven/space/atmosphere/ at 9K feet, the air
is only about 77% as dense as at sea level.  Thus, everything else
being equal (it isn't), the power loss from altitude alone would be
about 23%.

This assumes the mixture is correct at 9K which it won't be.  You
should expect additional power loss from non-optimal mixture strength.
Since small engines are now set to run very lean to meet EPA
restrictions, the degradation might not be as bad as in previous
years.  Still, a high altitude kit (different jetting) would be
appropriate.  Honda sells such kits for their GC series engines which
most of the ChiCom clones appear to be cloned from.  If a high
altitude kit isn't available from the generator's importer then
perhaps you could figure out exactly which Honda engine they cloned
and order an altitude kit from Honda.

Does the manual for the generator mention any sort of altitude kit?
Considering the range of elevations in China, I'd not be surprised to
learn that they'd addressed that matter already.

If you can't buy a kit then you can make one.  All you really need is
a different size main jet since the generator won't be idling much at
all.  If they cloned the Honda carb then the main jet should be a
brass screw-in element.

I used to make jets for "non-adjustable" carburetors fairly frequently
in days past before EFI displaced carbs on almost everything.  A spare
stock jet makes things very easy, as it can be modified without risk
to the carb if you screw up.

The drill (pun intended :-) is to close the jet's hole and then
drill/ream it to the desired size.  For brass jets I solder the hole
shut.  For jets drilled into the carb's pot metal body, epoxy works
well.

I use a combination of orifice drills and watchmaker's hand reamers,
both of which should be available from McMaster-Carr, MSC, etc.  I got
mine decades ago so I'm not sure of modern sources.

Orifice drills are designed to drill the orifices of gas and oil
burners when changing the output, converting from gas to propane, etc.
Mine start out at 0.015 and go up in 0.005" increments.

Watchmaker's hand reamers are tiny reamers used to ream the tapered
hole in a watch hand to fit on the shafts.  My set starts out at
probably less than 0.015" and goes up in several pieces to perhaps
0.100".  For watch making, one simply reams the hand opening until the
hand fits tightly on the shaft.  For carb tuning, one simply reams the
jet until the correct mixture is achieved.  I always record in my
tuning notebook which reamer and how far it protrudes from the jet so
that I can reproduce the jet when needed.

A low performance generator engine should be very tolerant of mixture
so it should be easy to get close enough with one or two tries.  If
the length of the metering channel is kept the same as stock (easy to
do with solder) and the entrance and exit tapers are maintained then
the altitude compensation will involve shrinking the AREA of the jet's
hole roughly in proportion to the reduction in air density.  At 9K
feet, for instance, you'd reduce the AREA of the jet's opening by
about 23%.

Once you get the mixture close you can tune it in by varying the float
level, the limits on that being overflow on the high end and
uncovering the idle jet on the low.

This sounds like a lot more work than it is.  Once you have the drills
and/or reamers in hand, making the change is perhaps a 15 minute job.
Drop the float bowl, remove the jet, solder shut, drill and deburr the
hole, re-install and that's it.

John


 
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