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Old 08-05-2014, 09:57 PM
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BarelyAWake BarelyAWake is offline
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Join Date: Jul 2009
Location: Maine
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Default Re: How to tune an engine with a temp gauge?

Originally Posted by Davezilla View Post
That's one thing I like about the CNS carb is that it has an enrichener circuit like most motorcycles have and it's a good tuning tool or if you need an emergency cool down you can just feather the choke enough to give it that little extra it may need on a really hot day or right after a hard run.
Indeed, I too appreciate the "in-flight" fuel/air mix adjustability offered by an enrichment circuit over the more basic "choke" design - while cold starts are made about equally easier with either, at speed & with a warmed up motor an enrichment circuit is far more useful for determining and/or optimizing fuel/air for those conditions.

Much like as what's found on small aircraft to enable the pilot to manually adjust to compensate for altitude, an enrichment circuit provides a measured amount of additional fuel, the amount variable to suit the application - unlike a choke, which just cuts off air, not nearly as handy for determining jet size modifications for example as you're reducing venturi size, not your typical tuning method when addressing jets.

[the following is not advice, can be harmful & is just silliness I do]
When I have a carb that has an enrichment circuit, generally I don't fuss about adjusting my carb's jets quite as precisely as otherwise, if I do it'll be a touch on the lean side (needle clip adj) as I tend to run with the enrichment circuit partially engaged to some extent anyway. As I've a temp gauge and am somewhat familiar with the preformance characteristics & assorted behaviors of the motor in question I'll simply adjust to suit as needed, when needed (friction lever on bars). An interesting example was the last rally I attended, meant for scooters & most being 150cc+ it was all my lil 49cc four smoker could do to keep up - so that meant I was running overspeed & overtemp all day in the sweltering summertime, redlined & screaming it's guts out I'd give it a touch of extra fuel not for preformance, but to quench the heat a bit. Once normalized (or less stress/speed/hilly terrain) I'd readjust back to "normal" cruise/preformance mix.

A bad habit I s'pose, one I picked up from small aircraft whose fuel/air mixes aren't really "set" anyway

Last edited by BarelyAWake; 08-05-2014 at 10:07 PM.
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