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Discussion Starter · #1 ·
2005 Rancher TRX350FM

I live in Texas and am planning on taking my atv to colorado. The highest elevation I will be driving is around 7,500 ft. Should I change out a jet or something in the carb to avoid fouled plugs, or will it probably be ok? If so, what exact part do I change? I looked at the part schematics and they say nothing about diameter of the jets.
 

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Your spark plug might blacken and get a little rich sooty deposit on it. Depending on how long you are at the high elevation, I might not worry about it.

At most, I might carry an extra new spark plug and install it if you have trouble. That way you won't potentially overheat your engine running it with a lean main jet back at your original lower elevation.

Rick

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Discussion Starter · #5 ·
Hi look the service manual for guidance. I spose if you’re above 5000 ft for a long time you could foul a plug or two. Yes there is a high alt jet.
So my manual lists the Main Jet to be #128S and the Slow jet as #42S.

Sorry, but I am still a little confused on what this parts diagram has and what I need.
https://www.cheapcycleparts.com/oemparts/a/hon/5053dd9ff870021c54bdcd7b/carburetor

parts 41 and 42 is likely where the issue lies. I guess I can call cheapcycleparts and see what they say.
 

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Discussion Starter · #6 ·

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You will need the next sized smaller main jet. You may need the next smaller pilot jet. The fuel screw may or may not adjust the slow circuit enough. I'd replace it to be safe and go back with the stock if it runs too lean.
 

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Please check the manual don’t think you need a slow jet resize. I only needed to change the main jet and kick the pilot jet back a little.
I usually run at 3200-4200 and occasionally run trail at 5000-6000. Good mix for me.
 

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IMO, 7500 feet is just a little below "high elevation". I wouldn't worry unless you have sustained travel of at least 9,000', or higher. At 12,000', certainly an issue. Just my opinion, but I have a lifetime of experience at high elevation.
 
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