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Discussion Starter · #1 ·
I have a 2005 Honda Fourtrax Rubicon 500 that absolutely will not start when cold. I have cleaned the carb, replaced the fuel enrichment device, use only non-ethanol premium fuel. Once the temp gets much below 0°C (32F) it is a no go for starting. Spark check shows good spark to the boot, priming the carb doesn't really seems to help. Any suggestions would be greatly appreciated!! Merry Christmas to all!
 

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If I recall correctly this era has an electric carb heater…. Might check it (I’d expect open circuit if burned out). Also give it a few seconds between turning on the key, and cranking.

Anything boarderline (weak battery, slightly fouled spark plug, fuel in carb bowl getting stale) can mess up cold starting.

Does adjusting the enricher effect how the engine runs when it does run? Even if it’s new it could hang up, and I’ve certainly done a carb I thought was clean… and had to redo it.
 

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Discussion Starter · #3 ·
If I recall correctly this era has an electric carb heater…. Might check it (I’d expect open circuit if burned out). Also give it a few seconds between turning on the key, and cranking.

Anything boarderline (weak battery, slightly fouled spark plug, fuel in carb bowl getting stale) can mess up cold starting.

Does adjusting the enricher effect how the engine runs when it does run? Even if it’s new it could hang up, and I’ve certainly done a carb I thought was clean… and had to redo it.
Hello and thanks for the reply. You are correct about the carb heater. I tested it when I did the carb cleaning and it does get hot so I think it's functioning. I usually allow it to warm for a few seconds (15 or so) before starting, perhaps it needs more. New spark plug installed, actually the one recommended for cold weather. Fuel is fresh and clean as I'm quite careful about stale fuel. The fuel enrichment works as it's supposed to, it will affect the rpm depending on it's position. I don't know if the ecu/cdi unit could cause it to react this way or not. I'm hoping it isn't the problem as they are pricey.
 

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Discussion Starter · #4 ·
Well I think I found the issue. I did a compression test and was only getting 75psi. Book value is 88-135 or so. To confirm it I did a leak down test at TDC and ran out a 3 gallon pancake compressor in about 30 seconds. To further confirm I put oil directly in the cylinder which bumped up compression to 95psi. Soooooo, one Namura top end kit, a valve lapping and a cylinder cross hatch and it's on the road to being functional again, I hope! Will advise if I am successful......
 
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