Chainsaw problem

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  #1  
Old 06-26-06, 06:16 PM
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Chainsaw problem

I recently purchased a Husqvarna 455 rancher. The saw came full of gas and oil, ready to run and ran great until I put new gas in the engine. I made sure the gas was mixed properly at 50:1 with 2 stroke oil. Now, the saw will idles OK, runs at low rev ok, but cuts out if the engine is pushed above half throttle. I drained out the gas tank and refilled the tank with new mixed gas (87 octane Cenex gas), but still have the same issue of the saw cutting out ias I go to near full throttle. I've adjusted the high jet (the new saws have limits on how much you can adjust - 1\2 turn) with no luck. I live at 2500 ft. altitude and cut at 3000-5000 ft altitude, although i don't know if that makes a difference. Any help would be much appreciated. Thanks!
 
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  #2  
Old 06-26-06, 06:21 PM
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Sounds like an air problem. Check the filter and carberator for any debris that might hinder the air flow. Clean the sparkplug also.
 
  #3  
Old 06-26-06, 06:27 PM
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I'm heading out the garage to check the filter and plug.

Also, come to think of it, the saw ran great with the first tank, but when i put in the new gas is when the problem started and it hasn't gone away since. Need higher octane?
 
  #4  
Old 06-26-06, 07:58 PM
mikesmalleng's Avatar
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Did you buy this new or used?
 
  #5  
Old 06-28-06, 01:13 AM
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Don't use higher octane. The higher the octane rating, the more your performance will suffer. It sounds like something may have gotten picked up by the carb when it ran out of gas. Any chance there could have been a bit of water in the tank, or in the new gas you put in? You might have to clean the carb out. If it was running fine at that altitude before, it should now with the same carb adjustments it had. I think something is clogged in the carb.
 
  #6  
Old 06-28-06, 02:32 PM
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Don't use higher octane. The higher the octane rating, the more your performance will suffer.
Cheese, could you please elaborate a bit? The higher the octane, the slower the fuel burns. That quality would be desirable in certain cases like high compression or pre-detonation conditions. If performance is reduced by higher octane, why is it the prefered fuel for aeroplanes and racecars?
 
  #7  
Old 06-28-06, 11:04 PM
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Correct, the burn rate is slower in higher octane fuels. This is only desireable in high compression engines or very hot running engines where the fuel will be prone to detonate prematurely if the octane is not high enough. Every small engine I've seen reccomends regular fuel only (when I paid any attention to the engine's manual). The slower burning high octane fuel is not what these engines are designed for. If it were a high performance engine running 14:1 plus compression, fairly hot, and under a moderate to high load, the higher octane fuel would be better. Low octane would pre-ignite and cause power loss and slow but sure engine damage.

There is a small window when the igniting fuel is turned into power. If the fuel is still burning after this window, the power from that burn is wasted and just goes out the exhaust. If it ignites too fast, it is creating pressure in the cylinder before the piston is at the correct position, and the explosion of the fuel impacts the top of the piston, creating a spark knock/predetonation ping, and the burn is over when the piston is still in the right spot for a burn to be occurring. Power is lost again. Kinda technical for a lawnmower engine I guess. You probably wouldn't notice much difference using either fuel in a small engine, but regular is reccomended.
 
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