One for the saw experts

[Gregford]

Hi all,

I was looking through a New Zealand on-line auction site and found this saw. It's a Husky 480CD which runs really fast. This is what the seller says:

"This is a Husqvarna 480CD chainsaw (80cc) that really moves. I think the previous owner or their workers have modified the carburettor to make it run real fast. I have cut the idle speed back as far as it will go but the chain still keeps moving this is no fault of the clutch. I think the idle speed is about 25% of the full motor speed a lot more than should be.
Now to describe the high speed. When it is first starts it will run as any other saw if not faster. As it warm up it gets faster and faster. It get to the point were the motor is screaming and I eased off on the throttle it order to avoid damaging the motor. When the fuel tank is near empty is its fastest running. It would not surprise me if the saw were capable 20,000 rpm."

I sent him the following message:

"Sounds like there is a partial fuel blockage to make the saw run like that. Even modified, it shouldn't rev like that. It sounds like a partial blockage which is why when you first start it it runs normally then it gradually leans out the mixture because the carb sucks less and less fuel over time. If it was possible to modify the saw to run like that, it would run like it no matter how full the tank is or whether hot or cold."

He replied:

"Hi, I have found that if a motor runs too lean it loses horse power even though it is running faster. This does not. This saw has run like this all the time I have had it. Thanks for your comments on this saw. "

Any ideas about why the saw would run that way? Always ready to learn (i.e. always ready to steal someone else's good ideas - LOL).

Greg

 

[Chopwood]

Air leak on the intake side.

 

[pgg]

Low jet screwed too lean, or maybe someones filed the butterfly open for idling, all the "20,000 revs" and "running faster and faster" is just B.S. The sellers a dreamer

 

[spacemule]

There are only two reasons for a saw not to idle slow enough to disengage the clutch. Either it's got an air leak or the clutch is shot. Right?

 

[HiOctane]

Air leak or the throttle butterfly is worn or not closing completely.You should have a pressure test on your saw.

 

[rreidnauer]

The 480CD was built to run at 8500 rpm. Perhaps a raceshop could make it do better, but this guy doesn't sound like such a person.

If it's acting like that, it's abused. Run the other way.

 

[pgg]

There are only two reasons for a saw not to idle slow enough to disengage the clutch. Either it's got an air leak or the clutch is shot. Right?

debris jamming the throttle linkage at the carb, happens sometimes

 

[Sprig]

Ditto Space and rreidnauer and all, back away from the auction, gut feeling is if its been running like that for a while its likely pooched by now, ya never know but the guy making 'oh wow race saw!' claims sounds like he knows squat or less "near 20,000rpm" ya riiiiiiiiighttttttt..................:hmm3grin2orange: :chainsawguy:

 

[Gregford]

Thanks guys,

I thought something was wrong with the saw but the seller claims that it doesn't lose power. I thought it must be a fuel starvation problem because the seller claimed that it revs higher and higher the longer he uses it and when the tank is almost empty it runs the fastest but he doesn't agree with me.

Anyway, I'd say the saw is toast by now. I wasn't going to put a bid in on it but it was more out of curiosity that I started the thread.

Thanks again

Greg