Any guesses on what might cause this

[GeorgiaVOL]

It was strange. Idles and cranks fine. Was easy to tune even though I was running it rich. Still cranks easily and idles. But when you pull the throttle and let go, it's off to the races running lean.

 

[GeorgiaVOL]

Kinda makes me think it is an intake problem that opens up during high load

 

[Mattyo]

kinda makes me think there is a bearing buggaring the seal....at higher rpm the leak shows itself. but it could be an intake issue as well.

this saw is old. if you haven't changed the crank seals, its time.

same thing with a car. ya can't just change the plugs and coils and call it a day. all of the rubber goes on an older vehicle. same on a saw. this saw has miles on it... so treat it as such. a carb kit alone is almost silly on such a saw....there's plenty more to be done before it can be a reliable runner.

 

[GeorgiaVOL]

Good point. I have seals and fuel line in order. When they get here it will be gone through in a more thorough manner.

 

[GeorgiaVOL]

I know I still have a lot to learn. That's why I'm here asking questions.

 

[Mattyo]

I hope its just an intake issue, and it can very well be that. But that doesn't mean that it wouldn't be best practice at this point to do a full teardown.

These days, when I'm buying saws, I ask.. when was the last rebuild. bearings etc. ...and who did it. If the answer is "i don't know" .... the price goes down.

I'm not familiar with the 285cd, but thats likely because its a generation before the saws I am familiar with. Just about everything that comes through my hands gets a full teardown, and those saws are 10-20 years newer than that one. best of luck whatever you decide to do.

 

[drf256]

Sure sounds like you're running out of fuel.

Pull the carb and check the gaskets. Check metering lever and spring. Check the screen on the pump side. Make sure you're needle isn't sticking. Change fuel line and filter.

I've never had a vac leak manifest at high rpm only, generally only fuel loss does what you say. Vac leaks typically manifest when the saw is pulling more vacuum, which is at idle, against a nearly closed throttle plate.

 

[GeorgiaVOL]

It only revs up after you pull the throttle and let it back out. If I pull the choke to slow it down it returns to idle. But as mentioned I will replace a few things that are due to be replaced anyway and go from there.

 

[drf256]

Then Jim may be correct. Loose carb bolts/cracked intake block or boot.

Something that would create a massive air leak when you pull back on the carb.

 

[XP_Slinger]

It only revs up after you pull the throttle and let it back out. If I pull the choke to slow it down it returns to idle. But as mentioned I will replace a few things that are due to be replaced anyway and go from there.

If you're bored while waiting for parts you can do a vacuum and pressure check without special equipment. Simplest thing to do is use WD-40 or brake cleaner while it's running to find a vacuum leak. To pressure check it, put a piece of tire tube between the muffler and cylinder, then between the carb and block. Use a rubber tipped air gun with your air compressor regulated at 8 - 10 psi and pressurize the case through the spark plug hole, make sure the transfers are open. I use soapy water in a spray bottle to check for leaks once it's pressurized. I know you're going to change crank seals and everything but in the spirit of learning these simple methods of testing your seals can lead you to your smoking gun and give experience needed for the next Saw that acts up on ya. I like to get out of "parts darts" mode whenever possible.

 

[GeorgiaVOL]

Cool idea. I might try that. Thanks

 

[XP_Slinger]

No prob. Cool saw btw

 

[GeorgiaVOL]

Thanks, this is all good practice before I get to my 266SE and 4 x 044s and a 440. 266SE I took down to the bare case halves and replaced everything, just never finished it.

 

[Wagnerwerks]

266SE I took down to the bare case halves and replaced everything, just never finished it.

You're going to fit right in near me..... Lol.

 

[Redfin]

Did you verify the throttle plate was fully closing as mentioned earlier?

 

[GeorgiaVOL]

Not yet. I had to rebuild my water well this weekend. It was a pretty bad weekend. Also had an unexpected $1000 bill arrive Friday.

 

[GeorgiaVOL]

Since I am tearing it down, is a base gasket delete a good idea on this saw? Or should I replace that gasket as well?

 

[Mattyo]

Check squish first....before teardown...then measure the gasket and see what kind of room you have

 

[MustangMike]

You can pressure test with a bicycle pump, just don't go over 10 psi.

 

[Motorhead]

Bad crank shaft bearing,The crank shaft goes into a high speed wobble allowing air to enter the crank case through the distorted seal.