Chainsaw Repair

I'll add this here for now until Tech gets there chit straight.

On the 550/545 AT carbs is a needle adjustment.  This needle controls to volume of air that can bypass the throttle butterfly in turn allowing someone to adjust the low end mixture.  This has come in handy for some experiencing throttle bog.

Factory setting is close to 3/4 from seat.  If the needle is backed out, more air is allowed to bypass forcing the Autotune to add more fuel at idle essentially richening the fuel mix.  If run in the opposite is achieved.  This has been verified by adjusting, running the saw and checking fuel settings.

Tech department insists there is no carb adjustments and all screws should be bottomed out    Although they are not from the factory.


Untitled by mweba1, on Flickr


Untitled by mweba1, on Flickr

Exit on engine side

Untitled by mweba1, on Flickr

Entrance on filter side.


Untitled by mweba1, on Flickr

What's a ticking test?

Kevin


spike60 sharing on blsnelling 550 that had troubles. (Brad had muffler modded the saw before ever running it).

OK boys, here's the doctor's report. Came up with error code #14: "The carb wants to provide more fuel than is possible at hi speed." Throttle, temp and fuel valve tests were all good. So, that leaves bad carb or air leak as possibilities. Brad put 32 minutes on the saw, so in my estimation, an air leak from the factory would have shown up right away. So we're looking at the carb.

Fired up the saw to see and hear for myself what was going on. Saw would not rev past 13,000, mostly staying in the 12,700-12,800 range. Didn't sound too good and I didn't even bother trying to cut with it. Plugged it back in and using the diagnostic tool, reset the fuel settings to the factory default numbers and then cranked her up again. Now the thing wants to rev like it's supposed to, and it kept hitting the rev limiter. Couldn't even read it with the tach. I saw 16,000 flash a couple times, which must be the rev-boost looking for a limb to cut. So, I took it out to the woods and ran a little less than half tank through it. Was cutting some 8"-9" ash and it went right through it and was holding 11,600 in the cut. So, it seems to be running fine for the most part. It did stall at idle a couple times, and there was a come and go hesitation coming off idle at first. Perhaps as the AT was adjusting itself from the factory default settings. Did a bunch of cuts on a 4" limb, and the rev-boost was evident, and mighty nice. Also, the error code did not reappear after I ran the saw.

So, did I fix it? Maaaaybe. Wasn't comfortable with those couple of stalls. I'm going to call tech service again tomorrow and get his opinion on the whole thing. I did already order a new carb which I'll warranty, but it was probably too late to ship this afternoon. Since Brad isn't exactly around the corner from me, we don't want the saw accumulating frequent flier miles. So, we don't want to take any chances with the carb. BTW, there is a way to replace carbs on these things without having to program them. All ya gotta do is put the original AT unit on the new carb.

I'm going to run it a bit more, and maybe compare it to mine for running characteristics.

The diagnostic tool, (how about we call it the "DT"), showed that the error code happened twice while you had it. So, I imagine that the second instance was what you posted above. And it looks like it reappeared as soon as it hit the wood.

I did a good 20-30 cuts and it was fine except for the stalling I mentioned. We'll get it sorted out tomorrow. I'm most anxious to hear what they think about resetting the fuel numbers and the problem seemingly going away.

There is also something on the DT that's called a "master reset" that sends everything back to square one. But they caution that this should only be done after major work was done to the saw. Still a lot to learn, eh boys?

 Quote Originally Posted by blsnelling View Post
How would this theory account for the fact that it ran perfectly for the first 20 cuts?

spike60
I'm still thinking it's just the carb. We are all naturally going to be quick to think problems are the somehow related to the AT stuff, but we still have to consider all of the other variables that you'd have to deal with in any saw.

I tried the saw today, and I noticed that the primer really doesn't fill and firm up like it's supposed to. I've run into this on a few 346's, and that has usually meant that a new carb was in order. The saw doesn't want to idle consistantly. It will hold at 2700-2800 and then just quit.

The carb did ship yesterday from SC, meaning it should be here tomorrow. Supposed to be freaking 93+ tomorrow so I'm going to be fortunate enough to be able to duplicate Brad's comfortable running environment.