The good, the bad, and the ugly

First for the good, I bought this baby as a Home Depot Rental 6400 in 2010. A little beat up but good compression, started and ran as it should, and had decent power in the 6400 setup. A few months later I put an OEM 7900 topend on it and it was NICE. I cut several loads of firewood with her over the next three years as well as using her to cut big logs into sections for chainsaw carving and even as a large blocking saw for carving.

 

And now for the bad. And by bad I mean mostly me not the saw. Last winter I was bucking up a large 36" diameter silver maple for table tops. Everything was going along nicely until the very last cut when in the middle of the cut the saw leans out and starts screaming like a banchee. Stopped the saw fueled up pulled the air filter and covers didn't see anything obvious but I had a bad suspicion that the saw had developed an air leak. Fired her back up and the idle was way too fast chain humming. I knew at that point I needed to quit but I only lacked a half a cut to be finished. Soooo, I did it. I know, I know I'm a dumb***.

Anyhow after getting back home and tearing into things I discovered a cylinder bolt nearly backed all the way out and the gasket sucked into the crankcase. Not good says I.
The P/C that I put on came with the non-metal base gasket and I have read in other places that this was a potential weak spot on these saws. I ordered the metal gasket and new cylinder bolts and buttoned her back up. The Piston and Jug looked fine. Fired, idled, and ran as it should. I'm not blaming it on the gasket as I admit that I never went back and checked the bolts after the install and some heat cycles as I should have.

Fast forward to a couple of months ago. Hadn't run the saw in a while and took it out to buck some big logs I had came across for carving material. The saw cut fine for a little while then starting leaning out again. Shut er down and grabbed another saw and went about my business. Finally had time today to check it out today. Fired it up and it idled ok, revved well so I decided on a test cut. Stuck er in a log and it fell flat on its face.

Started the teardown and here comes the ugly.
Forgot to mention the HD air filter earlier, Its important when installing these things to make sure the rubber boot between the filter and carb is not puckered.
How do I know this you ask? Stay tuned more to follow soon.

 

That rubber boot or whatever it's called is a bad design.

 

I've always preferred the low top, but I know there's a lot of love out there for the HD...

 

I think I'm going to see about stuffing a husky filter under there or maybe a k&n.

 

Some old nylons and call er good...

 

There's bound to be something better than stock but not the HD kit that has that boot. I don't like how it doesn't have anything holding it under the cover onto the elbow.

 

Sorry for the delay, had to run out for a bit. Now for the ugly, Here is the view through the exhaust port.

 

OUCH! or a mere flesh wound depending on which side of the pond your on.

 

When going over the saw this afternoon before tearing it down I noticed that the filter was sitting askew. The rubber boot that sits under the filter and on top of the carb has a tab that needs to be turned to the back of the saw toward the handle and pop into a slot to seal properly. Apparently the last time the filter was put back together that last step was overlooked by yours truly. Once again dum***. The carb had significant amount of dust in the plastic intake elbow and I'm sure the carb has an ample amount in it as well. My theory is that if that much dust was getting past the filter it was probably getting enough air to cause a lean condition. Thoughts?

 

Here she is with the jug off!

 

Here are some shots inside the cylinder sorry for the quality. Looks like just some smear, no scoring that I can see and nothing that will catch a nail. Should clean up ok what do you guys think?

 

Yeah that could have helped the problem. The jug should clean up. A new piston should have you back in business.

 

Some sanding with small flapper wheels.

 

The H jet on the carb was turned as far rich as the limiter would let it go. This has a zama carb the pic should show the number, are there different bolt on carbs for this saw?

 

Trim that limiter with a razor knife. There's a few that go on but not exactly drop in.

 

Just a few more pics and I'll be done. Looks like some discoloration at the end of the rod from the heat.

 

I'm done with pics for now but have some follow up questions.
1. Could there have been damage to the bottom end when the cylinder bolt came loose? There is side to side slop with the connecting rod where it connects to the crank but I cant feel any up and down movement.
2.I haven't checked prices on an oem piston yet but I suspect its pricey. What are your thoughts on putting a meteor in this thing keeping in mind I would like to have it ported if I can get it straightened out.
3.I have not checked the squish but has anyone been able to eliminate the base gasket on these saws?

Thanks in advance for any advice or suggestions. I will post the progress of getting it back up and running and some video now that I've figured out how to do it.