seized my 660, What did I do wrong?

[tex]

Here is the background...

Picked up a ms660 mag about a year ago with a burned up top end. Before tearing the saw down, I did a vac check on the case. All ok. I installed an NWP big bore top end. Tuned the carb all the out (rich) to the stops. Saw ran good like that, so I never played with it further. Ran the saw on and off through the summer with no problems, other than I thought that a 98cc saw shouldn't be able to be bogged with only a 25" bar.

So, I did a muff mod.

for the muffler mod, I drilled two 1/2" holes in the baffle, and one 3/4" hole out the front cover with a fabbed deflector. The screen I put inside is large enough that it is not restrictive to the flow. All said and done, I've added a 3/4" hole in addition to the stock hole for exhaust flow.

I pulled the limit caps off the carb, and started with 1/2 turn out on the low, and 1 1/2 turns out on the high (double the factory settings). The saw wouldn't start, so I increased the low setting to about 1 full turn before it would start. With the saw now running, I opened the low mixture trying to get it to 4 stroke. It never really did 4 stroke, but did slow down. I then leaned it to find my highest rpm which was at about 3/4 of a turn. I richened it from there back to 1 turn open, and then moved to my high mixture. I revved the saw to wid open, and began opening the mixture. Like on the low side, it never really 4 stroked, even at 3 full turns out on the screw. I let it back down to idle, and checked my low setting again with the same procedure, and ended up back at 1 turn out. Went back to the high side, and still couldn't get it to noticably 4 stroke. Changing the mixture did change its responsiveness when i'd blip the throttle, but I couldn't really get it to slow down by richening it up.

Long story short...the last time I let the throttle down, was the last time. Its seized tight...still.

Did I do something wrong with the tuning, does the carb need to be gone through, did I go too far on the exhaust, did the big bore kit have anything to do with it?

Any input would be greatly appreciated.

 

[lone wolf]

You said couldnt get it to slow down by richening it .Air Leak!

 

[gcsupraman]

Here is the background...

Picked up a ms660 mag about a year ago with a burned up top end. Before tearing the saw down, I did a vac check on the case. All ok. I installed an NWP big bore top end. Tuned the carb all the out (rich) to the stops. Saw ran good like that, so I never played with it further. Ran the saw on and off through the summer with no problems, other than I thought that a 98cc saw shouldn't be able to be bogged with only a 25" bar.

So, I did a muff mod.

for the muffler mod, I drilled two 1/2" holes in the baffle, and one 3/4" hole out the front cover with a fabbed deflector. The screen I put inside is large enough that it is not restrictive to the flow. All said and done, I've added a 3/4" hole in addition to the stock hole for exhaust flow.

I pulled the limit caps off the carb, and started with 1/2 turn out on the low, and 1 1/2 turns out on the high (double the factory settings). The saw wouldn't start, so I increased the low setting to about 1 full turn before it would start. With the saw now running, I opened the low mixture trying to get it to 4 stroke. It never really did 4 stroke, but did slow down. I then leaned it to find my highest rpm which was at about 3/4 of a turn. I richened it from there back to 1 turn open, and then moved to my high mixture. I revved the saw to wid open, and began opening the mixture. Like on the low side, it never really 4 stroked, even at 3 full turns out on the screw. I let it back down to idle, and checked my low setting again with the same procedure, and ended up back at 1 turn out. Went back to the high side, and still couldn't get it to noticably 4 stroke. Changing the mixture did change its responsiveness when i'd blip the throttle, but I couldn't really get it to slow down by richening it up.

Long story short...the last time I let the throttle down, was the last time. Its seized tight...still.

Did I do something wrong with the tuning, does the carb need to be gone through, did I go too far on the exhaust, did the big bore kit have anything to do with it?

Any input would be greatly appreciated.

If you couldnt get it to 4 stroke at 3 turns out there is a major leak somewhere (like lone wolf said) or there is an issue with the carb. Last saw of mine that did this needed a carb kit.

 

[00 steve]

you don't check the low adjustment by getting it to 4 stroke off it. the low adj is only for idle. idle should be around 2700 and it should accel clean. turn closed until it leans and then rich until it loads. set it to middle and fine tune to get it to accel clean. high side you set to 4 stroke. sounds like you need to double check for an airleak and set that carb right next time.

 

[jus2fat]

You said couldnt get it to slow down by richening it .Air Leak!

Yep..air leak....and likely incorrect carb adjustment.

And I will add..I'm not a fan of that NWP big-bore kit.

J2F

 

[Beer Gut]

Like already stated air leak, next time you start have the H and L out one full turn with caps out or cut. Thats the factory setting, your statement said you doubled the setting if caps were in and intact. Reading here I've seen both pos and neg for those P&C kits good news for you is they are cheap if you would have burned up new OEM ouch!!!! Either way it dosn't sound like you get proper tune adjustment either your carb isn't spitting enough gas or you are sucking air in from some where. Check the impulse line and intake boot for cracks if you already did leak down on crank case. If all check out rebuild the carb.

 

[asdf4240]

Agreed on the massive air leak.

Sorry but it sounds like you never found nor fixed the original problem which burned up the top end. I would check the intake, carb and fuel lines for cracks, assuming the case is sealed.

 

[TommySaw]

yup, air leak would be my guess, and I would recommend using cylinders from manufacturers with a better track record (not that there was anything wrong with the one you have). We set H/L needles 1 1/2 turns out to start with, then set H, then L/idle

 

[tex]

Well, I never did find what originally burned it up. I assumed it was strait gassed, because it passed a leakdown test. The intake boot, and impulse line were included in the vac test, so they should be fine. It ran good for a year.

What has me baffled is that the only thing that changed from running good to not was punching out the muffler...nothing that would have created an air leak.

I wasn't clear originally. It would slow up (a little) by richening the H, but not a noticable 4 stroke. Not noticable enough to find a set point anyway.

As far as my starting point, I doubled up what the factory sticker had. Next time i'll start them both out further to begin with and work them in.

Isn't the low tied into the high on these...something like 25%? I was tought to start with the low first or you won't be able to get the high correct. Maybe that was a different style carb.

Another question. Are there any tricks to getting the jug off with the piston seized in place? A little oil in the plug hole maybe?

Thanks for the input!

 

[nick 55]

Take a bolt that will thread into the spark plug hole, drill a hole in it and put a grease zerk in it. Use the grease gun to press it off. But unbolt it from the case first.

Nick

 

[blsnelling]

First of all, I think you misunderstood the standard settings. You said you started at 1/2 turn out. Is that what it says in the manual or on the side of the saw? If so, that's with the limiters in place. That 1/2 turn out was from the lean limit with the limiter, not from closed. Your saw will never run with 1/2 turn from closed. You should have started with both the H and L 1 turn out from closed.

Second, a chainsaw will never 4-stroke at idle. 4-stroking is never discussed when tuning the L. You ended up right with it 1/4 turn out from max RPM with it idling.

You used the saw all summer with it not 4-stroking even at 3 turns out? I can't believe it lasted anywhere near that long. ANY time you have an issue like that, don't use it! It will always end up where you are now.

You're going to have to get this thing back together and find your problem. Like so many others have already said, it sounds like a significant air leak. You also need to carefully go through the entire fuel system too.

 

[ZeroJunk]

It could be an air leak. But, since you tested the saw for leaks and found none it is just as likely a partially clogged high speed circuit.

And, it is also possible that you threw a clip somehwere in the process.

 

[tex]

First of all, I think you misunderstood the standard settings. You said you started at 1/2 turn out. Is that what it says in the manual or on the side of the saw? If so, that's with the limiters in place. That 1/2 turn out was from the lean limit with the limiter, not from closed. Your saw will never run with 1/2 turn from closed. You should have started with both the H and L 1 turn out from closed.

Second, a chainsaw will never 4-stroke at idle. 4-stroking is never discussed when tuning the L. You ended up right with it 1/4 turn out from max RPM with it idling.

You used the saw all summer with it not 4-stroking even at 3 turns out? I can't believe it lasted anywhere near that long. ANY time you have an issue like that, don't use it! It will always end up where you are now.

You're going to have to get this thing back together and find your problem. Like so many others have already said, it sounds like a significant air leak. You also need to carefully go through the entire fuel system too.

No No No, It ran for a year after I originally tuned it. Now, I re tuned it to compensate for the punched out muffler and blew it up.

I did mis-understand the factory sticker I realize now. So, should i figure on rebuilding the carb too?

 

[blsnelling]

So, should i figure on rebuilding the carb too?

You need to go through everything. That doesn't necessarily mean it needs a kit. It might just be dirty.

 

[saxman]

Let me throw something out here to think about. I agree it sounds like a classic air leak, but he stated that it ran fine until he opened up the muffler, then it locked up. Is it possible that some debris from drilling out the muffler got into the cylinder when he started it? Just a thought, either way it needs to be torn down and checked out so this doesn't happen with a third cylinder.

steve

 

[jra1100]

Let me throw something out here to think about. I agree it sounds like a classic air leak, but he stated that it ran fine until he opened up the muffler, then it locked up. Is it possible that some debris from drilling out the muffler got into the cylinder when he started it? Just a thought, either way it needs to be torn down and checked out so this doesn't happen with a third cylinder.

steve

My thought exactly, however as anyone who follows my posts knows, I'm not much of a chainsaw mechanic. JR

 

[tex]

Not saying that debris didn't enter the cylinder, but I was extra carefull to clean and blow out all the shavings. I had the muffler removed for all the work also, with the port covered up with a rag.

 

[jra1100]

Not saying that debris didn't enter the cylinder, but I was extra carefull to clean and blow out all the shavings. I had the muffler removed for all the work also, with the port covered up with a rag.

That should have been enough. See I told ya I don't know much about saws. JR

 

[NORMZILLA44]

I'm with the others, air leak yep if you can't get a carb to respond or 4 stroke, red flag. Bummer but that's how we all learn. I agree to go through everything now, spare no time or expensense.

 

[Anthony_Va.]

Yea man youre way off on carb tuning. Don't worry, everybody has to start somewhere. You should really read some of these carb tuning threads on this forum. It don't take long to flame a saw if it's running too lean.