Interesting thread Brad. Time consuming and full of frustration but when you discover the failing component we'll all be the wiser.
Problematic MS661
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Interesting thread Brad. Time consuming and full of frustration but when you discover the failing component we'll all be the wiser.But it was not 4 carbs......probably closer to 14!!lol
Adirondackstihl
Flyz, Fuel & Fotos
You went through all that previous hassle and didn't vac/pressure test 
The lines of who owns what isn't 100% clear, as Stihl wasn't allowed to buy Zama outright do to monopoly laws.
This saw is going to be the death of me, lol.
I started off this evening by putting the modded parts all back on my saw. I vac and pressure tested it, both holding steady at 10 PSI.
Out to the wood pile I went. The bog came right back, although not as severe, but it was there. So, I swapped on the carb from the other saw. No improvement. I then swapped the coils. Again, no improvement. I then went to quite a bit of trouble to swap out the wiring harness. Again, no improvement! While doing the harness swap, I also removed and carefully inspected my impulse hose, fuel lines, and fuel filter. Everything looked great.
So that this point, I installed all of my parts on Edwad's saw along with all mods. This included my wiring harness, coil, carb, ported cylinder, modded muffler, and Maxflow filter.. HIS SAW RUNS PERFECT with ALL of my parts! What is up with this thing?
Again, I went back to vac and pressure test my saw. This time I removed the flywheel and oil pump and sprayed it down with Windex, looking for any hint of a bubble. Nothing! I even dropped it down to 15 PSI of vacuum, which it will hold indefinitely. I then noticed that the sides of my straight walled intake boot were collapsing in, significantly. I had watched during operation and hadn't seen them move. None the less, I didn't like what I saw. I decided to install the original intake boot with the two large rubber washer. No collapse now under the same 15 PSI of vacuum!
The only parts of mine that I have no swapped to his saw is my intake, impulse hose, and fuel lines. And BTW, his saw has the bellow style intake boot.
I'm out of time tonight, but I'm wondering if this straight walled boot is actually the problem.
Is it possible to have a crank seal leak ONLY when it's hot?
I started off this evening by putting the modded parts all back on my saw. I vac and pressure tested it, both holding steady at 10 PSI.
Out to the wood pile I went. The bog came right back, although not as severe, but it was there. So, I swapped on the carb from the other saw. No improvement. I then swapped the coils. Again, no improvement. I then went to quite a bit of trouble to swap out the wiring harness. Again, no improvement! While doing the harness swap, I also removed and carefully inspected my impulse hose, fuel lines, and fuel filter. Everything looked great.
So that this point, I installed all of my parts on Edwad's saw along with all mods. This included my wiring harness, coil, carb, ported cylinder, modded muffler, and Maxflow filter.. HIS SAW RUNS PERFECT with ALL of my parts! What is up with this thing?
Again, I went back to vac and pressure test my saw. This time I removed the flywheel and oil pump and sprayed it down with Windex, looking for any hint of a bubble. Nothing! I even dropped it down to 15 PSI of vacuum, which it will hold indefinitely. I then noticed that the sides of my straight walled intake boot were collapsing in, significantly. I had watched during operation and hadn't seen them move. None the less, I didn't like what I saw. I decided to install the original intake boot with the two large rubber washer. No collapse now under the same 15 PSI of vacuum!
The only parts of mine that I have no swapped to his saw is my intake, impulse hose, and fuel lines. And BTW, his saw has the bellow style intake boot.
I'm out of time tonight, but I'm wondering if this straight walled boot is actually the problem.
Is it possible to have a crank seal leak ONLY when it's hot?
LRains
ArboristSite Member
I would be suprised if the vac test didn't show a leak if it's cracked but stranger things have happened. If the boots integrity is failing maybe that's the case. I have watched from your posts the frustration and it's nice to see you getting it narrowed down.
Haven't seen it but I could see a seal only leaking when heat is involved. By chance did you turn the crank while you testing pressure and vac? I always give the crank a couple spins while under vacuum and pressure just to check. I have found some seals that passed vac test until I spun the crank
Yes, I spun the crank both while under vacuum and pressure. I'm very seriously temped to replace both seals just on principle.
Will your saw run properly with the parts you removed from his saw to install your parts? If it won't, then the offending component is still hiding somewhere on your chassis. Candidates could include seals. I don't know how the flywheel could cause the symptoms you are experiencing, but you have it off so it is another swap candidate. You have exonerated a lot of the parts from your saw already by running them on his saw, but it sounds to me like you haven't found the right one yet.
No, my saw will not run right in any configuration that I have tried.
The flywheel. Yes, I forgot the mention that earlier and did forget to swap it. I can't imagine that being it, but I'm certainly game to try about anything at this point.
I installed his coil, wiring harness, and coil on my saw with the ported cylinder and modded muffler. All electronic components, minus the flywheel have been swapped from one saw to the other. Since his saw runs perfectly with my modded cylinder and muffler, I'm ruling that out. His saw runs perfectly with any parts I've had one it. Mine has the bog with any parts I've put on it. I have not yet run it with the original intake boot. I currently have his stock topend and muffler on it. I didn't have time to run it like that. I'm likely not to run it again until I install new seals.
The flywheel. Yes, I forgot the mention that earlier and did forget to swap it. I can't imagine that being it, but I'm certainly game to try about anything at this point.
I installed his coil, wiring harness, and coil on my saw with the ported cylinder and modded muffler. All electronic components, minus the flywheel have been swapped from one saw to the other. Since his saw runs perfectly with my modded cylinder and muffler, I'm ruling that out. His saw runs perfectly with any parts I've had one it. Mine has the bog with any parts I've put on it. I have not yet run it with the original intake boot. I currently have his stock topend and muffler on it. I didn't have time to run it like that. I'm likely not to run it again until I install new seals.
jmssaws
Addicted to ArboristSite
My stihl engineer buddy has a building full of 661's that just can't be fixed now matter what u change. When a tech at a dealership can't fix it they send it to stihl and then him, he said world wide it's a big problem, one that stihl is scrambling to try and fix. He gets warranty saws from all over but it's amazing how many are in his shop, most with a bog or seized for no reason.
To me it sounded like a lean bog. Brad, it seems odd to me that many saws would have crank seals that leaked only when hot......besides that, thanks much to brad for his hard work put into diagnosing this elusive problem.
Another thought, how about the crankcase? casting flaw in the crank throw area causing puddling?
Another thought, how about the crankcase? casting flaw in the crank throw area causing puddling?
Mtthwvn
ArboristSite Operative
I have not yet run it with the original intake boot. [/QUOTE]
Have you tried running his intake boot on your saw? Your intake boot collapsing could be a problem. The throttle closing abruptly while coming out of the cut and the saw at WOT could be causing it to collapse
Have you tried running his intake boot on your saw? Your intake boot collapsing could be a problem. The throttle closing abruptly while coming out of the cut and the saw at WOT could be causing it to collapse
The 661 I had problem with had its problems when hot, maybe poor crankcase casting is causing small air leak in crankthrow area when the mag casing is hot
I wouldn't assume that stihl has crappy castings, but after seeing many NEW dolmars with holes in the crankcase casting, it makes me wonder
There has to be 'good reason' stihl changed its design and stopped using Brads style intake. Maybe the rubber washer style rings some found inside their intake were a 'tempery fix' to prevent collapsing of the intake under operation untill a new design was made and produced. Brad removed his Rubber Orings in intake?? Brad is no dill and is closing in on this issue but my guess is intake as well. l'm sure he would have got to the bottom of this without AS, but by sharing and taking time to document the issue will make us all a little wiser.
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