Strange "Tuning" Issue Solved

[Chris-PA]

Recently I've been having running issues with my ported Poulan 2775, which had been one of my favorite saws and one I like to use for falling smaller stuff. It was almost like reverse 4-stroking, where I could tune it so it was clean at high no load rpm, and it would misfire and sound like it was running rich as it loaded up and the rpm dropped. Then lifting in the cut would clean up.

I swapped carbs and changed fuel lines, and checked the carb mount and intake boot. None of that made any difference. I was about to make a thread here to ask for advice, but then during dinner I remembered I had an old ignition module from a PP315 and decided to swap that in. It turned out to be the same part number, so I popped it in - and that was it!

The carb I put in is a WT-657 that I had blueprinted - removed the main nozzle, cleaned up all the casting flash and ground off the screw shafts. It has an accelerator pump too, which I like.

So now it runs like it used to. It's not a real high rpm screamer, which I always found strange given the porting. It probably needs more transfer duration, but I like how it runs now so I'm leaving it alone.

This is a tulip I dropped the other day, not too hard but large enough to give it a load. The chain is not narrow kerf, but a loop of Oregon 33SL I ground all the shark fins off:

 

[milkman]

I see why it's one of your favorites.

 

[Big_Wood]

Chris, i reported your post for inaccuracy. firewood CAN'T be cut with a poulan. it requires some of the higher end models from husky or stihl and even they need to be ported to do it.

 

[Chris-PA]

Chris, i reported your post for inaccuracy. firewood CAN'T be cut with a poulan. it requires some of the higher end models from husky or stihl and even they need to be ported to do it.

Well, I do have this Chinese clone.....

 

[Chris-PA]

So I wondered if the porting or the barn and chain was keeping the saw from running a higher rpm in the cut. So I swapped out the sprocket for a 3/8-6 lo pro, and put on a 16" bar and a loop or Carlton N1. The saw is light enough to run this as a limbing saw, and has great throttle response, but I will be putting the longer bar back on it as I like it for felling. Anyway, it mostly ran 10,000 to 10,800rpm, except for the 3rd cut where I dogged it in and bogged it. I ran it with a little more fuel on the H after I took the video and it had more power at lower rpm that way. So it's still not a screamer, but it definitely runs more rpm with lo pro, as you would expect.

 

[Chris-PA]

So I thought that I had fixed this problem, but it came back. I've been trying to diagnose it for quite a while now. The basic strange characteristic was that you could tune it to just barely 4-stroke at WOT no load, but as you loaded it further it would begin to break up. This is just the opposite of how these carbs normally work. It was not a fuel restriction as I could easily open it up to pig rich at WOT no load. Also, the saw got very hard to start, especially when hot - but it was not vapor locking.

While going over it I noticed that there was more radial play in the crank (both sides) than I liked, so it came apart. The bearings were fine, but I noticed that the thread forming screws that hold the engine together had drawn up a ridge around the holes, and this was holding the clamshell cap off of the cylinder casting. A few swipes with a flat file took them down:


That solved that problem - but it made no difference in how the saw ran. So the saw got a new carb, new fuel lines and a new coil, which also made no difference. Then the carb got bored out to 14.5mm in an attempt to reduce the fuel signal at lower air flows, but this also didn't help much.

Then today I think I finally figured it out. Usually when tightening a coil I let the magnets hold the coil against the flywheel and card spacer. While swapping the coil yet again, I noticed that as I tightened this one it was pulling away from the flywheel I had to use a screwdriver to pry it against the flywheel while tightening. And wouldn't you know it, the thing fired right up like it used to! I didn't have time to go back to the woods to try it tonight, but it seems like it's working right now.

While it was apart it got another mod. The rubber gasket that seals the carb partition always comes off. I've tried JB Weld, which worked for a while, but it came off too. So instead I make a spacer to press it against the partition out of perforated aluminum:

 

[Toyboy]

Interesting, my neighbor just picked up a non runner for $10. No spark so a new coil is on the way. Hope it does the trick. It came with a 20" bar which seems too much to me.

 

[Kostas]

So I thought that I had fixed this problem, but it came back. I've been trying to diagnose it for quite a while now. The basic strange characteristic was that you could tune it to just barely 4-stroke at WOT no load, but as you loaded it further it would begin to break up. This is just the opposite of how these carbs normally work. It was not a fuel restriction as I could easily open it up to pig rich at WOT no load. Also, the saw got very hard to start, especially when hot - but it was not vapor locking.

While going over it I noticed that there was more radial play in the crank (both sides) than I liked, so it came apart. The bearings were fine, but I noticed that the thread forming screws that hold the engine together had drawn up a ridge around the holes, and this was holding the clamshell cap off of the cylinder casting. A few swipes with a flat file took them down:
View attachment 525341

That solved that problem - but it made no difference in how the saw ran. So the saw got a new carb, new fuel lines and a new coil, which also made no difference. Then the carb got bored out to 14.5mm in an attempt to reduce the fuel signal at lower air flows, but this also didn't help much.

Then today I think I finally figured it out. Usually when tightening a coil I let the magnets hold the coil against the flywheel and card spacer. While swapping the coil yet again, I noticed that as I tightened this one it was pulling away from the flywheel I had to use a screwdriver to pry it against the flywheel while tightening. And wouldn't you know it, the thing fired right up like it used to! I didn't have time to go back to the woods to try it tonight, but it seems like it's working right now.

While it was apart it got another mod. The rubber gasket that seals the carb partition always comes off. I've tried JB Weld, which worked for a while, but it came off too. So instead I make a spacer to press it against the partition out of perforated aluminum:
View attachment 525342
View attachment 525343

I have the same saw but with piston and cylinder from a 4620(chrome plated cyl).The key from the original flywheel was shattered and i bought a flywheel from a Husqvarna 136(i think).The 136 flywheel must have more ignition advance than the stock Poulan flywheel,it made a huge difference on how the saw runs,it screams.Anyway,when i first got the saw,i assembled it by changing almost everything.P/C,carb,seals-bearings,lines,filters etc.After 3 years,p/c looks like new but it is time for a new carb kit(needle started leaking).These is the biggest problem with these saws,they won't hold the tune for long enough.My saw needs tunning from time to time,i wouldn't go anywhere without the splined tool.Let's say that a friend of mine bought 5 years ago a new MS211.Tha saw runs always the same since the first day,he didn't touch it once.I have only replaced the plug,air and fuel filter for him and thats it.

 

[Chris-PA]

I have the same saw but with piston and cylinder from a 4620(chrome plated cyl).The key from the original flywheel was shattered and i bought a flywheel from a Husqvarna 136(i think).The 136 flywheel must have more ignition advance than the stock Poulan flywheel,it made a huge difference on how the saw runs,it screams.Anyway,when i first got the saw,i assembled it by changing almost everything.P/C,carb,seals-bearings,lines,filters etc.After 3 years,p/c looks like new but it is time for a new carb kit(needle started leaking).These is the biggest problem with these saws,they won't hold the tune for long enough.My saw needs tunning from time to time,i wouldn't go anywhere without the splined tool.Let's say that a friend of mine bought 5 years ago a new MS211.Tha saw runs always the same since the first day,he didn't touch it once.I have only replaced the plug,air and fuel filter for him and thats it.

The cylinder on mine is plated too. The biggest problem with these saws is the vibration from the engine. My guess is that when they enlarged it to 46cc the counterweights were not large enough for the increased mass of the piston. The A/V masks it (and is in turn weak), but the vibrations rip the saw apart, especially with the poor choice of fasteners and lack of locking hardware.

The tuning on mine was always pretty consistent which is why this recent change was noticeable. However, one requirement with these saws is to add some sort of damper/support under the air filter mount, which was not provided on the early saws. The later ones had a rubber blister that sat under the filter mount, but they deteriorate and they are not attached so they are easily lost if the carb is ever removed. Without it the carb will resonate like mad at various rpms, which is detrimental to maintaining mixture control. The similar Husqvarna 136/137/141/142 has a metal mounting bracket at the front edge of the carb.

The other problem that can effect tuning is the stupid intake boot & plate design. The rubber boot deforms at the end where the impulse channel is formed, and the plate has slots that are not needed. The impulse can become connected to the intake.





Mine has been redesigned:

 

[Kostas]

The cylinder on mine is plated too. The biggest problem with these saws is the vibration from the engine. My guess is that when they enlarged it to 46cc the counterweights were not large enough for the increased mass of the piston. The A/V masks it (and is in turn weak), but the vibrations rip the saw apart, especially with the poor choice of fasteners and lack of locking hardware.

The tuning on mine was always pretty consistent which is why this recent change was noticeable. However, one requirement with these saws is to add some sort of damper/support under the air filter mount, which was not provided on the early saws. The later ones had a rubber blister that sat under the filter mount, but they deteriorate and they are not attached so they are easily lost if the carb is ever removed. Without it the carb will resonate like mad at various rpms, which is detrimental to maintaining mixture control. The similar Husqvarna 136/137/141/142 has a metal mounting bracket at the front edge of the carb.

The other problem that can effect tuning is the stupid intake boot & plate design. The rubber boot deforms at the end where the impulse channel is formed, and the plate has slots that are not needed. The impulse can become connected to the intake.

View attachment 525503

View attachment 525504

Mine has been redesigned:
View attachment 525501
View attachment 525502

Well,mine is type 4(i think the later of all) and have the rubber blister under the air filter adapter.It also have the metal plate for the carb without the 4 slots,it has only 2 holes(one up and one down).As for the carb adapter,you can buy the adapter,the impulse nipple and the intake boot from the 136 which are way better design(they all cost under 10$).As for the vibrations,i find my saw really good on this and 3 years now i didn't have a single bolt come lose.Anyway,all these issues are easy to fix(adapter from the 136,bigger and longer bolts etc),what i don't really like on this saw and it was what killed the saw at first time is the air filter-air filter adapter.It lets way to much saw dust enter the engine.I am very curious to see how is your saw on this matter and what did you to improve it there(if you did anything).

 

[Chris-PA]

Well,mine is type 4(i think the later of all) and have the rubber blister under the air filter adapter.It also have the metal plate for the carb without the 4 slots,it has only 2 holes(one up and one down).As for the carb adapter,you can buy the adapter,the impulse nipple and the intake boot from the 136 which are way better design(they all cost under 10$).As for the vibrations,i find my saw really good on this and 3 years now i didn't have a single bolt come lose.Anyway,all these issues are easy to fix(adapter from the 136,bigger and longer bolts etc),what i don't really like on this saw and it was what killed the saw at first time is the air filter-air filter adapter.It lets way to much saw dust enter the engine.I am very curious to see how is your saw on this matter and what did you to improve it there(if you did anything).

My Type1 2775 did not have the "Turbo Clean" scoop, and while trying to retrofit it I found there were considerable differences between the 36 & 40cc engines and the 46cc. The 36 & 40cc engines don't have this brass impulse nipple:


Rather there is just a hole. The carb mount has a projecting tapered tube rather than the extra molded hole and passage in the rubber boot:

Also I believe the casting around the intake port is smaller, but I could be remembering that wrong. I found that the partition/carb mount from a 2900 had the Turbo Clean setup and fit the 46cc engines, which is what is on mine now.

I've had zero issues with the air filter sealing - it stays very clean in there. The filters tend to clog up easily, but nothing gets past it. I wonder what the difference is?

 

[Chris-PA]

I got to run it for a little while after work today. I had to change the tuning considerably now that the spark is correct, and it ran like it should. Started properly too. The bored out carb is new, and it seems to work well.

I only had some ash to noodle for now. This is Oregon 33S 0.325" chain. It's sharp but the cutters are low and it's probably not the best noodling chain. The saw is mostly running around 10krpm, which is not bad for a 46cc saw.

Another ash fell the other day and I hope to get to that one soon, so there should be some appropriate wood to buck with this saw.

 

[birdcolonel]

Thanks, Chris.
What audio spectrum software is that? I like the layout.

 

[Chris-PA]

Thanks, Chris.
What audio spectrum software is that? I like the layout.

It's Audacity. I run it under Linux but I did get the windows version running on a machine to try out. I detailed it here: http://www.arboristsite.com/community/threads/measuring-rpm-from-video.281228/

It has created some controversy here among those who don't realize it's a standard technique used in many areas.

 

[Jeff Lary]

She runs very well Chris,.. but your saws always seem to.

 

[birdcolonel]

It has created some controversy here.

Huh?
Controversy? You mean on this site??


I'll get a copy and try it!

 

[HuskStihl]

I've said similar things before, but I'm pretty sure Chris could have figured out cold fusion in the time he's spent on these clamshells.

 

[Chris-PA]

I've said similar things before, but I'm pretty sure Chris could have figured out cold fusion in the time he's spent on these clamshells.

So they thought they produced fusion in the bubbles of a cold liquid did they? Musta been a good night....

 

[birdcolonel]

I've gotten "that look" many times and then the question, "what the %^**$## are you doing that for?"

Needless to say, I do a lot a things just to see what will happen. Life's a learning experience.

 

[bmwpowere36m3]

I remember, as a young buck, the first time I was on the road with my boss in PA... he mentioned Yuengling. I said, "no I' never heard of that Chinese beer".... hahaha, little did I know. Also a fan of Victory Brewing!