Poulan 2150 Build Thread

[Homer6679]

Attached is current version of the saw running against stock and the version described in post #9. Definitely a faster, stronger, smoother saw.

I will pull timing numbers tomorrow.

I touched up the transfers and made them flow better and take better advantage of raising the height. The change I made is shown in the picture attached.
Version 1 refers to the transfer shape in post #30 and version 2 refers to the current version.

I am working on sourcing some wood and I have another stock cylinder to run against the current cylinder when do get some good size wood to test on.

I am very curious as to what power could be made by lowering the squish. I also have 3 42cc cylinders and I will be testing to see what the power difference is between the 36cc vs 42cc.

Thank you to everyone who pitched in with advice and guidance.

 

[thompsoncustom]

Nice job on the transfers looks like you definitely increased flow there.

Another option for you to reduce chamber volume would be to make your own pop up piston. A torch and some aluminum blazing rod works.

Any idea on what your final width numbers are on the intake and exhaust? if your running the 38mm cylinder than you should be aiming for a port width of 25mm give or take if I remember right u might not be able to go to far past 65% as the port itself is not big enough.

Since your really getting into this figured I show ya a couple things. As you keep pushing the cylinder farther the restriction is going to become your carb as they are very small. Here is a Farmertec hd-12 fit on a poulan 42mm (wildthing)



Had to drill the cylinder for a brass barb to run a impulse line, grind the plastic intake for clearance, bend the throttle linkage and choke lever, drill the tank hole for bigger fuel line but it's not that bad of job. All done everything fits under the cover with the stock air filter on.

On this cylinder I brazed the combustion chamber but I wouldn't do it that way again as it caused the cylinder to warp and it still runs great but I ended up a lot lower compression than I was aiming for, think it's 180psi now.



I would probably braze a pop up on the piston by putting some aluminum tape on the sides of the piston and putting it upside down in the cylinder, Don't want it tight but just snug enough that it can't warp from the heat or if it does it cools back to it's original shape. Not the same as lowering the squish but will get your compression way up there. you'll have to hand grind the pop up shape or you can melt aluminum brazing rod and pour it into the combustion chamber to get the prefect shape and than heat the piston untill its hot enough for the brazing material to melt and put it on there but you'll still have to grind a spot for the spark plug.

Also really like you side by side video editing nice job there.

 

[Homer6679]

Nice job on the transfers looks like you definitely increased flow there.

Another option for you to reduce chamber volume would be to make your own pop up piston. A torch and some aluminum blazing rod works.

Any idea on what your final width numbers are on the intake and exhaust? if your running the 38mm cylinder than you should be aiming for a port width of 25mm give or take if I remember right u might not be able to go to far past 65% as the port itself is not big enough.

Since your really getting into this figured I show ya a couple things. As you keep pushing the cylinder farther the restriction is going to become your carb as they are very small. Here is a Farmertec hd-12 fit on a poulan 42mm (wildthing)

View attachment 1102796

Had to drill the cylinder for a brass barb to run a impulse line, grind the plastic intake for clearance, bend the throttle linkage and choke lever, drill the tank hole for bigger fuel line but it's not that bad of job. All done everything fits under the cover with the stock air filter on.

On this cylinder I brazed the combustion chamber but I wouldn't do it that way again as it caused the cylinder to warp and it still runs great but I ended up a lot lower compression than I was aiming for, think it's 180psi now.

View attachment 1102797

I would probably braze a pop up on the piston by putting some aluminum tape on the sides of the piston and putting it upside down in the cylinder, Don't want it tight but just snug enough that it can't warp from the heat or if it does it cools back to it's original shape. Not the same as lowering the squish but will get your compression way up there. you'll have to hand grind the pop up shape or you can melt aluminum brazing rod and pour it into the combustion chamber to get the prefect shape and than heat the piston untill its hot enough for the brazing material to melt and put it on there but you'll still have to grind a spot for the spark plug.

Also really like you side by side video editing nice job there.

The improved transfer shape definitely improved the saw. It felt more torquey in my opinion. I will pull measurements and timing numbers later today after work.

It didn’t even cross my mind to braze on a pop up. I have some rods and some scored up pistons to practice on so that will be my next objective. I’m not sure if there is a formula or something to estimate projected compression gains. For instance “x” amount of pop up equals “x” amount of compression gain, so I’m just going to go for it. If anybody has any advice or guidance that would be appreciated.

I do like changing out the carb to a bigger one, I saw that when you first posted but didn’t pay it much thought because I wasn’t at that point yet. I have a few questions regarding this:

How do saws become lazy when the intake is lowered to much?

Isn’t velocity increased dramatically when the charge is forced through the transfers regardless of how much charge is in the bottom end?

How does the carb increase performance? Obviously I know it can pull more air/fuel charge in at once vs the original carb but isn’t that limited to the area in the lower crankcase? You can only pack in so much charge in “x” amount of space/volume.

Does velocity equal atomization? And does atomization equal more power?

 

[NSEric]

If you're making a pop up piston make it too tall then grind it down until you have .020tho of squish. I doubt you can add too much compression with a pop up so dont worry about that. It's also easy to grind some of it off if it's too much.

If you lower the intake too much the idle is finicky to tune and the saw is slow to pick up revs from idle. Once revved up a bit they run good tho.

Once you get everything else maxxed out the carb is the bottle neck in air flow so adding a bigger carb can make more rpm and power.

With the chinese 52/58cc saws I built adding a bigger carb gets me more rpm in small wood but doesnt help much when the bar is buried.

 

[thompsoncustom]

The improved transfer shape definitely improved the saw. It felt more torquey in my opinion. I will pull measurements and timing numbers later today after work.

It didn’t even cross my mind to braze on a pop up. I have some rods and some scored up pistons to practice on so that will be my next objective. I’m not sure if there is a formula or something to estimate projected compression gains. For instance “x” amount of pop up equals “x” amount of compression gain, so I’m just going to go for it. If anybody has any advice or guidance that would be appreciated.

I do like changing out the carb to a bigger one, I saw that when you first posted but didn’t pay it much thought because I wasn’t at that point yet. I have a few questions regarding this:

How do saws become lazy when the intake is lowered to much?

Isn’t velocity increased dramatically when the charge is forced through the transfers regardless of how much charge is in the bottom end?

How does the carb increase performance? Obviously I know it can pull more air/fuel charge in at once vs the original carb but isn’t that limited to the area in the lower crankcase? You can only pack in so much charge in “x” amount of space/volume.

Does velocity equal atomization? And does atomization equal more power?

There is formula's and calculators online but I would just try to make it as high as you possibly can and if it ends up to high like north of 260psi than you could grind some off of it but I don't think that's gonna be a problem.

The saws can become lazy from to low of case compression which is the time from when the piston passes the floor on the intake till when the transfers open. So if your intake timing is 70 and your transfers open at 120 you have 50 degrees case compression. You want as much flow as you can get on the intake port but you also want as much case compression as possible which can make them work against eachother so it's a balancing act. If you lower the floor to much you will start to get a ton of spitback through the carb and with to little case compression the duration of force in which the air is coming out of transfers is lower and makes it lazy.

Bigger carb performance isn't as much from more fuel as more airflow. Say you open up your exhaust and intake and can move a max of 100CFM now it doen't do you any good if the max CFM through the tiny carb is only 50CMF.

 

[thompsoncustom]

Here's a pic of one done for a ms250 believe it was around 230psi like this.

 

[Homer6679]

Sorry for the delay. Been crazy busy here as of late.

Posted is the current numbers and a video of stock and current version cutting the new wood I sourced.

Current version is 7 seconds faster than stock.

Next objective is making a pop-up piston.

 

[Homer6679]

Pics of the 3/4 wrap handle that I made and the pop up piston. The pop up depth is .1" and raised compression from 140psi to 155psi. To me it seems like it should've been raised higher than that because I had to ground down the pop up to make room for the spark plug. I can't confirm any of the clearances however. Regardless, the saw feels more torquey in the cut. I'm going to be leaving this saw as is and move to other projects.

The video is stock vs. current pop version. All the work has resulted in an increase in cutting speed of around 40%. Overall, I'm pretty happy with how it turned out.

 

[thompsoncustom]

Good job, Ya surprising the compression wasn't higher but oh well definitely better than the stock saw.

You hold the throttle wide open when you checked the compression? I always pull my saw over with the choke on till I know it would pop if I had the ignition on and stop there and turn the choke off and turn it to normally running position and zip tie the throttle wide open and pull it a couple more times than hook up the compression gauge and start pulling. Seems to give accurate readings.

Cylinder wall or ring show any real wear? Might not hurt to throw a caber ring in it and use a red scotch bright on the cylinder. Something else you could try is porting the piston ring. That's where you add holes to the top or the sides of the piston to force pressure behind to ring to push it harder on the cylinder wall for a better seal. Something I haven't tired yet but plan to when I get around to working on my other wild thing.

 

[Homer6679]

So disaster struck and my pop piston blew up clearing some storm damage. Good learning experience to make sure whatever you braze on your piston better be fully joined/mated with the piston. So anyways I just swapped the 42cc cylinder that I had over to the saw. My 36cc build out performed the stock 42cc and 42cc with my muff mod. I did some port work on the 42cc and it now outperforms my former 36cc build. I Widened the exhaust about 70% of the bore and the intake half that. Not sure of the actual measurement in inches. Kept the same exhaust as well. I left the exhaust roof and intake floor alone. I also did a very risky technique of lowering the squish.

I put the cylinder in my vice and sanded the cylinder with my Dremel tool. I marked the depth to grind/sand beforehand with a sharpie roughly .020" and the only tool I had to check flatness was a speed square. I put extra gasket maker down and waited a fell day before trying to pull it over. Compression went from 120 to 155 and the piston is rough shape so it could be higher with a new piston and rings. Runs way better than before. Stock squish was around .04-.043". My digital caliper died and when I get a new battery I'll report with what my new squish is.

I was looking into swapping a larger carb on the saw and I know that an HD-12 will work as mentioned in this thread. I got to looking in my shop and found a Zama C1M that bolts right on with some minor adjustments to the plastics and bending the throttle rod.

The venturi is larger in diameter do the mean it is a bigger carb?
Or does venturi size not directly correlate with fuel flow?

 

[thompsoncustom]

So disaster struck and my pop piston blew up clearing some storm damage. Good learning experience to make sure whatever you braze on your piston better be fully joined/mated with the piston. So anyways I just swapped the 42cc cylinder that I had over to the saw. My 36cc build out performed the stock 42cc and 42cc with my muff mod. I did some port work on the 42cc and it now outperforms my former 36cc build. I Widened the exhaust about 70% of the bore and the intake half that. Not sure of the actual measurement in inches. Kept the same exhaust as well. I left the exhaust roof and intake floor alone. I also did a very risky technique of lowering the squish.

I put the cylinder in my vice and sanded the cylinder with my Dremel tool. I marked the depth to grind/sand beforehand with a sharpie roughly .020" and the only tool I had to check flatness was a speed square. I put extra gasket maker down and waited a fell day before trying to pull it over. Compression went from 120 to 155 and the piston is rough shape so it could be higher with a new piston and rings. Runs way better than before. Stock squish was around .04-.043". My digital caliper died and when I get a new battery I'll report with what my new squish is.

I was looking into swapping a larger carb on the saw and I know that an HD-12 will work as mentioned in this thread. I got to looking in my shop and found a Zama C1M that bolts right on with some minor adjustments to the plastics and bending the throttle rod.

The venturi is larger in diameter do the mean it is a bigger carb?
Or does venturi size not directly correlate with fuel flow?

Nice update to bad the pop up didn't work out. I've seen people sand the bearing pockets before tho nothing I have ever tired but the poulan is the perfect saw to test things like that on.

Now that you have figured out how to lower the cylinder you can keep going untill the piston hits and than sand the band to get squish back. Same thing porters do but with a lathe tho sanding also takes a lot more time. I think my 026 had .050 taken out of the band and around that off the base that saw was sitting at 230psi last I checked. Stock saws run around 150psi so new rings could be helpful and a very light deglazing on the cylinder be hand.

You are right the carb should flow more fuel if the venturi is bigger but you could also measure the jet size. I find the venturi(air) to be the problem when really turning up a saw as you can always drill out the high speed jet.