Poulan 2150 Build Thread

[Homer6679]

I'm using a 2150 as the first saw that I modify and port to start learning the craft. I chose this saw because a have a few cylinders on hand. That way if I screw something up, I can just try again at really no loss. I will be updating this thread with pictures and video in steps as noted below.

- Stock
- Muff Mod
- Muff Mod + Exhaust porting (Not changing timing numbers)
- Muff Mod + Exhaust porting (Not changing timing numbers) + Intake "Roughing"
- Muff Mod + Exhaust Porting + Intake "Roughing"

I plan to have the forementioned be my workflow so that I can Isolate variables at least a little bit to see what does what to the saw.

I am new to this and welcome any advice or feedback.

 

[Homer6679]

Here is the stock saw running, attached is a video. Not much to see, just here for comparison to later iterations. I will make 2 cuts for every iteration.

 

[Homer6679]

Here are some pictures of the muff mod that I did as well as a video of how it changed the saw.

 

[thompsoncustom]

any idea where your timing numbers are or how far you want to mod this saw?

I assume that saw is gonna be close to my poulan wild thing that I modified and it turned up really well. here's a video to give u an idea of what you can get out of them.

 

[Homer6679]

These are the timing numbers I pulled off the stock saw. I would like to go as far as I can with the tools that I have with the saw.

Here are the mods that I know of
- mufflers
- exhaust porting/timing
- intake porting/timing
- ignition timing
- squish
If I am missing any please let me know and I’ll add them to my list

This is a learning experience for me so the more I do the better. I have lots of spare parts so I’m not worried about messing something up the first time.

I would like to play with Changing the squish, however I don’t have a lathe. If you have a different method of playing with squish let me know.

 

[thompsoncustom]

well a exhaust around 105 would be much better for a small saw like this but she will be a high rpm one for sure. also your blow down is pretty long I would aim more for between 15 and 20 degrees. you can raise your transfers with a cut off wheel, not ideal but it works if your careful.

if you widen your ports to around 70% of the bore your limiting factor is going to be the intake/carb. I fit a hd12 on my poulan with some work but doable will normal tools.

you can fill in the chamber in the head to raise compression too instead of lowering the cylinder. I brazed the chamber in mine to up compression but there is a risk of warping the cylinder so if that's something u want to try do it before you spend the time porting.

 

[Homer6679]

I did some porting yesterday, before and after pics are attached. The goal was to open up the exhaust without touching the timing. I definitely touched the cylinder walls a couple times, but I thought it cleaned up nice for my first port job ever. I did notice the port shape is a hair different. But it timed out the same as before so whatever I touched with my bit must have been marginal after I did a quick chamfer of the port to clean up what I did touch, or my timing wheel was off. Either could be true. I did some cutting with the saw today and it seems to be more sluggish than the previous iteration. It is now similar to the stock performance. I believe my previous muff mod doesn't flow as much as it needs to accommodate the extra exhaust flow resulting from the porting. I will be doing some more testing/tuning and cutting with it tomorrow.

Any feedback good or bad on the port work would be appreciated as well.

 

[thompsoncustom]

I did some porting yesterday, before and after pics are attached. The goal was to open up the exhaust without touching the timing. I definitely touched the cylinder walls a couple times, but I thought it cleaned up nice for my first port job ever. I did notice the port shape is a hair different. But it timed out the same as before so whatever I touched with my bit must have been marginal after I did a quick chamfer of the port to clean up what I did touch, or my timing wheel was off. Either could be true. I did some cutting with the saw today and it seems to be more sluggish than the previous iteration. It is now similar to the stock performance. I believe my previous muff mod doesn't flow as much as it needs to accommodate the extra exhaust flow resulting from the porting. I will be doing some more testing/tuning and cutting with it tomorrow.

Any feedback good or bad on the port work would be appreciated as well.

if I had to guess why it runs worse it looks like you touched the top of the exhaust port.

With that saw there is no need to touch the top or bottom of the port at the cylinder wall side just widen the port.

great news these cylinders are dirt cheap and the last china one I ordered had prefect timing numbers, well I still lowered the intake a little but pretty close to prefect.

 

[Homer6679]

Played with tuning and different exhaust configurations. First I tried to open up the back exits a little more, then I ran it with no baffle in the muffler. Both didn't do much. They performed the same as previous mentioned in post #7. My next configuration is what is pictured. My theory is that with the porting I did the first muff mod couldn't support the increase in airflow. Therefore causing a restriction/limitation. To resolve this, I cut a 7/8" x 1 1/4" in the side of the muffler and built a shield to direct the exhaust outwards. The change made a noticeable difference when I was cutting, my first cut in the video attached doesn't do justice, the second cut however shows how much of a difference it made. I included "no timing change" in the title because of the reasons described in post #7

Compression is still at 150-155PSI and my top RPM is now 13k

Tomorrow I will "Rough" the intake and see what that does.

 

[thompsoncustom]

muffler looks good.

how are you measuring your exhaust opening timing?

from the two pictures in post #7 it's obvious timing was changed.

also what kind of wood are you cutting and what diameter? bigger wood would show small changes better but to late to change now.

 

[Homer6679]

I am measuring timing using the method the Tinman Saws shows in his "how to port" series. The way I am doing it is once I see light from my flashlight coming from the spark plug hole that is where I pull my timing number.

I'm still learning so there is a chance my timing numbers were incorrect. I will pull new ones tomorrow. I do agree that timing was changed just based on the port shape, however I'm not sure how much they have changed.

The wood is dry maple, I think it is around 10" in diameter. I am running out of wood and will have to source some more or get some 4x4's

 

[Homer6679]

I just timed a stock jug with the one I have ported. The numbers are attached in the picture. I triple checked these and they are accurate.

I will be roughing the intake today have a video up tonight hopefully

I’m going to opt for 9 4x4’s in a 3x3 square and use that for testing. It will be much more controlled and easier to compare. I will take a video of stock and latest iteration with the 4x4’s so that I have something to compare to.

 

[thompsoncustom]

those numbers look better than the first set listed.

if you fell comfortable raising your transfer to 120 will be ideal. that style isn't hard to do with a normal dremel and a mix of grinding bits.

I ended up at 76 on my intake after lowering the floor.

compression makes a big difference. if I had to do it again I would make a removable dome for the cylinder and try to get the compression about 200psi.

 

[Homer6679]

By raising the transfer what will that do in terms of performance?

What do you mean by removable dome?

 

[thompsoncustom]

By raising the transfer what will that do in terms of performance?

What do you mean by removable dome?

so by raising the transfer your going to start pushing exhaust out earlier and getting fresh air in sooner which ends up being more burnable mix in the cylinder. You can go to early and start back stuffing the transfer but in your case 15 degrees blow down is where you want to be.

The removable dome might not be something you want to try on you first go around but it is a way to up compression without a lathe or mill. It was used in motocross engines and basically its a chamber that goes inside your current one and shrinks the size down.


you will have to cast one your self but it's not terribly hard and doesn't require to much for special tools but you will need a tap and die set for sure. if it's something your considering PM and I'll help you.

 

[NSEric]

I am measuring timing using the method the Tinman Saws shows in his "how to port" series. The way I am doing it is once I see light from my flashlight coming from the spark plug hole that is where I pull my timing number.

I'm still learning so there is a chance my timing numbers were incorrect. I will pull new ones tomorrow. I do agree that timing was changed just based on the port shape, however I'm not sure how much they have changed.

The wood is dry maple, I think it is around 10" in diameter. I am running out of wood and will have to source some more or get some 4x4's

I watch the tinmans vids too, he's a nice guy but cant build a fast saw. He runs high exhaust and long blow down in everything, it's good for limbing as they rev high but they cut like stock dogged into big wood.
Getting the blowdown as short as possible without going too short is the key to having a strong saw. Keep the intake under 80 degrees or they get lazy and on a 50cc saw try to stay around 105 on the exhaust.

If I was porting that saw, I'd lower the intake to 78-79 degrees, raise the transfers to 118-120 and make the intake/exhaust wider. I dont know what the lower transfer look like, I only grind them a little on most saws, adding volume is bad if it's not adding a bunch of air flow, having big hogged out lower transfers will make the saw lazy.

 

[Homer6679]

Stock Saw with new wood for future comparisons.

 

[Homer6679]

Same setup as post #9

 

[Homer6679]

This next iteration all I did was rough up the intake a little bit. I saw a video on YouTube of a guy that did one of these saws and he roughed his intake. Not sure if I roughed it enough, it didn't seem to do much.

I'll be moving on to widening the ports, lowering the intake, and raising the transfers. Any opinions and what I should do first? I would like to do it steps so that I can see what each mod does to the saw like I have been doing.

I watch the tinmans vids too, he's a nice guy but cant build a fast saw. He runs high exhaust and long blow down in everything, it's good for limbing as they rev high but they cut like stock dogged into big wood.
Getting the blowdown as short as possible without going too short is the key to having a strong saw. Keep the intake under 80 degrees or they get lazy and on a 50cc saw try to stay around 105 on the exhaust.

If I was porting that saw, I'd lower the intake to 78-79 degrees, raise the transfers to 118-120 and make the intake/exhaust wider. I dont know what the lower transfer look like, I only grind them a little on most saws, adding volume is bad if it's not adding a bunch of air flow, having big hogged out lower transfers will make the saw lazy.

Tinman's videos are definitely a good place to start for any beginner, he does say that it his method and there are lots of way to achieve the same result. No complaints with his videos.

This saw is only 36cc, not sure if that changes any of the numbers you posted. The saw has open transfers.

Why is blowdown important? Does the fresh charge from the intake coming in sooner help push out the exhaust and therefore make a more efficient saw?
Not sure if my thinking on that is correct.

"adding volume is bad if it's not adding a bunch of air flow, having big hogged out lower transfers will make the saw lazy."
Could you explain this?

so by raising the transfer your going to start pushing exhaust out earlier and getting fresh air in sooner which ends up being more burnable mix in the cylinder. You can go to early and start back stuffing the transfer but in your case 15 degrees blow down is where you want to be.

The removable dome might not be something you want to try on you first go around but it is a way to up compression without a lathe or mill. It was used in motocross engines and basically its a chamber that goes inside your current one and shrinks the size down.


you will have to cast one your self but it's not terribly hard and doesn't require to much for special tools but you will need a tap and die set for sure. if it's something your considering PM and I'll help you.

Why is blowdown important? I'll pose the same question to you as I asked NSEric above.

I probably won't do the removable dome on this build but I'll eventually PM you about it.

 

[Homer6679]

I forgot to attach these to the last post