bigger carb for poulan wild thing?

[Ketchup]

Have you put a compression tester on it?

 

[thompsoncustom]

ya my gauge was coming in at 165psi. (also need to test my gauge)
Felt like it would be alot higher from filling in the chamber with aluminum.

also roughly measured the muffler openings. sitting somewhere between 125% and 150% of the exhaust port so it's good there.

 

[Powerstroke Cowboy]

I have been thinking about this build and I keep thinking about about the spark plug location. The picture you posted with the combustion chamber built up shows just how shrouded the spark plug is now. That in itself would hamper the ignition of the fuel/air mixture. That would affect rpms and overall power.

What if you taped the hole and put in a longer leed plug? That would get the plug down into the combustion chamber and get the spark where it needs to be.

Or you could tap the hole and then machine out the seat are of the plug deeper into the head and accomplish the same thing.

Two benefits of doing this would be.

A: Getting the spark into the combustion chamber for a more efficient and faster burn of the fuel/air mixture.

B: Raise the compression of the engine due to making the combustion area smaller.

I am sure there are more benefits as well.

 

[thompsoncustom]

I have been thinking about this build and I keep thinking about about the spark plug location. The picture you posted with the combustion chamber built up shows just how shrouded the spark plug is now. That in itself would hamper the ignition of the fuel/air mixture. That would affect rpms and overall power.

What if you taped the hole and put in a longer leed plug? That would get the plug down into the combustion chamber and get the spark where it needs to be.

Or you could tap the hole and then machine out the seat are of the plug deeper into the head and accomplish the same thing.

Two benefits of doing this would be.

A: Getting the spark into the combustion chamber for a more efficient and faster burn of the fuel/air mixture.

B: Raise the compression of the engine due to making the combustion area smaller.

I am sure there are more benefits as well.

Ya it's not an ideal shape but i'm not sure it would hamper the ignition at all. I was planning on maybe adding more aluminum in there and then reshaping the chamber as counter sinking it may help but 80 to 90% of the chamber has been filled in at this point so 90% of the air/fuel mix is being pushed to around the plug and i'm not sure anything is going to be gained there, I assume my gauge is just reading wrong at this point i need to test it with my brothers and see what it says. Since so much volume in the head has been removed it could be that the compression is keeping the rpms down at this point.

Can't really run much of a longer plug or i'll be smacking the piston unless I were to relief cut the piston.

here is a pictures of the plugs after 4 tanks and its not on the lean side at all which tells me it's either burning really clean or really hot around the plug, my guess is a little of both.

I do think your on to something tho and if you really wanted to put some work into it I think you could braze the original spark plug hole completely closed and redrill one in the center of the cylinder and then braze the head completely flat all the way across and redrill or counter sink the cylinder and the piston so in the end your spark plug ends up dead center in the combustion chamber you created 50% of it being in the head and 50% being on the piston side.

 

[Powerstroke Cowboy]

Ya it's not an ideal shape but i'm not sure it would hamper the ignition at all. I was planning on maybe adding more aluminum in there and then reshaping the chamber as counter sinking it may help but 80 to 90% of the chamber has been filled in at this point so 90% of the air/fuel mix is being pushed to around the plug and i'm not sure anything is going to be gained there, I assume my gauge is just reading wrong at this point i need to test it with my brothers and see what it says. Since so much volume in the head has been removed it could be that the compression is keeping the rpms down at this point.

Can't really run much of a longer plug or i'll be smacking the piston unless I were to relief cut the piston.

here is a pictures of the plugs after 4 tanks and its not on the lean side at all which tells me it's either burning really clean or really hot around the plug, my guess is a little of both.

I do think your on to something tho and if you really wanted to put some work into it I think you could braze the original spark plug hole completely closed and redrill one in the center of the cylinder and then braze the head completely flat all the way across and redrill or counter sink the cylinder and the piston so in the end your spark plug ends up dead center in the combustion chamber you created 50% of it being in the head and 50% being on the piston side.

It would be interesting to see how close the current plug is to the piston.

Another issue that could be with the plug being shrouded so much, and most of the charge being forced into that space for combustion, is, it can't put the force of the combustion over the greater part of the piston.

So if most of the air is contained in a smaller area it will not be able to travel outward as fast or efficiently to puts much pressure over the greater part of the piston. A lose of power and a slower reving/less responsive engine would be the result.

Let's say on combustion there is 300 psi (a number I just yanked out of thin air) in the cylinder. Now of most of the first bit stays in the shrouded area(the strait walls will keep it from expanding outward for a bit at the very minimum efficiently) and most plugs are 14mm. The area looks to be a little bigger so let's say it's .625 inches. Most of the pressure will be directed downward in that size. So, .625 and 300psi gives 187.5 pounds of force on the piston (obviously some of it will spread out on the rest of the piston.) But, with the plug un-shrouded and the combustion chamber shaped so the combustion can spread out and down efficiently you will see a lot more force on the piston. The bore is 41mm if you can generate the same 300 psi over the entire piston efficiently you would then have 480 pounds pushing down on the piston.


So I believe your plan of shaping the combustion chamber so the air/fuel mixture ignites and spreads outward efficiently is a great plan. If you could move the spark plug lower that would help as well. There's a reason the spark plug is sticking into the combustion chamber as far as it is.

Lots of rambling on my part. It's hard to put thoughts into words. I hope it makes sense. I apologize if it's nothing worth reading.

Regardless, it might just produce a good laugh from the smart engine guy's on this forum.

The air/fuel mixture needs to be able to light and travel out over the piston as fast and efficiently as possible. The shrouded spark plug will not let this happen. Fix that and I believe this saw will run differently.

 

[thompsoncustom]

It would be interesting to see how close the current plug is to the piston.

Another issue that could be with the plug being shrouded so much, and most of the charge being forced into that space for combustion, is, it can't put the force of the combustion over the greater part of the piston.

I can check and see how far it is from touching roughly.

Yes there is no way it is even and the PSI at the center of the piston is a lot higher because of the shape and I do worry about buring a hole in the center but I think your math is a little wrong or how your looking at it, you are using cylinder compression which really you would have to be able to measure the explosion pressure difference not compression. The compression is jamming it all into a tighter area which will increase the pressure released after the fuel it lit. 300PSI at TDC doesn't equal the same as soon as the explosion starts and the tigher the area the higher the PSI will be after the explosion. Tho 300psi over a larger area vs a smaller the larger would win out but we increase compression by shrinking the area and if you had 300psi over a larger area you would have to have more air/fuel to do so.

Lots of rambling on my part. It's hard to put thoughts into words. I hope it makes sense. I apologize if it's nothing worth reading.

Nah I really enjoy talking this stuff out and I think it helps everyone build better engines.

Have you put a compression tester on it?

I pulled the Schrader valve from my tester and it's a red banded one, need to find a white one somewhere and retest.
Also I raised my exhaust to 104 when I had it apart so i'll have to see if I pick up any rpms.

 

[Powerstroke Cowboy]

I can check and see how far it is from touching roughly.

Yes there is no way it is even and the PSI at the center of the piston is a lot higher because of the shape and I do worry about buring a hole in the center but I think your math is a little wrong or how your looking at it, you are using cylinder compression which really you would have to be able to measure the explosion pressure difference not compression. The compression is jamming it all into a tighter area which will increase the pressure released after the fuel it lit. 300PSI at TDC doesn't equal the same as soon as the explosion starts and the tigher the area the higher the PSI will be after the explosion. Tho 300psi over a larger area vs a smaller the larger would win out but we increase compression by shrinking the area and if you had 300psi over a larger area you would have to have more air/fuel to do so.


Nah I really enjoy talking this stuff out and I think it helps everyone build better engines.

I agree with you, the 300 psi I used is most likely not high enough. Hence stateing I just pulled it out of thin air for demonstration purposes. I will add this though, most gas engines see anywhere from 300 to 1000 psi at TDC during combustion. It can be more on higher modified engines. Obviously diesels will be high yet. Point being, the higher the pressure the more power you are losing, "if" the pressure is not placed evenly over the piston.

Thanks for bearing with my ramblings. I also like to thow thoughts out, just to see what others think about those thoughts.

That's one way I learn.

 

[thompsoncustom]

I agree with you, the 300 psi I used is most likely not high enough. Hence stateing I just pulled it out of thin air for demonstration purposes. I will add this though, most gas engines see anywhere from 300 to 1000 psi at TDC during combustion. It can be more on higher modified engines. Obviously diesels will be high yet. Point being, the higher the pressure the more power you are losing, "if" the pressure is not placed evenly over the piston.

Thanks for bearing with my ramblings. I also like to thow thoughts out, just to see what others think about those thoughts.

That's one way I learn.

Are you losing it tho? That's really the question I guess. If the same amount of fuel is jammed into a smaller space at a higher compression the fuel should burn more completely and the total BTU output should be higher. Also the downward force in PSI will be alot higher because the area is so much smaller and the pressure will raise at a much quicker rate but i'm not sure that equals more total downward force as the rest of the piston downward force is lower at ignition. But is it the same or higher/lower after the piston starts to move down? I have no idea.

Also I measured the plug length vs the top of the plug hole to the piston and it looks like I could go .040 more before the plug runs into the piston.

Here is the saw again with the exhaust at 104.

Timing Numbers 104/121/76

 

[Powerstroke Cowboy]

Are you losing it tho? That's really the question I guess. If the same amount of fuel is jammed into a smaller space at a higher compression the fuel should burn more completely and the total BTU output should be higher. Also the downward force in PSI will be alot higher because the area is so much smaller and the pressure will raise at a much quicker rate but i'm not sure that equals more total downward force as the rest of the piston downward force is lower at ignition. But is it the same or higher/lower after the piston starts to move down? I have no idea.

Here is the saw again with the exhaust at 104.

Timing Numbers 104/121/76

That's a good question. (if it's about me well I've already done lost it!!) But if it's about the saw, well I do believe some of it's potential is lost by the shrouding of the plug. There's a reason these engines are not built with the plug shrouded. Plus built so the expanding air from the combustion can travel outward and downward as fast and efficiently as possible.


In the last video it took 9 extra seconds to make the same cut as the first video. Was your chain duller in the second video?

It sounded like the saw has more rpms in the cut, but cut slower. Duller chain than the first video? How did it seem and feel to you?

Do you have a way to check rpms in and out of the cut?

 

[thompsoncustom]

That's a good question. (if it's about me well I've already done lost it!!) But if it's about the saw, well I do believe some of it's potential is lost by the shrouding of the plug. There's a reason these engines are not built with the plug shrouded. Plus built so the expanding air from the combustion can travel outward and downward as fast and efficiently as possible.


In the last video it took 9 extra seconds to make the same cut as the first video. Was your chain duller in the second video?

It sounded like the saw has more rpms in the cut, but cut slower. Duller chain than the first video? How did it seem and feel to you?

Do you have a way to check rpms in and out of the cut?

Ha I didn't even think about it when I wrote "are you losing it" ya i was talking about the saw. Also all good points there's probably a reason they don't build them that way.

It did fell slower in the cut today but also felt the rpm were higher which is where I want this saw to be. I did notice today this log has a bunch of little rocks on the top of it so i'll have to take a look at the chain. It seemed a little slow cutting smaller stuff today so it would make sense if it was the chain as the RPMs are higher but I never know how much of that stuff is just in my head the chain was freshly shaped in the first video.

Not sure if i'll play with this saw anymore than this as it doesn't see a whole lot of cut time in the real world other than a back up if i'm working on the ms260 or my brother has both my good saws (the ms660 also).....yes I loan him all my good stuff when he needs it but no one else they can have the wild thing.

Something else I would do to this saw would be to put a longer stroke crank in it if anyone know of a Husqvarna that would work or any other brand. Would be a lot of work but would be neat to build a stroker.

I do like that you can fell the power in this saw now. I noticed today when you romp on the throttle not cutting to can fell the saw twist just not what you would expect when you pick up this saw.

I will post up some compression numbers when I get the white schrader valves in.

No I don't have a tach

 

[Powerstroke Cowboy]

Ha I didn't even think about it when I wrote "are you losing it" ya i was talking about the saw. Also all good points there's probably a reason they don't build them that way.

It did fell slower in the cut today but also felt the rpm were higher which is where I want this saw to be. I did notice today this log has a bunch of little rocks on the top of it so i'll have to take a look at the chain. It seemed a little slow cutting smaller stuff today so it would make sense if it was the chain as the RPMs are higher but I never know how much of that stuff is just in my head the chain was freshly shaped in the first video.

Not sure if i'll play with this saw anymore than this as it doesn't see a whole lot of cut time in the real world other than a back up if i'm working on the ms260 or my brother has both my good saws (the ms660 also).....yes I loan him all my good stuff when he needs it but no one else they can have the wild thing.

Something else I would do to this saw would be to put a longer stroke crank in it if anyone know of a Husqvarna that would work or any other brand. Would be a lot of work but would be neat to build a stroker.

I do like that you can fell the power in this saw now. I noticed today when you romp on the throttle not cutting to can fell the saw twist just not what you would expect when you pick up this saw.

I will post up some compression numbers when I get the white schrader valves in.

No I don't have a tach

I knew what you meant when I read that. Just had to twist it and knock myself a little. What life if you cant joke about yourself?

A dull chain will keep the rpms up in the cut unless you put more load o. Trying to get it to cut.

I hear you. That style of saw requires a little more effort to keep taking apart than a normal saw.

It's definitely make more power than stock.

To be honest with you I am looking for a wild thing to mod. Thanks!!!

 

[thompsoncustom]

To be honest with you I am looking for a wild thing to mod. Thanks!!!

sweet.

figured out why the second cut was slower. oilers not working sometimes so it's fighting a dry bar and chain.

got the new schrader valve in compression only went up to 170psi so not much different.

 

[Ketchup]

I’ve had a lot of trouble with the oiler on mine too.

 

[Powerstroke Cowboy]

sweet.

figured out why the second cut was slower. oilers not working sometimes so it's fighting a dry bar and chain.

got the new schrader valve in compression only went up to 170psi so not much different.

That will make a difference in cut speed.

Is there a fix out there for the oilers?

 

[thompsoncustom]

That will make a difference in cut speed.

Is there a fix out there for the oilers?

Idk I ordered a new Chinese one. Since they don't use a real filter and just a spring looking thing I think i'll try to spread that for more flow but I think it's just bad by design.

 

[thompsoncustom]

I’ve had a lot of trouble with the oiler on mine too.

Is there a fix out there for the oilers

well got my new oiler in and tore it apart. only thing I could see to improve it was to make the flat spot on the shaft bigger so that's what I did.

Got it installed today and let it warm up to check and see how it's oiling....looking good so far.



I'll sharpen the chain and try cutting with it again and see if my time improves over the first video or not.