Nik's Poulan Thread

[barneyrb]

Jerry, my simple understanding of an impulse line is the tubing that runs from the crankcase to the carb (or carb adapter) and provides the impulse (push/pull or suck/blow generated by the upstroke and down stroke of the piston) to operate the diaphragms inside the carburetor. On most of the older Poulan saws the impulse is provided directly through a small hole from the crankcase through to the carb and therefore there is no impulse line as such. No need for a beating. IMO you had the balls to ask about something you don't understand.

so, it sounds like there has to be some type of impulse transfer between the tank and the carb for the saw to work. therefore, all saws have an "impulse line". correct?

Steve, you are correct in that the old "Poulans" had the impulse that came throught the intake but the newer ones (pro construction, not clamshell design) all have impulse lines such as the 335, 330, 365, 380, and the 3000-3600 timbermaster series.

Jerry, the impulse transfer is between the crankcase and carb not the tank and carb. If you've ever had a carb off and it had two lines going to the carb (and did not have a primer bulb) then one of those was the impulse line. A seperate impulse line is typically used on a saw that has a rubber intake boot and the carb is not bolted directly to a solid intake block.

 

[jerrycmorrow]

...Jerry, the impulse transfer is between the crankcase and carb not the tank and carb. If you've ever had a carb off and it had two lines going to the carb (and did not have a primer bulb) then one of those was the impulse line. A seperate impulse line is typically used on a saw that has a rubber intake boot and the carb is not bolted directly to a solid intake block.

seems all my saws have the carb bolted directely to the cylinder (haven't been into the craftsman yet) through a heat shield. also, they only have one line to the carb. so, i'm assuming that there's some impulse transfer directly from the carb to the case through the holes cast into the base of the carb which are matched on the cylinder.

 

[barneyrb]

seems all my saws have the carb bolted directely to the cylinder (haven't been into the craftsman yet) through a heat shield. also, they only have one line to the carb. so, i'm assuming that there's some impulse transfer directly from the carb to the case through the holes cast into the base of the carb which are matched on the cylinder.

Yes, if you look at one of the intake gaskets there will be a hole that is about the size of a 14gauge piece of wire, that will be the impulse hole.

 

[jerrycmorrow]

Yes, if you look at one of the intake gaskets there will be a hole that is about the size of a 14gauge piece of wire, that will be the impulse hole.

thanks barney. that's what i was suspecting. good to finally know what those holes are for. now i know why the saw wouldn't run once when i put the gasket on wrong. haha! as a followup question, is there any advantage/disadvantage to an exterior impulse line when compared to an "interior" impulse?

 

[Eccentric]

Well, the secret is still safe on ebay. You can't give one of the smaller Poulans away there. I rebuilt several 25s and micros here and tried to sell them there and couldn't get a good price for any of them. They are great saws but seem to be out of favor. Maybe I'll try painting one of them orange and white.

The only little Poulans that seem to have gotten the 'ebay vintage saw crazyness' are the Allis Chalmers rebadged saws. I've seen a few go for stupid money....

Hey Steve! While your splaining stuff.. I know the saws like 3400, have an impulse passage directly from the crankcase though the manifold to the carb. And some like my 380, have a nipple on the crankcase, with a separate piece of tubing to the carb.
I'm assuming, and I know one can get into trouble doing that!, LOL, On a saw such as 245, 5200, S25, etc that uses reed valve system. The reeds serve the same function? I never could quite grasp how they work.


Gregg,

On the 245/5200/S25 type reed valve saws (and all other reed valve saws), there is an impulse passage that runs from the crankcase to the carb through the manifold. The reed valve is simply a check valve that keeps the fuel/air charge in the crankcase from blowing back through the carb. The pump section of the diaphragm carbs still needs an impulse signal to work.....regardless of whether the engine has reeds, is a piston port engine, or has a disc/rotary valve. On a piston-port saw, the skirt of the piston opens and closes the passage from the carb to the crankcase. Different ways of doing the same thing. The very first 2-stroke engines (beginning of the 20th century) were piston-port. The reed valve setup is a much newer innovation. Motorcycles and chainsaws have gone from piston port to reed valve to rotary/disc valve, and back several times over the decades. The belief that piston port 2-strokes are a 'new' thing while reed valves are 'old school' is a misconception. I've seen multi-cylinder 2-stroke motorcycle engines that have had reed valves on certain cylinders, and disc valve on others (yes on the same engine) due to space/packaging concerns.

 

[promac850]

Also, here is a real good way to learn how the reed valve works...

HowStuffWorks "How Two-stroke Engines Work"

As you can see, the reed valve simply slams shut as soon as air flows against it's grain... thus keeping all of that precious fuel and air inside the crankcase to be delivered through the transfers and meet death and destruction when the spark plug fires...

It's a one way valve... about all.

Here's a pic of reed valves on a reed cage...

if you look at the cage, you can see it's v-shaped, which is one of the most common designs... you are looking straight at it... the air/fuel can come straight at your face, but as soon as it tries to go back, those reed petals slam shut against the cage, trapping the air/fuel mix in the crankcase.

Hope this helps...

 

[67 Mustang]

as a followup question, is there any advantage/disadvantage to an exterior impulse line when compared to an "interior" impulse?

Thanks, Gregg, Randy and Aaron for all your help in explaining impulse and reed valves. I can't say if there is an advantage to an impulse line vs direct impulse but as far as I'm concerned they have at least one major disadvantage. They have to be replaced. And from what I understand they can be a source of some serious problems if they leak and IMO another item that can break and cause troubleshooting nightmares. Many of the newer brand name saws use impulse lines and they are just another expensive trip to the parts store.

 

[OhioGregg]

Yea, What Steve said! :msp_biggrin: Thanks to all you guys that know this stuff. I was always in the dark so to speak, about just how the reed valve setup worked. I never even seen one, to my knowledge, until I got a few of these older Poulans.

Steve, the separate impulse line or tubing going from cyl. to carb, is probably more susceptible to damage or wear. But I suspect that it is the cheapest way of designing it, or building it from the manufacturing side of it. Lord knows, they just don't want to build stuff like they used to. Something that would last, even if it cost more to build.

I cant imagine what some of our beloved Poulans and others would cost in today's world if they still made them like they used to. Anyway, this old guy actually learned something today...LOL Never to old to learn.


Gregg,

 

[rms61moparman]

Thanks, Gregg, Randy and Aaron for all your help in explaining impulse and reed valves. I can't say if there is an advantage to an impulse line vs direct impulse but as far as I'm concerned they have at least one major disadvantage. They have to be replaced. And from what I understand they can be a source of some serious problems if they leak and IMO another item that can break and cause troubleshooting nightmares. Many of the newer brand name saws use impulse lines and they are just another expensive trip to the parts store.

I like the impulse PASSAGE much better than the seperate line.
MUCH less to go wrong unless some "yahoo" puts the gasket in wrong!!!LOL (we have all done it)

I am not above taking a small drill and opening that passage up slightly while I'm working in there. It may be my imagination but it seems to help with starting ease.


Mike

 

[jerrycmorrow]

thanks guys. i've learned something i always wondered about concerning impulse factors and reed valves. thus, this has been an extremely successful day.

 

[8433jeff]

thanks barney. that's what i was suspecting. good to finally know what those holes are for. now i know why the saw wouldn't run once when i put the gasket on wrong. haha! as a followup question, is there any advantage/disadvantage to an exterior impulse line when compared to an "interior" impulse?

One of the advantages is that you can separate the carb from the cylinder, avoiding heat, vibration, and debris, and actually "warming" the cylinder more evenly. Impulse lines are rarely a problem, in my experience. They are a pain to replace and hook up again, but so is my TV.

 

[promac850]

One of the advantages is that you can separate the carb from the cylinder, avoiding heat, vibration, and debris, and actually "warming" the cylinder more evenly. Impulse lines are rarely a problem, in my experience. They are a pain to replace and hook up again, but so is my TV.

I agree about impulse lines... I reused the God knows how old it is impulse line on the PM 850. Won't be the last saw to end up wearing the original part.

Fuel lines and carby kits, it seems fuel lines tend to go before a carb diaphragm will... so one diaphragm should last a couple of line changes...

The PM 850 also used the same carb kit... I never replaced it, since the diaphragm was supple and did not show any signs of becoming rigid and ineffective.

I'm going to have to build some shelves for all of these loud sharp cutter slinging apparatuses... lots of shelves... I'm supposed to get more of them somewhat soon...

Meanwhile, I will play with the Super 44 and the Poulan 3600 or that type/series saw and see if I can get them to roar again. The 790 will also have some progress done, the part of finding a place to bore that cylinder so the clearance between the piston and cylinder is just about right on the money... then I will hone it and slap her together... then sand blasting and painting of the tins...

Boy, these saws had a lot of sex and reproducing parties while I was out working... even the crippled ones did it too!!



Yes, TV's can be quite a PITA to set up... especially when they reside in an entertainment center cabinet with a solid back, with only a couple of holes for wires and crap to hook stuff up to.

 

[HeRoze]

Well, the secret is still safe on ebay. You can't give one of the smaller Poulans away there. I rebuilt several 25s and micros here and tried to sell them there and couldn't get a good price for any of them. They are great saws but seem to be out of favor. Maybe I'll try painting one of them orange and white.

if you got an xx laying around, particularly a parts saw, let me know!:msp_biggrin:

 

[joe25DA]

plastic lighter than mag?

Not in this case. I had my cousins 290 FB at my shop tonight, sharpen 2 chains for him (Dont bash him yet he does have a nice late model S25DA). The FB has the 16"/.325 on it and when I picked it up I thought "this saw is heavy!" for its power anyway. I weighed it, with fuel and oil and was just 14 lbs. Next I grabbed my 3.7. I have a 20" replaceable tip husky bar on it and 3/8" chain. Its weight? 13.5. I will post the pics tomm to prove it. Now WE all know there is really no comparison between the 3700 and FB, but still interesting to see.

 

[a. palmer jr.]

if you got an xx laying around, particularly a parts saw, let me know!:msp_biggrin:

I'm having to sort through some of my saws...I think I may have gotten a parts saw or two mixed in with the good ones. I try to keep them separate so I won't accidentally sell a non-running saw as a good one and vice versa. I guess that's what you get when you have multiples of the same thing.

 

[stubnail67]

I'm having to sort through some of my saws...I think I may have gotten a parts saw or two mixed in with the good ones. I try to keep them separate so I won't accidentally sell a non-running saw as a good one and vice versa. I guess that's what you get when you have multiples of the same thing.

what are you selling your micros for /poulan 2000 1800 that type orxxv pm me i live in fla 33709 thanks paul

 

[a. palmer jr.]

Closer to 10. I checked it real quick a minute ago, it has plenty of spark and compression, didn't use a compression gauge but feels like plenty enough so I'll probably fuel it up and see if she runs.

I cleaned the carb, put new fuel lines and carb kit in it but I must have done something wrong...The saw will start now and run but it runs super rich and spews fuel out the carburetor while running. I turned the H and L screws almost all the way in and it's still getting too much gas. I was careful to check the height of the inlet lever with the "W" gauge so that part is ok. I guess it's possible the spring might have slipped out of it's hole, don't know for sure. I'll have to tear it back down and see what I did wrong.

 

[a. palmer jr.]

what are you selling your micros for /poulan 2000 1800 that type orxxv pm me i live in fla 33709 thanks paul

I've been just selling them on the ebay auction for what they will bring. I don't have anything there right now, I've kinda switched to the small Homelites for selling. For some reason they seem to bring a lot more.
I really haven't thought of what they might be worth but my 1.8 finally sold for around $20. I've got another about like it which I'm gonna check out when I get time. I don't want anyone to be disappointed with any of them even if they didn't pay much. I won't be selling any of them before I check them out thoroughly

 

[redunshee]

PP525 Arrived

Well saw finally arrived and its in real good shape. Did notice some missing parts which I ordered. Missing the muffler gasket, thrust washer for sprocket/clutch and the safety lever for the throttle. Small potatoes , for sure. Saw ran briefly and wouldn't idle , so carb, may need adjusting. However I did notice that comp was only 115 or so. Ordered rings for it. Also ordered a new decomp button just to be safe. Will have something to do when parts arrive along with my pos 4018 Wildthing when new piston arrives.
Bob

PS: Don't know why I'm spending time on the WildThing, other than I refuse to let it get the best of me.

 

[a. palmer jr.]

Well saw finally arrived and its in real good shape. Did notice some missing parts which I ordered. Missing the muffler gasket, thrust washer for sprocket/clutch and the safety lever for the throttle. Small potatoes , for sure. Saw ran briefly and wouldn't idle , so carb, may need adjusting. However I did notice that comp was only 115 or so. Ordered rings for it. Also ordered a new decomp button just to be safe. Will have something to do when parts arrive along with my pos 4018 Wildthing when new piston arrives.
Bob

PS: Don't know why I'm spending time on the WildThing, other than I refuse to let it get the best of me.

I had a couple of saws this last year that I finally had to admit defeat to. One Craftsman saw just wasn't worth all the trouble I was going through and an Echo that just may have low compression. I let someone else try their luck on the Craftsman and the Echo sits in the garage while I work on something else.