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Weedeater porting question

Old 12-21-2005, 08:36 PM
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Gofli
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Default Weedeater porting question

Hi,

I have been messing with a couple conversions, one is a weedy, 4 bolt plastic backplate, spring muffler, from a featherlite trmmer, I dunno the displacement. I have smoothed and opened up the ports some, and stuffed the crankcase, but I dont seem to be gaining anything in power. It seems to turn 6000 rpm with either a 16x8 mezlik, or a 16x6 zinger, doesnt improve by more than maybe 300 rpm without the muffler. I have opened up the intake and exhaust quite a bit, including the carb and spacer. I know this is a vague description of what I have done, but why am I seeing no improvement? I have a homey converted as well, and its turning the 16x8 about 7200, havent done any port mods to it at all, but I have blocked the compression hole, eliminated gasgets, opened the carb a little, and gutted the muffler and added a stack. I need more power out of it if I am going to keep it on my 13lb lazy ace, which had until recently a g23. Is there a "porting 101" or "porting for dummies" out there on the web I havent found? Read a bunch here, but some of it is over my head, or deals with so many different engines, etc. I want to match my g23 in performance, basicly, without spending the cash. Playing with these things is quicklt becoming a hobby in itself.

Thanks,
David
Old 12-21-2005, 10:56 PM
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The_Pipefather
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Default RE: Weedeater porting question

ORIGINAL: Gofli


Is there a "porting 101" or "porting for dummies" out there on the web I havent found? Read a bunch here, but some of it is over my head, or deals with so many different engines, etc. I want to match my g23 in performance, basicly, without spending the cash. Playing with these things is quicklt becoming a hobby in itself.


Look at www.macdizzy.com

They have a bunch of two stroke related stuff there with photo essays and how-to's.
Old 12-21-2005, 10:58 PM
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air mail rcu
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Default RE: Weedeater porting question

The link doesn't work. Any other ones?

Disregard. It's working now. Thanks.
Old 12-21-2005, 10:59 PM
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Default RE: Weedeater porting question

He fixed it
Old 12-22-2005, 12:59 PM
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Default RE: Weedeater porting question

Most weedwackers have undersize carbs on them to limit RPM, so a bigger carb would certainly help.
Old 12-22-2005, 01:11 PM
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Default RE: Weedeater porting question

Gord,

I did open the carb up to approx 11mm. I'm thinking about removing the flywheel key so I can change the timing. I looked at that site some, but thats dealing with motorcycles and helps with theory, I was hoping there was some more specific info on converted trimmer/chainsaw engines. Gonna tear into that homey after I get back from xmas at the inlaws
Old 12-22-2005, 01:28 PM
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Default RE: Weedeater porting question

ORIGINAL: Gofli

Gord,

I did open the carb up to approx 11mm. I'm thinking about removing the flywheel key so I can change the timing. I looked at that site some, but thats dealing with motorcycles and helps with theory, I was hoping there was some more specific info on converted trimmer/chainsaw engines. Gonna tear into that homey after I get back from xmas at the inlaws
Maybe you could post the displacement of the engine. This would make it easier for the rest of us to give suggestions.
Old 12-22-2005, 01:57 PM
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Default RE: Weedeater porting question

Be carefull cutting the venturi as it is made to a specific shape for good suction. If you cut it out flattening the top, the fuel mix can be disrupted and you would be worse off than where you started. If you were to cut the carb it two you would see the venturi looks like a wing section. It would be like flattening off the top of the wing where the result would be a loss of lift. Best to see if you can match up the linkages with a bigger bore carb from your local chainsaw dealer. They usually have lots of used ones. At least I did when I was in the racket.
Old 12-22-2005, 05:16 PM
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Default RE: Weedeater porting question

Dunno the displacement offhand, from reading here it seems the featherlites came in an 18 or 21cc, but I think I have also seen someone say they had a 25cc. I can measure it the next time I have it apart.

Gord,

I have some more carbs coming, these two engines have single needles which is another drawback, the ones I am getting at least have both needles, not 100% sure of the venturi size. My local chainsaw shop is no help for used stuff, but I do have another one located I havent visited yet.
Old 12-22-2005, 06:10 PM
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teddywilk
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Default RE: Weedeater porting question

YOU SHOULD PUT A TIMING LITE ON IT BEFORE YOU CHANGE IT TO MAKE SURE IT NOT ALREADY NEAR THE 30 DEGREE TIMING. TO MUCH TIMING WILL HURT UR ENGINE!

FARMER TED
Old 12-22-2005, 06:19 PM
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Terbough Bob
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Default RE: Weedeater porting question

It's been my experience that exhaust tuning is probably the most important key to getting power out of a two stroke. Yeah carbs, yeah porting, but if you don't have a pipe that reflects the pressure pulses properly, it's all for naught. Two Stroke Performance Tuning by A. Graham Bell is a fantastic book and will provide you with more info and insight into the black art of two stroke tuning than you'll know what to do with. Through what I learned in this book, I was able to get 48.2 wheel HP from a '99 Honda CR125 running on C16. Next step is fuel injection via Megasquirt, and I expect to make over 50 HP. My point: BUY THE BOOK! You'll be amazed.
Old 12-22-2005, 11:32 PM
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Default RE: Weedeater porting question

if your trying the 25cc from the poulan wackers i had the one that converted to other attachments.mine had the springs on muffler.never got more than 74-7500 with an 16x6 mas wood.i gutted muffler and polished and opened up ports a little.stock ign.it did fly my sons balsa usa DVIII at 14lbs but not that good.gave up and traded it off.if you have a 18 or 21cc you will never match or come close to the g23 in my opion.my 25cc homy i did outperformed the poulan by a lot.i now have the homy 30cc 2 ring on his DVIII and its great.
Old 12-23-2005, 03:36 PM
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rollmyown
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Default RE: Weedeater porting question

Hi David,
It sounds like you have about 21CCs that you are playing with. The 25cc engine that followed the 21Ccc engine is the FL-25 and you can recognize it by it being a lot easier to trim the flange off than the 21cc. The 21s are about a 1-1/4" bore and the 25 is 1-3/8" bore. I converted 2 - 21cc engines. By porting etc., like you are saying, and boring the carb spacer to 1/2" (it can't go much bigger) and then using a 9/16" bore Zama carb, I get 7000 RPM from the 21s and I got the 25cc engine up to 8000 RPM. All with a 16-8 MA Classic prop. The 16x8 seems a bit large for the 21cc engines because the 25cc can accelerate noticably quicker. I have another 25 coming and will try to duplicate the 8K. You are correct about this type of engine work being another hobby. I am working on a airplane design suitable for the 21cc engines. The intake port on these things is what requires the most work. Playing with the timing will mostly get you a more tempermental running engine. These engines were not designed to be high performance engines for our use, so I have learned when to leave well enough alone, at least for what I intend to do with them. I am real pleased with the 8k, and all of them are light and run pretty smooth. (All of mine do have the spring connected muffler.) Its been a while since I worked on these and my memory isn't getting any better with time. I just rememberd also adding two 1/2" O.D. outlet pipes to the mufflers. With the small original hole in the muffler the engine can't breath at all. My old memory just reminded me that I also machined .020" from the bottom of the jugs on the 21cc engines, I did this because they don't have much compression to begin with. This is one part of how I got 7000 RPM out of the 21cc engines. The 25cc engine is the same weight, easier to convert, has more power and machining the jugs on the 25cc is not necessary. The 25cc, FL 25 which is the last of the 4 bolt crankcases, I think, is the best engine for our use in my humble opinion. I will take and post a few photos of the FL 25 features for identification purposes. There is a lot of Poulan engines and that does cause a bit of confusion, but the FL 25's crankcase is unique and easy to spot, once you see one. Hope all this helps. One other point is that the 21cc engines only turned 6000 RPM to begin with, that is how they became a hobby. 6000 wasn't enough, 7000 should be usable, for the right airplane. Corrected bore diameters, after measuring latest 25cc engine. I have also seen the same basic jug with a 1-3/16" diameter piston and much smaller ports. Maybe around 18cc? It seems the same crankshaft, and flywheel are used often on different models.
Old 12-26-2005, 04:11 PM
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rollmyown
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Default RE: Weedeater porting question

Hi David, Here is a few photos so you all can see what the 4 bolt 25cc Poulan Featherlite looks like, before they went to the 2 bolt backplate, a bolt on muffler (I think) and a different design carb spacer. I started the conversion on this one for the photos. This engine is about as easy to remove the flange on as a Toro. For reference the flange part removed that you see in one piece weighs 2 and 1/8 ounces. I leave part of the flange supports on as braces for the crankcase snout, which is easy to do. If you grind them off you will only remove a minute bit of weight. You do need to open the ports on these. I open the intake a lot and try not to compromise the carb pulse hole. The exhaust port needs a bit of squaring up and the muffler needs to be opened up. The single needle original carb needs to be replaced with a 2 needle also. I tried the single needle carb for reference and didn't get very high revs from it. For reference, the original carb from a 25cc has a 1/2" bore and a 8mm venturi. the Zama I use is a M29D - 86A with a 9/16" bore and a 9.5 to 10mm venturi. (Hard to measure without removing the choke.) In general I think these are nice fairly light weight and compact engines. They can still be found for reasonable prices. I got 8000 RPMs from my first 25 like this one with a 16x8 MA Classic and want to see if I can duplicate the performance with this one. I ran this before starting to convert it and it sounded very encouraging. Someone broke the Trimmer shaft on this one before the engine had much time on it. This is a common occurance with these. My first one had the plastic shaft mount broken off before it was ever run. I got them both off of ----.
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Old 12-29-2005, 05:00 AM
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Default RE: Weedeater porting question

Roll,

That looks exactly like what I have, except the cylinder. I have the 4 bolt, spring muffler, and 2 bolts for the cyl to crankcase, but the cooling fins are deeper on mine, and one side has notches for the bolt, while the other has holes large enough to allow the bolt to be withdrawn through the head. Yours appears to have a larger bore, but about the same outside dimensions to the fins. I bet mine is the 18cc.
Old 12-31-2005, 02:39 AM
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Red Baron Mike
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Default RE: Weedeater porting question

Here is a "URL" from a site with detail about blueprinting a Homelite engine...

http://testfly.0catch.com/homelite/e...lindermod.html

I have two Homelite 25s that I will work on to get more power.

Good luck,
Mike


Moderator's note: Edited link to remove period at end that kept it from working. --Jim
Old 01-16-2006, 06:11 PM
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Default RE: Weedeater porting question

Well,

Not much more progress on my end...I have flown the weedy on my big boy arf, but fly is all it would do, definitely NOT fun. Think I will scrap that one and use what parts I can on another engine. I am looking for a 25cc version now. The light weight is important on this plane, since its designed for a glow .91. It weighed 9.5 lbs with the 18cc. Looked at walmart, they had a cheap FL1500 blower(23cc), couple different trimmers with 25cc, including the model FL25, one that said it was a high output 25cc, model FLSSTHO. My homey runs decent with no porting as of yet, but its too heavy for this plane. I am also playing with an old Echo srm140da, but its gonna need ignition since its got a very heavy flywheel, and is setup to run clockwise as a trimmer.
Old 01-17-2006, 05:43 PM
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Default RE: Weedeater porting question

Hi Gofli,
I suspected that these Poulan engines, 21cc or less, would be marginal for power when compared to their weight. Did you have a way to check the RPM and with which prop? On ---- they are still selling the newer version of the 25cc Poulan weedeater, powerhead only, at a reasonable price plus the shipping. These are new engines and are the 2 bolt later crankcase versions. Maybe the cylinder from one of these would work on your crankcase, since you obviously have a mount and prop hub for it. I don't know this for sure but a hint could be the number on the flywheel, they seem to use the same flywheel on a lot of the engines. On my FL-25s and the 21cc engines, the number on the flywheels is the same, 25870. Maybe this small point can help. The cylinder on the 2 bolt crankcase engines is different. Dave Wallace has a thread with pictures of this later Poulan 25cc engine here on RCU that could also help. In any event I would think that the prop hub at least should fit the later engine.
Old 01-18-2006, 10:30 AM
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Default RE: Weedeater porting question

Roll,

I was getting about 6500 rpm with a 16x6 pro zinger. I would like to find a 25cc, as this one does not have much in the way of compression. Maybe I can swap the cyl's since I have so much work in the crankcase on this one already. I'm gonna look around today, see what else I can find cheap. I saw the Nville guy with the 35.00 shipped powerheads on ebay, but he says some are FL's and some are some other model..I want to make sure I get the same bottom end, since I need a light engine on this project, and for above reasons. Is there a different crankcase on some of thier models, or are they all the same, provided they are the 4 bolt rear cover?
Old 01-19-2006, 06:33 PM
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rollmyown
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Default RE: Weedeater porting question

Hi Gofli
I don't pretend to be an expert on all Poulans, but it seems to me that they use the same crankcase, crankshaft, and flywheel on several models. The piston and the cylinder seems to be what varies to change the displacement. The ports, especially the intake port, seems to be noticeably smaller on the smaller displacent engines. I have 2 - 21cc and 2 - 25cc engines and another cylinder and piston that I got with some other parts. This is my experience with Poulans. It looks as though the cylinders from the 21s would interchange with the 25s. As far as the new 25cc engine with the 2 bolt crankcase, I am not sure about it's cylinder interchanging with the older versions. As far as having work into a crankcase, that might not be a big deal, because trimming a FL-25, the one I posted photos on, is not hard at all. I have done two and I could do another one in less than 1/2 hour. They are cake to do, they are almost as easy to trim as the Toro 25.4cc engines in Dave Wallace's thread. The first 25cc FL-25 I did runs very well, after I ported the intake and exhaust, added 2 -1/2" pipes to the muffler and installed a bigger 2 needle carb. If you want to stick with Poulan, I suggest keeping an eye out for a FL-25, they still show up on ----.
Old 01-19-2006, 09:23 PM
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Default RE: Weedeater porting question


ORIGINAL: rollmyown

As far as the new 25cc engine with the 2 bolt crankcase, I am not sure about it's cylinder interchanging with the older versions. As far as having work into a crankcase, that might not be a big deal, because trimming a FL-25, the one I posted photos on, is not hard at all. I have done two and I could do another one in less than 1/2 hour.
Shoot,

I submitted a post last night to this, but somehow must have not posted. I got a new 25cc trimmer and a used homelite 33cc saw yesterday. Took the trimmer apart, and its a two bolt crankcase, bolt on muffler. Theres an o-ring seal on both the backplate and the cyl to crank, and the cyl bolt spacing does not quite line up with the older 4 bolt cases. The holes could easily be filed to make the cyl fit, but I think the porting would be really off and likely to affect the power, thats a guess cause I didnt look that close before abandoning the idea of using the old case. I wanted to use it because I have stuffed it and had the mount already made, but like you said its not that much work to repeat. The new cyl has a flat base, no ears on it extend into the case, and the o-ring groove is in the case, so it will be really easy to take material off the bottom of the cyl to raise compression. Gonna start cutting on it tonite, I'm still relatively in the dark about the timing and durations, and cutting ports, but I think I can at least get a little more power than stock out if it....what mods did you do specificly to get 8k out of yours on the 16x8? I want to use a Bolly 18x6, I need more thrust than speed with this plane. I really like that Bolly, I have a 14lb or so H9 Tcraft with a G23 on it that flew good on MA wood 18x6, now with the Bolly it leaps off the ground and will hang on the prop.

Thanks again,
David
Old 01-20-2006, 08:56 PM
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Default RE: Weedeater porting question

Hi Dave,
I am guessing that you bought one of the two bolt crankcase Poulan engines. I am not familiar with what the intake port looks like on those. I would be a bit conservative on porting at first because, as you no doubt know, you can always enlarge them further after a running test. On my engines as I said before I bored out the carb spacer to 1/2". Then I used a metal scribe to draw a line inside on the aluminum with the spacer installed. After removing the spacer, I could see a point from which to start. I followed the 1/2" outline and filed the intake downward in a internal curved shape. I stayed away from the carb pulse port on the right side. Now the port is 1/2" high and a bit more wide because I sort of brought the left side down and the bottom over to the left to create a squared off lower left corner. I made sure not to kick up any burrs at the cylinder inside surface. From the left corner across the port to the top right of the circle is a bit more that 5/8". This is a large as I could possibly go on the port. I wouldn't suggest being this radical at first with any engine. Then I worked over the exhaust port as much as I thought I could get away with, but it wasn't as radical as what I did with the intake. then you need to open up the muffler to let the engine breathe. As far as a 25cc engine turning a Bolly 18-6, I don't know. To begin with I am not familiar with the prop. A light airplane as you describe could very well be compatible. Next time I run one, I will try an 18-6 and see how it goes. I also need to see for myself if I can duplicate the 8k reading with the two 25cc engines I have now. Oh Yes, You mentioned machining the bottom of the cylinders. I removed about .020 from the 21cc cylinders because they didn't feel as though there was much compression and I wanted to see if they would be easier to start. This seems to have helped the 21s operation all around and they went from 6k to 7k with the same 16-8 MA Classic prop. I didn't do this to the 25cc engines, could be a possibility?? I would suggest trying this on your first engine first. There isn't a whole lot of material thickness to the cylinder mounting flange to begin with so check that and the spark plug clearence before you start cutting. I have also thought about sinking the spark plug a bit, the botttom thread and a half never get used as it is and this might be an idea. Maybe someone can comment on this? You were right, these engine conversions are a hobby unto themselves.
John
Old 11-07-2021, 07:17 AM
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Originally Posted by Terbough Bob View Post
It's been my experience that exhaust tuning is probably the most important key to getting power out of a two stroke. Yeah carbs, yeah porting, but if you don't have a pipe that reflects the pressure pulses properly, it's all for naught. Two Stroke Performance Tuning by A. Graham Bell is a fantastic book and will provide you with more info and insight into the black art of two stroke tuning than you'll know what to do with. Through what I learned in this book, I was able to get 48.2 wheel HP from a '99 Honda CR125 running on C16. Next step is fuel injection via Megasquirt, and I expect to make over 50 HP. My point: BUY THE BOOK! You'll be amazed.
yea I'm calling bs on that
Old 11-07-2021, 09:08 AM
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Originally Posted by K-Techcowboy View Post
yea I'm calling bs on that
I guess, 16 year old BS still is BS and needs to be called out?

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