Unknown plastic line on Mac 4600

[WVBrady]

Hi guys: I have a Mac 4600 that I have used just to cut up one medium sized pine tree four years ago. I was able to get it started two years ago, but due to some health problems, haven't used it since then. I was able to get it started this week and cut down some small trees (about 4"-6"). After I ran out of fuel and refilled it, I had trouble getting it started again. I took off the air filter and managed to get it started and ran for about a minute when a plastic hose and a black rubber piece a little over an inch long came loose and the saw died.

The black rubber piece fits into a slot on the left-hand side of the saw, just to the left of the primer bulb. Just below the slot are the letters: 'T', 'L' and 'H'. I am guessing that is where the carb adjustments were made on earlier models. The hose comes from the front, left, bottom side of the carburetor and goes into the rubber part.

I do not know the function of this tube and I don't know how it is held in. The hole goes all of the way through the rubber to the outside and contains a coil spring with a needle screw inside of it. I don't see how the plastic line can be secured in the rubber piece.

Sorry, no pics.

Can anyone help?

 

[Derf]

I have that saw. I'll take pics later to see if I can help. I'm not sure what you're referencing.

 

[WVBrady]

Here are some pictures I took. I am new at this, so please bear with me. The rubber piece is inserted from the inside and comes out where the orange surveyors ribbon is sticking out. The rubber piece has the pointed screw with the enclosing spring inserted through the hole in the rubber piece. The plastic tubing evidently fastens to the rubber piece inside where the carburetor is. The end of the tubing does not look like it was enlarged by having the pointed screw extended into it. One picture shows the tubing supported by a screwdriver shaft.

http://s496.photobucket.com/user/WVBrady/media/IMG_0059.jpg.html

http://s496.photobucket.com/user/WVBrady/media/IMG_0062.jpg.html

http://s496.photobucket.com/user/WVBrady/media/IMG_0062.jpg.html

Hope you can help me out.

Brady

http://s496.photobucket.com/user/WVBrady/media/IMG_0062.jpg.html

http://s496.photobucket.com/user/WVBrady/media/IMG_0063.jpg.html

 

[Derf]

Sure can,
Sorry I didn't take any pictures yet. From memory: [looking from above]

Basically, the hose that connects to the wall in front of the carb continues down to the lower cylinder, and connects to the top of the carb body. This is your impulse line. As the piston moves up and down it creates a vacuum that pulls a diaphragm in the carb allowing fuel to get squirted into the carb body.

The hose that comes up in the back right corner from the fuel tank below goes to the 90° elbow on the right side of the carb. This is the fuel line.

There should be a hose that comes up in the back left corner also, this is a primer "pickup" line, also from the fuel tank below (mine doesn't have a fuel filter on the hose if you look in the tank fill hole). It should route to the backside of the push-bubble. There will be two tubes on the backside of the push-bubble: a long one and a short one. I believe the long one is on the bottom, and the short one is in the middle? The push-bubble works by drawing fuel into the bubble from the long tube on the bottom, behind the rubber disc, and squirting it out of the bubble through the short tube in the middle (behind the hole). From the short middle tube of the push button it routes in an S-bend to the left side of the carb body, near the front (I think, but I'll take a picture tomorrow).

The rubber piece you keep referring to has nothing to do with routing the fuel lines to the carb, it is simply a screwdriver-alignment guide to help you find the tuning screws on the side of the carb body. T = Throttle, L = Low speed, H = High speed. If you don't know how to tune a chainsaw with these screws don't mess around with just turning them - do some youtube research on tuning a chainsaw.

These saws are pretty old, and the original hosing can get brittle over time from ethanol in the fuel. If yours aren't super flexible, it may be time to replace them. That may be one reason why it popped off.

When you do all the hose-routing, its best to not only remove the air filter cover, but the three screws that hold the top plastic housing and that whole cover. I always end up grabbing my T25 Torx driver, but I think a regular screw driver may work too on those screws. You'll have to undo the spark plug wire from the spark plug so it can route out through the cutout. As you remove the top plastic shield two things to watch out for: 1, the choke lever is no longer held in place, and can freely flop around and/or be removed, and 2, the rubber guide tubes that you see can be removed. They are just pressed onto the three mixture jet screws on the carb body.

Re-reading your post, I'm not sure why your saw died. The hose that came free went from the push-bubble to the carb, so you wouldn't be able to prime the saw if it were cold. However, it should still be able to get fuel and impulse, so it should run, although maybe a little harder to get started. If you're having some running issues, it could be that your mixture is messed up, which could be from the screws not being tuned right, or from an air leak. If an air leak, a simple test would be to get some carb cleaner, get the saw running, and then spray the carb cleaner around the rubber boot between the carb and the cylinder, or the top of the carb body. If the saw changes its idle speed when you hit the outside of the carb with carb cleaner, you have an air leak, and you'll need to order a carb-rebuild kit, but they're cheap, maybe $5 on bay. The downside is that getting the carb off on that saw requires disassembling half the saw to get it off! Let me know if you need more help.

 

[Derf]

Also, once you set the tune (or when tuning), don't run the saw without the air filter. Even if you aren't cutting with the saw, and there is no chips/dust in the air, the restriction caused by the filter affects the air/fuel ratio. If you remove the filter, you remove that restriction, and you let in more air. This will cause the saw to not run optimally (although it will likely still run), but it will run lean. Lean running 2-stroke engines are not good as they have decreased life spans. There is a reduction in the amount of fuel, and therefore lubricating oil that gets to the cylinder and piston. You can overheat the piston and it can scratch the walls of the cylinder, or just lock up in the cylinder. Not saying that would happen from running without an air filter, but understand what you are doing is leaning out the mixture when running with no filter.

 

[WVBrady]

Thanks for the extensive reply! It will be a few days before I can work on the saw. I have a big tree that my neighbor has offered to help me cut up and move and I think that this will be the last weekend that he will be available. He has been cutting the large trunk and I have been using my 18 " electric saw to cut up the branches.

The hose that was loose indeed came from the priming bulb and I was able to reattach it with the aid of a long hemostat. I think that it was knocked loose when the rubber piece came loose and was bouncing about. The hoses seem to still be in pretty good shape, perhaps because I have not used it a lot since the advent of alcohol in the gas. I do think that I had to replace the primer bulb in this saw several years ago when it became brittle and broke.

My owners manual says that the carburetor was preset at the factory and no adjustments are available. If it needs adjusting, to take it to the dealer. There are no holes for the T, L, and H. The only hole from the outside is the hole through the rubber piece. It would seem that it is just a plug to seal up what used to be access holes for the adjustment screws. The confusing thing is that there is one hole through it that had a pointed screw in it, surrounded by the spring. The rubber piece had come loose inside, and still had the spring and screw inside of it. In my pictures you can see the screw and the spring after I had taken them out of the rubber piece.

I am beginning to suspect that the rubber piece was just something that they had available in their parts stores and they enlarged the holes for the adjustment screws and plugged it in and that they used the screw and spring to plug up the hole that happened to be in the rubber piece. Do you see any function for the screw? Doesn't it look like some sort of adjustment needle?

Should I be able to see the three adjustment screws for the carb with the rubber piece removed? Is it in the right place?

My primer bulb always seems to have some air in it. Is that normal?

My Mac with a 20" bar did not cut nearly so well as my neighbor's Farm Boss. Would you expect it to do better? It seems to rev well and has good compression based on the feel of pulling on the hand starter. I had sharpened the chain with the aid of a guide, and he said that it looked like it was producing good chips. I also had sharpened the chain on my electric saw and it cuts about as well as the Mac.

Your help is greatly appreciated!
Brady

 

[Derf]

Hi Brady,
On my RM4618, which is a re manufactured 4600 with 18" bar, the rubber piece is different from yours. If you consult the IPL, it is an alignment guide for a screwdriver to find the adjustment screws on the carb. If you want me to take a picture, I can. But the rubber boot has three holes in it from the outside of the saw to the carb body. Each hole is centered over a screw on the carb body.

With the rubber piece removed, yes, you should be able to see the three adjustment screws on the carb. I'm not able to identify what your "pointed screw with spring" is, but I believe that may be your idle adjust screw. I'll have to check again your pictures compared to my saw, but the throttle lever should come into contact with a tapered part of a screw. The further out or in the screw sits, the more it "sets" the throttle lever from "nothing" towards "full" throttle during idle. Your screw may be completely "out" and therefore you are at the bare minimum for throttle during idle.

Although the manual states the carb is tuned from the factory, it is untrue that a two-stroke carb needs no adjustment to the mixture. Changes in altitude, temperature, fuel quality, oil ratio in mix, type of wood, sharpness of chain, length of bar, all effect the need to tune the carb. The manual probably alludes to no adjustment being necessary to make it easier for owners, just as most car manuals today suggest bringing your vehicle in for service for everything from wiper blade to spark plug replacement.

However, tuning a carb can be a learning experience, so the factory may also suggest bringing it to a service mechanic because 1) it can be difficult to tune yourself, especially for a beginner without a tach and only by ear, 2) tuning the carb too rich would cause excess pollution, which the EPA would be against, and 3) tuning the carb too lean would result in decreased lifespan of the saw.

It is fine if the primer bulb has some air in it, since the pickup tube in the fuel tank can sometimes suck up air as well as fuel if you prime the carb with less than a full tank. Don't worry about that too much.

A 20" bar is the max recommended length for your saw, especially in hard wood. I run an 18" bar on mine, and it helps keep the RPMs up and the weight down. These saws are classified as homeowner saws, and are in the "entry level" market, or for "light" duty. The Stihl farm boss was a farm & ranch saw, more of a "middle class"/light-medium duty saw. The 4600 is a 46cc engine, while the Farm Boss is (I believe) 56.5cc, and that bigger engine means more power for cutting harder and thicker wood, and pulling a longer bar better. However, our saws have better air filtration, based off the original "air injection" patent that is now held by Husqvarna (http://www.google.com/patents/US5367988). It also has a better spring-mounted anti-vibe system, compare to the Stihl rubber mounted anti-vibe. You can pull a longer bar, or get better RPMs on your 20" bar if you use a skip-tooth chain. Also, if you remove some of the internal restrictions in your muffler you'll gain a little better performance at the trade off to slightly more noise. Lastly, the type of chain used (Stihl chain stays sharp longer than generic chain) and proper filing of chain (which takes patience and practice) can be a deciding factor between two saws.

I would think the mac could cut better than the electric saw, but I've only ever used small pole-mounted electric saws equivalent to ~30cc gas engines.

 

[WVBrady]

I think I have finally figured out the function of the mysterious rubber piece. I think when my model of the 4600 was made, they no longer wanted the owner to make adjustments on the carburetor, so they cut out that section of the case containing the holes through which the adjustments could be made and stuck this piece of rubber to fill the hole. The only function of the pointed screw seems to be that it pushes against a metal bar to hold the rubber piece in place, but because it is only held in by the spring, it is not secure. I think I will just cover the hole with a piece of tape, so that in the future I will have access to the adjustment screws.

Here are several videos on tuning saws. I found the one by Mitch to be most beneficial to me, because it starts with the basics:

http://www.arboristsite.com/community/threads/chainsaw-tuning-101.250802/

The electric saw that I have is a Craftsman 18" with 4 "peak" hp. It never tripped the breaker on a 20 amp circuit. I found it to be very useful for trimming smaller branches from a downed tree, because one is not tempted to leave it running while moving from one spot to another.

Many thanks for your help,
Brady

 

[WVBrady]

Derf: You were right. The mysterious screw was the idle screw. I couldn't see the hole in "frame" of the carburetor, but I looked at saw that supposedly was sold as a rebuilt item (but is frozen up, for some reason) and it does indeed contact the throttle lever on the carb. I couldn't believe that the screw in a coil spring would be solid enough for such a application.

I still can't get the thing to fire, though. I put a used coil that I bought on ebay that supposedly was good and still no spark. I disconnected the kill wire to the on/off switch with the same result. I had the gap set to about 0.011 inch. I also took the coil off of the allegedly rebuilt saw with the same result. I don't know what else to try. I even rigged up a socket on the flywheel nut and spun the flywheel with a battery powered drill; same result.

 

[Derf]

Hello Brady,
can I ask you what experience you have testing spark? Before you conclude that you have multiple bad igniters, lets just make sure your method is correct. Make sure the kill switch is NOT off, and set to run. Disconnecting the wire to the kill switch is incorrect, as it breaks the circuit needed to allow the electrickery to run the spark. Rather, make sure the contacts of the kill switch are clean and making good contact. Hold the threads of the spark plug against a 'ground' - this could be the outside of the cylinder, or any piece of metal that connects back to the igniter to complete the circuit. In this case you'll see the spark jump between the two electrodes of the plug. Alternatively, hold the tip of the spark plug against a ground- in this case the spark will jump between the tip electrode and the ground. The spark will be small and white/blue when you pull over the saw, so don't look for it in bright daylight.

If you're sure that you don't have spark, you can try dismantling the spark-plug connection from the ignitor wire to see if that has gone bad. Remove the spark plug from the ignitor boot and remove the rubber boot from the insulated ignitor wire. There will be a small bare metal wire going through the rubber insulated wire with a coil to seat the spark plug. Make sure it isn't broken or overly rusted. Also check the insulated wire for breaks or cracks.

To get the saw running: Step 1 is to get spark. If that fails, you'll need to find a replacement ignitor unit.

Step 2 is compression: How does the saw feel when you pull it over? Is there resistance, or is it very easy? If you have a compression tester, dribble a little gas into the spark plug hole (the oil in the gas will help lubricate and seal the rings), then screw the compression gauge into the spark plug hole and pull it over until the needle stops climbing (about 5-8 times). It should be somewhere above 130PSI. If you have poor compression, you'll need to disassemble the motor and replace the rings. In more extreme cases you'll need to replace the piston if it is scored, or the crank seals if they went south.

Step 3 is make sure you have gas going to the carb: Is fuel running up the fuel line? On these older saws check to make sure the ethanol in the fuel hasn't destroyed the fuel lines. You can try using starter spray fluid or carb cleaner sprayed into the mouth of the carb to determine if you have detonation. Be careful not to use too much or you'll flood the cylinder. If you have detonation when using spray but poor running conditions, you may have a plugged fuel line, blocked up fuel filter, or varnished carburetor channels(likely if the saw has been sitting for a while). You'll need to take apart most of the saw to get the carb out of it in this model (pain in the ass), and disassemble the carb and spray all the holes and passage ways with carb cleaner. Blow them out with compressed air. Don't use dip cleaners as they can cause problems if used excessively. Also don't push any wires through the small holes in the carb. You may need/want to freshen up the carb diaphragm with new ones. A carb kit is only about $5.

Step 4 is setting the idle, low speed jet and high speed jet on the carb. This is the 'tuning' stage that you can learn by ear, but is easier with a tachometer. You'll want either one with a wire to wrap around the spark plug lead, or a wireless one (more expensive). They will help you set up the RPM range in the correct spec for your cutting. The proper high-speed tuning is initially set at wide open throttle (WOT) with the chain free spinning, and completed (dialed in) with the saw at WOT and the saw in a log of wood.

Two-stroke engines are pretty straight forward. If this seems intimidating to you just go slow. If you get stuck you can ask for general advice on the forums here. It can be a learning experience, and harder without someone showing you how to do this. If you want more help, maybe we can bargain and I'll make a youtube video going through all this on my saw identical to yours. LOL. Or you can always find a shop that works on two-stroke engines (lawnmowers, chainsaws, leaf blowers, etc) and they'll fix you up and get that old girl running again.

 

[WVBrady]

Hi Derf: Thanks for taking the time to write all of that.
Step 1:
I tried testing for the spark both by holding the spark plug to the head while cranking the engine and also with a spark tester with an adjustable gap. I couldn't see a spark with either method. I tried adjusting the gap to almost touching, but still couldn't see a spark. This was in my garage, which is not that well lit. I then ran across this procedure on another forum:

"More technical method:
1. Remove the top cover on the saw to expose the spark plug.
2. Remove the spark plug.
3. Attach one end of alligator clip wire to the spark plug boot, make sure the clip contacts the metal conducting surface inside the boot.
4. Attach the other end of the alligator clip wire to the hot end of a digital multimeter
5. Touch a good metal surface ground with your ground probe on the multimeter
6. Set the multimeter to 20v DC
7. Pull the saw over and look for the multimeter to react. Fluctuating readings means it works, no action and the ignition doesn’t work."

http://store.chainsawr.com/blogs/tu...992-how-to-test-a-chainsaw-ignition-for-spark

I tried this and did get a fluctuating reading. I switched to a 200v dc scale and momentarily got a OL reading, meaning it was above 200v. The author implies either it works or it doesn't. The spark on this saw must be pretty weak as compared to my lawn mower.

Then, I put another new spark plug in and finally managed to get the saw to run a couple of times for just a few seconds; it revved up and then died.

Step 2:
It seems to have pretty good compression; when I use the pull starter, I can feel the individual strokes. My compression gauge doesn't fit this small of a sparkplug, but I have an adapter on order. I did take off the spark arrester and muffler; the piston and ring look in good condition.

Step 3: This may be the problem. Originally it died on me shortly after contacting a metal wedge (but not immediately), so that made me suspect that it had sheared the flywheel key. I thought that the lines were still good, but I remember that I had to replace the purge bulb a couple of years ago because it had cracked. I think that one of the lines must not be making a good seal or is cracked, because the bulb has a lot of air in it. When the idle screw came loose originally, I think it was knocked loose by one of the lines to the purge valve coming off. I put it back on, but it may be leaking air someplace. I have ordered some tygon line to replace all of the lines. The Mac 4618 that I have that was supposed to have been reconditioned has lines that are literally as brittle as uncooked macaroni.

Step 4: My 4600 has no holes for accessing the high and low speed screws, but my 4618 does, so I plan to swap those parts to allow that access. The 4618 is basically a parts saw now, because it is locked up for some reason.

I was planning on going south for the winter, but so far our weather has been mild. I think that I will just stick it out for a couple of months now; if so, I should be able to either fix this saw or finally toss it.

I have been reading about the Echo CS-450 P. It has generally good reviews; I might get one of them if I can't fix this one.

Again, thanks for taking time to write all of that, and in time I will let you know, success or failure.

Brady

 

[WVBrady]

Derf: I don't understand this statement: " Disconnecting the wire to the kill switch is incorrect, as it breaks the circuit needed to allow the electrickery to run the spark. "
I thought that all that the kill switch did was to connect that part of the ignition module to ground. Does it serve some other function?

Brady

 

[Derf]

Hi Brady,
We'll get that saw working, especially if you have a parts donor. I believe that the switch on this saw is NC (normally closed) and allows a circuit from the ignitor -> spark plug -> cylinder -> switch -> ground. If you move it to stop/kill the circuit is broken and there is no spark.

 

[WVBrady]

Hi Derf: Are you still around? I apologize for not getting back to you sooner. I didn't have the right screwdrivers (T25) and also needed to get some clamps for the pulse line. I read that tygon was too soft for the pulse line, so I used vacuum line. I had to order some special hose clamps for that, because the regular automobile hose clamps don't work on that small of a diameter. After that, it was so cold in my garage that I gave up for the winter.

I did get it running this spring. I used the carb off of the 4618, because it had the adjustable screws. I did have to take a Dremel tool to drill holes in the case to access the carb screws. I also ground an access hole so that I could get a hex wrench on the carb more easily.

It starts easily and runs pretty well, but I think that I left it running rich just to be on the safe side. I got a compression gauge for small engines and measured 150 psi.

I found out that I had been using the wrong size file on my Granberg file guide. I thought that I had a 3/8" chain, but it is really a 0.325. When I finally got my chain sharp it really made a big difference.

My 4618 was supposed to have been factory refurbished, but it was missing a couple of pieces and was locked up when I got it. I had kept it too long to return it, so I had just put it on the shelf. I took it all apart and found out that the bearings were locked up. I sprayed Kroil in the bearings and every day would work on them, twisting them by hand. Finally, I got them loose. I couldn't see anything holding them; it must have been a very small amount of sealant. I wasn't able to ge it started right away, so I just stuck it on the shelf. I had too much work to do outside.

BTW, this was a real pain to type; there is a big delay in typing before the words appear. Is this normal?

Thanks again for your help,
Brady

 

[Derf]

Hi again Brady,

Normally there isn't a delay typing, I've used both the website through a web browser, and an iPhone app (Tapatalk) to reply to posts. I type less when I'm on the phone.

Yes, these saws are a pain to work on, they are a clamshell design. I'm glad to hear you got it running again though, your persistence paid off.

Generally all smaller saws less than 55cc use .325 chain - although you can run 3/8 (.375), which might be easier if you have a roll of chain and spin your own loops or only have a 3/8 file, the lighter chain works better on smaller saws.

I'm surprised the bearings were locked up. That shouldn't happen unless they maybe got rusty. Any chance the saw was getting wet while it was stored?

Trying to source parts, even hose and clamps at an auto supply house for small engines is usually an exercise in futility. Tygon line is fine for the pickup, but if your vacuum line works then call it a day. Just be aware that fuel vapor will still get into the hose, so if it isn't fuel safe check for deterioration after running it for the season.

Better to keep it running rich than lean. The extra oil will keep the piston lubricated. Watch some videos on YouTube for tuning a chainsaw by ear, or invest in a small engine tachometer. One that runs off a sensing wire wrapped around the spark plug will be cheaper than a wireless one. Maybe $30 on Amazon or eBay.

You can still get a few parts online for these saws. I think I picked up a replacement sprocket and chain catcher for mine last summer from JacksSmallEngines. Keep your mix at 40:1 gas to oil, and your chains sharp, this saw will cut many more years before it gives up the ghost.




Sent from my iPhone using Tapatalk

 

[WVBrady]

Thanks for the reply. Yes, the typing is much better today.

The biggest problem with thinking that the chain was 3/8" was that it wore a slot in my original sprocket. It seemed to fit, but there was just enough play to cause undue wear.

I also burned up my original bar, because I didn't remember to grease the sprocket on the end of the bar. My original plastic grease gun (made in Germany!) came apart, but I had one for bicycles that worked ok. I greased it after every fill-up until grease squirted out around the outside.

I could not see any rust on the bearings and after I had them loose they turned freely. That's why I thought there must have been some small amount of sealant or something similar; once it was gone, it was gone.

I would like to tune the saw using a tachometer, but I don't know what the target rpm would be. Do you know? That would give me a better feel for tuning by ear.

I found several references that helped me in working on the saw, but my computer died and I lost them. I also lost a few pictures that might have been helpful to someone else with this saw.

Thanks again,
Brady

 

[Derf]

Greasing the tip sprocket, some people say never to grease it (Stihl doesn't even have a grease hole). Other people say if you do grease it, it picks up more dirt, and you should then grease it religiously to keep pushing the dirt out. No consensus has been reached. On an 18" bar I, and perhaps others would think, that the chain lubrication should be enough to keep from wearing out the tip sprocket. If you rev the saw while pointing the bar at some white wood/paper, you should see oil splatter being painted. If not, investigate your oil worm gear. They are plastic on this saw and can wear out.

RPM range I don't recall. I don't think I've tuned it with a tach, only by ear. Of note, if you want a smidge more power, take apart the muffler and remove the baffle. You'll have to re-tune the saw then, and it will be a little louder, but it will breathe better and feel stronger.

Sounds like it's working for you now. Go cut some wood.


Sent from my iPhone using Tapatalk

 

[WVBrady]

I just noticed that my local ACE Hardware had some small spring clamps that I think would have worked for where the impulse line connects onto the case. They come in a variety of sizes, so I think one would fit.