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Basic 3120xp Mods

Discussion in 'Chainsaw' started by Wet1, Feb 2, 2009.

  1. Wet1

    Wet1 Addicted to ArboristSite

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    I decided to sit down and do some basic mods to my EPA 3120xp yesterday. I didn't want to put a lot of money in this saw, so I did what I could for as little money as possible.

    Like others, I finally got fed up with the 9,600 rpm limiter in my EPA 3120. I know husky has a non-epa coil and flywheel for this saw (I believe this limits around 11.5k) that is still sold in the ROW, but I wasn't crazy about spending a couple of hundred dollars on a saw I only paid $600 for to begin with. Romeo had told me the unlimited 272 coil can be adapted by changing the center poll/laminate and swapping in the stock piece, so I thought I'd give that a try. I should warn anyone considering doing this swap, the 272 has no limiter in it so it's very possible you could damage your saw since there's no safeguard with is coil... Please understand you could throw a rod or break your crank by doing this!!! Just want to make sure everyone knows this is a possibility when removing rev limiters...

    I bought a clean used 272 coil off ebay for $25 for this swap. Looking at the two coils, they appear almost identical other than the color. The spark plug wire comes out at a slightly different angle and the plug wire itself on the 272 coil was a little shorter.

    [​IMG]
    [​IMG]

    I started off by finding out what the timing was with the stock coil. I crudely found TDC and marked both the FW and a spot on the jug so I could read it with my timing light from the top. I suspect I didn't find exactly TDC, but I'm sure I was very close (+/- a degree or two). Close enough was fine with me, I just needed a reference point since my Snap On digital inductive advance timing light allows me to dial in the advance. With TDC marked, I found the stock green 3120 coil was giving me about 53° BTDC and advanced to around 24° as it reved up. Now that I had this info, I knew what timing numbers I needed out of the 272 coil.

    Since the pole/laminate in the two coils looked to be identical, I went ahead and installed the 272 coil without changing out the center laminate. The coil fit just as the factory coil did and with no issues. The plug wire location/angle did not hit the case on the saw, so I didn't have to notch the case at all (I thought I might have to given the slightly difference in the angle of the plug wire). The plug wire was a little short if I used the factory wire locations (clips in the plastic), but I just bypassed one or two of the clips and found it was still very secure and fit just fine. I could have changed the plug wire(s), but this worked so I decided not to screw around with it and chance breaking something.

    [​IMG]
    [​IMG]

    Not knowing what was going to happen, I decided to see if it would start w/o making any other changes other than installing the 272 coil. To my surprise, the saw started and seemed to run well. Checking the timing I found the saw was idling at around 51°, which was very close to what I was seeing with the factory green 3120 coil. After building up the rpm's with the 272 coil installed, the timing was again sitting around 24° BTDC... right where it was with the factory coil. I suppose the timing could be advanced a little to get a little more performance out of the saw, but I didn't want to bother. If the timing was not correct after installing the 272 coil, I would have tried swapping the center sections. If it was out by a lot, I would have needed to re index the FW. I would have done this by removing the FW and the key, and then relocate it to get the proper timing. Luckily, I didn't have to do this. The best part, no premature hammering of the limiter... music to my ears!!!

    Since the non- epa saws come with a larger high speed jet, and I wanted to open my muffler up a little, I had to richen my carb up a little. This saw doesn't have an adjustable high jet (I HATE NON ADJUSTABLE CARBS!!!), so I had to do some mods to the factory jet. To do this you have to access the carb and take out the high speed jet. You first have to remove the aluminum casting that sits over the carb (four allen screws). Once that plate is removed above the carb, the carb is free to be removed from the saw. You don't have to remove the carb to do this mod, but I wanted to clean the saw up a little so I elected to remove it by disconnecting the two linkages and the fuel line. You next remove the top plate on the carb (four small screws) to expose the high speed jet as shown below...
    [​IMG]
    The size of the jet is stamped right into the jet itself. My saw is fairly new and it had a 1.12mm jet in it. The non-epa saws sold in the ROW come with a larger 1.16mm jet. If I were only doing the coil change, I would have wanted this 1.16mm jet. Since I was going to open up the muffler a little as well, I decided to go a little larger. Warbo jets can be bought, but I didn't have one on hand (this was kind of something I just decided to sit down and do yesterday), so I reamed out my factory jet to about .0465", which is about 1.18mm. I don't know how close this will be to ideal, but I'm hoping this will be close enough. Once I get some time to do some cutting with it, I'll keep a very close eye on the plug for a while. I'm hoping this should be sufficiently rich to keep the saw safe since I wont be using it to mill. Did I mention I hate non-adjustable carbs???

    I next wanted to open the muffler up a little. I did this by removing the muffler and drilling four 3/8" holes around the factory exhaust exit. This area is curved and kind of tough to drill into because of the shape, so I drilled pilot holes with a 1/8" bit first before going to the larger drill bit. After I was done I removed any major burs and completely blew out the muffler to remove steel chips. Four 3/8 holes isn't a lot of additional surface area, but it should allow it to breath quite a bit better. The holes are actually a little larger than this because of the angle they are drilled at, but 3/8" was the size of the bit I used. I could have made the holes larger, but I didn't want to go crazy with it. I next cut the louvers out of the cover that holds the spark arrester screen. I started the saw w/o the screen in place and let it run for a minute or two to make sure any remaining steel chips that might have been stuck in the muffler had a way to escape. I later reinstalled the screen. I forgot to take some pics of this mod, but it's difficult to tell the muffler has been modded by looking at it... unless you know what to look for or start it up. The saw is noticeably louder, but it's not obnoxiously loud like some other saws I've opened up with much larger ports... kind of a nice balance IMO.

    My saw has always leaked a little black crud where the muffler meets the jug, not a lot, but it was noticeable. While I had the muffler off I wanted to find out what was causing this 'leak'. Placing a straight edge over the flange of the muffler, I found it had a couple of low spots, the worst being on the top where I was seeing the black build up. The flange area on the muffler is fairly thick steel, so I took a file to the flange to level it off. After filing it for a minute or two, you can clearly see the low spots in the pic below... and this was after I had already removed some material...

    [​IMG]

    I filed it down until these low areas were almost completely gone and then reassembled everything. After starting the saw, I did not see anything coming from this location, but time will tell. Although, I'd be surprised to see another leak there.

    I also installed a 8 pin sprocket and converted over from .404" to .375" chain. Pretty straight forward, but I did screw something up... I was cold and rushing to get back in the house while doing the final reassembly. In my rushing, I stepped on the bar plate and really disfigured it. I tried reshaping it, but it needs to be replaced now. Dummy...

    So how does the saw run? I wish I had more time to play with it before I had to cleanup. I went ahead and made a couple of cuts anyway and it's like a totally different saw. It really rips now! It's so nice not hearing that limiter banging away. With the unlimited coil it now seems to run like it should, before hand you had to really put a lot of pressure on the saw to keep it bogged and below the limiter. I need to get the bar plate replaced and spend some more time running it. I'll have to make an effort to watch the spark plug and try to keep the revs at a reasonable level with no load on the saw. All this only took a few hours with me tinkering around and cleaning everything as I went. I though about doing some porting and dropping the jug, but I decided against doing so for now since it already has plenty of snot. I can tell you its seems to run much better now and if nothing else, it should be much more fun to use (assuming it stays glued together :laugh: ). The parts cost me just under $70 for everything (coil, 8 pin rim, bar tip, and chain), so far it seems like I got a lot of bang for my money considering I also got a new rim and chain in the process. :)

    BTW, sorry about the pic quality... I was using my POS phone.
     
    Last edited: Feb 2, 2009
    NEP, w8ye, Spotted Owl and 7 others like this.
  2. blsnelling

    blsnelling Site Sponsor

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    Excellent information for all the 3120 owners. Any you did this yourself on the cheap too. I love it! Does the saw 4-stroke out of the wood at WOT? I'd trust that before I would the plug color. Plug color is just way to subjective IMHO, although it is another indicator to watch.
     
  3. jack-the-ripper

    jack-the-ripper AboristSite Guru

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    Thanks for sharing. Anyone posting their work like this, is how we gain more knowledge. Now get that video going. :clap:
     
  4. albert

    albert Addicted to ArboristSite

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    Good Read and info, another option would be a green 365/372 coil, I think some of them limit @ 13.5k, still higher than I think a 3120 should rev
     
  5. excess650

    excess650 Addicted to ArboristSite

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    Did you put a tach on it to see where it tops out? The manual that I looked at listed 11,500-12,500rpm max, no load.
     
  6. brncreeper

    brncreeper Addicted to ArboristSite

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    Where did you purchase the ream for the fixed jet? Or did you just go the numbered drill bit route?
     
  7. Wet1

    Wet1 Addicted to ArboristSite

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    Thanks Brad. Honestly I'm still a little afraid to fully let it spin at WOT for long w/o a load on it. I'm not an expert on tuning 2 strokes by ear, but it does sound like it's 4 stroking a little for the very brief amount of time I've let her rip. I need to spend some more time with it... something I don't have much of for the next week or two. :cry:


    Thanks! Sorry no video coming... no DVR. :(


    You're probably right about the 3120 reving too high. I didn't look into the 372 coil, they aren't as common. Are they a direct fit? Are all of them limited to 13.5k, or do you have to pick and choose?


    I have not put a tack on it yet, but I'm sure it's turning every bit of the 12k spec. I'll try doing this next time I have time to tinker around again.


    Both. I used the numbered bits as an index. I have had the reamers for years, sorry I have no idea where they came from as I bought them off a retired machinist. The jet as you know is brass and very soft. You can probably turn a 57 and 56 bit into the jet by hand (or with pliers) and not remove any excess material if you don't have reamers. Ive done this before with excellent results.
     
  8. blsnelling

    blsnelling Site Sponsor

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    Take any saw with an adjustable H needle on the carb. Screw it out so that you know it's way rich. Warm the saw up and then go WOT out of the wood. Turn it in until you hear it peak out. Then back up until it's barely not peaked out. That peaked out sound is what we call 2-stroking. That burble you hear when you begin to richen it back up is what we call 4-stroking. You want the saw just on the rich side of peaked out so that there a little 4-stroking. A good time to check is when pulling it out of an extended cut and the engine has max heat in it. BTW, it's much easier to hear on a muffler modded saw.
     
  9. Wet1

    Wet1 Addicted to ArboristSite

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    Thanks Brad. I actually know how to do it with an adjustable jet, it's just obviously tougher with a fixed jet since you can't make real time adjustments... You really have to work based on your experience, memory, and ear. I did hear a little burbling, so hopefully it's safe.

    BTW, good tip on doing the adjustment after making a cut, I've never done that... although I've found killing the saw in a cut is a good way to read the plug as well. Did I mention I hate fixed jet carbs?!?!?! :D
     
  10. Lakeside53

    Lakeside53 Stihl Wrenching

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    Great post!


    What Brad says about 4-stroking is correct, but.. it still may be too high for the saw (unless you're wanting to be a racer..). Choose the lowest WOT (with a reasonable length bar and chain) you are comfortable with, not the highest the saw will go while "just 4-stroking". I'd stay less than 12k on your saw. it won't affect your cut times materially.
     
    Last edited: Feb 2, 2009
  11. pastryguyhawaii

    pastryguyhawaii AboristSite Guru

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    Good thread. I'm a big fan of posts that teach me something, that's why I'm here. My Stihl dealer has a 3120 that was given to him as a debt repayment. He put in a new black coil but he says it needs a new carb. I think I could pick it up fairly cheap since he couldn't put it out as a rental and it's not a Stihl. I've always wanted a big Husky.
     
  12. B_Turner

    B_Turner Addicted to ArboristSite

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    Very interesting, and a great post.

    It surprises me that the 272 coil started with no changes, as when I tried a black 3120 coil with the EPA flywheel it would not start.

    And the magnets on the EPA and non EPA flywheels are roughly 15 degrees different in terms of how they are keyed as I recall.

    Also I would have expected the idle timing to be less advanced than your reading.

    I applaud your efforts and post and keep us informed of how it works out. You'll wonder how you ever put up with that hammerring. Again, I am a little surprised on the timing, as I would have expected the timing to be more changed when installing the 272 coil.

    In terms of the muffler leaking at the cylinder, every one I have seen does that a little. My latest new one was so bad I had them reorder a new muffler on warranty which was even worse. The third muffler was close enough that some lapping got it pretty good.

    In swapping the jets, I found in the long run it was quicker and eaiser to take off the top cover and pull the carb off. Makes it so much easier to make sure the gaskets between the carb and cylinder are aligned. The EPA (1.12mm) jet is only $2 at my dealer so easy to try making some different sizes. BWT, the 1.16mm jet isn't available in the US (the non EPA coil and flywheel still are).
     
    Last edited: Feb 2, 2009
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  13. Wet1

    Wet1 Addicted to ArboristSite

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    Thanks Andy. No racer here (yet!). You bring up a good point. When I do get around to revisiting the saw, I'll check to see what she's turning for max rpm with say a 28" bar. If it's really high (above 13k), I can try richening it up to bring the revs down. If it's below 13k I'll run it and see how the plug looks and see how she preforms... I don't want to foul plugs either. More time is needed at this point, something I don't have right now since I'm on the road.


    If you can get it cheap, I'd suggest jumping on it. If you need a big saw, the 3120 is hard to beat. In fact, (Andy don't read this) I think I prefer the 3120 over the 880, especially now that the limiter has been removed.



    B., I believe the black 3120 coil has a different mount/laminate, is this correct? If so, I suspect this is why the other FW would be needed. Actually, I think you could use the stock FW with the black 3120 coil, but you'd have to retime it for that 15° difference. Otherwise it should work just fine.

    As noted, the timing with the 272 and the green 3120 coil appear to be nearly identical. What I didn't check was at what point the timing is changed (vs rpm), but this seemed similar as well and I'm sure it would be irrelevant in actual use.

    My muffler had a pretty good dip in the flange on the top, probably 8 to 10 thousands. It took me about five minutes with a file to get it level... I'm surprised they never addressed this. Luckily there's plenty of metal there so it can be fixed.

    Agreed regarding removing the carb, it's easy and only takes a couple of seconds. :)
     
  14. blsnelling

    blsnelling Site Sponsor

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    Sounds like a valid plan.
     
  15. B_Turner

    B_Turner Addicted to ArboristSite

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    black and green 3120 coils

    [​IMG]

    [​IMG]

    I would have loved to know what your EPA 3120 would have tached WOT with no changes to muffler or jet.


    In terms of max WOT rpm, from what I've read you are playing with fire turning a 3120 at 13k.
     
    Last edited: Feb 2, 2009
  16. brncreeper

    brncreeper Addicted to ArboristSite

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    For those that don't want to use number bits, the Enco catalog shows a Model 619-1017 (.0440 in.,1.1167mm), and a Model 619-1018 (.0470 in.,1.1938mm). The web site does not pull up the product numbers, the phone number is: 800-873-3626.
     
  17. Wet1

    Wet1 Addicted to ArboristSite

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    Not a chance I wanted to take running an unlimited coil w/o adding more fuel. If the saw is turning higher RPM's more fuel is generally needed. I started it with the 1.12mm jet and it ran and reved up great, but I didn't want to let it run any longer than I needed to.

    Looking at that black 3120 coil, I can see why it wouldn't work with the stock FW since it has another pickup. If the non EPA FW has three magnets (which I highly doubt), you be forced to use the matching non-EPA FW. Otherwise, you should be able to retime the EPA FW for that coil, assuming the non EPA FW also only has two magnets.

    I've had a hard time locating info on max RPMs. I know what the factory manual states, but I'm sure this is based on the max RPMs allowable for their limiters. As some point my guess would be the rod will let go, but I have no idea where that point actually is. Romeo or any of the other big bore racers care to comment???
     
  18. Wet1

    Wet1 Addicted to ArboristSite

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    Nice find. If they are cheap, I wouldn't mind having one of both to have on hand. Are you going to place an order? If so, how much are they?
     
  19. brncreeper

    brncreeper Addicted to ArboristSite

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    They're $23 each, I think I'll wait. About the time I order them someone will come up with a source for a 1.16mm jet. (stevethekiwi?)
     
  20. B_Turner

    B_Turner Addicted to ArboristSite

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    My understanding is you don't really want a 3120 spinning up past 12.5k except at the races. If I had an unlimited coil in one of mine, I would be aiming more like 12k max for a safety margin for different fuels, etc. but that's just me as I like to run long bars and lean on them a little for fun.

    I don't mind the higher limited coil, except that it doesn't give me ANY information about how I'm jetted. My non EPA 3120 is on the limiter around 11.6 even with the non EPA jet, but I have no idea what it would run unlimited. Seems like StwkS 3120 runs 12.2k even limited and he likes it that way. (He says the black 3120 coil varies from 11,5 to almost 12.5 depending on the instantiation.

    Can someone explain to me about coils and why some coils have 2 "pickups" and some 3 pickups? 272, EPA 3120 have 2 and non EPA 3120 coil has 3. So it isn't to do with being limited. Although I've been told I'm a bit limited.....
     
    Last edited: Feb 2, 2009

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