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Duraforce Re-jetting Instructions Part 2

fordtech
16 years ago

Thanks to Tom_P_PA for the first 100 post thread, this to be a continuation of which I repost the instructions in this first post. Only 100 posts are allowed per Subject

"quote"

Also, the mikuni on the suzuki 2 stroke part number is 81-1030 which is matches the Duraforce "37.5" jet and is a #40.

1) Get a NEW main jet and pilot jet. Part numbers are 98-1357 and 98-7041. Also, get the paper gaskets (1 for the carb body and 2 for the heat shield), get a fuel line and in line fuel filter.

2) Note that the main jet 98-1357 is called a "77.5" jet. The "77.5" jet is the jet orifice size in one-thousands of a centimeter. The closest drill bit size is a #68 wire gauge drill bit whose diameter is 0.031 inch (and it fits into the orifice, and #67 does not).

3) Note that the pilot jet 98-7041 is called a "37.5" jet. Again, the "37.5" is the jet orifice size in one-thousands of a centimeter. The closest drill bit size is a #79 wire gauge drill bit whose diameter is 0.0145 inch (and it fits into the orifice, and #78 does not).

4) Get a wire gauge drill set (from #80 to #60), or better still, get drill sizes #66 (0.033 inch) and/or #67 (0.032 inch) for the main jet and #78 (0.0160 inch) for the pilot jet. You will need a hand chuck to mount these tiny drills. Do not use power tools. This results in an approximately 10% increase in the orifices for both jets. 10% is all that is needed.

5) Carefully hand drill the jets, apply gentle pressure. Note that the pilot jet center hole is to be drilled ONLY. Do not drill through the body of the jet, drill out only the 37.5 orifice. Use the #78 drill to oversize the pilot jet orifice (it is the first oversize). To oversize the main jet, you can use a #67 drill (0.032 inch), go back and forth and ream out unit the #66 drill (0.033 inch) just fits, or you can use a #66 (0.033 inch) drill - but be careful to not oversize the orifice.

6) Carefully drain all of the gas, remove and disassemble your carb adn replace the existing jets with the new modified (oversize) jets. Not the pilot jet is on the side of the carb and is covered up with a sticker. Take the sticker off to get access to the pilot jet.

7) Be real gentle when putting the new jets in, do not apply excessive turning force...a new carb will set you back $100.

8) Reassemble the carb and adjust the speed control vane one click slower. The engine speed may run fast after these mods.

9) Reinstall the carb with a new gas line and in-line fuel filter. Note, its a real good idea to install an in-line fuel filter. The carb jets are small and can plug up easily.

  1. Gas and go.

Your mower will consume a bit more gas but will not surge any more because your mower's mixture will be a little richer. However, the engine will be better lubed and cooled as a result. This cures surging and makes the mower runs like mowers of 10 years ago.

Comments (96)

  • Gardn_dlyte
    16 years ago

    Bill,

    I didn't use any loctite for the installation of the reamed jet. I omitted this as I was worried about the ability to pull the jet again if needed for fine tuning. A light snugging should be fine but be careful as brass is soft stuff. I will try it this way for a while and maybe Loctite it after I am fully satified with the jetting.

    The decal peels back easy enough and I only peeled it about half way to expose the piolt jet opening. Do it with very clean dry fingers, or it won't adhere again. I didn't and had to use a little contact cement on the back of the decal to make it sticky again.

  • tinkerer_gw
    16 years ago

    OK,
    Slow speed jet installed, main jet to go.
    As I stated, I didn't think my 22261 ran that poorly to begin with, so with just the slow speed jet installed, I don't know if there was any noticable inprovement. The only thing I could have done was to make a sound recording before and after and then compared the two. Maybe I will do that before I install the main jet. I guess I am looking forward to doing this, but I will have to wait until I get my hoist freeded up . My back has seen too much lifting and working while bending over, that I don't do anything anymore unless I can put it on the lift so that I can sit and have it at arms length.
    Will keep the group informed.
    Bill

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  • tinkerer_gw
    16 years ago

    Finally completed the re-jetting. As I mentioned in my other posts, I didnÂt think my dura force engine started or ran that poorly to begin with, so to make a constructive comparison is difficult. I can, however make some observations. 1. Engine does smoke a little more. 2. Starting is still the same. Prime once or twice, apply choke; starts on the first pull. 3. Increase in power? Prior to the re-jetting, I never really tested the unit for brute power but after the re-jetting, I thought I would give it a try. After it had thoroughly warmed up I took it through a section of hay field where the grass was knee high. It didnÂt even hesitate. That gurgle that is talked about turned into a powerful sounding hum and it proceeded to mow continuously with out the slightest hint of wanting to stall.
    Is re-jetting God's gift to the Dura Force? I honestly couldnÂt say. All I can do is to present my observations. The one aspect of the re-jetting that might not be obvious is the fact that it will probably run a little cooler, which is a good thing.
    Bill

  • dougmac
    16 years ago

    With this draught, I have not used my re-jetted 10424 for over a month and had used it only ONCE after the re-jet. Finally got out and cut the grass today and was wondering if anyone else's Re-Jetted Dura-Force does this ...

    Upon re-start (warmed up), engine "races" initially. Not sure how high an RPM it peaks at, but it is much higher than normal.

    Neither my old 1999 vintage 10323 OR this 2003 vintage (but bought new this year) 10424 did this before the re-jetting.

    My re-jetting consisted of the Suzuki Pilot Jet, Main Jet drilled to #67, and adjusted the govenor 1 click slower.

    Once it settles down, normal engine speed sounds about correct ... I also bought a Tecumseh Vibra-Tach, but have yet to use it.

  • fordtech
    Original Author
    16 years ago

    If one of you happen to knarl up a perfectly good carburetor, I have now aquired 3 used ones for spare parts. Two that have arrived to day are 98-7000 and one coming in is supposed to be a 98-7042

  • dougmac
    16 years ago

    I had also added a Stens 90Deg fuel shut-off and small B&S fuel filter during the dry spell. After a few minutes of cutting (engine wamed up) I noticed it was suging worse than it did before the re-jet. Only thing I could think of was the fuel filter was too restrictive. Pulled it out of line and it then ran normal.

  • fordtech
    Original Author
    16 years ago

    Interesting. That gives some credence to the theory that the fuel tank makes some contribution to the smoother running commercials. Simply a fuel flow/pressure change makes the difference?

  • tom_p_pa
    16 years ago

    I have a filter on all three of mine now with no restriction. I used a larger B&S filter.

    Regarding restricted fuel flow I have been mentioning...has anyone noticed the nipple on the end of the non commercial tanks? Both my 10323 and 10550 were hardly open at the end with a small nib of plastic restricting the hole from the manufacturing. Only about 20% of the nipple was actual free and open for gas to pass through. It appears when they chopped off the end of the nipple, it squeezed the plastic shut a bit. I would assume the plastic would be hot and it just pinched close a bit. This coupled with small jets = surging!! The higher tank with the gallon of natural head pressure, may be the reason the commercial units run better. The commercial nipple has a brass valve inside it and held tight with a hose clamp. This would make perfect flow through the intake of the brass valve.. I also am under the belief, the engine shroud is causing a difference in air flow affecting vane operation. Everything else in the mower is the same.

  • dougmac
    16 years ago

    Yes, it certainly seems logical that the larger tank would supply more pressure as would it's increased height in relationship to the carb inlet. Correct me if I'm wrong (have never seen a commercial model up close), but it appears that the bottom of the tank is higher than that of a regular Duraforce.

    What made me think "fuel filter" was something stated in an earlier thread. Someone had installed a large clear filter in-line that appeared to have a pleated paper element inside. Someone else came back saying that type of filter should only be used on engines with a fuel pump ... using it on a gravity-fed fuel line could cause irratic engine performance.

    The filter I used is a red B&S ... 1.37" dia. x 1.75" long o/a and appears to have just a simple screen inside it. I had used a screen type filter on my 10323 for years with no problems ... it was white plastic with two halves held together with one center screw that allows ports to be rotated for best fit. It is just I now wanted to add a shut-off AND a filter and this little red B&S was a 1/2" shorter and seemed to be the ticket. Looking at it now, I think there is room for this slightly longer filter ... but what difference can it make, they are both screen type filters that should have similar screen surface area !! The shut-off can't be all that restrictive, but maybe the combination of it AND a screen filter is. Many on here have added filters, but I think I may be the only one on here that has tried to do BOTH !!

  • mowsizlak
    16 years ago

    Yes, the tank on the commercial sits higher than that of a standard duraforce. However, my commercial surged like crazy when I first got it. I did the rejetting on mine and now it runs like a charm. I agree that there would be a less restricted flow of fuel to the carburetor with the larger tank and the brass elbow but it didn't help mine at all. It surged like heavy footed driver in bad traffic. It was an embarassment. Now it runs well. I can't believe that the commercials would have been given special treatment over the other duraforces. Same engine, same EPA standards to meet. In fact, I was at the dealer the other day picking up a gator blade and asked the guy there about the surging (I had already fixed mine) He said that that is the number one complaint about the duraforces and that everyone used to mowing with an older boy immediately thinks there's a problem with their new mowers if they've bought a duraforce. The mowers on the two engines are essentially identical, aside from the shroud and tank. I said before in a previous post that it must be a slight difference in the bore of the jets on a minority of duraforces that accounts for the mystery non-surgers. Think about it, all it takes is 1/1000th of an inch to turn a surger into a non-surger. This could easily happen during the manufacture of the jets. It would be an acceptable percentage of "defects" (hardly a defect, I know) produced. All things the same, each duraforce should run the same. Everyone who has had a surging duraforce (at least on this forum) have all looked to the carburetor and fixed the surging by oversizing the jets. All I know is my experience with my commercial and it surged like an S.O.B. until getting a jet-job. Aside from the fuel flow being VERY restricted due to a manufacturing error in the tank, or a plugged filter, I can't see how it could be anything else but the jetting.

  • tom_p_pa
    16 years ago

    I used the pleated filter mentioned on all my Duraforces after I rejetted them. I found too much junk at the main jet screen filter in the carb to feel comfortable with leaving as is, so I installed in line filters. They work great. The Briggs package never mentioned about fuel pumps...just said for all horsepower engines. These filters are better than the screens. The picture below is from a in line filter installed on my 10550.

    {{gwi:132574}}

  • lawnmowerdan
    16 years ago

    i installed the red briggs filter and a shutoff on mine too. no problems but i did have troudle with the white 2 peice filter doug recommends-it leaks! also the new carb i got has the older 7000 # on it but runs like a champ . so much for the theroy that the newer7042 is a newer and better desighn

  • dougmac
    16 years ago

    As cheap as those little white 2-pc filters are (and no gasket on screw if I remember correctly), I'd expect them to leak too. But I don't think it ever leaked for me.

    Since mowing this weekend, I've removed the gas tank to check for plastic obstruction in the hose barb (as others have mentioned) and found mine to be fine. I then re-installed my fuel line putting in the white 2-pc filter to see how that does.

  • gmeyer10
    16 years ago

    Tom P PA, Back on July 20th you said you were thinking about increasing your jets one more size on your 10550. Just curious if you did this - what sizes are your jets at this point and are you staying or going up?

    I'm rejetting my 10550 this weekend and would like your input.

    Thanks.

    Greg Meyer

  • enosli
    16 years ago

    I suppose it's time for me to chime in. Today after nearly 7 years of use, my '98 10324 Lawn-Boy decided to continually and consistently surge when not under load. In all the years I've owned it, I've never had a problem with the mower.
    I took the air filter out and dismounted the carburetor to find that a lot of dirt had gotten sucked around the back of the filter and into the carburetor. As a result, it was pretty dirty, but I gave it a thorough cleaning.
    My question is would it be wise to replace the jets with a stock set or should I also be re-jetting the carburetor like others? Like I said, it's been running great for all these years..no problems other than this one now.
    What do y'all think?

    Thanks.

    PS - Hope I'm not doing anyone a disservice by posting this message in this thread, but I thought it was somewhat related.

  • 1saxman
    16 years ago

    I would not replace or alter the jets if you are satisfied with the way it runs, assuming it runs the same when you get through with it.

  • tom_p_pa
    16 years ago

    Greg, if you are not aware, please review the first 100 responses on "Duraforce Re-Jetting Instructions." This is actually Part # 1 and has a wealth of information. Print it before it gets removed from the site. The procedure is very simple.

    I never went up to a larger bore yet. I will do it at some point, but I have not had the time as of yet. Just became too busy.

    The 10550 runs a world of difference better than pre rejetting, but I am confident I can improve it by going up one more on each.

    In regards to the pilot jet, a #79 bit fit my stock jet, and I bored one bit larger with a #78 bit. In regards to my main jet, a #69 bit fit my stock jet, and I bored one bit larger with a #68.

    My bits were "cheapie" ones on ebay and am guessing they are off tolerance. I believe on most main stock jets a #68 will fit and you should bore with a #67.

    Regardless, just see which ones fits, and go up in size.

    If I had to do it over, I would go up 2 on each. I think I get get some more gurgle and burble sound out of it.

    The stock Duraforces run way too lean. My engines run remarkable cooler now, which has to increase its longevity.

  • tinkerer_gw
    16 years ago

    Please explain how you know the engine is now running remarkably cooler. I know there are such things as remote thermometers, is that what you used?
    Bill

  • fordtech
    Original Author
    16 years ago

    Tinkerer, I dont know what Tom uses but the common tool today is the laser thermometer. These are sold in abundance on Ebay.

    Here is a link that might be useful: laser thermometer

  • tom_p_pa
    16 years ago

    Much easier method. After I mow my lawn, I lick my finger and then touch the engine head just just below the spark plug and count how long it takes until it starts to hurt. Before rejetting 3 seconds. After rejetting 8 seconds. See, it runs cooler. LOL.

    Actually, after I use my mower, I hose down the top deck and then flip the mower on its side and hose the underdeck portion along with some hand assistance on removing clumps (I find this more effective than running the engine and spraying the hose under the deck). I then wipe the top of the deck down with a towel.

    I noticed the "hissing" water sound hitting hot engine parts was reduced. And when wiping down, I noticed the engine was much cooler. I use an old tee shirt on the deck and on the exposed engine base below the shroud. You can feel the heat on the face of your hand.

    So I guess you can say my observation is based upon sound and touch.

    Now that you mention about thermometers, it would be an interesting study to actually measure before and after rejetting for those who have not rejetted.

    One can easily take a bulb thermometer and hold it to the side of the mower using some sort of clay over the top of the bulb to hold it onto the engine. Mow your lawn and then take several measurements after a specified running time. This should be done over 2 or 3 weeks so we get enough data. After rejetting, do the same measurements.

    Any pre rejetting takers ???

  • tinkerer_gw
    16 years ago

    The Laser Thermometer is what I was thinking about. I would be interested it hearing the results if someone has one of these and would be able to take temperatures, while engine was running, before and after re-jetting.
    Bill

  • pete_p_ny
    16 years ago

    I agree, my engine is totally running cooler. My engine used to be scorching hot upon shutting it down after an hours running time. You can feel the radiant heat off the engine. The reduction is noticeable to me.

    Also, someone posted an article from a magazine that analyzed the Toro Duraforce when it was first introduced. I recall the article saying the engine ran leaner and hotter and some extra cooling fins had to be added to reduce extreme heat. It is no secret about Toro purposely creating a lean engine.

  • jsouth3
    16 years ago

    Pilot jet is it the idling speed or the low speed jet your talking about

    Thanks
    Jerry

  • rdaystrom
    16 years ago

    A pilot jet is the same as a low speed jet. It controls low speed fuel/air mixture. An idle screw adjusts idling speed.

  • AJY16
    16 years ago

    Bumpitty bump-bump!

    This post has been quiet and someone recently mentioned re-jetting his DuraForce. I would hate for this valuable knowledge to be lost!

    Happy mowing!

    AJY

  • rangers_275
    16 years ago

    that would be me. as soon as i grab some new parts, i am going to test my DF out and see how the surge is... especially after a good carb cleaning. if it still surges as badly as it does (a # 98-7000 carb) i am going to find a bit set and have at it. i have the zuki jet already, so i may just swap it out and only rejet the one instead of both. have not decided yet. for my memory, anyone have the part numbers for the two LB jets and the zuki jet? is there also a great place to buy a bit set that has a good price AND decent quality? eBay makes me nervous with their great prices, but if i recall, didn't someone have a bad experience with them?

    Rangers

  • 1saxman
    16 years ago

    On pre-compliant engines, a mixture screw (needle valve) was used to control mixture. This was very handy, as you could enrich the mixture for more power in hard cutting conditions or just make little adjustments as the climate changed with the seasons. Many early post-compliant engines continued to have the needle valves but with limiter caps on the screws like on cars in the '70s. If you could find an early carb like this that would fit, the Duraforce would be cured for good.

  • pete_p_ny
    16 years ago

    Saxman...did you ever re-jet? Curious as to your findings if you did.

  • AJY16
    16 years ago

    suzuki 2 stroke part number is 81-1030
    standard main jet 98-1357
    standard pilot jet 98-7041

    Don't bother drilling out a standard jet, splurge and get the 'zuki jet. It makes the job VERY simple. No worrying about broken bits and all that.

    I got the bit I needed from a local hobby shop. They were excellent quality and were kept in little vials behind the counter. Another place with decent quality is tower hobbies. (see link) They also sell pin vises(an absolute necessity) and individual bits.

    If your machine surges and you are hesitant to take the "re-jet plunge" don't be. It was the best thing I've done to any of my outdoor power equipment. Even at high noon when it's 100 degrees and 99% humidity my LawnBoy puts a smile on my face! And re-jetting one of these things isn't hard at all, it just sounds a little intimidating!

    Here is a link that might be useful: bit set

  • HZR03
    16 years ago

    Thanks to everyone for all of the info! Rejeted 2004 Duraforce last week. It's a lot more fun to use now. Redrilled orignal jets and reused all gaskets. 67 & 78 It will now start without primming.
    Larry

  • lawwnbboy
    15 years ago

    Hi everyone,

    Thank you Tom P for this post. I just bought my first silver series dura-surge, and i cant wait to re-jet it. Why does the post recommend buying new Jets? Why not drill out existing Jets? I see that HRZ03 did this, did anyone else try that? I am very inclined to take this route, no sense to me throwing more money at this than is necessary.

    Please advise.

    Lawwnbboy...

  • bigal_mo
    15 years ago

    There is no need to buy new jets or gaskets - just drill out. You do not need a pin vise either, just pliers to hold the bit as you are just drilling brass. A good starting point is to drill only 1 size larger on both jets - see how it runs then. A warning, if you have a set of drill bits do not get them mixed up as they are very tiny.

  • lawwnbboy
    15 years ago

    "There is no need to buy new jets or gaskets - just drill out. You do not need a pin vise either, just pliers to hold the bit as you are just drilling brass. A good starting point is to drill only 1 size larger on both jets - see how it runs then. A warning, if you have a set of drill bits do not get them mixed up as they are very tiny."

    Thats what I was picking up. I hear you oud and clear on all 4 of these points. Thank you.

  • pete_p_ny
    15 years ago

    The one bit is so small...just be patient and use some oil. It feels as though nothing is happening, but all of a sudden, it "breaks through" and you are done.

    Mine too, no priming anymore, may be once at times, but not 5 or 6 like the old days.

    Did Saxman ever re-jet yet??

  • lawwnbboy
    15 years ago

    Woo hoo!! I got my drills and vice!!

    I will be drilling tonight...

  • pete_p_ny
    15 years ago

    There is also a Part One....but not sure if it is still around anymore. Many helpful tips.

  • lawwnbboy
    15 years ago

    Help. Please.

    I got my drills last night, and began the re-jetting. After removing the carb, i found, i think, the main Jet. The main jet is the one that feeds into the carburetor 'throat'. is this correct? i bored this out using the 67 then 66 wire gauge drill. mission accomplished.

    Then i started looking for the pilot Jet. its nowhere to be found. is this possible? what is a pilot jet? where is the pilot jet? is it the inlet Jet from the gas tank?

    of course i reassembled the mower last night expecting the surge to be gone, but it was just *slightly* still there. :(

    thanks in advance guys.

    Lawwnbboy.

  • lawwnbboy
    15 years ago

    BTW, the mower is the 10247, silver series push...

  • snuffyinatl
    15 years ago

    Look on the side of the carburetor, you will see a sticker with some mumbers. With clean hands, carefully peel the sticker back. Directly underneath is the pilot jet. It controls the idle mixture. After the rejet, put the sticker back on. You should not have to remove the carb to get to the pilot jet.

  • lawwnbboy
    15 years ago

    OH YEAH. Thanks snuffy!!

  • lawwnbboy
    15 years ago

    Thanks for all the pointers guys, my mower is running very nice now. Mine was a trade in to a local lawn mower repair shop, and all it needed was gas and a re-jetting. It cost me $25.00. A good deal indeed.

  • pete_p_ny
    15 years ago

    May be saxman will re-jet ??

  • bigal_mo
    15 years ago

    Lawwnbboy, Good to hear all is ok in the 2 cycle lawnboy world. What size did you drill your pilot jet?

  • lawwnbboy
    15 years ago

    Thanks bigal_mo, it is good. something else i did after re-jetting was to take the mower and drop it onto a pile of leaves which accumulate on my north facing wall of my house, it didnt even slow down. this beast is strong.

    I drilled the pilot jet with a 78 wire gauge drill. the vice that i bought couldnt even grip it so i had to eventually take the drill bit, hold it with pliers, then holding it still i twisted the pilot jet onto it slowly. i didnt break any bits during the process. it got hung up a few times but i backed out and redrilled over and over until it broke through. a very simple process.

  • stevanrk
    15 years ago

    Hi. I just wanted to revive this thread for a bit more clarification. I copied the url for the parts list of my 10323. I have the wire drills bits and am ready to rejet, but wanted to know why the pilot jet is not listed in the parts list. The part number (98-7041) is also not listed. The mainjet is clearly identified and is not a problem, but is there another name for the pilotjet. Slowspeed, idle and 37.5 also do not appear. Does the 10323 simply not have a pilotjet? I haven't looked behind the sticker on the carb yet, so I have no idea yet. Thanks in advance.
    Regards,
    Stevan
    Here is the Link:

    https://lookup2.toro.com/request/getpub1.cfm?PubID=13009&PubNum=3321-570&Lang=EN&Cust=anonymous_user&xCaller=lawnboy&Filesize=2394941&vKey=1983392&PubType=11

  • tom_p_pa
    14 years ago

    and part 2

  • rls39
    13 years ago

    Thanks very much to the guys that provide the info above, particularly the specifics on how to drill out the carb jets. I was having nothing but grief with my Lawn Boy. I finally followed the above instructions and added running a drill through the fuel tank outlet to make sure there was no fuel starvation issues and installing a fuel shutoff and Briggs in-line fuel filter. The formum that deals with the air vane throttle operation was also helpfull. Once all this was done, the engine started on the first pull, which it hasn't done in years and has a new healthier sound to it with lots of rpms and power.
    So thanks very much guys, your info was most helpful.

  • mis4mike
    12 years ago

    Many thanks to FordTech and the forum for posting these instructions. My DF 10550 lives again! I had a real bad engine speed surging problem that was really annoying. I followed the instructions on drilling out the carburator jets--it now works perfectly, runs like my old lawn boy that I used for 22 years with that happy two-cycle sputter when not under load.
    I enlarged the pilot 0.002" (from .014 to .016") using a #78 wire gauge drill and the high speed jet to .033" using #66 wire gauge drill.

  • bbstacker
    9 years ago

    I know it has been a while since these postings, but I just now discovered this great site. I have a Lawnboy 10252 with a 107-4607(98-7042 old number) carb. Mine has all of the aforementioned problems and I wondering if I could re-jet mine to these specs. If not, do you think I could perform the 10% increase in regards to the pilot and main jets if my stock sizes do not correlate to the above carbs?
    Thanks for any help you can throw my way.

  • bbstacker
    9 years ago

    I received my bits today, and the go/no go specs worked out for this carb. as well. Wish me luck.