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Discussion Starter #1
hi i have a problem with my surging duraforce. what are the part numbers on the jets that i need to get to fix the problem. and is there anything else i have to do to fix the surgung. thanks so much
 

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I'd buy the 42.5 pilot jet Briggs & Stratton part # 801308. That is the cheapest and easiest solution to most mixture related surging. There are other sizes like the 40 jet for the pilot available off the shelf or you can drill jets both the pilot and high speed. I've done all of them and they all can work, but a 42.5 pilot jet is the easiest.

Surging can also be caused by a dirty carb, warped crab, sticking air vane, weak governor spring, and poor crank shaft seals.
 

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Discussion Starter #6
ok but its only a slight difference correct? im not going use double the gas right?
 

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If you do a search there's a few different posts where some have measured fuel consumption:

http://www.mytractorforum.com/showthread.php?t=51353

I personally haven't noticed a huge increase in fuel consumption, but I'm also not using the mower commercially nor mowing a huge lawn.

If you're really worried about fuel consumption you can start with just a #40 jet (part number 81-1030) first. But the #40 jet costs around $10 versus $5 for the 42.5. The #40 works for some but not all. At the very least I'd pull the entire carb, clean it thoroughly and replace the governor spring and rejet just the pilot. If you don't want to spend $10 on the #40 you can use a #78 wire drill bit on your stock pilot jet. This has cured the surge on some of my duraforces.
 

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I did the 42.5 on a Dura I had and it worked great. I used a tad more gas but it had power and no surging. I think this jet is for a Toro/LB snow blower 2 stroke of course. I have only one Dura LB left and it's still in the box but I think I'm going to get the jet and put it in the parts bin for the future.
 

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Discussion Starter #9
thanks guys. does anyone know if theres pictures on how to change the jets or drill holes?
 

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Ive read through the Duraforce surging discussions and just some quick comment/logic on the butterfly vs jet issues;

Its assumed Toro/Lawnboy spec'd the butterfly plate with the smaller .055" dia. hole for the R-Tek (snowblower) carb, because LESS airflow is required during winter operation (cold air being more dense, containing more oxygen). Conversely, they spec'd the butterfly plate with the larger .100" dia. hole for the Duraforce mower carb, because MORE airflow is required during warmer summer operation (hot air being less dense, containing less oxygen).

Curiously, Toro/Lawnboy ALSO spec'd a larger 42.5 Pilot jet on the winter carb (R-Tek snowblower). Now this could be due to either the cold air containing so much more oxygen that the smaller air hole was still not enough to maintain proper air-fuel mixture ratio without surging at idle, or they ran a slightly richer mixture on the R-Tek due to the EPA's looser emission regulations on winter spec engines (relates to temperature -vs- atmospheric ozone depletion etc).

To point out the apples to oranges (R-Tek vs. Duraforce);
-The R-Tek is piston ported, Duraforce is Reed valve.
-The R-Tek is spec'd to run at 3800-4000 rpm, Duraforce 2900-3000 rpm.
-The R-Tek is spec'd at 50:1 gas;oil mix (richer mixture), Duraforce 32:1.
-The R-Tek pilot \ main jetting is 42.5 \ 73.8, Duraforce is 37.7 \ 77.5

The Duraforce mower engine should have the larger hole "summer" plate and be jetted accordingly. Using the smaller hole winter plate will starve the mower engine for oxygen in warmer weather causing a "rich-run" condition, unless it is "jetted down" to deliver less fuel as well. A check of the spark plug color will verify either way.

If you have "lean-run" surging (too much air, not enough fuel), then the order of business is 1) Make sure you have a correct and clean air filter in place 2) Check for vacuum leaks around gaskets, seals, air cleaner housing etc. 3) Make sure the inside of the carb is clean with no dust/dirt/debris clogging passages or jets 4) Try a larger pilot jet 5) Try a larger main jet.

My tinkerings with the Duraforce carb thus far have been limited, but apparently it shares the same pilot jet with the Suzuki 47P 2 cycle engine. Maybe someone can chime in if it also shares the same Main Jet design with the 47P as well. Here's some info on the 47P I've compiled; Carb info - so you can source jets anywhere, not just through mower $hops with Toro/LB/B&S pn's: Suzuki 47P 2 cycle, Mikuni B style butterfly carb, Mikuni part numbers;

Pilot jet (N101.043, 16mm long, 6.5mm head), available in increments of 2.5.
p/n: N101.043-37.5 (.375mm dia. holes), Pilot Jet #37.5 (LB "Duraforce")
p/n: N101.043-40 (.400mm dia. holes), Pilot Jet #40 (Toro "Suzuki 47P")
p/n: N101.043-42.5 (.425mm dia. holes), Pilot Jet #42.5 ("R-Tek", stock)
p/n: N101.043-45 (.450mm dia. holes), Pilot Jet #45 (Motorcycle shops)
p/n: N101.043-47.5 (.475mm dia. holes), Pilot Jet #47.5 (R-Tek high output)

Main jet (N102.221, 9mm long, 6mm head), available in increments of 2.5.
p/n: N102.221-75 (.750mm dia. hole), Main Jet #75 (Motorcycle shop)
p/n: N102.221-77.5 (.775mm dia. hole), Main Jet #77.5 (Toro 47P "High Alt")
p/n: N102.221-80 (.800mm dia. hole), Main Jet #80 (Toro 47P, stock)
p/n: N102.221-82.5 (.825mm dia. hole), Main Jet #82.5 (Motorcycle shop)
p/n: N102.221-85 (.850mm dia. hole), Main Jet #85 (Motorcycle shop)

One thing tinkerers discover quickly is the 2 cycle engine, for all its simplicity, is actually a finely tuned machine from top to bottom. This becomes apparent quickly when messing with air-fuel delivery systems engineered into designs by the factory, such as air cleaner housings, air filters, carbs, jets.
 

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If you pull the jet on the side of the carb (covered by a piece of tape), clean it with spray cleaner and a very fine wire. My DF was surging (after many years of smooth running), and that's all it took to stop the surge. It got gummed up with some oil residue that thickened up over a few months of non/limited use.
 

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Ive read through the Duraforce surging discussions and just some quick comment/logic on the butterfly vs jet issues;

Its assumed Toro/Lawnboy spec'd the butterfly plate with the smaller .055" dia. hole for the R-Tek (snowblower) carb, because LESS airflow is required during winter operation (cold air being more dense, containing more oxygen). Conversely, they spec'd the butterfly plate with the larger .100" dia. hole for the Duraforce mower carb, because MORE airflow is required during warmer summer operation (hot air being less dense, containing less oxygen).

Curiously, Toro/Lawnboy ALSO spec'd a larger 42.5 Pilot jet on the winter carb (R-Tek snowblower). Now this could be due to either the cold air containing so much more oxygen that the smaller air hole was still not enough to maintain proper air-fuel mixture ratio without surging at idle, or they ran a slightly richer mixture on the R-Tek due to the EPA's looser emission regulations on winter spec engines (relates to temperature -vs- atmospheric ozone depletion etc).

To point out the apples to oranges (R-Tek vs. Duraforce);
-The R-Tek is piston ported, Duraforce is Reed valve.
-The R-Tek is spec'd to run at 3800-4000 rpm, Duraforce 2900-3000 rpm.
-The R-Tek is spec'd at 50:1 gas;oil mix (richer mixture), Duraforce 32:1.
-The R-Tek pilot \ main jetting is 42.5 \ 73.8, Duraforce is 37.7 \ 77.5

The Duraforce mower engine should have the larger hole "summer" plate and be jetted accordingly. Using the smaller hole winter plate will starve the mower engine for oxygen in warmer weather causing a "rich-run" condition, unless it is "jetted down" to deliver less fuel as well. A check of the spark plug color will verify either way.

If you have "lean-run" surging (too much air, not enough fuel), then the order of business is 1) Make sure you have a correct and clean air filter in place 2) Check for vacuum leaks around gaskets, seals, air cleaner housing etc. 3) Make sure the inside of the carb is clean with no dust/dirt/debris clogging passages or jets 4) Try a larger pilot jet 5) Try a larger main jet.

My tinkerings with the Duraforce carb thus far have been limited, but apparently it shares the same pilot jet with the Suzuki 47P 2 cycle engine. Maybe someone can chime in if it also shares the same Main Jet design with the 47P as well. Here's some info on the 47P I've compiled; Carb info - so you can source jets anywhere, not just through mower $hops with Toro/LB/B&S pn's: Suzuki 47P 2 cycle, Mikuni B style butterfly carb, Mikuni part numbers;

Pilot jet (N101.043, 16mm long, 6.5mm head), available in increments of 2.5.
p/n: N101.043-37.5 (.375mm dia. holes), Pilot Jet #37.5 (LB "Duraforce")
p/n: N101.043-40 (.400mm dia. holes), Pilot Jet #40 (Toro "Suzuki 47P")
p/n: N101.043-42.5 (.425mm dia. holes), Pilot Jet #42.5 ("R-Tek", stock)
p/n: N101.043-45 (.450mm dia. holes), Pilot Jet #45 (Motorcycle shops)
p/n: N101.043-47.5 (.475mm dia. holes), Pilot Jet #47.5 (R-Tek high output)

Main jet (N102.221, 9mm long, 6mm head), available in increments of 2.5.
p/n: N102.221-75 (.750mm dia. hole), Main Jet #75 (Motorcycle shop)
p/n: N102.221-77.5 (.775mm dia. hole), Main Jet #77.5 (Toro 47P "High Alt")
p/n: N102.221-80 (.800mm dia. hole), Main Jet #80 (Toro 47P, stock)
p/n: N102.221-82.5 (.825mm dia. hole), Main Jet #82.5 (Motorcycle shop)
p/n: N102.221-85 (.850mm dia. hole), Main Jet #85 (Motorcycle shop)

One thing tinkerers discover quickly is the 2 cycle engine, for all its simplicity, is actually a finely tuned machine from top to bottom. This becomes apparent quickly when messing with air-fuel delivery systems engineered into designs by the factory, such as air cleaner housings, air filters, carbs, jets.
Good stuff Viking, thanks for those Mikuni part #s...this will make sourcing very easy!

Curiously most of the surging DFs were fixed with a #68 wire drill bit (which is just about .8xxmm) on the main jet and an R-Tek 42.5 pilot. I did swap in a couple of the "correct" throttle plates and they ran incredibly STRONG.

I'd say in the 30+ DFs i've built the ANTI-SURGING path would be
1. Replace throttle plate (with correct (98-7047))

1a-1b. If you don't have the updated plate i've had success replacing the pilot with a Suzuki 47P #40 pilot (these are twice the cost of the R-Tek jet)

2. Throttle Plate and R-Tek pilot with a .800 main jet or #68 wire drill the stock DF main jet.

I'd be curious to see specs on the F series and V series main jet sizes. I have inclinations to increase the size of the main jet and bump power with a free ported or drilled muffler.
 

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Excellent post viking and brad! Great information

First and foremost make sure your carb is clean. You will have to pull it off to verify the correct plate, so you might as well give it a good clean!

As I have done before I ALWAYS make sure it has the correct plate. Either drill it out or buy the correct one, via part numbers stated in the other threads and this one I believe as well.

This sometime takes care of it and it doesn't surge at all anymore. Sometimes it doesn't. If this is the case I then replace the pilot jet with the larger Briggs jet. See other threads for part numbers.

I have never had to do anything after this. This has fixed the 10+ DF's I have had. Everyone of them!!!


Best of luck and if you get into it and have questions we are here! Just take pictures.


Edit: GTP you beat me to it! Couldn't have said it better myself:)
 

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Curiously most of the surging DFs were fixed with a #68 wire drill bit (which is just about .8xxmm) on the main jet and an R-Tek 42.5 pilot. I did swap in a couple of the "correct" throttle plates and they ran incredibly STRONG.
This is logical, considering the Duraforce is a 144cc engine and the Suzy 47P is 121cc, I'd expect the Duraforce to require more air & fuel to maintain the same engine speed, utilizing the same carb specs (cross sectional venturi area).

I'd say in the 30+ DFs i've built the ANTI-SURGING path would be

1a-1b. If you don't have the updated plate i've had success replacing the pilot with a Suzuki 47P #40 pilot (these are twice the cost of the R-Tek jet)
This one has me baffled and would it be interesting to know more. Presuming "don't have the updated plate" means having a Duraforce with the incorrect winter R-Tek plate (smaller holes), I would expect those small (holed) plate Duraforce engines to be running rich from the factory, and require smaller jets to match the smaller airflow, not larger jets. That is, unless of coarse LB happen to put waaay too small of jets in those small plate carbs (to meet EPA regs. etc.) as well, still leaving them running lean. If that is in fact the case, I'm surprised those small plate engines ran at all, or at least didn't come back to the dealers with scorched pistons or holes in them from running way too lean.
 

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This one has me baffled and would it be interesting to know more. Presuming "don't have the updated plate" means having a Duraforce with the incorrect winter R-Tek plate (smaller holes), I would expect those small (holed) plate Duraforce engines to be running rich from the factory, and require smaller jets to match the smaller airflow, not larger jets. That is, unless of coarse LB happen to put waaay too small of jets in those small plate carbs (to meet EPA regs. etc.) as well, still leaving them running lean. If that is in fact the case, I'm surprised those small plate engines ran at all, or at least didn't come back to the dealers with scorched pistons or holes in them from running way too lean.
Interesting you say that because it always consufed me as well as to why it "should " be rich yet richening it up seemd to alleviate the problem (not entirely correct it).

As a matter of course I never tried to wire fit the problematic jets to see if i could gauge the size of the jet (fitting wire bits to size them) to in fact see if LB cut the main jet size in order to squeeze compliance out of them (this most likely in my opinion is the reason). They were limited to a series of production run serial numbers, either by mistake (bad production batch) or they knew inspectors were in the factory?:lalala:

Perhaps i will have to take that surging carb I have saved and inspect that main jet and pilot, i already know it has the small hole. As for not killing the motors, i know a bunch of the ones I have that had been surgers and the owners couldn't stand them parked them after running them only a few times, shops couldn't fix them so I ended up with minty mowers for cheap.:sorry1:
 

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Discussion Starter #17
Diddy. We have gone over this already:) do a search on dura force surging. Also click all the links on the treads. There is a great write up on what to do. If u think it uses too much gas running right then just change it back

http://www.mytractorforum.com/showthread.php?t=158246
Great thread below
http://www.mytractorforum.com/showthread.php?t=59888
http://www.mytractorforum.com/showthread.php?t=51353
http://www.mytractorforum.com/showthread.php?t=112222&page=2
yes we have. i somehow couldnt find those ones when i searched
 

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yes we have. i somehow couldnt find those ones when i searched
totally understand. I have been there too;) Hope you get it figured out, these DF's are outstanding when tuned right. You think they are powerful now, just you wait until you give it some more fuel!!!
 

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All of my Duraforces except for one came with the small hole plate. One of my '99's came with the large plate, but my '98 did not. I'm running the large plate on two mowers with a 42.5 and it has just a bit of surge when cold and unloaded. The rest I'm running the small plate with drilled pilots and mains at 78 bit and 67 or 66 bit respectively. They run great as well, perhaps a bit better than the 42.5 and large plate mowers in my opinion. I think I'll have to test the larger plate with the other jet combinations after reading this thread.


edit: had wrong bit size on mains
 
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