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Discussion Starter · #1 ·


I posted this up on MTF a few years ago. I haven't seen a guide on how to fix the surge in 75% of the Duraforce's that I have come across. I can't take credit for any of this. It is a compilation from posts at MTF and my experiences fixing over 40 of these mowers. Some with a slight surge and some that were almost like off and on.

Now I have had my 10323 for a long long time, and have used it so much. It has never surged at all, just ran so amazing. now my grandpa's 10323 has never run right. I will get to that after a bit.

Anyway I got a 10550 a while back and it surged a bit. Nothing terrible like my grandpas, which will barely run. But it did surge. So i have been digging around this forum quite a bit about all the DF surging issues.

So I ordered up the Briggs & Stratton 42.5 Jet, part number 801308.
I also ordered up a new throttle plate Lawn boy part number 98-7047.
Total parts bill was $4.42.

First i looked at the pilot jet, it was the 37.5 jet, so i put in the 42.5 jet. This really didn't make too much of a difference. So i finished up mowing up my leaves in the back, and thought I would check to see if I had one of those smaller holes in my throttle plate. Took off the carb and looked and yeppers, the hole in my throttle plate was A LOT smaller then the replacement one I ordered, 98-7047. So i took that smaller one out and put in the replacement one. Really easy to do!

Started it up and it smoked a bit and ran what seemed to be too slow. So i turned up the RPM 4 clicks, and bam sounds so good now. Just like my old 10323 that i recently sold. Soooo much power. WOW. That is all I can say is WOW. Its like running the mower on idle before and now its all opened up. Its night and day difference. Im so excited!

Can't wait to tackle my grandpas 10323. I have all the parts for his as well. If anybody has a Duraforce that surges even a bit, I would highly suggest looking at your throttle plate, and getting the proper one and installing it. Also getting the larger B&S pilot jet and installing that as well.

So a step by step cure for the surge. This has worked on 100% of the Dura forces that I have come across.
1. Clean the carb. Including taking out the pilot jet on the side and clean it. It is under a sticker. This will let me verify everything.
2. I make sure the float is the right height, 1/2" above the base of the carb when upside down.
3. Replace needle and seat if needed.
4. Verify that the throttle plate has the proper vent hole. It's the plate at the back of the carb, closest to the engine. If its the tiny hole, then take a pair of plyers and pull it out. Replace it with the correct part number. Yes they made a mistake and put in the wrong one. Make sure that you note the position of the flat part of the throttle plate
5. Put it all back together and fire it up. Let it warm up, use it for a while.
6. If it still surges a bit, put in the B&S jet. Its on the left side, when you are mowing, of the mower on the outside of the carb. It is under a sticker originally. Put in the new larger jet.
7. This will fix it every time! If you think your mower is now running too slow, then adjust the governor collar 2-3 clicks up to increase the RPM.
8. Mow what ever you want now. Look out because you will not be able to stop this mower with grass. It will simply smooth out the taller and thicker grass you mow.
9. Seriously the power is un-real. Gas consumption may go up a bit but it is mostly un-noticeable in my opinion.

Other guys have had success with drilling the main jet. I have never tried it as this "system" has worked every time.
 

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This works great.. I tried it back when I had a 10303. I didn't replace the throttle plate though.. Just the jet.

I agree it makes these things like beasts.. You simply cant bog them down!

-Stan
 

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Discussion Starter · #4 ·
Cool! great idea. I didn't even think about it being a sticky. I feel honored. Hope this will help others with these mowers. They truly are awesome when tuned right
 

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I saw this same thread started by Wolfy bumped back up on MTF's Walk behind section today. This being the time of year to pull out the mowers and get them ready to go again, I thought I'd go ahead an bring it back up to the top here again.
 

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Thanks Wolfy, more info please!

I have a 10252 and it surges a bit. Not so much when mowing (under load) but I was wondering if the plate you refer to could be drilled out since you say the hole is too small and the new part had a larger hole. Could you provide the size of the hole in the correct plate, and can I drill it out? And the pilot jet... is it marked as to size? I pulled mine and saw that the one tiny hole is intersected by two larger holes, and they were all open, but I did not see markings on the jet. Thanks in advance!
 

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Duraforce Throttle Plate

From the information I have been able to find on the forum the diameter of the throttle plate holes is as follows. The small hole is .055 (1/18") or just a little bit smaller than 1/16". The large hole is .10 (1/10") or a little smaller than 1/8". Should therefore be fairly easy to use a couple of drill bits to gauge the size. Bill
 

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I wanted to see what all this Lawn-Boy hubub was about and picked up a 10324 with a duraforce 2 stroke last week.
The previous owned said the throttle started acting strange and when I got it home I could see the governor spring was all uncoiled and bent. I disassembled the whole carb and found out the plastic throttle shaft was wobbling around in a wollowed out plastic carb body. Grrrr. I ordered a new carb ($50 plus shipping). As you may be aware, they are only available in a build it yourself package of individual pieces. That part didn't really bother me.
To get to the point... I thought it was very odd that this "new" carb came with the "small hole" butterfly. Penny for scale on the left, old disc in the center, and new one on the right. I put it together (with the original "large hole" disc) and will try it out in the morning
 

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I suppose it's possible that when they put that kit together they put the incorrect throttle plate in there, especially if the kit has been on the shelf for a while. Just make sure to put in the bigger hole one or drill the new one out to match the old one. Bill
 

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Discussion Starter · #10 ·
All, thanks for answering the questions and posting up the pics! Very helpful addition! Yes the larger hole is the correct one. Use that! or like Bill said drill it out.

Dale, yes do what Bill said there. If you can post up your results!
As for the pilot jet the factory one should have a 37.5 label on it on the outside, in other words on the part you can see when it is installed in the carb. The part you put your flat blade screw driver into. The briggs jet is 42.5.

That is just the size of the opening in the tip of the jet as far as I know.
 

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I ordered the B&S 42.5 jet Part #801308 ($5.30), and the Lawn-Boy Throttle Plate Part #98-7047 ($0.85), for my 10424 GoldPro Push. The guy I got it from drilled out the jet, but it still surges a bit, so I'm going ahead with this fix. I'll let everyone know how it works out. Also, I have 2 questions.
1. The guy I got the mower from said he's had several cases of the surging problem be due to a leaking main seal. Anyone else ever have this problem?
2. I won't say where I purchased the throttle plate and jet, but shipping was more than the cost of the parts($7.95)! Total for the 2 parts was $14.10. Anyone know where to get these parts cheaper?
 

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Many times it is cheaper to order and buy from your local dealer (Toro, small engine shop, etc.) The cost of shipping many of these small parts is crazy and the web site usually just has a flat rate so you can't just ask them to stick it in a mailing envelope for a couple of bucks postage. Bill
 

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Tried the following, but in the end changing the high end rpm from 4000 down to the recommended 3000-3200 range is what solved the surging with my friend's LB 10323:

1. Holding thumb over primer hole. No difference.
2. Loosening gas tank cap. No difference.
3. Switching back to a 32:1 fuel ratio. No difference.
4. New carburetor adjusted to owner preference rpm. No difference.
5. Larger hole in throttle plate (.10"). No difference.

62040


Mower would surge and die within 30 seconds. Now it will mow an entire yard with no problem. I turned this dial counter clockwise 10 clicks.

62041
 

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That is great that you were able to get the surge figured out. The Duraforce seems to be a love/hate relationship. When they are dialed in and running correctly they are a beast. When they surge, most would rather kick them to the curb. Just curious why the mower was running at 4000 RPM's to begin with? Bill
 

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... Just curious why the mower was running at 4000 RPM's to begin with? Bill
Bill, good question. I don't have a clue. Mower is quite old and belonged to the owner's mother originally. I'm tempted to put the original carb back in it and tweak the rpm again so it's closer to the recommended 3000 - 3200 rpms. Betcha it works fine, but I'm a little burnt out on it to tell you the truth. This is the only Lawnboy I've ever worked on although this is the second time for this one. I've taken the carb off it at least 4 times now.
 
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