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Concerning a 10323 Duraforce, entirely hypothetical of course, if one were to accidentally hit a stick large enough to distort the shaft-to-flywheel key, could this cause a surging issue? Perhaps being slightly out of time?

It seems Mrs Rumrunner May have induced this condition while mowing today. Fine one minute then, wham! Lots of surging. I'm feeling mighty I'll.

Yes, and more than likely sheared the flywheel key. Takes more time than anything to fix, just replace key.

Why did you have to be honest with me? I guess it's better like that. Tell me, is there any way I can tell if that's the culprit?

Thanks Rivets, much obliged.

Do a you-tube search on re Laing flywheel key. It's not that hard, you can do it.

If the surging coincided with hitting [whatever] --- meaning there was no surging before the hit -- then it's probably the flywheel key.

However, it is early in the season so if you have gas in the tank leftover from last year, you may want to try fresh gas.

Well, I was actually hoping for a broken key, but I hardly get what I wish. I pulled the flywheel and was fully expecting it to be broken because I doubt there was more than 100" Lbs breakaway torque on the nut. Pulling the flywheel from the shaft was the hardest part and it broke my heart to see the key 100% unharmed. I even magnified it without the slightest distortion or crack present, maybe a bit of rust at the bottom but negligible. So, here's the history and what I've looked for and considered:

I bought this in 1999 (new) at Lowe's, back when they used to sell them and the parts. I'm expecting it to be running fine for another 10 years. I remember lawn-boys being like that. Before I left home in 1984, I was still using a 1963 brick head.

one month ago I installed a new carburetor (by kit) and it ran like new again. We've mowed with it 3 times. I drained and swabbed out the gas tank, got a new in-line shut-off valve at the time of carb replacement. I searched high and low and found Lawn-Boy oil at O'Reilly's in town, which really surprised me. I figured that Lawn-boy claims their oil is best and it has a stabilizer in it, so I'd keep using it with fresh gas. Be advised, it was running great until 2 or 3 days ago.

I bought a new Coil about 3 weeks ago since the old one was acting up. When I removed the flywheel today, I pulled the coil off and found all kinds of stuck on muck on the contacts face, from I don't know what, but cleaned it up really shiny and clean today.

I looked at the spark plug and checked it was clean. I replaced it at the time of the carb. I've been using one of the really hot E-3 "Diamond Fire," I think they're called. At the parts store, they call these "one-shot-one-kills," because they start on the first pull.

I unplugged the fuel line and opened the valve and drained out what was in the tank. About half the tank drained through the valve and line within, probably 30 seconds. Looks free to me.

I removed the jet that's in the side of the carb body, I guess this is the "low pressure" or "Inlet" jet? Anyway, just to see and found it in brand new and squeaky clean condition.

Of course I checked the air filter, which is new also.


Now, the owner's manual says to use "Regular" unleaded gasoline. That was in 1999. It seems I read something not long ago (within the last week, and it may have been on this forum somewhere) that claimed so-called "regular" isn't so good these days and to use better mojo gas instead. I really can't remember what it was for, but it was for some type of lawn tool. What do you all think? What about the plug I'm using? Sure, it's new, but can there be one "Too hot?"

Look folks, I know this is quite a lot of info (TMI) but I want to let you in on everything so we have the best shot at figuring it.

And as always, I appreciate your help more than you'll realize.

About the gas/oil -- if you're using fresh gas, I think you've eliminated that as a culprit. I wouldn't worry about regular vs premium.

I've never had a Duraforce but there is an issue with that engine tending to run too lean. Look in the Lawn-Boy forum for a thread that deals with that. I think there's a fix involving replacing the jet (carb) -- the thread even gave a specific part number to use.

If you can't find that thread, ask me and I will find it.

I remembered enough about the thread in my last post to find it easily: link to Duraforce surging fix.

Two-Stroke said:

About the gas/oil -- if you're using fresh gas, I think you've eliminated that as a culprit. I wouldn't worry about regular vs premium.

I've never had a Duraforce but there is an issue with that engine tending to run too lean. Look in the Lawn-Boy forum for a thread that deals with that. I think there's a fix involving replacing the jet (carb) -- the thread even gave a specific part number to use.

If you can't find that thread, ask me and I will find it.

Click to expand...

Two stroke the part number is Briggs and Stratton Part #801308 for the duraforce idle circuit. it cleared up that 10424 that i was working on. I just drilled both a 10547 the other day and it worked too. the thread is 10424 idle circuit replacement and it has the size bits i used.

Let me get this right, the "IDLE CIRCUIT" is the external jet on the side of the carb, the one that was once under the sticker when new? I need to make sure I'm looking at the right part. With a name like "idle circuit," it makes one think of electrical components, even though "circuit can apply to anything closed.

Happy Saturday.

Rumrunner said:

Let me get this right, the "IDLE CIRCUIT" is the external jet on the side of the carb, the one that was once under the sticker when new? I need to make sure I'm looking at the right part. With a name like "idle circuit," it makes one think of electrical components, even though "circuit can apply to anything closed.

Happy Saturday.

Click to expand...

That is correct. i have heard it called idle circuit, idle jet, metering circuit. Whatever its called it usually gets clogged easy and causes surging. If you replace that part and it still surges you need to get a #67 micro drill bit and drill the main jet. After you drill and When you start the machine you will see what the EPA did to the duraforce engine by making them design them that way to pass emission standards. They basically killed the brand.

Thanks, turfboy1997. I'm glad you found this thread.

Thanks for the tip. So, which one's the Main Jet?

Also, just a couple replies up you stated a #67, but on your surging thread you mentioned a number 76, or a size ranging from #75-77. Is 76 what you meant?

Just my opinion, but in your case I would not punch (drill out) the main jet with a micro drill. If you don't know what you are doing, you will cause more harm than good, and you will end up buying a new jet or all new carb. I have punched over a hundred jets and there are times that I have had to replace parts because I made a mistake and went too fast. It sounds easy for a mechanic, with the right tools, but not worth the time, money and effort for the average person. Would be cheaper for them to purchase a new jet and replace.

OKAY I got my Briggs idle jets in today. Didn't make one bit of difference. So, I decided to pull the carb apart and check everything. Ready for the funny stuff? I remember reading something about the governor side throttle plate having incorrect hole sizes. BE ADVISED: Some of the new carb rebuild kits come with the wrong plate, even today. I swapped it out with my old one and seems to do better until it just died on me. Something told me to look at the plug and I couldn't believe what I saw, black and dripping with oil. What gives? As I said before, I'm using the gen II oil at 8oz per two gallons. I changed the plug and all was better, but when finished I looked at it and I found it pretty ugly too with oil drippings.

Now, my questions from before remain unchanged, plus new ones now:

Why did it run flawlessly after rebuild with the wrong throttle plate?

Why was all perfect until the machine killer wife hit a stick, but with an intact flywheel key?

Why could the machine be smadging plugs now?

What can other causes be for the surging? It still is doing it some.


Thanks again all.

Here's my opinion. You don't have near the machine as the one you used back in the day. I can't offer any more advise than what you already have about fixing it. I've had a few DF and liked none of them. Push 'er to the curb. Find you an older F series, and you won't go wrong! Good luck.

Well, now that you mention it, I got my hands on a model 8253 yesterday. It was free, and for a good reason- it looks worse than bad. I think there's only a slight chance of it ever running again. It's just a plaything to make me a better 2-cycle guy. I have stuff to do, but I'll tear into it in the next couple weeks.

Rumrunner said:

Let me get this right, the "IDLE CIRCUIT" is the external jet on the side of the carb, the one that was once under the sticker when new? I need to make sure I'm looking at the right part. With a name like "idle circuit," it makes one think of electrical components, even though "circuit can apply to anything closed.

Happy Saturday.

Click to expand...

I have a Duraforce engine that would surge. The carburetor has a small piece of black tape on the side. If the tape is pulled off, there is a brass jet that can be screwed out of the carburetor. The jet can be reamed slightly larger with a very small drill bit or a torch cleaning tip. The Lawn Boy engine that had this jet gave problems because the jet was too small in order to meet emission standards. I did two of these and the mowers ran like a new engine afterward. Be very careful and don't ream the hole too much. Do it with caution.

It is possible the float has been adjusted out of spec do to the violent hit, or the float valve (needle valve) has been damaged. Not enough fuel in the bowl will create a lean condition.

If it was running fine without surging before, I wouldn't go drilling nuttin. That isn't the problem and you could really mess it up..

I can make mine surge easily by leaning out the main jet/high speed nozzle. You have one of those that's adjustable on yours?

Surging 99% of the time is caused by either too much or not enough fuel getting to the cylinder. Float level would not caused by a hit. Clean and rebuild the carb first.

Rivets and WhyZed, thanks for the advice. I've been reading and intend to work on it some soon. I've just been busy lately. I do realize I need to pull the carb, but I honestly hate pulling the Duraforce carb. I know, I'll make it happen by Sunday. No, I don't intend to drill any jets yet.

Rivets, speaking of punching jets, I haven't done that yet, but my curiosity is up. I imagine I may eventually just for the sheer fun of it. I believe you about not wanting to do it if I haven't before. I guess that's the reason I'd play around with the notion. Of course, I'd have a couple of new jets on hand too. So, having said that, perhaps you could pass some of that knowledge around on the subject.

Very simply put, punching a jet means to increase it's size by less than .001 at a time. This is done using micro drills and a Pin vice drill. Doing this will allow more fuel to enter the different passage ways in the carb and produce a richer mixture. Doing it wrong will result in carbon buildup in the cylinder, plugs carbon fouling, back firing in the muffler, excess fuel consumption, etc.