Another Duraforce Surging

6065 Views 30 Replies 14 Participants Last post by Croc, Jun 17, 2009

DocDoug

Discussion Starter · Jun 7, 2009 (Edited)

Another Lawn Boy Duraforce Surging

By now, I am certain that enough has been typed regarding the Duraforce surge. Having said that... here is my story.

I have a used 2001 Duraforce that I paid $25.00 for. The mower would not start. I removed and cleaned the carb AND the two jets. I replaced the seat and valve, installed an in-line filter and shut off valve and replaced all carb gaskets. (I didn't replace the float.) I verified that the flywheel shear pin was in good shape and installed a filter material in the primer bulb. As well, I ensured that the gap of the spark plug was .030 and the air gap of the flywheel was the gap of a business card. I washed, cleaned and dried the fuel tank. The upper and lower seals looked good with no oil leakage. Finally, I ensured that the exhaust port and muffler tube was clear. (It was VERY clean and clear.)

After my repairs, it started on the first pull. (I run 35/1 Mobile 2T oil, 87 octane fuel) I adjusted the mower to 3,100 rpms in the fast mode. The mower surges a little in the fast and mid-range. (It drives me nuts.) The slow speed is fine with a nice burble.

I spoke to a small engine mechanic who works on LBs and explained the lean theory. He laughed and stated that the fix is most always to replace the gov spring. I will try this next week.

Comments welcomed on the gov spring replacement theory to fix the surge.

By the way, I am not a fan of the LARGE rear wheels you see.

Thank you,

Doc Doug

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1 - 20 of 31 Posts

echoman

· #2 · Jun 7, 2009

You need to reattach the retainer back onto the fuel line at the carb. This will help keep the primer hose from contacting the govenor which can produce a throttle issue.

FordTech

· #3 · Jun 7, 2009

25.00, such a great deal. Wish they could be found around here.

petr

· #4 · Jun 7, 2009

I agree with Echoman. Also check to make sure that the throttle control on top of the airbox does not hit the air vane.

Pete

imaLawnBoyFreak

· #5 · Jun 7, 2009

I think i have everything to convert that into a smaller 8 inch wheel

LawnboyTim

· #6 · Jun 7, 2009

Great Find! I havent ever used a high wheel lawnboy. Looks really clean too.:congrats:

DocDoug

Discussion Starter · #7 · Jun 7, 2009

Re: Another Duraforce Surging - LARGE Wheels

Funny thing... I didn't realize that I failed to reattach the fuel line to primer line retainer, UNTIL I looked at my photos. :duh: I had every intention of doing this with the reassembly.

With respect to the surging, at the moment neither the primer line nor the throttle control on top of the airbox is contacting the air vane.

One other note... the mower came with a Champion CJ8Y plug installed. According to Champion's website, the factory NGK BPMR4A plug cross references to Champion's CJ8Y. I don't think a new plug would stop the slight surging.

The LARGE wheels are different. I can't say they made mowing or pushing the mower easier. If any thing, the large wheels made it more difficult to maneuver in tight area. (I can't figure out the advantage of these wheels?) I too believe that I have spare parts to convert this to a small wheel mower.

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dougmac

· #8 · Jun 7, 2009

I too was always curious to know the functional purpose of these big wheels ... never have I used one, so I can't offer an opinion.

I'd leave it alone just for the uniqueness of it ... unless of course some expecive or NLA part "unique" to the high wheel feature was wore out and affected mowing performance or pushing ability.

Doug

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knightrider

· #9 · Jun 7, 2009

What about pulling off the fuel filter......making sure that it's not inhibiting the flow to the fuel bowl......

DocDoug

Discussion Starter · #10 · Jun 7, 2009

I just pulled the LARGE wheels and determined that they have bearings in them. Given this, I will leave them alone until they wear out. With respect to the fuel filter, I looked closer and I installed it backwards. I reversed the filter, confirmed that it flows well and reinstalled. I started him up and have the same symptoms. I let it cool, loosened the carb screws and snugged them back up (thinking they may be over torqued) and STILL have the same surge in fast mode. I then clicked the spring a few to tighten the tension. Still surged. I held the vane in place in medium and fast mode and no surge. If there was an air leak or it was running lean, wouldn't I hear this now?

I am trying a new spring this week and will report back.

Doc Doug

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capstan

· #11 · Jun 7, 2009

Re: Another Lawn Boy Duraforce Surging

DocDoug said:
By now, I am certain that enough has been typed regarding the Duraforce surge. Having said that... here is my story.

I have a used 2001 Duraforce that I paid $25.00 for. The mower would not start. I removed and cleaned the carb AND the two jets. I replaced the seat and valve, installed an in-line filter and shut off valve and replaced all carb gaskets. (I didn't replace the float.) I verified that the flywheel shear pin was in good shape and installed a filter material in the primer bulb. As well, I ensured that the gap of the spark plug was .030 and the air gap of the flywheel was the gap of a business card. I washed, cleaned and dried the fuel tank. The upper and lower seals looked good with no oil leakage. Finally, I ensured that the exhaust port and muffler tube was clear. (It was VERY clean and clear.)

After my repairs, it started on the first pull. (I run 35/1 Mobile 2T oil, 87 octane fuel) I adjusted the mower to 3,100 rpms in the fast mode. The mower surges a little in the fast and mid-range. (It drives me nuts.) The slow speed is fine with a nice burble.

I spoke to a small engine mechanic who works on LBs and explained the lean theory. He laughed and stated that the fix is most always to replace the gov spring. I will try this next week.

Comments welcomed on the gov spring replacement theory to fix the surge.

By the way, I am not a fan of the LARGE rear wheels you see.

Thank you,

Doc Doug

hay Doug try takeing a pipe-cleaner(shannnneeelle stems)(sold an jo-an fabrics) and run it trugh the carb jets

ps your fule filter is on backwords

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FordTech

· #12 · Jun 8, 2009

The larger wheels are best for rough terrain lawns and fields. If you have a lot of bumps in the lawn and ruts the large wheels roll easier over them. Also good for ditches and curbs.

DocDoug

Discussion Starter · #13 · Jun 11, 2009

I purchased and installed a new vane spring. The old one was in fact stretched. As well, I removed the two jets, again, and wire cleaned each. I then sprayed each with carb cleaner and air. Assuming it doesn't rain tomorrow, Maryland has been receiving rain 5 out of 7 days for the last two months, I will test the mower and report my findings.

When I purchased the spring, the small engine mechanic again stressed that enlarging the jets is a cover-up for another problem. He too has a Duraforce and works on LawnBoys. He said he will be shocked if the new spring and wire cleaning of the jets does not fix the surge. I hope he is right! :i_praying

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mtgrs737

· #14 · Jun 11, 2009

Sounds like you have covered the bases pretty well.

One question though: does the exhaust smoke when warmed up in the fast run throttle position with the surge? If so you may have a rich surge condition caused by excess fuel getting to the engine. If so I would replace the float, I have had many go bad on me with the DF carbs and replace them with the inlet valves.

I would suggest if the new governor spring does not fix the surge and there is no excessive smoke with the surge then you open up the main jet one drill size.

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es_bob

· #15 · Jun 11, 2009

I haven't had to drill out the jets on my df mowers, just had to remove the pilot jet and push a piece of wire through the nozzle to clean it out. Let us know if your problem gets solved with what you did.

DocDoug

Discussion Starter · #16 · Jun 12, 2009

Go figure... another rainy day in Maryland. As a result, I didn't get to test him today. Forcast is clear and sunny for tomorrow evening, Saturday and Sunday! I can't wait to test the boy!

> mtgrs737 wrote: "One question though: does the exhaust smoke when warmed up in the fast run throttle position with the surge?"

No, I don't recall noticable exhaust smoke when warmed up in the fast run, with the surge. (Good point though!) I should add that when the fuel is switched off and the engine continues to run only on the fuel in the bowl, the surge continues till the end. Based on this, I honestly don't think the float is an issue.

As my wife says, if it ran perfect when you bought it... you wouldn't like it. I realize she is right. Like many here, I LOVE TO TROUBLE SHOOT!:bannana:

I will report back NLT Sunday.

Doug

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mtgrs737

· #17 · Jun 12, 2009

I had one that rich surged once, took me a while to wake up to that fact as the lean surge is so common. Just think what a good mower it would of been right out of the box if they would of had an adjustable carb!

DocDoug

Discussion Starter · #18 · Jun 13, 2009

I tested the Duraforce after replacing the throttle spring and cleaning / running a wire through both jets. RESULT - Same exact condition. I used the Duraforce for 30 minutes and couldn't stand it. I pulled out the trusty F engine and finished the job.

There is one more possibility before I enlarge the jets... replace the float and spark plug. It can't hurt. I am truly getting tired of R&R the carb on this thing.

If the mower was truly running lean, wouldn't it smooth out when I partially choke the engine? At any rate, when I choke the motor it simply surges the same. Likewise, when I shut the fuel off and allow the engine to die, it continues the surge till the end.

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leeave96

· #19 · Jun 13, 2009

Sounds to me like a re-jet is in order.

Good luck,
Bill

FordTech

· #20 · Jun 13, 2009

Thats how so many of these mowers end up getting bought up cheap. Others can turn trash into treasure.

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