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Discussion Starter · #1 ·
I bought a new lawnboy 2-cycle goldpro today and for the first 2 minutes of use it surges but....the guy who runs the mower shop said its gonna do that and its typical of that mower. Thats not what im worried about the thing im so worried about is that it dosent sound to loud....it just dosent sound like its whinding out at all....im used to 2-cycles running wide open but this just seems to have a farely steady low rpm. Is there a way of turning the carb up?? Or is this a EPA carb that cant be adjusted?
 

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Last year when i bought my lawnboy the dealer cranked the rpms up on mine some, I didnt see what he turned but it has more rpm to it then it did when he first fired it up
 

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Discussion Starter · #4 ·
I couldnt find any screw adjustments on the carb...I was able to play with the rev limiter to get higher rpms...untill you let go of that little fan blade that pushes off the flywheel.
 

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Bunton
The DuraForce engine is a fixxed jet carb.
The surging is caused by lean jetting.
There are a guy on another fourm that gives detailed information on how to rejet the carb and cure the surging problem.
He does not reccomend a LwnBoy for commerical use with a stock carb due to the lean factory settings.
 

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Yes they are two jets.
The low speed jet is hiden by the parts number sticker on the side of the carb.
The main jet is located inside the of the nozzle which is in the carb body.

The factory Low speed jet is a size 37.5
The factory High speed jet is a 77.5

If you were to drill the Low speed jet out to a 39 and the High speed out to a 79 using wire gage drill bits and a hand drill. Your Lawnboy will wake up.
 

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I have did the mod to 10 or 12 DuraForce engines for people.

What I do is buy a new set of stock jets for the carb to start.

Then drill the old jets.

Since the low speed jet is located on the side of the carb and easy to get to. I start with it.

If you remove the low speed jet. You will notice that they are two small holes on the side of it. And of course the hole for the jet itself on the bottom. This bottom hole is the only one that you want to do anything to.

I enlarge the low speed jet to 38 to start. Then reinstall and check for any surging. I have found that enlarging the low speed jet to a 38 or 39 normally does the job.

When drilling the jet out. You just want to drill through the jet "hole" and not all of the way through the jet body. Make sure that you clean the brass shavings from the jets before you reinstall them.

If after drilling the surging stops. Then remove the main jet and drill it out the same over size as you did the low speed.

Example. If you drill the low speed from 37.5 to 39. That is 1.5 over size. Add 1.5 to 77.5 = 79. Drill the main jet to a 79.

Then adjust the governor vane tension to slow the engine when you move the throttle from Flow to Fast.

It takes time to do the mods correctly and requairs that you remove the carb severel times during the operation. I wish that I could just drill every jet out to X size. But as anyone should know. Every engine is different.

Two things that you must be aware of.

#1. Doing any carb mods will void the warranty. That is why you want to buy a new set of jets. LOL

#2. Your fuel comsumpion will increase a little. For your engine will now by able to get a better supply of fuel. Which in turn will allow for more oil for lubing and it will run cooler.

I have not had the first complaint after rejetting peoples carbs. And have one dealer wantting me to do a couple of his personal mowers for testing.
 

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You can adjust the RPM's by turning the plastic gear on the throttlle control on the carb. You may need to tip it sideways so you can really see it good. I have bumped up the R's on both my 6.5 Duraforce'. The surging id due to the emmisions crap, but it should be a steady purr, while mowing consistent grass. When the mowers is just sitting there it will surge and it is normal.
 

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Discussion Starter · #13 ·
Do you have to force that little plastic piece?? I tried forcing it to turn on the spur gears but it would just bend and twist the shaft...I tried lifting it off the shaft and it wouldnt budge.
 

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The adjustment plastic wheel adjust clockwise and counterclockwise. You will feel it click. It does take some pressure but don't make it click several times the adjustment is sensitive. Be careful not to damage the little spring as well. I adjust mine with the mower running (VERY DANGEROUS) just so I can hear the immediate results of the adjustment.
 

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I have a 1993 Lawnboy model 10424 that has this surging problem. I bought it used and I can not find the drill bits to enlarge the jets. Can you substitue a different jet and from what to get around this drill bit problem or is there another way to rectify the surging. You would think they could not sell these things the way they run.
 
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