Set Duraforce to 3k RPM ... Really?

[calvin1]

I just bought a duraforce engined LawnBoy and I had to do some work to get it running right. It's almost there after cleaning the carb and changing out the spark plug. It still surges a little on idle and part throttle but I think it's some junk still in the idle port and I added a cap full of MMO to help move it along. I see from Google that surging is common on these but mine doesn't do it at full throttle so it's not as bad on mine as some others have seen.

The one question I have is in setting the max governed speed. The manual I got from lawnboy.com says to set the click wheel adjuster on the governor so that the engine runs at 2900RPM +- 300RPM. When I first put my tach on it it was running about 3200 RPM so I dialed it back and now it hovers around 3k. This seems REALLY slow. IIRC, the last LawnBoy I had was supposed to run at 3600RPM, which it did with ease. Does anyone here have any experience with setting up these DuraForce engines?

 

[Cujet]

Go with 3600 RPM.

The reduction in speed was/is driven by trial lawyers.

There is no technical reason for a 21 inch blade to turn only 3000 RPM. Nor is there a reason to turn such small displacement engines so slowly.

We could go on and on about the perceived risks. But the fact remains, we have been running lawnmowers at 3600 RPM for a full 100 years now. The number of problems associated with this is truly microscopic in my opinion.

In fact, a case could be made that mandatory lower RPM also carries risk.

 

[dwendt44]

I'm a little more cautious myself.
I set my new Lawn-boy to 3200-3300.
There's no iron liner in many newer engines so I'm not
taking chances for now.
May turn it up a little more next year.
A good quality oil is a great idea on aluminum cylinders.

 

[S2500Dog]

I had to fix a 4.5 HP Briggs and Stratton Engine for my 20 inch Murray. The fool who I brought from screw the carb and all of the necessary springs that make the engine idle correctly. I did a full rebuild and cleaning of the carb, full tune-up, flush engine with Pennzoil Platinum and change over to Quakerstate Ultimate Durability, cleaned the gas tank, and finally installed new idle springs so that the engine could stop redlining when running. Now it starts and run perfectly on the first pull.

 

[Johnny]

One of my Lawn Boy mowers has the Toro Duraforce engine and it has always had some surging when first started. After it warms up the surging goes away. I read on one of the mower forums that some of the guys are putting in larger jets to solve this problem. Anyway, I agree with Cujet, 3,600 RPM is where mine is set and it works great. My 45 year old Lawn Boy has a slide throttle on the side for when I have to mow tall thick grass, and when I open that thing up it is humming along around 4,200 RPM.

 

[Cujet]

Originally Posted By: dwendt44
I'm a little more cautious myself.
I set my new Lawn-boy to 3200-3300.
There's no iron liner in many newer engines so I'm not
taking chances for now.
May turn it up a little more next year.
A good quality oil is a great idea on aluminum cylinders.


Remember, the mower does work. To accomplish that work, the engine creates pressure in the cylinder (obviously). What's not so obvious is the governor system regulates the engine. If you are doing the same work at lower RPM, the pressure is increased, thereby, increasing cylinder wear.

If you are doing the same work, but at a slower pace, the number of cylinder combustion events are exactly equal.

Conclusion, 3600 RPM is ideal for mowing heavy grass. You can always reduce RPM's when appropriate.

 

[calvin1]

Well I got the tach out and bumped the governor up so that full throttle is at 3800 RPM. No-load WOT is about 4200 so this gives the governor a little headroom to work with. At that setting pulling the throttle all the way back brings it right to the 2900 regulation speed. The sweet spot seems to be 3400-3600. At that point it gives enough power without surging.

What I can't figure out is that although everyone says this engine is made to run lean mine actually acts like it's running a little rich. It smokes heavily until hot and four-strokes once or twice every fifteen seconds or so. When my old adjustable LawnBoys ran like that I'd turn the mixture screw half a turn lean and they'd be good.

All in all I'm really pleased with this mower. I wish I could get this much good use out of every $60. It has the self propel and with that and the Gator blade spinning 3600 RPM this thing is a beast. I think it will get even better once it burns through the 32:1 + MMO that came from the PO and I can run it on the 42:1 that seems to work better.

 

[Best F100]

calvin,

I will vouch for everything you said. I happen to own:

1) A 2 cycle, 6 1/2 HP, Lawn Boy Duraforce with Easy Stride (Personal Pace) self propel and Electic Start w/ a Gator Blade. Engine is set around 3200 rpms give or take.

2) A 3 speed, 6 1/2 HP, Commercial Duraforce with an orange, 1 gallon gas tank and orange steel wheels. Added newer Lawn Boy rear wheels so that you can replace just the worn tread & not the wheels.

3) A 2 cycle, Snapper with a Wisconsin Robin engine for bagging leaves.

4) My mom owns a 2 cycle, Toro with with a Suzuki engine.



I don't think you can find a stronger mower than a Lawn Boy Duraforce with a Gator Blade. Tall grass and wet tall grass are no problems. They are finicky mowers with those plastic carburators. However, if you ever come across a used, 2 cycle Suzuki powered or Wisconsin Robin powered mower - buy them. Those engines are more durable and unbreakable. Your kids will be using them, long after you are dead & gone, after trying to wear those engines out.

 

[BigRich954]

Ive use to turn a 5hp HP Briggs and Stratton engine at 6k and up to 7k and it lasted for 2 years. I took it apart to port and inspect it. every thing looked good would still be running it today if my mom didnt throw it out years ago

 

[calvin1]

I think I figured out why it seemed to be running rich. I added some oil to the filter and it blew smoke no matter what I did. I squeezed as much oil out as I could and it's better. It seems like at higher RPM the air filter can't flow enough air and the vacuum in the carb starts to climb like the choke is on. There's got to still be oil on the filter media; that won't come out with just some squeezing. I'll just need to make sure to clean and oil it more often.

I also added a shut-off and filter to the fuel line but I still need to make a filter for the primer bulb. It starts fine with just the choke so I don't know why they even put a primer on it. My first LawnBoy (late 70's) had a primer but no choke, the last one (early 90's) had a choke but no primer and now this one has both. Too bad it's also the carb vent or I'd just cap it and be done with it.

 

[Steve S]

Where do you guys finding these 2 strokers I missed buying one several years ago and still guys are finding new ones.

 

[calvin1]

Originally Posted By: Steve S
Where do you guys finding these 2 strokers I missed buying one several years ago and still guys are finding new ones.
Mines not new. According to the serial number it was built in 2000. It wasn't an easy find either. I've been trawling craigslist for months and everyone seems to know that these are worth extra money. This one was a good find because it was running poorly because of neglect but only needed the most basic of tune-ups to get it back to full strength. There was a contractor that had two runners and a parts hulk all for $130 that I was going to buy before this one showed up closer to home. That was the better deal - would have probably turned a profit on selling of what I didn't need - but it was over an hour away. You just have to be patient. Living at the edge of a major metropolis doesn't hurt either.

 

[Steve S]

I live is the semi boonies in a close to third world of a city.

 

[boraticus]

I have my twenty year old, 140 cc two stroke Echo mower set to spin up to 4500 rpm. It's rated at 4.5 hp at 2800 rpm. So, at 4500, it's making a lot more power. I'd guesstimate probably close to 8 h.p.

It has a variable throttle and I can set it where I wish. Heavy wet grass, crank it up. Light dry grass, slow it down.

 

[Best F100]

Originally Posted By: Steve S
Where do you guys finding these 2 strokers I missed buying one several years ago and still guys are finding new ones.



Since you are living in California, the odds of finding a 2 stroke mower (good condition) are the worse there, than in the rest of the country. Because of state emissions regulations, California banned them about a decade before they were last sold in the rest of the USA (2002 for Lawn Boy Duraforce).

In my non scientific study, I have found the highest concentrations of "late" model Lawn Boys sold in the Midwest. In particular, Wisconsin, Minnesota, Indiana and Michigan. Also in the hills of Pittsburgh and the hilly state of West Virginia. These mowers will not starve an engine, when cutting on a slope. I would search Craigslist in major cities, also Lawn Boy dealers in those areas on those on their web site. You would be surprised at the number of dealers, or individuals with never fueled, or little used 2 stroke mowers in their back rooms and barns. Of course, some owners are asking (and sometimes getting) high dollars for these mowers. Sometimes over $1200 on ebay.

I paid $300 for my Wisconsin Robin powered 2 stroke Snapper, last year, from a Michigan Snapper dealer. No scratches were on it, and paint was still on the blade. It had a "sold" sign on it when I got there. But when I got there with cash in hand..... You know what they say, money talks, and you know what walks. I never have known a dealer to turn down cash. With the bagger on this mower, it will suck up the proverbial quarter on the ground. Great for fall leaves.


It's like hunting for a Supermodel to date. The numbers are few, but the chase and the reward is out of this world.


There is a dealer in the midwest who is doing a brisk business restoring Suzuki powered Toro 2 stroke mowers to like new condition. That is how I acquired my other mower. Expect to pay over $500 for them. A fair price when you consider that you will NEVER wear out that engine in personal usage. Those were many landscaper's favorite mowers - before being banned. PM me for more information.