Trouble with 2 Stroke - '90's Lawnboy

Page 1 of 2  
Howdy All;
I have a lawboy mower that was built in the early '90's that I am having a lot of trouble getting it to run. I can find the model and serial number if it is relevant but I don't have it handy: it says "4hp Commercial" on the tank cover and no PTO for self-propell. It has been very picky about gas since I bought it used two years ago; it won't run if I leave gas in the tank so I drain what is left over back into the can.
The first day I used it this year it fired up with just two pulls and the throttle at full choke. Ever since then though when I've tried to start it the best I would get is a quick and easy start like the first time but it dies and refuses to restart after about 90 seconds of runtime. If I try to restart it sometimes I will get one or two strokes to light off will not run.
I removed the carb and cleaned it out and also cleaned out the tank, both with carb cleaner. I also pulled and replaced the old plug, which was fouled pretty bad after just one season. Neither of those things has made any difference. I am using 87 octane gas straight from the pump mixed 32:1 with real Lawnboy oil as per the markings on the mower.
I'm handy and could follow directions, but I've run out of things to look for. Does anyone out there have a suggestion for what may be wrong with me or my engine? I'd like to keep it running if possible as I can't afford a new mower that could hold a candle to this old beast, when it is running at least :).
Thanks, Matthew
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 15 May 2006 09:44:53 -0700, snipped-for-privacy@gmail.com wrote:

Air cleaner clogged or wet?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@gmail.com wrote:

Could it be in your area they've recently switched to 10% ethanol, and your jetting is now 14% off?
Dave
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I don't know what the schedule or regulations are for the blends but I am near Chicago so it is a definite possiblity. How would I compensate for that? The gas that ran great was left over from late last year so it might have been winter blend. I played a little with the adjustment on the carb but it didn't seem to make an difference. It could have already been flooded though.
Can this old beast be tuned to run on E10 or E15?

I tried it without the filter or cover just to see if it would start/run on the sidewalk and that didn't make any difference.
Matthew
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@gmail.com wrote:

If the carb is sophisticated enough to have jets, you'd get a larger main jet and pilot jet.
If it doesn't have replaceable jets, adding a little intake restriction might turn the trick.
Dave
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 15 May 2006 09:44:53 -0700, snipped-for-privacy@gmail.com wrote:

Gas tank screen/fuel line dirty????
Oren
"My doctor says I have a malformed public-duty gland and a natural deficiency in moral fiber, and that I am therefore excused from saving Universes."
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Greetings Matthew...
Ok you have done some good stuff there.
You cleaned out the gas tank, good start.
Did you make sure that the gas was flowing when it was reconnected to the carb??
Ok moving over to the carb, its a pretty simple setup with a float. I presume you look the bowl off and cleaned that out right? Depending on the unit, some carbs have a screw on the bottom that also has two little holes going through it. In the center of that screw SHOULD be a hole that can EASILY get gummed up with 2 cycle gas. Make sure that's clean. Did you make sure that the float in the carb is clean and free moving?
Now one thing you can easily see is the primer. Some machine dont have one others do. If you have a primer, when you prime it look into the carb. The jet is right in the middle behind the choke butterfly. When you prime you SHOULD see a squirt of gas shoot up out of the carb. If not, enough gas isnt getting into the bowl for a few reasons.
Dont dismiss a bad fuel line either, small cracks in it can cause all sort of funny behavior.
Tom
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I'll check that. I know what you are talking about, but I didn't realize it was anything more special than a small bolt so I will make sure it is clean.
I'm pretty sure the float and its valve are working because the bowl fills as it should but doesn't leak from the jet even when I blow into the gas tank (I know, I know). This one is too new to have the primer bulb; it has a separate butterfly for the choke instead. I know gas gets as far as the bowl, but can't guarantee that it gets any farther.
Matthew
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I think I've narrowed it down to the ignition side. I pulled the plug, closed the safety switch and touched the plug threads to the cooling fins: no spark. I removed the ignition module and cleaned up the contact areas with a sanding pad and reinstalled it. I gave the engine another spin and got one spark. After that I couldn't get anything else.
This is the second lawnboy I've had that died this way: the ignition module works when it feels like it, which is rarely. Is this something that is common with these engines? Is there something I could be doing wrong that these things die out from under me after just a couple of seasons in my hands? The plug is brand new and all the contact points are shiny and clean on both the engine block and the module itself. I also made sure to gap the plug and the module/flywheel to spec.
Matthew
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Didn't realise they still made 2-stroke mowers even in the 90s. Do they still? Remember them from when I was a kid. I have a 2-stroke snowblower that I idiotically bought used off a guy moving to Florida- works fine, though I can hardly be bothered with it- mixing, etc. 2-stroke makes sense for portable devices, but a mower? That said, I understand your frugality- good luck.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

alright, I'll take the bait:
4-stroke makes sense for a car, but a mower?
Seriously, 2-stroke is great for a mower. The power to weight ratio is better than a 4-stroke and the simplicity of operation makes for a durable, light, cheap machine.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Ok, I'll take it, too. Maybe I should get a 2 stroke mower- my yard has steep slopes. Used to drive a Saab way back when, but it was a V-4 Ford tractor engine(I had to switch it out once)- just missed by a couple years the 3 cylinder 2 stroke variety. BTW I've always considered the Wankel (such as Mazda used) a sort of 2 stroke- for better and worse- great power to weight ratio, poor separation between the strokes, thus emissions/ mileage limitations, burned valves, etc.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

All of the oil you put in the gas ends up in the air, incompletely burned.
Yes, 4-stroke is more expensive and heavier. However, good ones tend to last a lot longer than 2-stroke (many of which can basically be considered disposable engines), usually quieter, usually easier to start, and they're certainly a lot cleaner in operation.
Each has their place.
--
Chris Lewis, Una confibula non set est
It\'s not just anyone who gets a Starship Cruiser class named after them.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
It would be helpful if you knew what you were talking about. My 1986 (that's right - 20 years old) Lawnboy starts strong and runs stronger that any push mower engine i've ever had. And believe me, I've had a lot of them, Briggs and Techmseh. You claim that 4 strokes are "usually quieter", "usually easier to start". Wrong on both counts. My LB starts on the second pull EVERY time and is the quietest mower I've had. The great thing about the Lawnboy is that there are needle bearings at the bottom end constantly bathed in clean oil. I'm seriously expecting another 20 years out of this mower.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

My lawnboy is 3 years older than yours. So there! ;-)
It starts second pull every time, as long as I remember to tilt the thing when I prime it, and the condensor hasn't gone bad, and it hasn't been idle too many years.
Then again, the 1973 6HP Tecumseh 4 stroke wood chipper starts first pull (except when the carb got gummed up after sitting idle in the rain and snow for about 5 years).
And the 1970 12HP 4 stroke Kohler has always started quickly - even with a blown head gasket. Except in the winter. Try starting that LB at -30C sometime.
The kohler is considerably quieter than the LB except when it backfires.

How can it get bathed in oil? It's a two stroke. It don't have no oil bath.
I said _usually_. A decent 4 stroke Honda or the like with compression reduction during start will start easier than virtually any 2 stroke. And will be quieter given remotely comparable mufflers.
Certainly, 2 stroke has a considerable power-to-weight advantage over 4 stroke. At the expense of (usually) higher RPMS, more noise, sometimes more difficult starting, and a smoke cloud of partially burned oil.
--
Chris Lewis, Una confibula non set est
It\'s not just anyone who gets a Starship Cruiser class named after them.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Chris Lewis wrote:

No, it 'don't have no oil bath' , whatever that is. But remember that stuff you mix with the gas in a 32:1 ratio? Right! The oil!. Well, guess what Chris, that same oil, because of the design of the 2 stroke engine is pulled into and through the crankcase before it's burnt in the cylinder. The oil bathes the bottom end constantly. And, with each stroke a new charge of the mixture is brought in through the carburetor. Ain't education wonderful?

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Ever notice what happens to oil on a metal surface when you pour gasoline on it? Oops! Seems like the gas and oil in a two stroke are quite at odds with each other. The gasoline wants to break down and rinse the oil off the surfaces it's trying so very hard to lubricate!
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Sigh.
You know, I don't expect everyone to have taken not one, but two small engine repair courses as I have and intimately know the details of how four stroke and the three types of 2 stroke engines work, but at _least_ you should know the difference between having a _bath_ and having a _shower_.
The oil-gas mix in a two stroke is atomized in the carbureter, and pulled thru the crankcase and thence to the intake port. Thus, the insides of the motor are showered with a gas oil mix, and the oil is then run thru the cylinder head and (partially!) burned before being dumped into the atmosphere.
As for example, the pilots of certain aircraft in world war one were continuously sprayed in the face with a partially burned laxative (they used castor oil in those days).
Meanwhile, in a four stroke, the crank and cylinder head is mostly isolated. The oil is in a _bath_ at the bottom of the crankcase, and the crank, and bottom end of the piston rod splash (and to a certain extent are bathed _in_) the oil at the bottom of the crank. The oil _stays_ in the engine and doesn't spray anyone in the face.
So, no, a 2 stroke doesn't bathe its parts in oil. But a 4 stroke does.
--
Chris Lewis, Una confibula non set est
It\'s not just anyone who gets a Starship Cruiser class named after them.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Chris Lewis wrote:

I didn't realize I was dealing with an "expert". You know, I've never had my Lawnboy or any two stroke engine spray oil in my face. Maybe it's a common occurance and I just hasn't happened to me. Hmmm. Actually, the oil in a four stroke Briggs/Techumseh style engine resides in what's known as a sump. In engine terminology, the sump is the area below the crankshaft in a four stroke. In cars, the sump and the oil pan are one in the same. That is for wet sump engines. Dry sump engines have an external oil tank and feed and return lines leading to and from the oil pump. An oil "bath" on the other hand was how air cleaners worked in the days before disposable paper elements. So Chris, knowing 'intimately' how small engines work, answer a question for me: If the two stroke engine doesn't bathe its parts in oil, how on earth does the engine get lubricated? How has my Lawnboy lasted twenty years now without siezing up? You know, I would think that lubrication would be vitally important in two strokes, given that many of them turn between 10,000 and 20,000 RPM routinely. You stated that the insides of the two stroke are showered with the gas/oil mix, but not bathed. What's better, a shower or a bath? Here's what I know. I've had both Techumseh and Briggs engines throw rods and punch holes in crankcases. Any yes, I've changed the oil according to schedule. The newer Tec/Briggs lower end engines especially can be considered throw aways after a few years of service. My Lawnboy, on the other hand has gone twenty years without any major repair work of any kind. And that's cutting a half acre twice a week.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Chris; You have to use a good lawnboy to understand.
I personally have a lawnboy commercial unit, it works freaking great. It will basically cut and suck up anything on the lawn. I received a Honda unit from my parents. The engine on it is real nice but it just doesnt have the vacuum power to take the excess clips off the lawn. Its a problem with ALL 4 cycle engines/mowers. You need to have some recent suction and a 2 cycle by design spins up higher than 4 cycle lawn mower motors.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Related Threads

    HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.