Author Topic: lawn boy 2 stroke?  (Read 26550 times)

0 Members and 1 Guest are viewing this topic.

Offline mullet_boy1969

  • Newbie
  • *
  • Posts: 21
  • Karma: 0
    • View Profile
Re: lawn boy 2 stroke?
« Reply #15 on: February 18, 2007, 02:48:25 pm »
brad: Porting on this block will be more hassle than its worth i think.  The cylinder and head are one peice, so itll be hard ot get in there.  Ive got a book with some good formulas on porting though (exhaust port area, port timing), so i imagine ill do what i can. The same goes for the pipe, i can make one tuned to my exact engine specs. (its amazing the amount of math that goes into a pipe, who knew)  I think 20 horse would be shooting a bit high, 10 is more realistic.  If i could end up with only 8 horses even i think that engine would be competitive.  Last years race an 8 horse tecumseh engine w/a mikuni carb won the mod class. (keep in mind the mod class had atleast 5 "mowers" with 4 wheeler/street bike engines in them, and a snow mobile powered mower). so i realy think if i keep it light weight and gear it correctly i could have a very competitive mower on my hands. Oh and by the way thanks for all the help you guys have given me.  I posted this on a kart racing forum too and only got one responce so far.  

mowdak1: You can make up for lack of torque with higher rpms from the motor and a lower gear ratio.  And i agree in its current state theres no way that engine would pull a 400lb mower and turn blades.  I dont have blades to turn, the mower weighs 100lbs or less and i only weigh 160.  The engine itself isnt stayin in its current 4 horse state either.  I'm guessing on a redline rpm of 7000 rpms (almost twice what the STOCK briggs ill be running againt turn), and horses to end up at round 8-10. 2 strokes can make so much more power over stock just through pipes and porting, just read brads post.  so ill have a 275-300 lb mower with around 10 horse versus the average 400 lb briggs powered mower with 10-12 horses.  I for one think that would be a close race.

Offline mowdak1

  • Highly Mowtivated
  • ****
  • Posts: 4349
  • Karma: 73
    • View Profile
    • North Dakota Lawn Mower Racing Association
Re: lawn boy 2 stroke?
« Reply #16 on: February 18, 2007, 02:52:26 pm »
Well... be sure and let us know how it truns out!

Offline mullet_boy1969

  • Newbie
  • *
  • Posts: 21
  • Karma: 0
    • View Profile
Re: lawn boy 2 stroke?
« Reply #17 on: February 18, 2007, 03:08:00 pm »
I'm hoping it turns out good.  I'm going to build this engine and try it.  If it fails (more likely than anything it will but im hoping it wont) i have a briggs 10.5 flatty i can use.  two strokes just fascinate me and i think that motor could be used against the stock briggs.  The old kart racers used mcculloch chainsaw engines, wich in a sence cant be to far off from a lawn boy engine, and those will smoke any flat head of today on a kart.  Any one have a suggestion on  "stock" looking carb for this engine?  The stock unit isnt gonna cut it and i wanna keep this thing stock looking atleast a little bit.

Offline MTDrider1160

  • Turf Warrior
  • **
  • Posts: 425
  • Karma: 6
  • Gender: Male
    • View Profile
    • PALMRA
Re: lawn boy 2 stroke?
« Reply #18 on: February 18, 2007, 04:40:33 pm »
You could walk faster than it.

Offline mullet_boy1969

  • Newbie
  • *
  • Posts: 21
  • Karma: 0
    • View Profile
Re: lawn boy 2 stroke?
« Reply #19 on: February 18, 2007, 05:03:33 pm »
I dont know if i could walk faster.  maybe run faster.  maybe.  i just took the engine apart, and i found some great news.  theres a TON of port work i can do on this thing.  its only 4 small cirlce ports, so i can add boost ports, or make the existing ones bigger.  either way its going to be very simple to do.

Tom the Canuck

  • Guest
Re: lawn boy 2 stroke?
« Reply #20 on: February 18, 2007, 11:11:59 pm »
good, and stock looking isnt going to ever cut it... you'll never find one,because stock looking is stock performing.

Offline mullet_boy1969

  • Newbie
  • *
  • Posts: 21
  • Karma: 0
    • View Profile
Re: lawn boy 2 stroke?
« Reply #21 on: February 18, 2007, 11:52:48 pm »
It doesnt have to look exactly stock.  Just beleiveable that it might come on a lawn boy mower, not like a minuki slide carb or something.  Maybe a walbro?  I'm thinkin maybe like a carb off an 8 horse kohler or something.  I'm sure ive got somethin laying around to feed it.....

Tom the Canuck

  • Guest
Re: lawn boy 2 stroke?
« Reply #22 on: February 18, 2007, 11:54:11 pm »
just run a mikuni and put some old grease and stuff on it,say when you found the engine it had that on it...

Offline mullet_boy1969

  • Newbie
  • *
  • Posts: 21
  • Karma: 0
    • View Profile
Re: lawn boy 2 stroke?
« Reply #23 on: February 19, 2007, 12:16:23 am »
i suppose i could use a 22mm mikuni i have layin around.  Im no sure if i wan to do that though, because then i have a lot more setting to mess with.  The tractor carb i have in mind only has the idle air screw and the main jet needle screw to worry about.  I love the grease idea though, i may try that.

Offline Brad Butler

  • Newbie
  • *
  • Posts: 19
  • Karma: 0
    • View Profile
Re: lawn boy 2 stroke?
« Reply #24 on: February 19, 2007, 12:24:58 am »
could you get me a pic of your cylinder? You may not be able to do much with the port timing or angles with the head not being able to come off, BUT, widening and/or raising the exhaust port does show some real gains, but you also lose compression, and since you cant mill that head, i dont know what you can do about that loss, except maybe get a piston with a higher compression height or whatever. You can also port the intake windows, port the hole in the piston, polish the ports, level the piston (make the top of the piston level with the bottom of the ports), epoxy an air ramp in the intake, and set the angles of the lower transfer openings.  :woo:  :omg:


You said you had an extra cylinder right? and the head is made on? if i were you, id cut the top of it off and see if i could fab it up to use a gasket and bolts like a regular head (you could drill holes in the fins in order to make "studs" and just run bolts through those holes to hold the head on) Doing this you would be able to rechamber the head (huge gains here) and increase compression.  ;)


Has anyone noticed, those KT100 kart motors (regular 2 stroke, 100ccs) make over 16 horses? and thats running with a can, not a pipe, and not alot of mods, you can make way more hp with a pipe. The reason why your motor is rated at 4hp im willing to bet is because of the small detuned carb, and the throttle limiter. Dont you guys think if i had my blaster limited to 4000rpm i wouldnt have any power? Its like this, when im riding, and i get up into the 6-7k range, i hit whats called the "powerband" in a 2 stroke, and once i hit that powerband, the front end is up in the air, and im movin on out.  8)




If the 4 hp were capable of that through gearing alone, and it can be produced at a third of the cost, don't you think the manufacturer would be building riding mowers with 4 hp motors and 8 speed transmissions on them?   

Its simple, 2 strokes are being slowly banned in production due to strict manufacturing standards and emissions rules. The reason they dont use them is because at high rpms a 2 strokes oil/gas mixture is being wasted out of the exhaust, and thats horrible for emissions. They dont use them on riding mowers today because in order to make it have enough power youd have to let it rev up higher, which would mean no passing the emissions standards. Another big factor is reliability, 2 strokes aint that reliable, unless you know how to handle them. A 2 stroke is reliable as you make it. Alot of people would be blowing up their mowers if they were 2 strokes. Noone wants to mix gas and implementing an oil mixing pump and other things u need to run a 2 stroke on a mower would cost alot too. So theyre probably doing the best with making 4 strokes.  :P

Offline Brad Butler

  • Newbie
  • *
  • Posts: 19
  • Karma: 0
    • View Profile
Re: lawn boy 2 stroke?
« Reply #25 on: February 19, 2007, 12:27:42 am »
Mulletboy, you cant use a 4 stroke carb for a 2 stroke. 2 stroke carbs have different things required for the thicker gas that goes through them mixed with oil. Your best bet would be to go on ebay and find one off a 60-85cc 2 stroke dirtbike. Or even a walbro carb intended for a kt100 kart motor.

Offline mullet_boy1969

  • Newbie
  • *
  • Posts: 21
  • Karma: 0
    • View Profile
Re: lawn boy 2 stroke?
« Reply #26 on: February 19, 2007, 12:51:06 am »
I'll see if i cant get a pic up tomarrow.  The ports on this thing are... odd..but easier to work with because of this.  i can change the intake timing by filing on the piston if i need to.  same goes for exhaust timing.  and you hit the nail on the head with that thing on the kt's, thats been some of my resoning behind this.  if that little engine can make 20 horses piped, why cant i make 10 piped.  I didnt know you couldnt change uses between 2 and 4 stroke carbs either, i always thought they were the same stuff just rejeted.

Offline Brad Butler

  • Newbie
  • *
  • Posts: 19
  • Karma: 0
    • View Profile
Re: lawn boy 2 stroke?
« Reply #27 on: February 19, 2007, 01:08:43 am »
Thats what i always thought too, but after speaking with alot of people (including 2 stroke engine builders) ive learned alot of things, that being 1 of them.  8) Im here to share my knowledge, if you need to know anything just let me know.  ;)

Offline mullet_boy1969

  • Newbie
  • *
  • Posts: 21
  • Karma: 0
    • View Profile
Re: lawn boy 2 stroke?
« Reply #28 on: February 19, 2007, 01:18:16 am »
one thing i learned from reading up on pocket bike mods (very similar design to the lawn boy engine) is i can run with out a base gasket (one between the cylinder and crank case) and gain compresion there, i just have to compensate for the wacked up duration by filing even more off the ports and the piston.  And before anyone gets worried by no gasket i mean using something like yamabond to make a very thin gasket instead of the old milimeter thick one.

Offline Brad Butler

  • Newbie
  • *
  • Posts: 19
  • Karma: 0
    • View Profile
Re: lawn boy 2 stroke?
« Reply #29 on: February 19, 2007, 01:25:45 am »
that wouldnt be a very good idea. youd mess your timing a whole lot by doing that i think. Why not just weld the top of the dome for more compression?