Motorcycles, Snowmobiles, Go-Carts, ATV's and Golf Carts - lawnmower racing continued...

looks like they closed our thread :thumbdn: lets continue it. have any questions about your tractor then just ask and someone will help

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Hey I am new to these forum things but, it seems like a good place to get help. Well on with the question I have built a racing lawnmower and have raced it twice and came in second twice,it seems to be really fast but the mower that beats me is walking the dog on me there is no way I can catch him, I know he is running a 14.5 hp and i am running a 12 hp, I am running a 4" pulley on the front and a 2.5"on the back. i have changes the exhaust from 1" coming out of the motor to 3/4" and turned it to build back pressure and then made it bigger ( 1"x3/4"to 2"to2 1/2") out the back (or side).is there anything else I can do to get more speed without changing the engine

you can up the rpm's a little, probablly a extra 100, briggs engines can stand up to it, i mean i had a 3.5 i tried to blow up by removing the governor, thing never blew, just drank the gas, done the same to other briggs engines, never did they give up. you can try a bigger pulley up front, and a smaller out back, and bigger tires on the back. try some quality synthetic oil like mobil one or amsoil and redline, just does wonders in air cooled engines, makes em run smoother as well.

yea I have already rigged up a throttle pedal that pulls on the govenor rod itself,that give me some more rpms but how far can you go, and how long can you run it wide open, the last race we had we run 1 lap around the local dirt track 1/2 mile it really seemed like that was pushing it to much, not scared to push it just don't want to buy another motor if you know what I mean, limited cash flow!!! And I thought that bigger tires would slow you down, and make it alot more top heavy,well I know it make you tipsy in the turns but would they make it faster?I really appreciate the input need all the help I can get new to the whole racing thing. Ron :wall:

well, wide open on the governor for a few seconds, but they are built stock, to run 3600, i've run em around 4,000 and not a problem, though i'd stick with a few seconds to be on the safe side, briggs connecting rods are much better then tecumseh :D , briggs does make racing parts for engines though. i myself havn't raced mowers, go carts though, bigger tires always did em good. though it would make em more top heavy, guess you don't know the other guys size tires? though only difference in the engines if they are stock, is hp, they both run at 3600 rpm unless otherwise set. i do hear you on the engine, not cheap, what is it, a I/C? what mower frame is it on? if you want to beaf it up with performance parts every now and then, you can check the briggs website, i think they should have some good racing parts for em.

Go up another inch or so on the front pulley. I dont know if that will hurt your top speed though, or maybe its your acceleration

:thumbup: yea its a 12hp I/C engine mounted on a true value lawn chief not really sure of the real manufacturer, do you have to tear down the motor to remove the govenor? because I have my throttle cable hooked to my govenor rod does that by-pass the govenor or is that only pulling to the govenor speed? And tha guy is running 18x8.50x8 I think and I am running 18x9.50x8, I have been thinking of going up on the front pulley but it causes the clucth pulley to hit it,any body got any solutions for that with out doing alot of fabricating? : :wall:

I/C, very good engine. the bigger pulley up front will hurt acceleration. though, for the pulley, maybe a smaller clutch pulley? true value mower. kinda sounds like a mtd, not sure though. as for the governor, don't remove it, unless its built to hold the rpms, what you have is good, as for holding it, like i said, whatever you feel comfortable with, but i wouldn't go all out, just for a few seconds. pulling on the governor arm will override it for as much as you put on it, one thing though ( ohv's are more forgiving ) the valves will begin to float and not shut all the way, you could also try a bigger hp engines carb, as long as it fits for a little more air flow, or rework the original.

hey v8 driver I really appreciate all the good info, I am going to try a few of the things we talked about and see what happens. Ain't that what racing is all about anyway, If you don't blow you aren't eally trying to hard are you? well if you have anymore ideas :thinker: please post it thanks ron

do any of you know if the exhaust should be free flowing or should I build back pressure? :confused:

a little back pressure is easier on the exhaust valve, but still doesn't do much, a straight just sounds better, how do you have it rigged? way i like is straight out, or out, then a elbow to curve it upwards into a exhaust stack, cut the pipe at a angle and there you go.

dont cut the pipe to a single angel because it will allow you to "suck a valve" meaning motor needs new valve rods, new valves and a whole lot of work. you need either the end of it to get smaller or put a right angel pipe on the end. make the front pully bigger, this will slow your acceleration down but raise your top speed. try putting more air in the tires. weld the front axel thing so it wont pivit. if not, i recomend it , this will allow you to take turns faster. dont hold the govenor wide open for more then like 5 seconds because it will bust a valve. trust me ive done it twice. cant say i ever threw out the rod. had one light on fire and got hit by a truck the same one that lit on fire (not at the same time)

you can cut the pipe at a angle on a side valve, more for looks and deflection really...... as for busting a valve on a side valve, never had it happen nor seen it from another friend who actually raced 5hp briggs engines with governors removed. and one of my pushers, old max series briggs 4 horse i recently picked up ( needed a carb rebuild bad! ) pushing 4,000 rpm i use it occasionally for heavy grass. last engine i used for such was a 3.5hp i removed the governor intirely, only thing that went wrong was it drank a full tank up in a few minutes :D fun to have fun with free stuff. then i have a 1980 murray riding mower, just love to rev it up. still havn't gotten to it to do pulley mods, still has the 8hp briggs on it going to swap it out after it dies for a I/C model of the same hp, or bigger maybe, briggs engines can really stand up to abuse. as for the front axle, yes weld it so it doesn't pivot if you already havn't.

Hey,

New to this forum. I just got a 11hp robin for cheap. I was told it came off a generator. The shaft tapers from .9" to 1" over 1.75". Does anyone make a torque converter for this type of shaft or do I need to fabricate my own? I would like to put this engine in an old golf cart we have.

I dont think so. MAYBE you can take it to a machine shop to be turned on a lathe, but Most shafts are straight.

Jim

:) Hey guys, i'm kinda new here and was reading over this thread and found some great ideas. We have a motor sports complex a few miles down the road, that does pulling, mud bogs and sand drags.
At the end of this seson, a few of us got together to discuss next year. We were doing garden tractor pulls this year and are trying to get a series together for maybe lawn tractor sand drags next year. This should be very interesting as there were some wild ideas being kicked around. All tractors will be requied to use "turf" tires, no paddles. After that it is based on fuel type and horsepower rating. I am currently helping build a tube frame "unlimited" tractor. It will use basically an "open" modified kart engine, based on a 5hp briggs, burning 30% nitro model R\C car fuel with a carb off an old CRF125 honda dirt bike. We have had the engine fired up on 20% nitro, and it sounds violent, to say the least. This thing only weighs 275 lbs right now, with the driver 145lbs of that so it should be extremly fast, or extremely dangerous. :alarm: :eek:
We still have alot a fab to do, but it kinnda shows that you can do almost anything if you just plan it out.

:) I am currently helping build a tube frame "unlimited" tractor. It will use basically an "open" modified kart engine, based on a 5hp briggs, burning 30% nitro model R\C car fuel with a carb off an old CRF125 honda dirt bike. We have had the engine fired up on 20% nitro, and it sounds violent, to say the least. This thing only weighs 275 lbs right now, with the driver 145lbs of that so it should be extremly fast, or extremely dangerous. :alarm: :eek:
We still have alot a fab to do, but it kinnda shows that you can do almost anything if you just plan it out.

Thats not gunna give you much power.

If you really want power...

Order a new cam for the thing. Crane and Comp cams recently began making cams for Karting motors, as most of the 4cycle racing motors start out life as a 5hp briggs.

Get one wih a higher lift and higher duration.

Also Order stiffer valve springs, and valves with shorter stems.

Order a forged connecting Rod, and a new carb jet, and Mix your own gasahol.

All can be bought from www.tsracing.com

Dont waste your time with that other carb either, just Order a new jet from the site.


Jim

Hery whats up guys,glad to see we got this thing going. so while I got you whats up with grinding cams can you do it on a 12hp? does anyone know where you can get performance parts for a 12hp I/C briggs motor old flat head oh yea what the heck is a L-head have heard it mentioned several times but have no idea ?? :wall:

oh yea does anyone know where you can get a tach for these lawnmower engines??? :confused:

I think you misunderstood me Kartracer, this engine is an OPen modified that was raced on a kart and pulled around 80 mph at summit point Wv. It is as maxed out as it can get, but on the kart it ran straight methonal, we are adding nitromethane to the mix. So it will either go or blow. I wish there was an effective superchager available for these engines, because nothing says POWER!!! like a blown nitro engine. I wonder if one off of a nitro Harley could be adapted to work, but i think that would be a little much

We have a few dfferent carbs around the shop, we will see which one works the best for this project

www.hscsuperchargers.com does superchargers and turbos for the briggs engines.

I think you misunderstood me Kartracer, this engine is an OPen modified that was raced on a kart and pulled around 80 mph at summit point Wv. It is as maxed out as it can get, but on the kart it ran straight methonal, we are adding nitromethane to the mix. So it will either go or blow. I wish there was an effective superchager available for these engines, because nothing says POWER!!! like a blown nitro engine. I wonder if one off of a nitro Harley could be adapted to work, but i think that would be a little much

We have a few dfferent carbs around the shop, we will see which one works the best for this project


Oh I didnt realize it was already a kart motor.

Anyway, be careful with nitromethane... it has a tendancy to corode the **** out of aluminum. you will want to run regular gas through the motor at the end of a race day.

Jim

yeah you're right it does eat aluminum like candy, but we start it on gas and switch back to gas for 2 minutes before final shutdown,. Hopefully that is enough to clean it out,. This thing sounds awesome on gas, and total insane on nitro, it has almost a "top fuel" crackling sound as it idles, and lets out a viscious bark when we crack the throttle,.

We are using a Horstman steel crank and rod with roller bearing on both ends of the crank,an older horstman cam, and a "squash" plate to keep the head and cylinder from trying to go into orbit,. I'm going to cc this engine because i'm not quite sure of the compression ratio, but the owner said it was around 13:1,. We ran this engine on a Margay Mirage kart frame, and we got 9800 rpm out of it, so it is no stranger to high rpm, high stress racing

yeah you're right it does eat aluminum like candy, but we start it on gas and switch back to gas for 2 minutes before final shutdown,. Hopefully that is enough to clean it out,. This thing sounds awesome on gas, and total insane on nitro, it has almost a "top fuel" crackling sound as it idles, and lets out a viscious bark when we crack the throttle,.

We are using a Horstman steel crank and rod with roller bearing on both ends of the crank,an older horstman cam, and a "squash" plate to keep the head and cylinder from trying to go into orbit,. I'm going to cc this engine because i'm not quite sure of the compression ratio, but the owner said it was around 13:1,. We ran this engine on a Margay Mirage kart frame, and we got 9800 rpm out of it, so it is no stranger to high rpm, high stress racing


haha margay Mirage... thats Oldschool. Im looking to buy a Margay bravo 1.4 for this season, but I run 2 cycle road course.

As for CC, Go on the WKA(world karting association) website, and look at thier tech section. A stock briggs displaces 206.4 cc give or take, so Id imagine its hovering around that.

What kind of exhaust are you running? They make different pipes to give alter torque ranges and stuff ya know.

Jim

Wow kartracer, someone who knows what a Mirage was,cool, finally someone who has been around the sport.

My dad and Uncle used to race with the V.D.K.A ( virginia dirt kart association). They ran limited modified heavy, modified heavy, open modified heavy( see a trend here lol) and 100cc controlled stock heavy. And won the state championship in 1988 for 100cc controlled stock, running a yamaha KT-100S.

I ran limited medium for a few races, and had a blast, until i was T-boned by other kart and my left knee got pinned between his fornt bumper and the steering column support on my kart. My dad saw it happen, becuase i dont remeber much about it. Last i can remember, i was spun out and saw the kart coming toward me. Next thing i can remember is waking up on a back board and trying to figure out what happened. I saw my kart about three days later, and about fainted. the left nerf bar was caved in to the frame, and the frame was sitting cockeyed. The left front was bent up, so the other three wheels were on the ground, but the left front had about 2 inches of air under it, needless to say, that was it for me. lol That was in '91 and i still have a limp from that.
Tough lesson at 16 yrs old

sorry about the rant there. Kartracer, right now we are using a straight open header pipe. We will probably switch to a supertrapp exhaust for adjustability and noise control. We got warned Sunday night by the local police about firing it up after 9 pm. :alarm: PARTY POOPERS!!!!!!!. I guess some people just dont appreciate the sound of a monster single cylinder roaring to life, but i can understand. :blah:

Yeah, the cops def. dont appreciate it :mad:

Anyway, I Runa kt100... Can and pipe, but I run for points in Can.


Jim

WE used to have a cool officer who would respond sometimes when we were firing the kart engines. He was pretty amazed at how rough these engines sounded, but he retired a few years back. Now all we got is yahoos, who think the badge makes them god or something. Thank god these clowns were not around when we were racing, because we would bolt the engine on the kart after freshening it up and run up and down the street to "shake down" and break the engines in. We always went on the theory of " break it in as you will run it" and only had 2 engine failures. One thrown rod in the modified and we seized one 2 stroke up.

WE used to have a cool officer who would respond sometimes when we were firing the kart engines. He was pretty amazed at how rough these engines sounded, but he retired a few years back. Now all we got is yahoos, who think the badge makes them god or something. Thank god these clowns were not around when we were racing, because we would bolt the engine on the kart after freshening it up and run up and down the street to "shake down" and break the engines in. We always went on the theory of " break it in as you will run it" and only had 2 engine failures. One thrown rod in the modified and we seized one 2 stroke up.

yeah sometimes the cops are pretty cool. Just dont mouth off and they will sorta get to know you (or at least theyve all gotten to know me :eek: ) Anyway, my friend has that thoery, and its wrong... your screwing yourself. When I ring and hone an engine, I usually let it idle for about 10 minutes, and let it cool completely. Later, or another day, Ill let it idle for 5, giving it th ocasional extra throttle, then ill run it at a bit higher than idle. When it cools off again, I run it at an idle to get it warmed up, then I juice it every once in a while, towards the end of the session, I willgive it a few seconds of WOT, but its bad because there is no load on the crank. I have yet to blow an engine doing this.

Also, When you build engines, you absolutly MUST use assembly lube. So many people dont do this, and they get scoring on the crank pin, and aroudn the wrist pin, and sometimes in the cylinders.

Jim

Luckily we did not have a clock in the garage, so we played it off like we did not know how late it was, and just got a warning.

This engine is getting the slow and easy treatment during break in, I've never had any experience with nitro personaly, but know if its power potential. nitro-methane is a combination of nitro and methanol, correct? My dad gave me a bottle of some type of realy light oil(i cant read the label anymore). He said it was an lubricant that they used to mix with methanol for a little added protection, since methanol has no lubricating properties. we have been mixing it with the nitro for break in and it seems to work great.

We have the engine on the frame, and are using a centrifugal clutch to drive a lawnmower transaxle to put a small load on the engine. I have never broke an engine in "free" wheeling. I kinda like at least some load on an engine while it is running, but that is just me, i guess.

Nitromethane isnt a mixture of anything. Its got a chemical make up of its own. Its just sometimes mixed with alcohol, because fo the potential to blow up an engine. The NHRA, at one point, didnt have rules abotu how you could mix your nitromethane, and guys would blow up thier engines, literally, endangering the crowd. So now, its mixed in a certian ratio with methanol or ethanol. That the model airplane stuff your using is only about 50% nitromethane, if that. You can get the real deal from VP racing fuel but its big$$$

Anyway, the thing about nitromethane is that you can burn a hell of alot more per stroke.

If im not mistaken the ratio of pounds of air needed to burn a pound of gasoline is like 15:1

Nitro is like 2:1, so its a hell of alot more power.

Just be careful with the stuff, and Make sure you tear down that motor after every few hours of use, probably 5-10 and make sure you dont have any cracking along the crank, and that the wrist pin isnt wearing funny. Replace the head gasket when you do the tear downs as well, because Nitromethane really takes its toll on an engine.

Jim

what ever happened to finding a lawnmower in the trash building exhaust swaping pulleys and hauling ass for under 100 bucks. guess im outta date, but yet i still deal with the popo :alarm:

Thanks Kartracer, i wondered how that formula worked. The stuff we are using is 30%, so i guess it is only 30% nitromethane and 70 percent methanol.

Luckily I have a good friend, who runs a machine shop, so we can tear the engine down, fairly often and Magna-flux everything for cracks.

I have noticed this thing like running extremly rich. I mean rich enough to be blowing some raw fuel out the header, is this normal.

And i finally got the C.R figured out, it is 13.25to 1

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