B&S bigboy

[gsmotorsports]

Hey guys im rebuilding the engine i took off my snapper riding lawnmower in my high school power tech class. Its a 15 horse I/C OHV Briggs and Stratton vertical shaft engine. I know go karts tend to use a horizontal shaft engine but just leave that up to me. What I need help with here is if theres any aftermarket stuff I can put on this engine. The model # is 281H07-0111-E1 and from what looking ive done I cant find anything along the lines of aftermarket cams, doing anything with wider valves, or lightweight cranks. I realize this may not be the ideal go kart motor but even if I have to just go back to stock parts I'm going to mill the head down. We have all the milling tech at the school that any shop could ever need and all the time i could ask for to do this. Any info would be great I've already got the engine appart and everything so let me know if you guys can find anything. Thanks

 

[armyvet]

if your serious get a flat slide carb with a accellerator pump from a dirt bike and mod it to work with your briggs.get a good exhaust set up as well.

 

[slideways]

You'll be looking for lawn mower racing parts for that motor. Check EC Distributing, ARC, Precision Cams.. Head porting, a good carb and exhaust should be all you need. If you are going over 5000rpm for some reason the ARC rod and flywheel would be a good idea.

How are you going to use it on a kart? Mower gearbox?

 

[DirtTrackRacer_07]

G-Force racing might be helpfull for you. All they have is racing lawnmower parts.

http://www.g-team.us/parts.htm

 

[gsmotorsports]

You'll be looking for lawn mower racing parts for that motor. Check EC Distributing, ARC, Precision Cams.. Head porting, a good carb and exhaust should be all you need. If you are going over 5000rpm for some reason the ARC rod and flywheel would be a good idea.

How are you going to use it on a kart? Mower gearbox?

Ill use a right angle gearbox with a 1:1 ratio and set the axle up just like a normal go kart. But should I put the centrifugal clutch before the gearbox or after? or does it even matter?
thanks for the help guys
also im trying to make this a budget ish build. anyway I can use the stock stuff but machine it myself? my school has all the tech to do so I just dont know what all i can do

 

[modelengineer]

I'd put the clutch before the gearbox if you can, just so that it's not turning all the time. If it whines a bit then it could get a bit annoying at idle. Really though, it won't matter if it's before or after.

 

[gsmotorsports]

Yeah I didnt know if that would hurt it any or not but the more I thought about it the more i got to thinking less moving parts at idle would make more sense. If I wanted to mill the heads down a little bit how far could I go? a friend of mine told me .02 or .03 but I wanna make sure before I just go ahead and do it. Anywhere to find cheap rebuild kits as well? the local small engines guy wants to charge me about 80 for a carb rebuild kit and the gaskets and such. Dont know if thats any good or not everything seems cheap to me since I started this project since I'm used to workin on V8's and such lol
Also should I remove the governer setup from the engine as well? or just leave it in there for reliability? My teacher wants me to leave it in there but I feel like I could get a lot more power out of it if I took it out..

 

[slideways]

80 is way too much for a rebuild kit. Check ebay... you probably don't even need all the parts in the kit.. just the bowl o ring and maybe the needle and seat. You'll have to remove the governor to take advantage of any other modifications you do. As long as you dont run it like an idiot wide open all the time it should be fine. The stock valves will float and act as a governor of sorts.

 

[DirtTrackRacer_07]

If you plan on runnin a little hard, build a intake manifold and run a carbuerator off of a 110cc or 90cc bike on it.

I imagine that you can pick two or three of them up on ebay for 80 bucks.

That man is trying to rob you.

 

[redsox985]

Walk in and tell him you're not an idiot and you know what the kit costs. Be respectful but assertive and tell him it's a ridiculous price.

 

[gsmotorsports]

That would be the price for the carb kit and a rebuild kit for the motor as well. not just the carb kit sorry if i didnt make that too clear. I reread it myself and yeah ti wasnt too clear. But isnt valve float a bad thing? is the piston valve clearance in these engines great enough so that when they do float they wont punch through the top of the piston?
Again im planning on milling the heads a bit so would the clearance be a problem then? or would it still be greater?
Also how would I go about building an intake manifold? just find some sort of pipe that I could throw on there or what?

 

[slideways]

You shouldn't be bouncing off of the valves heavily. Its just a little bit of a limiter. I wouldn't worry too much about them punching a hole in the piston.. usually the motor cuts out enough that you'll lose revs before that happens.

A straight shot intake manifold would help mostly with top end.. not really necessary if you are just making what is basically a little souped up lawn mower engine. If you were planning on doing full porting and polishing of the head and getting a big cam then i'd say to go with a custom manifold with a slide carb like a 28-30mm ish size. I'm not sure if the Briggs Animal manifold will work but those fit alot of different motors and setups.

 

[Bluethunder3320]

dont pay 80 for a rebuild. thats how much it should be if that for an entire engine rebuild.

i saw someone modify a riding mower and it got up to 35mph easily. i might be ble to contact him on youube if ya want.

 

[gsmotorsports]

dont pay 80 for a rebuild. thats how much it should be if that for an entire engine rebuild.

i saw someone modify a riding mower and it got up to 35mph easily. i might be ble to contact him on youube if ya want.

yes please do and let me know what he says. Like I've said I still cant find any aftermarket-like parts for this thing and it is gunna need done eventually so i can get a grade on it. Thanks again guys

 

[slideways]

www.heymow.com DO NOT POST ON THERE... that you are hopping up a lawnmower for fun.. they will kick you out. They are hardcore about safety and sanctioned mower racing. Just read about single cylinder motors in the Briggs OHV and Vanguard section.


But seriously you shouldn't really need to mod this thing to have it make power. Mill the head a little like you said.. do a little smoothing of the intake port, make a header and go up one jet size in the carb. Along with tossing the governor you should have a fun reliable motor there.

 

[gsmotorsports]

ha i literally just posted on there like 5 minutes ago... oh well. okay but where am I going to find jets? and specs on how far I can mill the head down? I just want to make sure I'm doing stuff right before I'm tearing this thing apart again to find I need a bunch of new parts since I messed up one little thing.

 

[slideways]

You can find them in a junk carb in a junkyard or ebay or wherever. You can also just drill yours out with a number drill set from ebay or Harbor Freight. They are very small numerical bits that you hand screw into the little brass jet to make it one size larger. If you go too big you can always just re-solder it closed and drill it again.

 

[Bluethunder3320]

alright, heres the vid i saw

http://www.youtube.com/watch?v=BN5di_Dfjzg