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Author Topic: First post, go easy on me. Briggs 12.5hp question.  (Read 1925 times)
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insidegroove
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« on: September 22, 2013, 09:39:22 AM »

Ok......i have been scrolling through past topics all the way to 2007 to look for an answer to my question but not really seeing it so i will ask. i bought my first racing mower last week, it is nicely built with a brand new custom front end that is way more rugged than factory. lowered, widened....real nice, and has a great running 12.5hp Briggs motor....fires right up and purrs like a kitten. the guy said he "raced it", but when i got it on the track the first time i was disapointed because it was only going about 9mph  Sad i started researching all kinds of websites and realized it was all in the pulleys, it had a 3.5" on the front and a 6" in the back, and the governor was still connected......boring. i spent a few days trying out different pulley combos and it now has a 4.5" in the front and a 3" in the back. i temporarily disconnected the governor and ran the throttle cable directly to the carb.......it had lots more speed with these few changes. i was so afraid to blow the motor though so i have hooked the throttle back up to the governor now. on the track i am running on, my tach is showing my RPM reaching 3950 at the end of the straights but it seems to be topping out just a bit too soon.......my question is....how many RPM can be safely turned on a stock 12.5hp briggs motor? when i say stock i mean stock, no billet flywheel yet (saving for one now). i also found a 2" rear pulley last night at a nearby shop......do you think if i put the 2" rear pulley in with the 4.5" pulley in the front....will i get just a bit more top end speed while keeping the RPMs down to a safe level? thank you everyone  woo
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insidegroove
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« Reply #1 on: September 22, 2013, 11:31:50 AM »

27 views so far and not a peep? anyone lol?
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valleeracing
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« Reply #2 on: September 22, 2013, 12:04:46 PM »

Have a transaxle ? If so try a 8 on motor 3.5 on axle
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Brent

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« Reply #2 on: September 22, 2013, 12:04:46 PM »

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insidegroove
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« Reply #3 on: September 22, 2013, 01:20:17 PM »

yes it has a transaxle. an 8???? wow.....i had a heck of a time finding a 6" for the front and held off because it was cast iron and $53 haha......thanks though...i will be looking for an 8

as far as RPM.......any idea if 4000 is safe for a pure stock motor?
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valleeracing
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« Reply #4 on: September 22, 2013, 05:00:29 PM »

I ran one for a year at 5k no prob at all
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Brent

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« Reply #5 on: September 22, 2013, 05:38:39 PM »

What class do you intend on running in?
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insidegroove
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« Reply #6 on: September 22, 2013, 08:04:49 PM »

Aircamperace - not really sure honestly.......i own a dirt go kart track, 1/10 mile bullring. i bought the mower not knowing much about them at all and am already having a blast learning. i know we have two town fairs nearby that run mowers each year, but i need to find out what divisions they run. i ran the mower today at the track as a special treat for everyone......turned a lap on the clock at 12.046 (first ever mower time haha) the karts run about 10 second laps so it wasn't far off........i just feel like it's topping out speed wise much too soon before the turns. FUN FUN FUN!!!
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royalblu68f100
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« Reply #7 on: September 23, 2013, 06:53:20 AM »

Find a Tractor Supply Company they have pulleys with hubs that you weld in.  Dont get the cast pulleys they weigh too much.  How good are the brakes on this thing?  I ask because we take safety seriously.
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You never win a race by focusing on one aspect of the race!  Motor isn't everything, but you better have a good one!  Chassis too!  But remember, a driver can take a slow machine and make it faster!  I may not have/be the best of any of these but I'm trying!
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insidegroove
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« Reply #8 on: September 23, 2013, 05:24:33 PM »

GREAT advice Royal!!! I found the 8" one today at tractor supply....unfortunately they didn't have the weld on hub but they ordered it for me. less than $30 for both pieces, versus $86 the local pulley shop wanted for a cast iron 8"
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willenglish
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« Reply #9 on: September 23, 2013, 06:50:58 PM »

The question Chris asked you about the brakes is important...and went unanswered. That mower ....all racing mowers... needs improved brakes. That thing will spit you out and stomp a mudhole in you if it has poor to no brakes and the right situation comes along.
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William L. English, jr.
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« Reply #10 on: September 23, 2013, 06:55:52 PM »

3650 is the only safe RPM with the stock flywheel. 

Any faster you need a billet wheel. 

If your racing it you need improved steering and brakes.   

There are a lot more safety items you need as well.  Start reading here.

http://www.heymow.com/index.php?board=2.0
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Paul Krueger
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insidegroove
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« Reply #11 on: September 23, 2013, 08:40:50 PM »

ok...a far as brakes.....i have a master cylindar, brake lines and caliper for the racing karts we race......the issue i am having is the smallest hub for the brake disk we have in our catelogs are 1" diameter.....the rear axle of the mower is 3/4" diameter. i was thinking of welding a 1" diameter spacer onto the axle, and adding a keyway so i can install the brake disk. how do you guys get a disk onto a 3/4" axle?
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« Reply #12 on: September 23, 2013, 09:19:31 PM »

So you currently have no brakes.   

You need to stop racing that.   


There are adapters out there. Do NOT weld on the axle.  It will make it weak where you weld. 

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Paul Krueger
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GunSlinginJoe13
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« Reply #13 on: September 23, 2013, 09:47:33 PM »

You can get a 1 inch axle.  I would just get 1 1/4" axle there's parts for them any where
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insidegroove
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« Reply #14 on: September 24, 2013, 07:41:52 AM »

but isn't the transaxle all one unit? i didn't think i could just put in a bigger axle?
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