Building a Go-Kart for school

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  #1  
Old 09-28-05, 06:52 PM
viper37
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Building a Go-Kart for school

I am building a go-kart for school, and I need some suggestions for the motor. I already have a whole chasis design ready and I feel doesnt need to be altered.

I recently picked up a Brigg's and Stratton 60102 2 HP engine. It has been sitting on my side yard for a few years. I cracked it open today and got rid of all the carbon buildup on the top of the piston, and made sure the cylinder walls were clean. I cleaned the carb and all intakes. The engine now starts on a single pull at half throttle no choke. Pretty good if you ask me.

What I need help on now, is safely maximizing the power for this engine. I already know the basic things such as tuning the carb, I just need some other info.

I dont know what type of sparkplug system will give me the hottest spark. The magneto is a little bit rusty, which I can fix with some sand paper. Is there an inexpensive upgrade magneto I can get for it that will boost the voltage of the spark? Or is that somehow controlled by the engine?

Also I would like to dump the muffler for a straight shot exhaust pipe, with no sound dampening. That is not an issue where I am going to be using it.

Also, I had plans of re routing the intake with some hosing to the front of the engine, seeing as it sits right next to the exhaust pipe sucking in hot air. Will this help performance?


Are there any other mods I can do to this engine that will safely maximize horsepower? (safely meaning the piston wont shoot straight through the top of the case)

Any help would be greatly appreciated!

-Matt

P.S. Maybe a 4 barrel carb with top shot N02 would help? hehe
 
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  #2  
Old 09-29-05, 01:15 PM
v8driver's Avatar
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you can check out brigg's website, for performance cam's and connecting rods and blocks, no moving the carb will not help, it can be worked over and the intake made bigger to make it easier to breathe, the straight pipe is a good idea, but it'll need a little backpressure. nothing can really be done to the mag, now you could step up from that tiny engine, and get a 5, 6, 7, or 8hp on up engine. that will give more power. mostly these engines can be found on old tillers or generators that were hardly used. also if the connecting rod will be stock, you can up the rpms a 100 or so, i've run em over 4,000, but stock you don't want a grenading engine, blowing alluminum left a right. if it did throw, it would most likely go out the back of the crankcase on the power stroke.
 
  #3  
Old 09-29-05, 03:35 PM
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ya, my thoughts, before going and tricking out a 2 horse, you are far better off with a bigger engine.

Or perhaps no matter what size engine you have the whole concept is tricking out the motor. Either way.

My sons go-kart has a 5hp on it, and i feel is just right for him.

Since alot of racing engines pur 5hp , since there is a division for the 5hp, there is alot of performance parts out there for that engine. Which could also mean cheaper to get and easier to find.

Alot of times im always seeimg a supply of used perforamance parts on e-bay for 5hp briggs.

Now you didn't mention how the compression was on the 2hp, however you mentioned removing the carbon, actually the carbon itself causes come minor gain in compression, since is creates a reduced area.

Although I have not done mods to my sons engine.

I have heard of people doing the following-

bigger vavle and intake, stiffer, tougher springs on the valves.

Bored out to the max, performance rod and bearing.

shaving off a thousandths off the head.

advancing the timing.

racing fuel

hotter spark like you mentioned. You can get plug that will do this also, with out going into the ignition.

However, did not know how beefed up you wanna go.

you go to much and you be rebuilding the engine more often.

I rebuilt a 10 hp briggs for my rider a few years ago and I took it to a machine shop and had it bored and valves done, 3 angle valve job.

Is the gokart for fun or racing ?

My kids go kart is for the yard, with gear ratio calc, you can come up with the hp and speed. I found that on a go-kart website.

dont have the link no more, just the program.


sporty
 
  #4  
Old 09-29-05, 06:38 PM
viper37
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Thank you very much both for excellent response's. I plan on using a 3 speed shifter off of a bike to attain speed, so it will shift almost identically to a car.

It is just for use puttering around the highschool track and on the football field, and maybe possible rideing around the neighborhood. Nothing extreme like racing or going off road.

I have another question, I know about a cyntrifical clutch's functioning, but I dont know about placement. Would I place it off of the engine, or on the driveshaft?

Also as far as ignition, sanding off the magnito contacts cant hurt. What kind of plug would you reccomend to get a hotter spark?


Thank you very much for the help, I know these may seem like novice questions, but I appreciate it very much.

-Matt
 
  #5  
Old 09-29-05, 06:50 PM
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you can check out splitfire plugs, i beleive they are at autozone....for racing. yeah sanding the flywheel and mag clean can't hurt, gap it with a dollar bill so that it slides out with a little force, but doesn't rip, then check for catching. a clutch, what i'd prefer is a solid axle, clutch on crank of course, chain to the axle, but it doesn't corner well, but gives power to both wheels equally. bigger tires out back of course... though i would go with a 5 horse if you can get one..... 2hp just isn't too powerful, even for a gocart. but it will do you....oh and for compression, if its over 100, your good. use some synthetic mobil one in that puppy, it'll run even better.
 
  #6  
Old 09-29-05, 07:51 PM
viper37
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Thank you kindly, do you have any reccomendations for a clutch tho?
 
  #7  
Old 09-29-05, 08:13 PM
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any clutch that will do, they make regular clutches for go carts, that last a couple years or so, then they make a little more expensive racing clutchs that will last alot longer, your just looking for one thats keyed to go onto the crank, and is held on with a bolt, to the crank, then chain from the clutch to the axle?
 
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Old 09-29-05, 09:28 PM
viper37
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Thats a 10-4.
 
  #9  
Old 09-30-05, 05:08 PM
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OK a few things I noticed here.

1. Racing fuel will be of NO benifet, because a stock 2hp briggs doesnt have NEARLY enough compression to have to worry about detonation(pre-ignition)

2. The carb on a briggs doesnt really draw in hot air when on a go kart or minibike, because its moving. The only way to improve performance would be to do like a ram air sort of thing, and I dont really think it would do much for you. You can remove the breather tube from the carb, so its not sucking in any hot air from the crankcase, although that wont help much

3. Carbon buildup does not help compression. While It reduces the Combustion chamber volume, It is offset by the fact that small engines dont have very tight rings, so that extra bit of compression is lost. Also, The extra carbon is like having a taller piston on thier, which reduces the volume of air the piston can draw in. Also, you dont want to shave off a few thousandths on the head, you would want to add it, because the head volume doesnt really affect how much air/fuel mix is drawn into the engine, so by having smaller heads, you can get a higher compression ratio.

4. Stronger springs are only important in High RPM situations. If your revving a thousand or two rpms higher than what it was deisgned for, you risk floating a valve. Floating a valve Reduces performance in Engines, because the valves cant close fast enough, but In an OVH design, you risk hitting the top of the piston, and most likely bending the valve stem, or causing some other fun things like that.

5. As for Ignition, Id say look for a magnetron engine, Those are CDI style ignitions (capacitor discharge Ignition) And they are Solid state, as opposed to MBI (mechanical breaker ignition) which you have on thier now. CDI type ignitions dont slowly break down, they run strong and then fail, there is no in between like with points and condensors.

6. I wouldnt worry about Plug heat too much. We Do that with our racing motors (I run a 21hp yamaha kt100) which cranks out 15 thousand RPMS. Its not so much important in abakc yard kart. If you want a good read on tuning the engine with a sprak plug, check out the denso plug website. Just use a stock plug. As for Splitfires, Nobody really uses those at the track. Autolites are good plugs, while they last. Thier life is typically short. Densos run strong as well, however the cap on top is screwed on, as opposed to most other brands where they are pressed on, so sometimes the vibrations will cause the caps to unscrew, leaving you with weak or no spart. Denso's however, have the broadest line of heat ranges, which is nice for tuning. NGK are also decent plugs. If you dont mind spending $7 for a friggin spark plug, check out iridium cored plugs.

8. I say the best thing you can do is look for a 5hp briggs and stratton engine. This is what most 4cycle racing motors are built off of. Crane Cams and Comp Cams make camshafts for these motors. You can build a pretty strong racing motor yourself with basic hand tools for about 550, including a brand new motor. Parts will run 250-300, so If you can get a briggs motor that has no scoring in the cylinder, your good. You can get a Longer duration, slightly higher lift cam(120) , New valves with a shorter stem length to accomidate for higher cam lift(30), stiffer springs(30), a new head(50), and 2 tighter compression rings (25), and A forged connectiong rod(25-50) You will be ok with a stock wrist pin and piston.

Granted, you wont be able to squre the crank or properly hone the cylinder but youll still get a good 3-5 more HP out of the thing, as well as another 1k rpms at least.

For tools, you can get away with basic stuff...

3/8 socket set
A basic set of wrenches
A pair of needle nose pliers
A pistoin ring compressr (less than 10 at any autoparts store or sears)
Torque wrench

These tools will allow you to build a fairly high performance engine yourself. Granted, To do this properly you hsoudl take off the flywheel and hone the engine, but for what yoru doing, youll be ok.

IF you are interested in building a motor, start a new thread, and I can point you in the right direction.

Jim
 
  #10  
Old 10-09-05, 07:57 AM
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I think 2hp is a bit low 3.5+ would be better,tho 8+would be great fun
 
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