Modifying stock 3-5 hp carbs?

[offroadwhatever8]

On my 3 hp briggs, im alreagy porting the the intake port and shaving the head. I was wondering if there were any ways to mod the stock carb to get a little bit more power out of it. :confused1: My goal is to get as much power out of it as i can to try to stay alway from buying a 5 hp. (for now) Thank's John

 

[RuppParts]

take out choke, drill main jet and run alky...drill stock jet to .040

 

[minidragbike]

I wouldn't run alky with a stock bottom end motor. Alky is used for all out built performance motors.

What you can do is have the carb bored, and honed to .710" This doesn't seem like much but it would help the flow of the motor. The hard part is finding a matching throttle butterfly. Or you can always find a old stlye briggs tillotson carb manifold, and bolt on a small chainsaw tillotson carb.

 

[offroadwhatever8]

alright, thanks guys

 

[RuppParts]

mini, why no alky? It has no adverse effects on bottom ends. I have used it for years without ANY problems what so ever. Makes MUCH more power than gasoline and is 1 VERY simple way to boost HP. Alky will make a bigger HP percentage gain on a stock motor as compared to a hot rod motor being switched from gas to alky. Stock classed go kart racers who have to use stock engines(except for blueprinting) have used alky for years. It is the only fuel for 4 cycle kart racers. They have NO problems with it

 

[philip metzner]

i have been running alky in my race karts since about 1980, and it is a easy conversion, but we change our oil after every heat and feature and use a synthetic oil that is more tolerent of alky contamination. we also work real hard to keep the best ring seal possible. i dont know how it would work with a worn engine with petrolium oil in it.-phil

 

[minidragbike]

mini, why no alky? It has no adverse effects on bottom ends. I have used it for years without ANY problems what so ever. Makes MUCH more power than gasoline and is 1 VERY simple way to boost HP. Alky will make a bigger HP percentage gain on a stock motor as compared to a hot rod motor being switched from gas to alky. Stock classed go kart racers who have to use stock engines(except for blueprinting) have used alky for years. It is the only fuel for 4 cycle kart racers. They have NO problems with it

Your right alky does make more power then gas. But to get the most power out of the combo you will need to add more static compression. And you will need to add more ignition timing. Alky loves the best of both. Now what normally happens when a motor starts to make more power, the power band rises. Not by to much by just switching to alky alone. But the factory rings don't have the correct ring gap to run alky. This means more blow by pass the compression rings and by the oil rings and into the crankcase. All of this is bad news for non-bearing inserted rods, and aluminum bore cylinders. Plus the fact you have to run twice as much alky as you do gas to run the motor correctly. This means that if you can run on a full tank of gas for 30 minutes. You can only run on alky for 15 minutes before you run empty.

Now there is also a lot more upkeep by running alky even when you have the correct components. Changing the oil about 3 times more then gas. And flushing the carb, and cylinder with gas when ever your finish racing is a must. This is the main reason why some guys hate alky so much. But if the racing is just that serious then you will need it.

That's why I carry a alky minibike, and a gas minibike for different purposes.

 

[minidragbike]

Normally you get about a 15% increase in power from alky alone. Now you can make that percentage increase with more timing, and compression. But you have to make sure you motor is completely built for it.

In kart racing were everyone has the same style blueprinted motors you have to run alky. Or either be left behind. But these motors cost well over $1000 and are built from the ground up to be a full competition motor.

Stock class isn't really stock.

It's a blueprinted alky converted carb
Stock class racing aftermarket cam
Billet stock length rod with bearings
Blueprinted ignition timing
Block prep (align bore, decked, honed, and even welding if needed)
Ring gap set, rings fitted
Cylinder head milled
3 angle valve job
stiffer valve springs to match the cam profile
crank end play checked
Now torque everything down to the correct recommended torque spec's and DYNO the motor.

And I'm sure I'm leaving out a lot.

 

[johnf.357]

briggs 3 hp carb jet

HEY MAN
I TOO HAVE A 3HP AND IT RUNS WAT TO RICH,CAN I JUST CHANGE THE JETS TO LEAN UP??

WHAT SIZE??

WHO HAS EM??

tHANX FOR YOUR TIME JOHN.357