3 hp Briggs Question

leoofc

Member
Finally got a 3hp briggs at an estate sale for 10 bucks. I always loved the way a white 3hp briggs looked on a red framed minibike. Anyway, the motor was a 110 volt 1300 watt generator also. When I took the generator part off, the motor had a tapered keyless shaft. Question is, will a proper keyed straight crank from a similar 3hp same model no fit this engine? Maybe a different code would mean the different crank?
 
It takes a different crank. They can be changed, but probably not worth the effort or expense.
You may be able to work with a local machine shop to adapt something to work.

See if you can find an old snowblower or walk behind leaf blower (commonly used 3HP engines back in the day.) They also will have low hours on them because of their limited use.


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I just finished up my snothrower 3 hp refresh for my boys mini bike. I found a nice carb resembling the race style, cleaned it up nice and swapped it out with the old pull out choke style. Lapped the valves, matched the springs, experimenting with different depth heads. Since I have 6 or so spare and a brand new harbor freight belt sander. I tell you what starting to feel like ol Jimmy Glenn in the shop now! Lol just messin. But I have found more is not always better. New style carb put a ton of top end power available but I noticed I lost half of my bottom end torque. Any answer to why that happened? Also before I make a mistake would it help to drill out metering holes or not? On gas nothing special. Next project is to make a sight block so I can try out all these different cans I have without fully swapping them out constantly. So far 3 different camps have given completely different numbers. I'm sure its probably pointless but I have the parts, tools and 3 of my 5 kids willing to watch it all go down so I might as well have fun with what I got. Any ideas would be fun to examine. Thanks have a good one. R.I.P Alvin Nunley
 

flattop1

Dawg 89
The metering hole might have something to do with it .
Or it could be the throttle shaft butterfly offest .
The pull type -my understanding ; was the better carb .
Plenty of spares and a real good reamer set might be a gain there .
 
Kinda of like installing an 850 Holley on your daily driver.
You can't just throw bigger parts at an engine -- everything has to work in concert with one another.
Putting a larger carb on moved the powerband UP with the better flow, but loss in velocity. Then you've got the bigger bore carb hitting the smaller port, which you addressed, only to make bigger and lose more velocity, and with that, throttle ability and bottom end.
The fuel metering holes should be fine if you did not bore the carb. They are already appropriately matched to the size of the bore to be run on gasoline.
You will need to work on a cam to match the power band that you want to achieve next.
That's a whole other long-haired discussion. :)
 
Kinda of like installing an 850 Holley on your daily driver.
You can't just throw bigger parts at an engine -- everything has to work in concert with one another.
Putting a larger carb on moved the powerband UP with the better flow, but loss in velocity. Then you've got the bigger bore carb hitting the smaller port, which you addressed, only to make bigger and lose more velocity, and with that, throttle ability and bottom end.
The fuel metering holes should be fine if you did not bore the carb. They are already appropriately matched to the size of the bore to be run on gasoline.
You will need to work on a cam to match the power band that you want to achieve next.
That's a whole other long-haired discussion. :)
I'm not sure the new carb is any bigger because it came off a 3 hp as well. Should flow a lot more since it is open with out choke and the other obstructions like the big chunk for the breather scew like the other one had. Thanks for the knowledge. One more thing I am curious about is cam twisting. I have herd it's a nightmare but what do I have to lose? I was looking around my old kart supply magazines and seen where a cam twister thing used to be for sale. Just wondering if there was a DIY solution to getting it done?
 
I'm not sure the new carb is any bigger because it came off a 3 hp as well. Should flow a lot more since it is open with out choke and the other obstructions like the big chunk for the breather scew like the other one had. Thanks for the knowledge. One more thing I am curious about is cam twisting. I have herd it's a nightmare but what do I have to lose? I was looking around my old kart supply magazines and seen where a cam twister thing used to be for sale. Just wondering if there was a DIY solution to getting it done?
The key to twisting is having/making a fixture to keep the cam straight. I have one for the 5HP flathead that I still use occasionally. You can make one from a couple pieces of angle and an old cam sawn in two. Look at some photos and you should be able to come up with something to try.
 
Any chance you could post a pic of the one you have? I havent found anything on the topic other than the small pic in the old checkered flag fuel magazine I have. Not much to go by.
 

sundog

Member
Cut the taper off, drill and tap 3/8 NF then make a straight shaft that will thread into the crank that's bigger in diameter. Then weld it in and machine it to size. Straight shaft crank good enough for a 3hp mini bike.
 
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