4 HP briggs and stratton
- Thread starter tenlizard
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Ibnzmonkey
Keep Austin Weird
Good job on the restoration. Looks and sounds good. Get yourself a set of craftsman snap ring pliers for like $20 @ sears.
oh and i am repainting the engine white because this kind of paint i'm using is heat resistant and gas resistant. it looks pretty good so far. will post pics when i'm done. i might get a mikuni carb on ebay so it will be better but it's unlikely!
what size/kind of mikuni carburetor would fit my briggs 4hp? someone please send me an ebay link of it. all the ones that i'm looking at says like honda, suzuki, ski doo, but there isn't one that says briggs and i'm confused because people have said that they use these on briggs engines. and by size i guess i mean mm?
jr dragster T
New member
Dont get the mikuni carb. Keep it stock. IMO only add a mikuni if your doing a proper build up.
jr dragster T
New member
Well when/if it breaks then look into it.
Kenny_McCormic
Kartless....
buy a used one
Jerryburger
Admiral Annoy
You'd have to do a bit of Assburgering to get the Mikuni to fit the Briggs- they have different mounting types. I found a whole bunch of adaptable mounting flanges in the DennisKirk snowmobile catalog they sent me with my order.
As far as carb size, here is my Assburger Estimate: 20mm. Based on my wife's carbs on her bike. Bear with me....
Each 20mm carb can handle an 87cc cylinder all the way up to 9000 rpm, no problem. Your motor is about 138cc. I took the cc's that the 87cc cylinder is flowing at 9000 rpm (783000cc) and divided it by your engines cc capacity, and came up with a potential 5650 rpm.... which means even the 20mm carb is a bit on the big size. (On a 5hp B/S, it'd be good up to 3600 rpm.) They sell the 20mm carbs on Ebay for $30. You'll also have to mount the gas tank higher so that it'll gravity feed. I'd think this carb and about a 12" straight pipe on the exhaust would do pretty well.
As far as carb size, here is my Assburger Estimate: 20mm. Based on my wife's carbs on her bike. Bear with me....
Each 20mm carb can handle an 87cc cylinder all the way up to 9000 rpm, no problem. Your motor is about 138cc. I took the cc's that the 87cc cylinder is flowing at 9000 rpm (783000cc) and divided it by your engines cc capacity, and came up with a potential 5650 rpm.... which means even the 20mm carb is a bit on the big size. (On a 5hp B/S, it'd be good up to 3600 rpm.) They sell the 20mm carbs on Ebay for $30. You'll also have to mount the gas tank higher so that it'll gravity feed. I'd think this carb and about a 12" straight pipe on the exhaust would do pretty well.
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i just got a pressure guage and my engine reads around 75psi so how am i supposed to know what my engine should read? i also did a test on my newer 4hp engine and it read 95psi so i don't know how to reference if it's good compression or not. all i know is engines are rated in cubic centimeters (cc) and i don't have a guage that measures cc only psi. what should the psi be for a 4hp briggs?
jr dragster T
New member
Are you refuring to compression?
Kenny_McCormic
Kartless....
You cant test compression on most small industrial engines, the decompression system will screw the reading up. Briggs service manual procedure is to grab the flywheel and trow it into the compression stroke, if it bounces back its got compression.
yes i looked at oscaryu1's new movie on youtube and it showed that compression testing thing. i tested my compression and it's 75psi after running and that's good. i did the math algebraicly and it said for a 4hp engine with 186.7cc it should be 76psi to meet 4hp. right now it's like 3.95hp which is close enough. if i ordered new rings which would be like 22 dollars including shipping it may bounce it up to 90-95 psi and it would be about 5hp. right now i am very pleased with my engine. i took the duct tape off the lead for the spark and that made it start better and it had less spark misses. i also made my coil pretty close to the flywheel but not touching it and that made it go WAY better. i wasted gas because i thought water got in it...actually a little did...but with the coil closer i bet it could've burned all of that water away with the power stroke because of evaporation. so that's the story of my engine...so far!
Russ2251
AZUSA:Powered by LAWN-BOY
Coil gap should be .010.
Not likely.
Kenny_McCormic
Kartless....
Rebuilding it wont make it make more than factory power, your thinking is clouded. if it runs and doesnt burn oil the top end is fine.
Kenny_McCormic
Kartless....
You cant test compression on a small 4 stroke engine like this one with any accuracy. There is not much that can be done with a a 4hp briggs to improve power past a straight pipe and governor removal, if you want to build a motor get a 6.5hp clone.
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