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Old 09-17-2019, 10:17 AM
Abone Abone is offline
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Default Briggs 5hp budget performance mods

I wanted to get a kart to rebuild for my grandkids, ended up with a trailer full of rust that was once 5 go karts. I have 3 refurbed, one for the kids, two are sold (got my money back on the original buy) and the worst of the motors and two frames are left. One is a live axle. The fuel tank on the last one was trashed, the chamber that the Briggs main jet sits in was rusted away, so I'm looking at a manifold adapter and a 22mm concentric carb with a remote tank, gravity fed mounted on the back of the seat. Might go with a straight exhaust. Plan to do the "eyebrow" porting and maybe the bowls, hoping to get the compression back up with a thinner copper head gasket.
1. Am I dreaming or will any of this work?
2. Is there anything else short of expensive race cams, heads and blocks that I should consider?

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Old 09-17-2019, 10:21 AM
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"Concentric"?
Whaddya mean by that?
Otherwise sounds fun, but you'll probably need the high RPM of governor removal to feel the power increase.
And if you do that I'd upgrade the con rod to make sure it survives.
Flatheads are a non renewable resource!
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Old 09-17-2019, 10:43 AM
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Sure it will work. Just adding a straight tuned-pipe exhaust really uncorks these engines and creates a boost you can feel in the seat of your pants.

The eyebrow mod is a finicky procedure and questionable (unless you’re going whole hog on everything else). I’m sure it helps but make sure you don’t shave down too much from the top of the cylinder as it reduces compression.

Thin cylinder head gasket is a great idea as well as decking the block.

Got pics of your kart and engine stash? We like pics.

EDIT—wait a minute, how old are your grandkids?
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Old 09-17-2019, 11:03 AM
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I think the OP wants a fast kart so he can "play" with his grandkids.
IDK.
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Old 09-17-2019, 12:46 PM
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I don't know what those old briggs flywheels are rated for, but you might want to upgrade to avoid shards of metal in your back. I don't know how effective it is or if it's even worth it, but you can advance timing with an offset flywheel key.
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Old 09-17-2019, 03:15 PM
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Since you know you have carb issues you may consider adapting to a mikuni, a tillotson, even a clone carb. All of which will need a custom intake and fuel pump but can be set up to deliver reliable service if you have skills and patience, especially since you are talking about modding the engine anyway. Mikunis can be a pain...but seem to work well once dialed in. I haven't had the pleasure of tinkering with a tillotson...so...and the Honda's and clones we all know too well. They work but I think they get flakey when used with a fuel pump...but that is just my opinion and it means nothing. Unless it has been modified, all bets are off then...
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Old 09-17-2019, 03:16 PM
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The common factor of all these suggestions?
They need governor removal and a billet rod.
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Old 09-17-2019, 03:19 PM
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Oh, and I too get concerned about flywheels. Just as the poster above mentioned. If you don't replace it at least build yourself a blast shield...but seriously...who knows how many RPM will take to shred it...
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Old 09-17-2019, 03:54 PM
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The Raptor 1 and 2 came with a regular flywheel #555067. Don't have the info on Raptor 3 right now. I think stock they would run around 6kRPM. Open class racers ran em 9000+.

The problem is you don't know if someone put em on with an impact or tried bashing em off with a hammer. Visually you may see deformation from a hammer blow as well as a surface cracks. But subsurface discontinuities would require some type of NDT (non destructive testing) such as Magnaflux.

Dye penetrant will help to detect surface discontinuities, or the redneck method using kerosene and chalk powder.

Or just buy a new one. If you don't want to spring for a shiny billet unit.
http://www.ufranks.com/cart/index.ph..._detail&p=1196
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Old 09-17-2019, 06:03 PM
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Quote:
Originally Posted by Randy H View Post
The Raptor 1 and 2 came with a regular flywheel #555067. Don't have the info on Raptor 3 right now. I think stock they would run around 6kRPM. Open class racers ran em 9000+.

The problem is you don't know if someone put em on with an impact or tried bashing em off with a hammer. Visually you may see deformation from a hammer blow as well as a surface cracks. But subsurface discontinuities would require some type of NDT (non destructive testing) such as Magnaflux.

Dye penetrant will help to detect surface discontinuities, or the redneck method using kerosene and chalk powder.

Or just buy a new one. If you don't want to spring for a shiny billet unit.
http://www.ufranks.com/cart/index.ph..._detail&p=1196
It's a yard kart that's been sitting in a barn so long that the gas tank has rusted out...do you really think the flywheel on it would be safe to spool up to a continuous 6k rpm? I wouldn't bank money on it.

He has grandkids with access to it as well. There are options. Safety first. I do a lot a ballsy crap. A crankcase will contain most of a thrown rod...but you are looking at what, maybe .045-.060 at most sheet metal keeping chunks of flywheel and magnets off you if that thing comes undone? Who knows what kind of corrosion the flywheel has undergone over the years. Not worth it. Maybe for us old codgers...if we had some way to cage it up...I wouldn't chance it around kids. Don't think those little rascals aren't clever enough to ride that thing when no one's around because they are...you can confirm that with JT if you don't believe me...he prolly knows some little rascals...40 years ago I used to be one...
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Old 09-17-2019, 08:14 PM
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I say if your concerned get a billet flywheel or a new Briggs flywheel. I've seen a number of flywheels and haven't witnessed the massive corrosion you speak of. That's just my experience. Surely if it's pitted or questionable in any manner it should be replaced.

I would be more concerned about a crack that isn't visible. Especially a micro crack below the surface of the material in question. That's what I mean by subsurface. Sometimes I forget the target audience here.

I really don't think some kind of rigged cage is the answer. For many, would be fabricators, I would see it as a false sense of security.
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Old 09-17-2019, 10:30 PM
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Quote:
Originally Posted by Randy H View Post
I say if your concerned get a billet flywheel or a new Briggs flywheel. I've seen a number of flywheels and haven't witnessed the massive corrosion you speak of. That's just my experience. Surely if it's pitted or questionable in any manner it should be replaced.

I would be more concerned about a crack that isn't visible. Especially a micro crack below the surface of the material in question. That's what I mean by subsurface. Sometimes I forget the target audience here.

I really don't think some kind of rigged cage is the answer. For many, would be fabricators, I would see it as a false sense of security.
I'm not necessarily saying some rigged cage is the answer. But it would beat the crap out of running some unknown part that was produced who knows when. Briggs ceased production of their Raptor line 20 years ago. I highly doubt this guy has a yard kart with a Raptor of any kind on it. Most likely just a plain old 5hp L series or the like which is more likely to have come off the line 30 years or longer ago. Essentially it's an antique. Just because you don't see the hidden corrosion doesn't mean it isn't there. Iron and cast aluminum don't get along over the years. It creates a condition called dissimilar metal, or galvanic corrosion where the metals come in contact on the underside and are hidden from view. You cant see it, but it's there. The beauty of that glorious Briggs was it was an inexpensive engine and even though it was never designed to last 30, or 40, or maybe 60 or even I think a century or longer...it's still here and it's gonna be here...the danger lies in things like people putting their trust in iron magnets staying in an old cast aluminum flywheel...ain't gonna happen bruh...they fail all the time, ask any racer, even a new one will get you. My biggest gripe I ever had about a briggs was when they went to the in tank carbs.

Anyway, he can do what he wants. It's his stuff. I'm not here to argue with you. You talk a lot about the Briggs Raptor series and that fine. Those were racing engines. They weren't put on yard karts. I understand there were supposedly OEM or stock parts in them. But as a mechanic I would also tell you that in general most things labeled as 'racing' parts have a higher quality standard out the gate to start with. You can take that or leave it. It's kind like 'racing' gas and 'race' cars...'race' engines and 'race' parts just ain't the same...but hey...what do I know...nothing...it's kinda like airplane parts...oh wait...I'm an airplane mechanic...they're different...

take spark plugs...

spark plugs for airplanes are awesome...NOT...cheap ones go for 30-40 bucks a piece...then there are these things....

https://www.skygeek.com/rem38s.html?...MaAo5YEALw_wcB

People always want to say parts are parts until they bring home a big box of parts as pieces...that's when they realize quality counts and it's the hidden snake that bites you.


do what you wan't, you can't sell me on anything one way or the other...I'm already in the know...

And by the way, I'm not trying to be conflicting with you, I am just trying to share years of knowledge. Just be glad you aren't the unlucky devil who has to buy those plugs up there...but then again...if you have to ask...you wouldn't be able to afford them anyway...

If you are curious the plug mention above, they are common in all sorts including J-3 cubs and up. Each cylinder has 2 plugs. Many times people will run 2 different types. Usually 1 expensive and one cheaper. It's a mixed bag, you see all sorts. Some plugs will be upwards of 200 bucks each. A big 6 cylinder will have 12 plugs...so it gets spendy.

Anyway...our hobby is cheap...parts ain't parts...not to me anyway...
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Old 09-18-2019, 05:01 AM
Randy H Randy H is offline
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https://4cycle.com/karting/threads/b...pm-5hp.106462/

Here a little bit on the subject. Brian Carlson has decades of experience with flatheads.

I do to but not at his level.

I actually prefer experience and hands-on knowledge (and part numbers) as opposed to straw man debate tactics.
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Old 09-18-2019, 07:13 AM
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Wow. Thanks for the safety info. Really had no idea that a slight port job and intake/exhaust mods might allow 7k+ rpm. The kart I have in mind is the largest of them, and has a live axle and center mount with a high back seat and roll cage. If I achieve any of the levels of concern voiced here, a steel shield will be easy to fab. Yeah. I want to ride it myself....only one of the grandkids is a real enthusiast, I will NOT allow her access unless I think it safe.

Ok, ignorance exposure time. If I make the fire breather we are concerned about, how much would I have to spend on billet flywheels and rod?
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Old 09-18-2019, 07:28 AM
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Quote:
Originally Posted by Randy H View Post
https://4cycle.com/karting/threads/b...pm-5hp.106462/

Here a little bit on the subject. Brian Carlson has decades of experience with flatheads.

I do to but not at his level.

I actually prefer experience and hands-on knowledge (and part numbers) as opposed to straw man debate tactics.
I guessed you missed the part about me being a mechanic. If you are thinking there is a straw man debate going on here I'm not the straw man. Debate over before I take your insult personally.
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Old 09-18-2019, 08:53 AM
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Quote:
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Wow. Thanks for the safety info. Really had no idea that a slight port job and intake/exhaust mods might allow 7k+ rpm. The kart I have in mind is the largest of them, and has a live axle and center mount with a high back seat and roll cage. If I achieve any of the levels of concern voiced here, a steel shield will be easy to fab. Yeah. I want to ride it myself....only one of the grandkids is a real enthusiast, I will NOT allow her access unless I think it safe.

Ok, ignorance exposure time. If I make the fire breather we are concerned about, how much would I have to spend on billet flywheels and rod?
Whoawhoawhoa. You'e NOT going to turn 7K with only flow mods.
The max RPM is dictated by valve spring weight, and at really high RPM, ignition timing.
At 5500 RPM, the valve float point for ungoverned flatheads, the risk with a visually all good flywheel isn't too high. But perhaps too high for turning your grandkids loose on it.
You have to remember, racers didn't just turn 7K with a stock 'wheel, they did that for looong track days.
I am not guaranteeing a stock flywheel at high RPM is safe.
If nothing else, get the billet flywheel for the performance increase. With less rotating mass, the engine can rev up faster.
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Old 09-18-2019, 09:05 AM
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Heck JT, I wouldn't let you, me or anyone else on an unknown, unprofessional inspected 30 year old flywheel turning 7k. None of us know what shape it's in. It's site unseen and untouched by any of us and we are foolishly arguing about something we should assume is bad until proven good. It's just too easy and cheap enough to replace. You buy more Briggs parts than me lately, how much is a reasonable aftermarket flywheel JT? Something trustworthy but not overly expensive? Something that will put him in his desired RPM range? You could probably give him a parts estimate for that matter.
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Old 09-18-2019, 09:48 AM
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Quote:
Originally Posted by BigWes View Post
Heck JT, I wouldn't let you, me or anyone else on an unknown, unprofessional inspected 30 year old flywheel turning 7k. None of us know what shape it's in. It's site unseen and untouched by any of us and we are foolishly arguing about something we should assume is bad until proven good. It's just too easy and cheap enough to replace. You buy more Briggs parts than me lately, how much is a reasonable aftermarket flywheel JT? Something trustworthy but not overly expensive? Something that will put him in his desired RPM range? You could probably give him a parts estimate for that matter.
Easiest solution: put a nice thick piece of sheet steel between the motor and your seat back, and if it explodes, oh well the Steel will absorb the impact.
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Old 09-18-2019, 10:04 AM
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Quote:
Originally Posted by BigWes View Post
Heck JT, I wouldn't let you, me or anyone else on an unknown, unprofessional inspected 30 year old flywheel turning 7k. None of us know what shape it's in. It's site unseen and untouched by any of us and we are foolishly arguing about something we should assume is bad until proven good. It's just too easy and cheap enough to replace. You buy more Briggs parts than me lately, how much is a reasonable aftermarket flywheel JT? Something trustworthy but not overly expensive? Something that will put him in his desired RPM range? You could probably give him a parts estimate for that matter.
Yeah, we can't know what condition his wheel is in, it's really up to the OP, but it is in everyone's best interests to warn people.
Here's a really nice looking NOS flywheel for $36:https://www.ebay.com/itm/Briggs-Stra...MAAOSwQmRdQP0h
I would put this on my engine as it looks unused.
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Old 09-18-2019, 12:04 PM
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will a 3hp flywheel fit on a 5hp if so bet i am gonna have a high revving 5hp for free
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