2019 - Ultimate Yard Kart

[JTSpeedDemon]

40 MPH Capabilities unlocked!!

Woot woot woot!
Everything's hooked up(better than before) and it RUNS!!
The weather's not great, so I haven't ridden it yet or had a chance to fully rev it out, but everything is a-ok!
The fuel line had a small kink in it, so I remedied the problem with some 90 degree fuel line fittings, so that's no longer affecting fuel flow. I also removed the in line fuel strainer since the tank has one built in.
No oil leaks, and the only oil it burned was a little puff early on, but that was just the oil I applied to the piston and cylinder wall during assembly. No traces of burnt oil after that!
Video coming!

 

[Budget GoKart]

I may or may not have gotten a 8hp industrial briggs with a phat straight pipe and a performance carb for my yerfdog. Just sayin

 

[JTSpeedDemon]

May or may not????
Come on Trevor! Don't keep me (guess what I'm gonna say next) GUESSING!!
That's what, the 3rd engine on the Yerf Doge??
Even if I got an 8 HP I would not put it on this kart, since there's just not as many upgrades.
It'd make a good Radio Rod mill, though....

I need to get my chilly butt outside today and do some testing on the Hothead(It's around 40 F ). I'm gonna hijack the GPS from the car to keep track of my speed.

 

[Budget GoKart]

Well the first briggs 8hp had problems I didn't know how to fix at the time. The 212 was not powerful enough for my needs and the subie doesn't run and I don't have money for a new carb. It's 130$ on ebay! And this one may or may not be in perfect condition with a straight pipe and performance carb. I just wanna keep yall guessing even thought it's pretty obvious lol.

 

[JTSpeedDemon]

I bet if you sold off some projects you could get that Subie running.....
My dad helps keep me from getting too many projects to manage, but I'd rather have one really nicely running one to ride.

 

[Budget GoKart]

I bet if you sold off some projects you could get that Subie running.....
My dad helps keep me from getting too many projects to manage, but I'd rather have one really nicely running one to ride.

That's the idea there jt I only have the Coleman, ken bar, yerfdog, and rat mower. If I get anymore they will be trades that I just sell for cash so I can get other stuff upgraded. The manco 445 is my grandpa's and the motorcycle is my brothers. I'm making a new update video on my stuff later. And the subie is being kept but there's a chance I'm trading something off to get something for the subie to go on

 

[JTSpeedDemon]

HOLY SCAT!!!!
This thing is SO FAST!!
It actually feels quite composed at speed, which I wasn't expecting. Man can this thing scream!! No oil starvation problems, only carb tuning issues. Took me about 1/2 hr. of riding and tuning before I figured it out and got it right. Almost scary fast.
Thankfully the neighborhood streets were pretty empty, didn't even come close to wrecking.
The GPS battery ran out before I got it tuned, so I don't have a MPH number, but the butt dyno says it's turning up a lot harder. I plan to take it out again today with the phone speedometer running to get some numbers.

 

[Budget GoKart]

Wow sounds awesome I gotta tear down my yerfdog today

 

[JTSpeedDemon]

Official Top Speed!

38 MPH!
Granted it was on a slight downhill slope, but it did rev to valve float! I could actually hear the valves floating a bit, but by that point I was grittin' my teeth and keeping the pedal to the metal!
I think it still had a little more, plus there are probably slight discrepancies in the GPS system.
A car came up while I was at top speed, so it was a good test of my brakes. I was able to stop with plenty of safety.
So according to the DIYGK speed calculator, I was turning approx. 5400 RPM. So it looks like the heavy duty valvetrain doesn't give me a huge RPM increase, but again, these numbers are far from perfect. I need to get a tach on this thing.
Since the governor engagement is gone, even low to mid 20s feel way faster! And it just sounds AMAZING at high RPMs!
Again, I had to fiddle with the tuning, but it was awesome!

 

[Bansil]

 

[Budget GoKart]

Glad your happy with it I'm not happy with my briggs though also I got rid of my 5hp it didn't seem like it was worth rebuilding considering I literally have no money for anything but I might sell my subaru 13.5hp soon

 

[JTSpeedDemon]

I was worried about this thing burning oil, since it produced two small puffs of white smoke after the upgrade, so I tested it this morning.
I started it up cold(around 45-50 degrees F), and held my hand behind the header.
For a little bit it produced some very slight white smoke/vapor and blew some carbon and liquid onto my hand. It smelled like oil, but I can't be 100% sure, it could have just been the smell of exhaust, carbon, and a bit of unburnt gas. It then died out due to tuning issues.
Once I started it up and it was warm with correct tuning, then it was just fine.
None of this affected the oil level noticeably.
Eventually I'll probably hone and replace the rings, but for now it'll be fine. I think the intake valve guide is also worn, since when I had the head off, it had some slight side to side play.
Anyone know the part numbers for the valve guide tools? I have the part numbers for the valve guides.
Little things here and there to fix, but overall I'm happy!

 

[JTSpeedDemon]

Wow! Found a genuine Mikuni 22mm on Ebay for less than $30! GPS can't hold a candle to that!($70!!!!)
https://www.ebay.com/itm/Mikuni-22m...592776?hash=item5445ff0148:g:L74AAOSwKlhdGhp6
I'll probably upgrade to a Mikuni if I can't get this carb working right. It needs tuning every time I ride it, and it slowly leaks.
I suspect I need a new carburetor body gasket and mixture needles.
But if needs be, Mikuni it is. If not, the Flo-Jet is still pretty nice.

 

[JTSpeedDemon]

Wow, yikes. Looks like big money blowing is in my future.
To fix up this carb will cost at least $50!
To install a Mikuni 22mm, assuming GoPowerSports will sell me a manifold for $20, it will be about $72, but less hassle, plus more performance. Plus since we're not too far from GPS, I could get around the shipping.
I'll see what GPS says on the adapter.
And parts are pretty hard to find for this Flo-Jet nowadays, so I might not have much of a choice other than going with the flow of upgrades. But at the same time, it would be cool to keep it on the road. ARGH! Decisions, decisions!

EDIT - I think the gas is leaking around the venturi area into the lower area of the carb. I think at this point, I'm just going to pull the carburetor apart, put some gasket maker on the suspect surfaces, check everything again, and hope it works.

 

[Randy H]

IDK what GPS has. Maybe you could hack up a Predator intake and modify it.

If I'm able to get around next spring (hoping), I plan on whipping up a batch of intakes for the 3,5 and 8hp L heads.

A Briggs part #691922 will work for about $40.

For around $50-55 Studz has these.
https://www.studzracing.com/searchresults.asp?Search=Briggs+intake&Submit=

 

[JTSpeedDemon]

Valve Train Mysteries Solved!!

So just today I got a repair guide from the library on Briggs L-heads.
Look what it says!

17. Some engines may be equipped with a heavy duty exhaust valve or exhaust valve seat made of Cobalite. The Cobalite exhaust valve is marked on the valve head (Figure 40) with letters "TXS," "XS" or "PP-XS."....

....18. Some engines may be equipped with a rotator (B, Figure 32) on the exhaust valve. The rotator turns the valve a slight amount each time the valve opens, thereby wiping away deposits which can cause valve burning.

And as you can see in this pic, my exhaust valve says TXS on it, so it's got the heavy duty Cobalite exhaust valve!!
And the Figure 32 in the book, showing a rotator? It matches the retainer thingy on my exhaust valve!
The book also says that the engines with different valve springs have an exhaust valve with greater wire diameter.
Finally cleared the fog!
That's awesome though that I've got a full heavy duty valvetrain, though!

Also I was reading in an engine building book about rod/stroke length ratio, and with the 5" con rod and the 2.44" stroke, the rod/stroke ratio is about 2/1. The book says that's good for high RPM power, but it doesn't mean anything special since there is a lot of Briggs flatheads out there.
Just a fun little fact I found.

 

[Randy H]

That's good info. Got a pic of the front cover? Or date of publication?

Got a couple with 4.5" rods. A fair amount of grinding, all over the place to make that happen,. An aircraft mechanic type would scream bloody murder.

Wiseco piston with a single Dykes ring. With the required compression height there isn't room for two.

 

[JTSpeedDemon]

Published in 1994.
235+ pages of great info! I highly recommend it.
I basically looted the library of all applicable small engine books.

 

[JTSpeedDemon]

Woop!!
The leaky carburetor is officially FIXED!!!
With a properly modified screwdriver, I managed to loosen the emulsion tube and mate it to the other surfaces, and I flattened the carburetor body with a single cut file(The shiny surfaces in the second pic).
I also added a little silicone to the gasket around the bowl vent just to make sure.
The tuning seems much less temperamental now, and there is positively NO leaking!

I think some more high speed testing is in order.....
.....as soon as the weather is a little nicer.

 

[JTSpeedDemon]

BOOYAH! That's what I'm talking about! Started first pull, cold!

Ok yeah, I checked it again today, and it's still bone dry leakage wise!

Also out of curiosity, I was kinda worried about preignition with the high comp head and hotter spark plug, so I pulled the Autolite plug out. It had carbon deposits on it, but I can attribute that to the last time I rode it with the leaky carb.
The tip had a good, healthy bronze-tan color to it, indicating proper heat range according to my Haynes small engine manual. So I cleaned it up, stuck it back in, and started it up.
Totally perfect, the carb repair fixed the tuning problems, I don't even need new mixture needles!