Anyone know how to make these faster?

[ItsTeslaDude]

Additionally, it's running a 30 series torque converter and its not fast enough for me. Any suggestions?

 

[madprofessor]

Standard rule of thumb for small engines is to increase air intake and reduce exhaust restriction (replacing factory airbox and muffler with hi-flow filter and a header pipe). If that's not enough, then...............More fuel needs more air in and out to burn, so only after that's done you can increase the main jet size, either by buying a larger jet or by using an orifice bit of a reasonable size to drill out the existing jet.
Note: Don't drill out the jet unless you know exactly what you're doing, and you have the right set of orifice bits to slowly increase the orifice size by very small increments, let's say 5%, and maybe 10% maximum at a time. Too big will flood the cylinder, and you can't go back from too big.
Your setup apparently has room for a larger axle sprocket. Larger = more acceleration, less top speed. Smaller = vice versa.

 

[Millwright]

What is your tire size and gear ratio?
How fast is it now?
Does it accelerate quickly from a stand still?

 

[ItsTeslaDude]

Wheels are 18", torque converter is running a 12 or 10 tooth I dont remember with a 54 tooth on the sprocket

 

[ItsTeslaDude]

She only hits 20mph on flat ground but she accelerates at a quick but not absurd rate. I also can't stop and start moving again on a hill or the torque converter starts smoking

 

[Millwright]

Larger tires or smaller driven sprocket will give you more speed, but at the cost of low end power. It sounds like you are already a bit lite on the low end power.
I'd be tempted to go with a bigger engine.
With the 18" tires, I'm wondering if you have a bigger heavy kart?
maybe a 420cc with a 40 series TC would do the trick?


I'm new to the kart scene here, so I'm just talking this out. Im Not as experienced as others on this site.

 

[bob58o]

If running 18” tires with 54 : 12 sprocket ratio on a 30 series (which has 0.9 :1 overdrive when fully shifted), unless my rusty math is wrong... 3600 RPM would be around 48 mph. (If 54 :10 sprocket ratio 3600 rpm would be ~40mph) Since you are only getting 20mph, two things might be happening. Either you are not getting up to 3600 rpm - or the CVT is not shifting. Either way, I think you might get more top speed by changing your gear ratio (assuming the engine and TC are functioning properly) or using smaller tires. A smaller front sprocket, larger rear sprocket, or both ... might improve your situation.

I think I had the 8T Front TC sprocket with a 54T rear sprocket when I had a 212cc with 30 series TC and 18” tires. 8T compared to 10T will give 20% more bottom end and might help the TC power through the shift.

 

[madprofessor]

I personally wouldn't go with a tiny CVT sprocket, just don't like them. Smallest for me would be what usually comes with a 30 series, 12-tooth for #35 chain, and a 10-tooth for #40 chain. You've got plenty of room for a larger axle sprocket instead.
I got very similar results by putting a hotrodded (15+ hp.) 212cc in a kart too heavy for it. The real horsepower in it only appears at much higher rpm than the kart could get up to with its tall gearing. Only got 22 mph from a kart that was planned to go about 55 mph on a 12:60 ratio (1:5). Your slow speed top end and smoking belt definitely means you have the same problem.
Changed axle sprocket for a 12:72 ratio (1:6), still not enough. Changed jackshaft's secondary sprocket from a 24-tooth to a 16-tooth for a (1:9) ratio, test is yet to come. NOTE: That's on 16" tires, your 18" makes your situation even worse than mine.
So get a larger axle sprocket and a longer piece of chain for it. Don't tiptoe around with it, go big right from the start, 72-tooth minimum.
BTW: You need a good strong return spring on that throttle lever. Got a step-on bathroom weight scale? Put it under each of the 4 tires, nobody in the kart, tell us what the 4-weights total is. Found out mine was 520 lbs. that way.

 

[panchothedog]

I own 4 karts like yours. 2 seat, live axle, 30 series torque converter on all of them. Engines range from a 6 hp stock 196 cc to a heavily modified predator putting out 16-17 hp. They ALL have 10 tooth sprocket on the drive clutch and a 60 tooth sprocket on the axel , and they all have 18" tires on the rear. That is the correct gearing for good acceleration and decent top speed. Your kart is too high geared. Also if your TC is smoking it sounds like your drive clutch
( the one on the engine) might be sticking. Go on to the Go Power Sports
website they have a good video on how to clean it and it isn't hard to do at all.

 

[Millwright]

Am I wrong in thinking that having more HP , especially at lower RPM, will allow a better gear ratio for top end speed?
6:1 seems to be the " go to " ratio regardless of engine size or mods.
Also, hot roded engines don't see the torque benefits until the higher RPM?
So, 6:1 across the spectrum doesn't really add up for me.

 

[madprofessor]

I don't want to make any blanket statements about hp./rpm on all motors. Only sure about my own in the way it got modified.
Very important is the cam choice, mine is a diyperformance Superman 265 (265 lift) cam that increases low end torque. Very much needed since my 15+hp. only appears way up into the high rpms. 22lb. valve springs keep valves from floating above 5K rpms. PVL flywheel's rare earth magnets fire the coil at 28 degrees BTDC, advance key makes that 35.2 BTDC. The performance coil isn't any "hotter", it just has the resistors disabled so it won't retard the timing at high rpms. The .036 main jet feeds the fuel from a pulse fuel pump, but tank is mounted above for gravity anyway. Compression's increased with a .020-over rod and a .012 SS head gasket. And it all comes out of a 30 series CVT.
The confluence of all these factors means that the higher the rpms get, the more hp. gets produced. If my gearing is too tall for the lower hp. of lower rpms to make it go fast enough to raise the rpms, then that's where I get stuck, at low rpm not giving me enough hp. to go any faster. Just need to cross over that tipping point where the rpms get past, dunno, let's just say 4200 rpms to logarithmically add hp. to the speed, which adds more rpm/hp., which adds more rpm/hp. which..................etc.
So I keep increasing the gear ratio from the CVT sprocket through the jackshaft to the axle, trying to get the rpms to wind up high enough to unleash all that hp., hopefully making it freaky fast from off the line to the finish line. New 9:1 ratio currently awaiting testing.

 

[OPmini]

off topic but.... those are some fugly welds, I guess you watched whistilin diesel's welding tutorial. lol

 

[madprofessor]

you can increase the main jet size, either by buying a larger jet or by using an orifice bit of a reasonable size to drill out the existing jet.

21pc Micro Drill Bit Set Wire Gauge Index Size 61-80 with Swivel Head Pin Vise | eBay
In case you do decide to drill out your main jet, the link above is for a bit set to do it. The 212cc stock jet size is usually about .028", which is wire gauge #70. My .036" main jet selected for me by my performance guy is wire gauge #64, etc., etc............set goes from too small for anything sizes up to .039" size, which is wire gauge #61. Comes with a pin vise for twisting by hand, don't put it in a drill. ($10)
Fits ALL160 / 212 cc , Clone Engines Race Filter Kit w/ Custom Jets | eBay
To save you from drilling your own, this link is for the hi-flow air filter w/correct adapter that you must have before increasing your main jet size. Don't know how/if it would attach to your Briggs. It comes with both main and the low jets (Predator only) chosen by my performance parts supplier and advisor for best performance. ($34)
Predator 212cc / Hond / Clone Master Carburetor Blueprinting Kit | eBay
This link is also from my performance guy, comes with a jet drill bit set, .014"- 039". It's for rebuilding a stock 212 carb, and hopping it up. Lots of extra duplicate parts, for replacing instead of cleaning, but also has a carb passages cleaning pin set. Highly recommended for folks who have Predator 212's. ($37)
NOTE: Comparison to Predator 212 is due to ft./lbs. of torque. Your Briggs is 9 ft./lbs., Predator is 8.1 ft./lbs.

 

[bob58o]

The issue I ran into was price for a larger 1/2" pitch axle sprocket. I forgot exactly which was the highest tooth count I could find in the basic price range. Looking for higher tooth count (higher than around 54 or 60T) sprockets for #40, #41, or #420 chain were much more expensive. It is true that small TC sprockets are not ideal. They will need to be replaced more often than a larger sprocket would and will probably shorten the lifespan of the chain as well. But a 8T TC sprocket is a $15 part. And it will tell you if a 20% (if currently using a 10T) change in sprocket ratio is what the kart needs. If it performs much better, then you know what the issue is. And you can decide if it justifies the price of a larger rear sprocket with around 65-72T to use with a 10T sprocket. You might consider #35 sprockets but I think you run into similar issues using the 12T #35 sprocket (that comes with TC kits) with a max rear sprocket tooth count of 72 with the 3/8" pitch chain. Larger tooth count sprockets get more expensive.

I didn't read the part about the smoking belt. I would replace the belt with new and get a quality belt. A comet belt - or some others are also highly recommended but I don't recall the name. They are usually about $25-$30 for a quality belt. The cheap belts that are sent with the kits are good for a limited time only and need to be replaced more often. For less down time for maintenance, I prefer the Comet belts.

 

[madprofessor]

I've resisted getting into the split sprockets talk again, but now will say again, I'll never use an axle sprocket with its own hub again.
Price considerations: (Using #35 chain and sprockets) A one-time $15 investment in a carrier hub with a standard 5.25" bolt circle and a bore to match your rear axle allows use of $16 split sprockets from then on. The 1st link below goes to a standard carrier hub, and the 2nd link goes to a carrier hub for single-wheel-drive setups.
Main consideration: Ease of changeout. You do like a regular sprocket one time to put the carrier hub on, by removing a wheel, maybe a wheel hub, a bearing or two, maybe a brake disc, and the old sprocket. Then put it back together again, all for a new sprocket with a tooth count that may not work out right. With a carrier hub, you can change out split sprockets with 6 bolts using an Allen wrench in about 5 minutes flat. The 3rd link goes to a solid split sprocket, and the 4th goes to a lightweight split sprocket.
Unihub - Sprocket Hub | AZ2556 | Azusa 2556 | BMI Karts And Parts
Universal Aluminum Sprocket Hub Adapter Plate | 445683 | BMI Karts And Parts
#35 Split Sprocket | 6335** | BMI Karts And Parts
WMS Tuck & Run #35 Split, Full-Tooth Sprocket | 6535** | BMI Karts And Parts