Hard solid clank of driver engagement, not slow........

[madprofessor]

30 series type generic CVT got tested on hotrodded Predator 212 running 6:1 gear ratio off of CVT on 520 lb. kart plus 165 lb. pilot. Everything brand new except for the pilot with the iffy trigger foot.
Have to baby the gas pedal (plenty of total travel in pedal) on a standstill start to get it to ease forward slow. Anything more than a tiny movement of pedal engages it solidly with a strong clank, a little jerk into forward motion, just not with any authority at all pressed into the pedal.
Gets rolled forward just a tad, reflex to the slight jerk and the clank noise makes me back off and try again (a "pump" of the pedal for a second), clanks even harder. Impatience and aggravation then lowers the hammer until next stop.
Also, just once when slowed down to turn around, maybe 10 mph. at most, the CVT belt got jammed deep into the driven unit, locked up the tires on asphalt. Popped it out with screwdriver, hasn't happened again yet. Only 1.7 miles total on test run.
Any way to get smoother takeoff from standstill? And why did the belt jam in the driven when under no load?

 

[Denny]

You are not going to like what I have to say but if you let it roll around in your head for a while and think about it you will come to realize I may have a point.
First off I never realized you were trying to push around 700lbs.
1. You are asking a small 5hp engine to push around 700lbs. Even though it is hot rodded, it is too small.
2. The 30 series and the tav2 were only designed to work on 5 or 6 hp stock engines. Heck even Manco stepped up to a 40 series when they used a 8 hp engine. Why do you think that is? Not just because they used a 22” tire.
3. Even golf carts use bigger engines, tires, cvt systems and brakes. They weigh a little less to boot. I don’t remember exactly but their gearing is lower also. But that was just to slow them down.
I compared golf carts to your buggy because because they are close in size and weight. Just think about this for a while, maybe a day or two, and I think you will realize this is not the drivetrain for you in this kart. In a lighter kart (under 200 + driver) your “hopped up” engine may be a rocket. I’m not trying to bash you or beat you up, just educate you.
My recommendation would be step up to a 420 engine and 44 series primary and secondary clutches. If you don’t believe me go to Gokart Supply and just do some research with the different series clutches and drivens. It will open your eyes and you may even learn how flawed some of your thinking may be. I’m not trying to pick a fight or put you down, just point you in a correct direction. Good luck!

 

[madprofessor]

Appreciate the honesty, but mainly the confirmation. Was already looking at the conclusion that I'd probably got it all wrong. When rpm's didn't wind up (to where the real hp. is) with new 6:1 ratio, only 31 mph. which is likely only 3K rpm's, it became pretty convincing.
Unfortunately a 420 isn't in the budget. Could have bought one outright at the start for what I have in the 212cc, $99 coupon at HF, well over $300 in hotrod parts. Next build is to be a super light bare bones build (BareBallz) using existing wheels/tires and steering wheel, so the 15hp. would be too risky to move over to it in favor of a stock 420 even if in the budget. Rocket is right.
Going to order a smaller jackshaft sprocket for secondary chain (24-tooth existing, so maybe 16-tooth?) for more torque, that's the easiest way out right now. Finish the build and sell it off like original plan.

 

[Denny]

What I would do is build the Rocket kart now and put the big one on the back burner. To keep costs down scavenge parts from the big one for Rocket. After the Rocket is built, tuned and sold revisit the bigger one with a better plan.

 

[madprofessor]

That actually would be the preferred plan, but there's a space issue. The 9' long x 4'wide "SchizoBallz" takes up all the room in my shop.
Shop was the original equipment room at the church. Contained the original Carrier open-frame chiller and the chilled-water pump, the huge expansion tank, and assorted crap.
Got the chiller and the pump along with their slabs taken out when I put in the Trane chiller (3rd chiller, sits outside), and new dual-pump system and new X-tank in another room. Big space left, lots of varied stuff in it, but current kart's got to go.
BTW: Promised our Boy Scouts troop that I'd keep next kart around awhile, maybe let them take it on some campouts, and play with it at the church during weekly meetings. That's why it would be terrifying to see those kids in a 15+hp. kart weighing only 160 lbs.

 

[Denny]

Wow, you are in a bind then. The only idea I have in that case is going to a 18x8x8 tire to get more meat on the road and stepping up to a larger in diameter secondary or driven. See the 6” is considered an overdrive unit for more speed (top end). Gokart supply has the 7” secondary (driven). You may still need to lower your gear ratio some more in addition. That’s all I got. Good luck.

 

[madprofessor]

???? Unsure how the tires 2" taller than my 16" (kind of skinny on 8" rims) would improve anything. Even though I am going with a 33% smaller jackshaft sprocket for secondary chain.
Actually have right now an extra full set of 16" tall tires on 8" rims that are 8" wide, had already planned to cut and extend rear axle to fit them, but also curious how getting that extra meat on the road changes things also. Still learning stuff from you folks.
Can easily see an advantage in a larger driven unit, more torque. Had no idea it worked in a different manner than my stock 6" unit.
Any difficulties with fitment on larger driven, and does it use same existing shaft? What about larger belt requirement? Currently has the asymmetrical, does larger driven use the same?
BTW: Does a series 30 CVT and a 40 CVT function in the same way if swapped outright, just much beefier on the 40?

 

[Denny]

Just an opportunity to put more rubber to the road with a little larger footprint.

 

[madprofessor]

Saw the 7" driven on GoKartSupply, only $39.50 for it. No info there though on belt size, if larger belt needed. No matter, going to get the 16-tooth sprocket in and installed first, see what that gets me. May be enough to get the job done by itself.
Am looking forward to the 8" wide tires getting installed. There will be a full video of all the kart features on youtube before I sell it, and the 8" wide tires will look great. Got a lot of paint touchups, cleaning, and maybe waxing to do before then, first appearances and all that.

 

[madprofessor]

Epiphany about sudden hard clank of clutch engagement: I'm assuming it's the flyweights slinging out and grabbing the drum.
Good ole days abusing the '73 Barracuda w/automatic, I'd hold the brake at start and apply the gas strong against it, then leggo the brake and drop the hammer. Didn't snatch anything.
I'll try holding the brake on the kart against the gas and let it try to engage, then do a Barracuda repeat. Bet it launches smoothly.

 

[Denny]

If you put the lite weights in the driver that may be doing it too.

 

[karl]

Unfortunately a 420 isn't in the budget. Could have bought one outright at the start for what I have in the 212cc, $99 coupon at HF, well over $300 in hotrod parts.

If your willing to put in some effort , and get your hands dirty, look at the used market.

I got less than $300 into a junkyard kohler 674cc twin, hopped up, most expensive part was the twin 24mm barrel intake manifold.
About $20 into the clutch setup, CVtech driver from a scrapped utility vehicle, driven from an old snowmobile, and the OG belt from the 20-30 year old utility vehicle. Stronger than most all off the shelf solutions.

Total bout $700 into the kart, I hop on it and send it hard all the time without any second thoughts. After a year have yet to adjust the
tractor supply #50 roller chain. Just ride.

Rips alight in my opinion, just suggestion look away from the major kart sites, and explore other avenues.
I avoid kart specialty shops , only when absolutely necessary.