No Power to wheels

[SardisPaul]

I thought I would be the good guy and buy my grandson a Kart for Christmas...as the saying goes, "no good deed goes unpunished".
The kart is an off road with a preditor 212cc 6.5 hp with a converter. The converter was a 30 series (asymetrical) and was running ok but did seem to struggle on inclines. After a few short rides ( maybe and hour in total) it started smoking the belt, and soon had no foreward momentum.
The converter was pitted and seemed to have seen better days so I ordered a new ( knock off) on to replace it. Install was straight forward but the new one has a belt that is 3/4" wide, the old one was running a 1/2 Comet belt 3200394 4213-139 (asymetrical). Everything I see says that a 30 series shpould be a 3/4". In any case I have zero poer to the wheels. Below are some specs & I apologize for the long post but without some guidance to get this fixed, this kart is going to go away and I'll have to find the kid a new 4 wheeler.
#40 chain
Driven = 10 teeth
Drive = 54 teeth
Rear tire = 22x11-8 22" tall from floor to top of tread
Front tire = 15-6-6 14" tall
Drive & driven pullys alighned with straight edge as were the chain sprockets.
Distance between converter pully centers is 6-11/16 " the rear (driven) has a 6" dia
The converter drive and driven pullys both open and close with the throttle ( seem to function normal ...sorry did not take a video of that)
The Kart rolls free and easy both directions when pushed.
The converter belt tension is about 1-1/4" halway between pullys
The chain tension is 1/4" to 1/2"
Any suggestions would be greatly appreciated

 

[Master Hack]

Assuming the engine is running properly...
My first guess would be the gearing is too high. You need a better belt also. I forget what kind to get...
Denny what is the belt to replace the Yakasuki belt? The Yak hair belts are good for 20 minutes or 20 yards.
22 inch tires and 5.4:1 might be too much.

 

[Rat]

The kart is an off road with a preditor 212cc 6.5 hp with a converter. The converter was a 30 series (asymetrical) and was running ok but did seem to struggle on inclines.

Your gear ratio is too low

After a few short rides ( maybe and hour in total) it started smoking the belt, and soon had no foreward momentum.

The cheap belt they come with is only good for making sure everything is functioning properly, but barely. Beyond that you're doing good to get more than a days riding out of them ESPECIALLY if the FD ratio is off.

The converter was pitted and seemed to have seen better days so I ordered a new ( knock off) on to replace it. Install was straight forward but the new one has a belt that is 3/4" wide, the old one was running a 1/2 Comet belt 3200394 4213-139 (asymetrical).

measure the Center distance between the crank and jackshaft, if its a common 30 series clone with a 6" driven you should get 6-15/16

Everything I see says that a 30 series shpould be a 3/4". In any case I have zero poer to the wheels. Below are some specs & I apologize for the long post but without some guidance to get this fixed, this kart is going to go away and I'll have to find the kid a new 4 wheeler.
#40 chain
Driven = 10 teeth
Drive = 54 teeth
Rear tire = 22x11-8 22" tall from floor to top of tread
Front tire = 15-6-6 14" tall

Only the drive tires matter for figuring out the final drive ratio (I often abreviate as FD)
If you get a 9t for the jackshaft youll have an FD of 6.22:1 which should pull like a freight train.
my set up is 9/54 with 2.50-18 motorcycle tires which have a standing inflated hight of 23.9 inches

Distance between converter pully centers is 6-11/16 " the rear (driven) has a 6" dia

Are you sure it's 6-11/16? The standard norm is 15/16

The converter drive and driven pullys both open and close with the throttle ( seem to function normal ...sorry did not take a video of that)
The Kart rolls free and easy both directions when pushed.
The converter belt tension is about 1-1/4" halway between pullys
The chain tension is 1/4" to 1/2"
Any suggestions would be greatly appreciated

A 9t jackshaft sprocket combined with a GENUINE COMET 203589A belt should have it moving again and climbing hills like it should

 

[SardisPaul]

Your gear ratio is too low

The cheap belt they come with is only good for making sure everything is functioning properly, but barely. Beyond that you're doing good to get more than a days riding out of them ESPECIALLY if the FD ratio is off.

measure the Center distance between the crank and jackshaft, if its a common 30 series clone with a 6" driven you should get 6-15/16

View attachment 145346

Only the drive tires matter for figuring out the final drive ratio (I often abreviate as FD)
If you get a 9t for the jackshaft youll have an FD of 6.22:1 which should pull like a freight train.
my set up is 9/54 with 2.50-18 motorcycle tires which have a standing inflated hight of 23.9 inches

Are you sure it's 6-11/16? The standard norm is 15/16


A 9t jackshaft sprocket combined with a GENUINE COMET 203589A belt should have it moving again and climbing hills like it should

Thank You for the reply: yes on the measurement (see added pics). May be hard to see but 1/16th shy of 6-3/4"
I was worried about the tire size but had no idea what a good ratio would be. If I order a 9th for the driven side of the converter...are all shaft sizes the same? Better to Mic it I suppose.

 

[SardisPaul]

Your gear ratio is too low

The cheap belt they come with is only good for making sure everything is functioning properly, but barely. Beyond that you're doing good to get more than a days riding out of them ESPECIALLY if the FD ratio is off.

measure the Center distance between the crank and jackshaft, if its a common 30 series clone with a 6" driven you should get 6-15/16

View attachment 145346

Only the drive tires matter for figuring out the final drive ratio (I often abreviate as FD)
If you get a 9t for the jackshaft youll have an FD of 6.22:1 which should pull like a freight train.
my set up is 9/54 with 2.50-18 motorcycle tires which have a standing inflated hight of 23.9 inches

Are you sure it's 6-11/16? The standard norm is 15/16

I'm sure Comet belts are the leaders, but are there any other brands that are Ok (like can be found on Amazon) or no?

 

[Denny]

Genuine Comet Belts Only!!! Get rid of the cheap belt. That kart should have a 8 hp engine, 40 series cvt from the factory. Since you don’t you need to make some adjustments to the gear ratio which as is is too high. 60 tooth axle sprocket and an 8 or 9 tooth drive sprocket should get you a lower gear ratio and long belt life.

 

[Rat]

I'm sure Comet belts are the leaders, but are there any other brands that are Ok (like can be found on Amazon) or no?

I litteraly just bought two Comet 203589A belts off ebay for 59.24 shipped. There are no others that last like a genuine comet belt.

Thank You for the reply: yes on the measurement (see added pics). May be hard to see but 1/16th shy of 6-3/4"
I was worried about the tire size but had no idea what a good ratio would be. If I order a 9th for the driven side of the converter...are all shaft sizes the same? Better to Mic it I suppose.

They all have a 5/8 jackshaft that is shouldered to something like 16mm through the bearings.

The Golden ratio for Karts is 6:1 however your 22" tires are a downside, but again putting a 9t behind the driven will give you a 6.22:1 and I can promise you it will be an impressive performance gain and gentler on the belt.

This first-hand knowledge comes from experience using various ratios ranging from 3.6:1 to 5.4:1 and eating belts to turn the 18" tires standing at 23.9 inches inflated BEFORE learning about the golden ratio here. The 6.22 will do you right considering you're turning tires that stand an inch lower than mine although I'm sure you've got more weight on those tires than I have on mine. I'm not running a 6.5 hp predator 212 either though, I'm running a built 208 that is yanking the chain with in the ballpark of 12hp and 14ftlbs of torque, no governor, and will spin a peak of 5800 rpm but pulls hardest between 3800 and 4200

Sorry for the ramble

 

[Rat]

Genuine Comet Belts Only!!! Get rid of the cheap belt. That kart should have a 8 hp engine, 40 series cvt from the factory. Since you don’t you need to make some adjustments to the gear ratio which as is is too high. 60 tooth axle sprocket and an 8 or 9 tooth drive sprocket should get you a lower gear ratio and long belt life.

He should be fine with a 9t to go with the 54t he has on the axle, that will give him 6.22 after all. I don't trust the 8t personally since Ive heard they tend to fly apart, but a 9t turning a 60t would be interesting to say the least.

 

[SardisPaul]

He should be fine with a 9t to go with the 54t he has on the axle, that will give him 6.22 after all. I don't trust the 8t personally since Ive heard they tend to fly apart, but a 9t turning a 60t would be interesting to say the least.

So thankful for the info...going with the 9t and Comet belt. Will update when they get here!!

 

[Rat]

So thankful for the info...going with the 9t and Comet belt. Will update when they get here!!

If it gives you any performance issues instead of only gains with the new belt and 9t, you could pair a 60t to the 9t which would be an evil FD... it comes out to 6.66:1

I highly doubt that will be necessary at all.

I have no doubts that the 9t alone will not only play nicer with the belt, but the ratio will give much better acceleration especially up hills. Due to certain experiences, I consider it safe to say it will also allow you to get into the ideal rpm range of the engines power and actually gain some top speed since it won't be fighting the gear ratio to get there or hold it.

In other words it should be able to actually wind that driven all the way up into its OD range and do around 35-40 mph flat out on level even terrain, maybe more given the rear tire size.

Be aware you may have to play with the spacing a little bit between the driven and driver, a lot of the 9t are wider than the 10.
Also it came to my attention that many of the 9t sold as 5/8" (15.88mm) are in fact only 15mm. It makes me wonder if most of them are running ackshafts that are 5/8" through the bearing and shouldered to 15mm for the running gear hardware

 

[Denny]

Just a 9 tooth will not be enough! But hey what do I know?

 

[Rat]

Just a 9 tooth will not be enough! But hey what do I know?

You know enough that I probably should have paired a 9t to my 56t a lot sooner instead of trying to force other pairings to work.

Instead of being a smart@ss, how about you explain why 9/60 is going to work better for him than 9/54.

Granted I've only got around 330lbs (combined total) on 2 tires standing at 23.9 rolling diameter.

I'm guessing that even if his combined total weight is the same on 22" turf tires, there's still more mechanical drag because he's got 2 more tires to roll... I'm figuring his unloaded curb weight is the variable I'm overlooking aside from that anemic 212

 

[Denny]

Well for starters he isn’t trying to get it to roll on 2 skinny high pressure tires on smooth pavement. 22”x11” tires at the recommended 5 psi leave you with a mighty large contact patch on the earth.
You keep trying to compare your mini-bike to a Gokart. It’s like trying to compare a Cadillac to a Honda motorcycle. No comparison. Gokarts need more gear and the smaller you get engine wise the lower those gears need to be. 40+ years of playing with gokarts tells me this. Now you add in bigger tires to the mix and you need to go lower yet.

 

[SardisPaul]

Take it easy guys. I'm enjoying the different angles ( both of you are trying to steer me in the right direction).
While the kart is "off road", that for my grandson anyway. is a path through woods cleared with a tractor and ridden down to dirt with 4 wheelers. Some longer inclines ( nothing "steep" ). It also includes flat running down a gravel road and grass field.
Yes, I think there will be a big difference between a kart and bike (esp with a small engine), but I'm not looking for the kid to be running 30 MPH through trees (I'm too old for a divorce !!).
My concern was (NOW) there is no power to wheels, but as you both have explained..crap belts will do that. I am going to try the comet belt and a 9t sprocket ( with the 54t). I can always go back and replace the 54 with a 60. One question about the comet belts is about the measurement of 6-11/16. Comet's lowest measurement is 6- 15/16. Is that going to be too tight?

 

[Denny]

It shouldn’t be. But if you go to the GoKart Supply website there is a chart for size range there. Lower gearing 6:1, 7:1, 8:1 etc. = more torque, power, less speed. Higher gear ratios 5:1, 4:1, 3,1 = more speed, less power.

 

[Rat]

Yes, I think there will be a big difference between a kart and bike (esp with a small engine), but I'm not looking for the kid to be running 30 MPH through trees (I'm too old for a divorce !!).

The only reason I said anything about probably gaining some top speed is because being over geared tends to lug the engine enough that it can't make it's full power potential thus never runs the sheaves at full shift... effectively limiting the top speed while crippling the acceleration and eating belts.

Once a more appropriate FD is found the engine doesn't have to overwork to shift the sheeves which then means less wasted (or rather previously unmade) power to shift the sheeves out fully... better for the belt, better for the engines long term health, better for acceleration, and assuming the sheeves were opening half or less previously due to the overgearing a top speed gain

One question about the comet belts is about the measurement of 6-11/16. Comet's lowest measurement is 6- 15/16. Is that going to be too tight?

All belts stretch to some degree as they run in, the cheap ones just never stop.

Once you run the belt in it will be fine.
(Last I checked 15/16 is bigger than 11/16)

 

[Rat]

I'm sure you'll be fine

 

[SardisPaul]

Ok, finally have an update. Sorry so long, kinda been under the weather. After I did quite a bit more reading on gear ratios/ tire sizes, I decided that if I was going to get it going, I'd go with the "evil" ratio. I put in the 9T & the 60T sprockets...yes had to re-shim to get everything aligned with a straight edge. Cut a new # 40 chain (much better motor position to get slack out). Runs like a BaT outta Hell!!!! Hills/slopes are no longer a problem. Turned grandson loose with it and now convinced I'll have to put a throttle limit on it or my wife and daughter are both going to kill me.
Now to figure out how to get front tires to bite more for turning...before I have to weld on the frame from a tree hit LOL!
You Guys Are Awesome! Thank You So Very Much!
I'll try to get a short vid posted soon

 

[Denny]

Glad you saw the light! Massive torque is way more funner than speed.

 

[Rat]

Glad you saw the light! Massive torque is way more funner than speed.

Id have to call that debatable, but going up a hill at a slugs is certainly agitating.