lack of speed

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mnmbarna

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Hello experts. I have I Baja dune 150 that I've been trying to get running for a while.(whenever I get time) I just put in a brand new 212cc 6.5hp from harbor freight, and a 30 series TC. Has 10 tooth jackshaft sprocket, 72 tooth axle sprocket, 22inch rear tires, engine rpm's are 3800. The speed calculator says I should be getting 34.5 MPH. But I can't get it to go over 13. And that's wide open on the street. Any ideas? Ty
 

itsid

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really?

... it's a sheer miracle that thing moves at all.

reason is simple.. you can't (the engine can't) provide enough power to shift the TC up, so that you can get to speed..
it's stuck in low (torque) mode because your "power to gear ratio" ratio ;)

you sure about it being 10T on the TC and 72 on the axle (7.2:1) ?
(since the ten tooth is #40 chain.. and a 72T #40 axle sprocket isn't exactly common.)
or is it 12 and 72 ? (6:1)

Anyways, try 8:1 or lower to get it to go.

'sid
 

mnmbarna

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I agree, had to be something to do with ratio. The axle sprocket is welded on, so I can't change that. And I can't find a clutch sprocket that's 5/8, #41, larger than 10 tooth that the teeth are centered on the hub. The only ones I see online are flat on one side, and the keyed hub on the other. If I did that, my alignment would be off. Don't know how much room I have to move the engine.
 

OzFab

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Although Alex's explanation is sound (TC not shifting) we've seen many karts/buggies with that same config that seem not to have any problems; my thought is that, perhaps the sheer size & weight of the buggy is too much for the little Predator...

IIRC, that particular buggy came with a 150cc GY6 engine which has a higher rev range & slightly more torque than a 212cc Predator (10.5 ft/lbs @ 6500rpm as opposed to 8.1 ft-lbs. @ 2500rpm); it may not seem like much but, it's enough to make the difference...
 

mnmbarna

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If I get the rpm's up, it should b ok? In that case, couldn't I take the governor out? I read somewhere else that as long as you don't go over 5400 rpm for long periods of time, it'll b fine. Cuz the rpm is what I need to lock up the TC, right?
 

itsid

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bigger AXLE sprocket... NOT clutch!!

that'd have the exact opposite effect (higher ratio, even less torque)

'sid
 

landuse

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Guess I'll try bigger clutch sprocket. Who knows how long THAT will take. I hardly have time to mess with this as it is.

Do NOT get a bigger clutch sprocket. You will be making it worse. What you have to do is get a bigger axle sprocket or SMALLER clutch sprocket. You want to get a bigger number when you divide the 2 numbers, not a smaller number
 

Half-breeder

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Ive installed a stock HF212/TAV2 (#41) on a 450lbs (total weight) kart, w/ 22" (2PR) wheels at a 7.2:1 ratio (10T>72T). I adjusted the driven setting to the 3rd notch, to allow a longer period before the driven kicked into play. It did ~30mph roughly.

... a possibility of the lack of speed 'may' be the driven isnt preloaded. You can find out if you happen to adjust the driven engagement spring position. (Setting #1 and #3 are backwards in the vid... my bad).

https://www.youtube.com/watch?v=kmGY0qsgW4Y

... and if you're insistent in lowering the ratio to an 8:1 (top speed ~25-30 depending on TOTAL weight)... 9T #41 5/8" shaft.


... my .02 scents.
 

mnmbarna

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Thanks for all the info guys. Although, I am getting a little confused. I've read a lot of threads on here, and other forums, that refer you to the speed calculator. Since my axle sprocket is welded on, I click on clutch sprocket button. The larger it goes, the mph goes up. Anyways, I've tried all 3 settings on the driven and didn't seem to change anything. But, maybe I did something wrong. So, I'll give it another go. If that don't work, I'll try the 9 tooth sprocket.
 

Half-breeder

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How/why are you confused?!?!? what you're explaining is exactly what they said above.

You may wanna read ALL what is answered when asking a question ...
 

itsid

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mnmbarna, yes, increasing the clutch sprocket will increas the speed..
BUT ONLY if your engine has enough power reserve to do so!

Your engine (with the current gearing) does NOT EVEN HAVE ENOUGH power to move the kart at it's current gearing;

thus you will need to increase TORQUE not speed (aka lower gear ratio // higher number)
you cannot change your axle sprocket??
well then you're screwed. period

the chance left if you do not want to buy a new axle where you can change the sprocket is buying an engine with 9hp or more..
that in turn would require buying a new TC as well (your's isn't exactly made for engines that size)

So yeah...

'sid
 

mnmbarna

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Half-breeder, the confusion, like I said in my previous reply, came from the info I entered into the speed calculator(on gokartsupply.com) verses the threads in this post. They're conflicting views. Anyways, thanks for the tc preloading video. I tried the different settings and got up to 23 mph on the street, though it took about a block to get up to that.

Itsid, since my engine doesn't have enough power(3600 prm), would it make any difference at all if i took out the governor to give it more rpm?

As for getting a bigger engine, the engine i had in the kart before this 212 predator was a 420 predator(13hp I think?). When I bought the kart, the previous owner had the 420 engine with the 30 tc. I later found out those weren't compatible to each other, so i bought a 40 tc. But then found out the backing plate for the tc wasn't going to work with the bigger tc. I tried making one from 1/4 steel plate, got the mounting holes, crankshaft hole, and jackshaft hole drilled out ok, but ran into problems with the js bearing set up. I tried a few different pillow block bearings, but they all failed under the load. So, that's when i just got fed up with it, and got the new 212 engine and 30 tc, hoping that it would be enough to at least have the kids drive around in. Which, it does. They love it, but when I get in, I want more out of it.

We're planning on selling it to get a 4 seater we saw at a dealership, but still, I wanted to get the most performance from it before I sell it.
 

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itsid

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you lack power (more exactly TORQUE) you cannot replace that with more rpm.

you need a correct gear ratio (aka buy a new axle or have the welded sprocket removed!)


'sid
 

Bladerunner

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Make sure your TC is preloaded correctly. Read: it should be a HUGE PITA to change positions on the driven spring. If it was an "easy" task it means you are doing it wrong.

Oops looks like you got it. You can change your gear ratio lower by switching to the 7" driven. Also, you can probably adjust your governor to change the rpms up to 4300rpm. If not, you can remove the governor because the cvt will limit your rpms anyway (but don't run it to high rpm without load... On the ohv you will break parts).

The cvt makes use of about 1krpm powerband. You can adjust the engagement by changing driver springs and weights found at BMI. Increasing it to 2900 will change your shift/max rpm to approx 3900 depending on driven spring position. Also change your idle speed up to 2.3k or so, because your low speed drivability will be much worse. Ya might eat more belts, however.

Changing driver springs, adjusting gov max rpm, and switching to a 7" driven should net you good results.
 
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