79cc Predator with Tav 2 CVT

jeffreykogan

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Mar 1, 2021
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Would the TAV2 transmission be a good fit with the 79cc Predator? I only ask because the TAV2 is a CVT and can go from a 3:1 to a 1:1 gear ratio. This might be a better option than the stock 79cc transmission in the gasbike kit.
 

JerryAssburger

Active Member
Mar 11, 2017
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Salem Oregon
Hi jeffreykogan. I'll throw my 2c worth into the ring. I am running a Lifan/Doodlebug 2.8hp with a TAV2. I chose the TAV2 because I needed a jackshaft setup anyways, and wouldn't you know it- the jackshaft cost just as much as the deathrow TAV2. So, I reasoned the variable ratios to be an advantage.

Here is what I have run across, so far:

The engine shaft is shorter and smaller diameter and needs to be adapted to the TAV2. Not so bad, actually. They sell the 5/8 to 3/4 `adapter on Ebay for cheap, and I got a 3/4" split collar to give the TAV2 driver something to butt-up against. The only "challenge", if you want to call it that, is lining up the driver and driven pulleys by where you lock down the collar on the engine shaft.

Advantages- it works as advertised as a clutch and variable ratio transmission. On my Cranbrook I am running a 6>1 final drive ratio, which by itself, is WAY too tall, even for a 212 Predator. But with the TAV2, it pulls from a dead stop just fine, even with my 240lb lard-butt on it.

Disadvantages- It sticks out to the left almost 2" further than a similar cent-clutch/jackshaft setup. Not as horrific as it sounds, really. The top speed is barely hitting 30mph. BUT- that isn't the final word for my situation: I have adapted a carb from a 2-stroke engine kit, and I haven't "dialed it in" yet. I am also 240lbs, which probably the reason the 2.8hp can't top 30mph. I plan on properly jetting the carb and putting a less-restrictive exhaust on it, which can only help.

I would think your 79cc Predator is of similar performance compared to my Lifan 152F. Both are capable of 4500-5000 rpm with minor mods, which means they could potentially make around 4hp.

Honest opinion- the little motors can barely swing the TAV2 to its fullest potential, but sometimes that's "good enough". I have ran the TAV2 on a predator 212 on a gokart, and that is truly a great match. I am doing my best to document my trials and tribulations on the Lifan/TAV2/Cranbrook thread.

Best of luck.
 

jeffreykogan

Member
Mar 1, 2021
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27
18
Hi jeffreykogan. I'll throw my 2c worth into the ring. I am running a Lifan/Doodlebug 2.8hp with a TAV2. I chose the TAV2 because I needed a jackshaft setup anyways, and wouldn't you know it- the jackshaft cost just as much as the deathrow TAV2. So, I reasoned the variable ratios to be an advantage.

Here is what I have run across, so far:

The engine shaft is shorter and smaller diameter and needs to be adapted to the TAV2. Not so bad, actually. They sell the 5/8 to 3/4 `adapter on Ebay for cheap, and I got a 3/4" split collar to give the TAV2 driver something to butt-up against. The only "challenge", if you want to call it that, is lining up the driver and driven pulleys by where you lock down the collar on the engine shaft.

Advantages- it works as advertised as a clutch and variable ratio transmission. On my Cranbrook I am running a 6>1 final drive ratio, which by itself, is WAY too tall, even for a 212 Predator. But with the TAV2, it pulls from a dead stop just fine, even with my 240lb lard-butt on it.

Disadvantages- It sticks out to the left almost 2" further than a similar cent-clutch/jackshaft setup. Not as horrific as it sounds, really. The top speed is barely hitting 30mph. BUT- that isn't the final word for my situation: I have adapted a carb from a 2-stroke engine kit, and I haven't "dialed it in" yet. I am also 240lbs, which probably the reason the 2.8hp can't top 30mph. I plan on properly jetting the carb and putting a less-restrictive exhaust on it, which can only help.

I would think your 79cc Predator is of similar performance compared to my Lifan 152F. Both are capable of 4500-5000 rpm with minor mods, which means they could potentially make around 4hp.

Honest opinion- the little motors can barely swing the TAV2 to its fullest potential, but sometimes that's "good enough". I have ran the TAV2 on a predator 212 on a gokart, and that is truly a great match. I am doing my best to document my trials and tribulations on the Lifan/TAV2/Cranbrook thread.

Best of luck.
So let me ask you this, do you prefer the automatic clutch or the tav2? You seem to be quite knowledgeable in this field, which is why I ask.
 
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JerryAssburger

Active Member
Mar 11, 2017
147
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Salem Oregon
So let me ask you this, do you prefer the automatic clutch or the tav2? You seem to be quite knowledgeable in this field, which is why I ask.
Thank you, but I just tinker with this stuff. I guess the best way to compare your options is like older cars..... remember when automatics were more convenient but decidedly slower than their manual-shift counterparts? (I might be dating myself.) The TAV2 is not incredibly sofisticated compared to, let's say, a computer controlled, double clutch 7-speed auto with a lock up converter, but sometimes, it's good enough. I like it, because if it's geared right, you don't have to worry about it over-revving and you still get decent starting acceleration because of the variable ratios. The downfall is that it does sap some of the power, and some of the smaller motors can barely swing it. Your top speed will suffer, though.

Hope that helped.
 

JerryAssburger

Active Member
Mar 11, 2017
147
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Salem Oregon
So let me ask you this, do you prefer the automatic clutch or the tav2? You seem to be quite knowledgeable in this field, which is why I ask.
Ha! Sorry I didn't answer your question! I like the TAV2 over the clutch. I like the way it has great take-off power, and how it adjusts the ratio as you accelerate. It's pretty "No Muss-No Fuss" once dialed in. That is my opinion- not fact.
 

jeffreykogan

Member
Mar 1, 2021
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Ha! Sorry I didn't answer your question! I like the TAV2 over the clutch. I like the way it has great take-off power, and how it adjusts the ratio as you accelerate. It's pretty "No Muss-No Fuss" once dialed in. That is my opinion- not fact.
Both of your answers helped quite a bit, thank you. I have both the tav2 and the centrifugal transmission. I will try both and I will keep your advice in mind.
 

jeffreykogan

Member
Mar 1, 2021
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It has been done. This offers a crap ton of torque, however the top speed is lacking. I am going to change from a 44t rear sprocket to a 40t. It is much smoother than the centrifugal clutch, as there is virtually no shaking. I recommend the switch if you can do it, but be warned, it is not easy.
20210313_210036.jpg
20210313_233004.jpg
 
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JerryAssburger

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Mar 11, 2017
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Salem Oregon
It has been done. This offers a crap ton of torque, however the top speed is lacking. I am going to change from a 44t rear sprocket to a 40t. It is much smoother than the centrifugal clutch, as there is virtually no shaking. I recommend the switch if you can do it, but be warned, it is not easy. View attachment 106640 View attachment 106641
Woo Hoo! Looks great!
I had to run my setup as, TAV2 10T-60T on the rear, giving a ratio of 16.8>1 on the starting end, to 6>1 on the high end, (which the little Lifan can't manage with my lard butt on it) It advances the belt to about a 1/3" from the top of the driver when maxed out.
Are you running it directly from the TAV2 to the wheel without a jackshaft? If so, I'd recommend a larger rear sprocket, so that you can use more of the TAV2's range, plus you'll pull even LARGER stumps!
I think the lack of top speed is just a function of our limited HP on tap. Mine is struggling to hit 30mph, but I've got some issues to sort on the motor before I call it done.

Keep us posted! Fascinating stuff!
 

jeffreykogan

Member
Mar 1, 2021
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Woo Hoo! Looks great!
I had to run my setup as, TAV2 10T-60T on the rear, giving a ratio of 16.8>1 on the starting end, to 6>1 on the high end, (which the little Lifan can't manage with my lard butt on it) It advances the belt to about a 1/3" from the top of the driver when maxed out.
Are you running it directly from the TAV2 to the wheel without a jackshaft? If so, I'd recommend a larger rear sprocket, so that you can use more of the TAV2's range, plus you'll pull even LARGER stumps!
I think the lack of top speed is just a function of our limited HP on tap. Mine is struggling to hit 30mph, but I've got some issues to sort on the motor before I call it done.

Keep us posted! Fascinating stuff!
The thing is, I need to hit at least 35 (or at least close to it) since I ride this thing on the road, so I was going to switch from a 44t rear sprocket to a 40t rear sprocket. I run the rear sprocket of the tav 2 directly to the rear wheel. Is this a switch you recommend (going to a smaller gear size)? I realize that I am not going to have the same amount of torque, but I'm trying to really squeeze a bit of speed out.
 

Sidewinder Jerry

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Dec 19, 2011
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With these engines they're only going to give you so much. Therefore unless you can increase performance/hp going to a higher ratio will only cause engine strain.

An option could be to run a fixed geared internal geared hub as a jack shaft. This way you'll have a much wider range and can shift according to your tachometer readings along with being in the best ratios for a given terrain.

 
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jeffreykogan

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Mar 1, 2021
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With these engines they're only going to give you so much. Therefore unless you can increase performance/hp going to a higher ratio will only cause engine strain.

An option could be to run a fixed geared internal geared hub as a jack shaft. This way you'll have a much wider range and can shift according to your tachometer readings along with being in the best ratios for a given terrain.

In order to increase horsepower, would reboring the carb work? I don't have the tools for it, so I was going to order a carburetor from affordable go-karts.com that was rated for a 79cc engine (Pictured below). Would this be a viable option?
Screenshot (2).png
 

curtisfox

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Dec 29, 2008
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Jerry he said there is plenty of torque, so first try the sprocket change, maybe even a 38 tooth. Also that carb would not heart even if stock, the way it is the carb would be a big difference., not so much speed just response. exhaust would be the next thing from affordable go-karts.com would also be a good choice...................Curt
 
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