Predator 79 Transmission Options?
- Thread starter ColdCruiser
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ColdCruiser
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Nice.
D
Deleted member 26224
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I think you are overthinking this way too much. You've got a weak governed engine and you're further weakening its power output by going with 4 chains into an internal hub gear, so basically 5 ways for it to lose HP if (when) ONE of those goes out of alignment. Also, when you have the drive from the engine on one side and the output to the wheel on the other side, it puts a turning stress around the seat tube on all your components further stressing the drive shafts and reducing efficiency.
An ungoverned 79cc will rev out to around 6000rpm. There is a lot of small stuff you can do for now, like shaving the head .030" or more, advancing timing, opening up your intake and exhaust for example. THEN you can think about gearing-
Easy steps for any 4-stroker:
1. Set your gearing to top out just under max RPM at the speed you wanna go. IE 5500rpm @45mph ~ 9.4:1
2. Set your centrifugal clutch accordingly. You won't have good takeoff with the stock silver spring 2000rpm engagement, so put a black spring in there with either six heavy shoes or alternating heavy and regular shoes (AGK). Go to their website and buy the black spring and six heavy shoes. Don't even look at the green spring. Black spring with all heavy shoes = green spring with regular shoes. Mixing shoes will give you a full lockup around 3400rpm with an engagement of around 2500rpm, and all heavy will be around 3100 lockup and 2350 engagement. You won't even need to pedal to take off.
I know you might say oh well it's all setup and all... well believe me just try it. I went through all the stuff above, even made my own shift kit, setup a CVT, then went to single speed and now 2-speed. If you don't have any VERY steep hills around you then single is the way to go.
On my 2-speed I run a 8.15:1 top gear, 11.8:1 low gear, I have the black with all heavy in the primary and a yellow with all regular in the 2nd gear, it pulls hard in first gear then shifts at around 4800 rpm. After some more mods to the carburetor will be changing springs and shoes for even higher rpm shift to keep the engine in its power band (4000 - 5400)
An ungoverned 79cc will rev out to around 6000rpm. There is a lot of small stuff you can do for now, like shaving the head .030" or more, advancing timing, opening up your intake and exhaust for example. THEN you can think about gearing-
Easy steps for any 4-stroker:
1. Set your gearing to top out just under max RPM at the speed you wanna go. IE 5500rpm @45mph ~ 9.4:1
2. Set your centrifugal clutch accordingly. You won't have good takeoff with the stock silver spring 2000rpm engagement, so put a black spring in there with either six heavy shoes or alternating heavy and regular shoes (AGK). Go to their website and buy the black spring and six heavy shoes. Don't even look at the green spring. Black spring with all heavy shoes = green spring with regular shoes. Mixing shoes will give you a full lockup around 3400rpm with an engagement of around 2500rpm, and all heavy will be around 3100 lockup and 2350 engagement. You won't even need to pedal to take off.
I know you might say oh well it's all setup and all... well believe me just try it. I went through all the stuff above, even made my own shift kit, setup a CVT, then went to single speed and now 2-speed. If you don't have any VERY steep hills around you then single is the way to go.
On my 2-speed I run a 8.15:1 top gear, 11.8:1 low gear, I have the black with all heavy in the primary and a yellow with all regular in the 2nd gear, it pulls hard in first gear then shifts at around 4800 rpm. After some more mods to the carburetor will be changing springs and shoes for even higher rpm shift to keep the engine in its power band (4000 - 5400)
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ColdCruiser
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Tony, thanks for your response. Yes, I have a tendency to overthink things a little bit.
I built the thing to haul my ~70lb dog around with me. The hub shifter is awesome.
It doesn't matter to me if it loses a little hp. That's why I used a 79cc instead of a 49cc. It has power to spare. I do need to get rid of the governor guts but only if I want to go faster. The law for a CA moped is 3.5 hp.
The whole project has been about gearing and the gearing is done. Maybe I'd do it different next time but it seems to be working pretty good for me now.
At 5,500 rpm in THIRD gear, it should be pretty close to 40 mph. It goes 25 mph at 3k now.
I definitely want a clutch that engages at a higher rpm! I tried to order the modified clutch from AGK but they cancelled the order. I spoke with them directly and they said they thought I was a thief. I explained and argued but they refused to budge. So, I'm over them and can't recommend them either. So, I will need to find the black springs and heavy shoes (or a modified clutch) somewhere else.
In AZ it is FLAT, but I'm taking this thing with me to explore the Pacific Northwest lakes and rivers. There might be some hills.
I still have a lot to learn about everything but the fun part is riding it. I need to tune the carb so I'm going to put a different air filter on it first. After that, it might be good enough and it's time to get on with the riding!
Thanks again for your comments and the clutch info.
I built the thing to haul my ~70lb dog around with me. The hub shifter is awesome.
It doesn't matter to me if it loses a little hp. That's why I used a 79cc instead of a 49cc. It has power to spare. I do need to get rid of the governor guts but only if I want to go faster. The law for a CA moped is 3.5 hp.
The whole project has been about gearing and the gearing is done. Maybe I'd do it different next time but it seems to be working pretty good for me now.
At 5,500 rpm in THIRD gear, it should be pretty close to 40 mph. It goes 25 mph at 3k now.
I definitely want a clutch that engages at a higher rpm! I tried to order the modified clutch from AGK but they cancelled the order. I spoke with them directly and they said they thought I was a thief. I explained and argued but they refused to budge. So, I'm over them and can't recommend them either. So, I will need to find the black springs and heavy shoes (or a modified clutch) somewhere else.
In AZ it is FLAT, but I'm taking this thing with me to explore the Pacific Northwest lakes and rivers. There might be some hills.
I still have a lot to learn about everything but the fun part is riding it. I need to tune the carb so I'm going to put a different air filter on it first. After that, it might be good enough and it's time to get on with the riding!
Thanks again for your comments and the clutch info.
D
Deleted member 26224
Guest
Also you don't have engine braking. That is kind of a dealbreaker for me. With single you'll be able to regulate you speed with the throttle. No more of slowing down with engine going back to idle, then ramping it up and slamming that freewheel every time.
As far as CA hp and speed limits don't even trip. My 3.5hp is pushing 5 and I got friends with faster bikes. I been pulled over only for riding on a bike path, but I've flown by cops at 45-50 without a second look... The plate might have something to do with it...
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D
Deleted member 26224
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Also you have to think about your max rpm range. Removing the gov will give you another 2k rpm so using the black with mixed will be good, but if it tops at 3600 you might wanna get the green too so you can tune it for 2-2.3k
ColdCruiser
Member
I found the parts that Tony was referring to so I'm posting it here for reference:
CLUTCH UPGRADE
https://cometkartsales.com/Max-Torque-Clutches/
$8.50 Max-Torque Replacement "Garter Spring"
Silver = 2200 rpm
Green = 2500 rpm
Black = 2900 rpm
$12.50 Max-Torque Wedge Style Heavy Clutch Shoes (6 pcs)
CLUTCH UPGRADE
https://cometkartsales.com/Max-Torque-Clutches/
$8.50 Max-Torque Replacement "Garter Spring"
Silver = 2200 rpm
Green = 2500 rpm
Black = 2900 rpm
$12.50 Max-Torque Wedge Style Heavy Clutch Shoes (6 pcs)
ColdCruiser
Member
I'm getting ready to add a "high flow air filter" and had some trouble finding an filter for the valve cover vent tube, ...until I did a search for "UNI Breather Filter" and it came right up on Amazon. I needed a 5/16" push-in type. It was $15!!
D
Deleted member 26224
Guest
Cool. Well I blew my motor and installed the 212. Making an exhaust header for a vertically mounted motor is tricky! Cause the exhaust port faces forward.
Also if you gear it for a lower top speed make sure you get a cheapo tach/hr meter off eBay, the single wire type. You don't wanna over-rev the engine on a downhill; That's how I blew my engine. I've been riding without one but I figured the RPMS and such in excel to make sure I never overrev; my 2-speed shifts under 5500 and the wind resistance limits top end rpm to 5000ish with a 6.6 top gear. With a top speed setup for let's say 6k @ 35mph it will be very easy and tempting to blow it up going downhill. Keep us updated and post some pics!
Easy way to calculate speed for 26x2.0" tires: rpm*0.077/ratio
Also if you gear it for a lower top speed make sure you get a cheapo tach/hr meter off eBay, the single wire type. You don't wanna over-rev the engine on a downhill; That's how I blew my engine. I've been riding without one but I figured the RPMS and such in excel to make sure I never overrev; my 2-speed shifts under 5500 and the wind resistance limits top end rpm to 5000ish with a 6.6 top gear. With a top speed setup for let's say 6k @ 35mph it will be very easy and tempting to blow it up going downhill. Keep us updated and post some pics!
Easy way to calculate speed for 26x2.0" tires: rpm*0.077/ratio
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ColdCruiser
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A 212!?! Tony, you're a maniac but your ride looks great.
I've been thinking about what you said and it makes a lot of sense. My clutch is probably the cause of my issues because I have the idle turned way down to keep it from taking off without me. I also figured a tach would be mandatory to keep the revs down until I get a chance to build a new motor proper without the governor. I was going to source one on ebay but have been putting it off because I'm extremely broke right now. I'm looking forward to rebuilding my clutch and adding my new air filter with rejetted carb (AGK actually sold to me!). I haven't been able to ride the thing for about a month now but not a big deal because it's been 110 degrees everyday here in AZ.
Be safe on that monsta!
I've been thinking about what you said and it makes a lot of sense. My clutch is probably the cause of my issues because I have the idle turned way down to keep it from taking off without me. I also figured a tach would be mandatory to keep the revs down until I get a chance to build a new motor proper without the governor. I was going to source one on ebay but have been putting it off because I'm extremely broke right now. I'm looking forward to rebuilding my clutch and adding my new air filter with rejetted carb (AGK actually sold to me!). I haven't been able to ride the thing for about a month now but not a big deal because it's been 110 degrees everyday here in AZ.
Be safe on that monsta!
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