79cc vs 212cc Predator

[Scott.D.Lang]

well according to gps between the 3 I have built they did a very min of 40 and that was with a fairly low gear and way to much low end for my liking on a bicycle and I weight around 260lbs. the other 2 builds ran between 48 and 52 had decent pick up much better then all but one 2 stroke Ive built but neither of them had the mid or top end power that my 2 strokes have had.

now all that said Im not saying that the gps is 100% right and with the last 2 I did have to pedal from take off not to get a very bad shake but I only had to spin the crank a few times and the cops never looked at me twice after they seen me pedal from a stop. once either engine hit 3k they had all the power I needed for running around chicago had no problem doing 30 to 35 mph from stop sign to stop sign with the last to and would max the first one out in 1/2 a block.

 

[TheNecromancer13]

your gps must be funky then, I have taken all 3 of my upgraded 79ccs past radar, and they topped out at 37, 38, and 43, and the one that topped out at 43 has very little torque, and I only weigh 155 lbs.

 

[Scott.D.Lang]

I wish I could use radar but everywhere I see the radar setups Im in town so not going all out but I pass them reguraly at 30 to 35 mph with a lot of throttle left.
I always hope to pass one of the radar setups when Im out of town on a nice stretch of road where I can open it up and see what it says but I have not been that lucky lol.
The very first one I built the gearing was way to high but that was because my dumb ass could not wait for the 56t and used a 44t I had till the 56t came when I got the 56t I also made the 2nd gear 4 teeth more then the original gear I had.
the 79 has good power for these bikes and with very little done to them they pull good all the way through the rpm range.

on the bike Im building now ill never see top end because I very rarely do more then 30 or so and more then 45 on a bike is not something I do often when I did go for top speed I always backed out before the motor wound to tight the idea of a rod throwing at high rpm between my legs

 

[ultralight01]

What's odd is that on bikes, these engines without upgraded springs or a flywheel will go up to 6500 RPM seemingly. On a go kart they do 5500 max. Maybe these speeds were going downhill, but that speed on flat ground seems impossible because of the valve springs.

I'm ordering parts now, fuel tanks, fuel line, fork, wheels, CNC sprocket and adapter, jackshaft keyed axle, disc brakes... it goes on forever. Engine was $100 and all parts add up to $350.

 

[Scott.D.Lang]

yea mine started floating the valves 6000 to 6500 rpm. most of the time I did my best to stay under 5k.

 

[ultralight01]

Odd. Like I said, the valves float at 5000-5500 on a kart

 

[Scott.D.Lang]

maybe it has something to do with wheel size I agree it is strange I did not know that about the carts. one thing I did notice about my first 79 build after about 600 miles it would start to float the valves around 5700 rpm

 

[ultralight01]

They need a valve adjustment every so often right?

I just realized, you always upgrade parts on a 212 to prevent a flywheel orr conrod failure. A 79cc produces less power and may be able to turn 8000rpms without upgrades. Scotto's 99cc does so with no flywheel or conrod upgrades.

 

[Scott.D.Lang]

I never did any valve adjustments. but that said out of the 3 79s I used only one of them did the springs seem to weaken and allow valve float at a lower rpm over time.

I would not try to push one of these engines much above 6k myself with out at least a flywheel ( which arc has now ) and not above 7k without a better rod.

from my past experiences with building motors a lot of time if you have a high rpm motor it is not the hp that brakes the motor but the stresses created from the rpm. The higher the rpm the more stress put on the rod no matter the hp. if you get lucky and get a perfect stock rod you may be surprised at how high you can turn the rpms but one weak spot in the rod will show itself quickly under high rpms.

Also though you would have to upgrade the valve springs , cam ( most likely ) and do a good port and polish job, and maybe even valves to get that type of rpm.

Now all that said if you plan on trying to get a 99/79 hf motor to spin 8k rpms be very careful and try not to push the motor if any thing dont seem right for your safety.

 

[Springfieldscooter]

Will the 3d clutch work with the 79cc via an adapter sleeve?

 

[Scott.D.Lang]

http://motorbicycling.com/showthread.php?t=61426

read this post it will show you a lot more about the 3d clutch

 

[curtisfox]

3D is the best thing to come along seance i had my factory Monark motorbike, back in the 50's. It had a disk clutch, just pull the lever and it would free wheel, let go and pedal start. So easy and trouble free..............Curt