I'm getting ready to start my second build. I have decided to run the 79cc HF predator motor. For the guys that run them, with the governor removed, what kind of rpm are you safely running? And for the guys who run them pumped up, say high compression, the bigger cam, stronger valve springs, free flow exhaust and bigger carb, what kind of rpm with your go fast set up? I'm trying to set up gear ratios and need to know what the top end is at rpm wise. I'm going to be running a moped rear hub laced to a 26 inch tire rim. The hub has built in reduction transmission of 12.5 to 1. . I want to run direct drive from motor to reduction hub, but ratios are not my forte. Any ideas out there for what size I would want for a motor pulley? Yes this is going to be belt drive. Thanks for help if you have it.
79cc predator question?
- Thread starter Uncle Bob
- Start date
I haven't found much info on the 79 as far as valve spring upgrades. AffordableGoKarts.com has a little info on hot rodding it, but a lot of the parts aren't in stock any more. I heard the 212 springs can work in the 79 as an upgrade, but I don't have a confirmation on that one, so take it with a grain o salt.
From agk's website, it seems that once the governor is removed you shouldn't try pushing it past 6k. It probably won't do it anyway as the valves will float. I don't believe these are interference engines, so floating valves wouldn't be too terrible. But I wouldn't try pushing it more.
From agk's website, it seems that once the governor is removed you shouldn't try pushing it past 6k. It probably won't do it anyway as the valves will float. I don't believe these are interference engines, so floating valves wouldn't be too terrible. But I wouldn't try pushing it more.
On my 99cc Pred, it's got all the mods and I push it to 7,250 rpm most of the time and up to 8,200 rpm frequently. The only mod that is really needed now and of some importance is a billet flywheel and connecting rod.
Do I live dangerously? Too some extent......sure! I do the same with the 79cc Preds as well.
Shame on me......please don't do as I do, seriously!
I run the 18lb. springs on the small Preds and the valves don't float.
Do I live dangerously? Too some extent......sure! I do the same with the 79cc Preds as well.
Shame on me......please don't do as I do, seriously!
I run the 18lb. springs on the small Preds and the valves don't float.
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Where can you find the 18lb valve springs? Actually, where do you find any upgrade parts for the 79?
Awesome. It sounds like you have built a real power house there!! That should put me in the ball park for the 99c. Its (79cc) the same stroke just smaller bore so rpm should be about the same. Where did you find the valve springs? and what pound rating are they? what overall reduction are you running? top speed? Thanks for you help here.
The 79cc seems to not be getting much attention from the after market world. Not much out there for it. That seems strange to me. It's really the perfect bike motor between potential for hp and weight.
I've been using the HF79cc engines. Using a double reduction my gear ratio is 11.85:1. In my experience it will just reach 6500 rpm or 44 mph with 18 lb valve springs. It's comfortable cruising at 35 mph. We also remove the governor. Not a torque monster in the bottom end but it is a nice mid range cruiser. Keep in mind the flywheel is cast iron. I haven't heard of one coming apart, but would still keep the rpms down. Best way to do that is to leave in the stock springs.
Where did you find the 18 lb valve springs? I will be using the .224 intake lift, .231 exhaust lift cam. Also I'll be running a gear reduction moped hub, ratio is 12.5 : 1, belt driven. Do you have any idea what size motor pulley would be best to run? I will be lacing a 26" bicycle rim to the hub. The hub is awesome with the built in reduction, brakes and a lever that will disengage the motor drive to let me peddle. Motor drive is on the left side and the peddle sprocket is on the right. Thanks for your help.
I have a 79cc that only has the rev limiter removed. With a 11.818 : 1 raito, it cruises nicely at 35 and tops out around 40 with stock springs at 6000rpm. It can get up to 6400ish but that's when the valves start to float. Im 200lbs and it will comfortably do 35 all day.
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Excellent! 6000 is very respectable. I think I'm going to install the AGK cam and up the springs, of course exhaust and intake upgrades also. My final drive ratio will be at around 12.5 to 1, I'm 6ft and 220lbs. If I can hit 35 mph top end I would be pleased. Thanks for posting your info!
