Motorized bicycle speed mods

M

Motor awesomeness

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Hey guys, turns out i got a kit (80cc 2 stroke 2 hp, i clocked at almost 30 flat out and i want to go faster for free or a couple bucks. Any ideas? Ill buy a boost bottle for 20 bucks soon.
 
That's pretty fast for a new kit, it'll go faster as you continue to break it in.

Also the general consensus is that boost bottles are a waste of money and won't really increase performance.

Not much you can do to it for free, except for porting (do a forum search, lots of good threads on that) and making sure your bike is tuned correctly. If you were willing to spend some extra, you can also get an upgraded exhaust (expansion chambers) or a nicer carb.
 
tuning is difficult before engine runs in well - if you do want a bigger carb, get it after getting better exhaust
 
Ok guys, this is its current state: ran 1 gallon of break in gas through it and im now running it flat out 2 miles a day during the week and its purring quiet and really smooth now. Also the speed was right out of the box. Since i need a fillup soon, what octane rating of gas would you recommend? Im using 89 octane and comventional 2 cycle oil
 
I have gathered during my time here that high octane fuel may not be as useful in these engines as you think, not nearly as useful as finding low/no ethanol fuel.

theres a brand of two stroke oil called opti-2 (I think) that I have heard reccomended many times (never tried it though)


also I just wanted to add: Dude, you love that bike, LOVE IT! Treat her well, be as good to her as you can. By the sounds of things you hit the engine jackpot.
 
Yes its a great engine and i love it. Its smooth, fast, and great for long distances. It vibrates ar speed making a tickling feel, but its great. You said high octane isnt too necessary so could i just stick to midgrade? And thanks for the recommendation. Ill fill up with shells new nitro plus hopefully and get some extra performance because the gas has friction modifiers that lube the cylinder and cleans better. Too bad the shell station is a bit far and the closest is speedway.
 
mine did about 35 out of the box. had a bunch of issues because of fabrication and around 6 months of no riding because it took me that long to figure out my idle screw was pushed all the way in causing it to idle to the moon. after i fixed that it ran like a dream. i added a cheap carb and expansion chamber to it(the pipe now costs nearly 200 bucks, i got it for around 30 last year) and it does around 45 or so. had to re-gear it because the pipe added a ton of bottom end and cut the top end in half. Put on a 36 tooth sprocket and it still powers up hills with no problem. Turns heads everywhere i go. I added a Rocket Racing CDI to it too. I didn't have the cash for a lightning one, and i'd heard it was decent. my bike used to not idle for more than a minute, but now it idles perfectly. Actually building a skyhawk gt frame right now. I just don't have the cash to buy the spacers for the fork, so i'm postponing it for now. Starting some temp work next week.

Good luck on your build and be careful with your gas tank. they're quite fragile.
 
The only mod that I found that was free --- and increased speed, was in modifying my speed runs ---- to all downhill......

Seriously though, 30mph is a great number fresh from the box! It'll even get better with time.
 
The best FREE MODS are #1 shave the head down 1 to 1.5 millameter and #2 port match then port & pollish with a Dremel( rototool) #3 exhaust. Take end cap off & cut stinger short then drill out the baffling & main pipe. #4 cut out the piston skirt on intake side. Makes more power by letting more gas in.
#1 good for 10-12 km.
#2 good for a few km. More
#3 good for 3-5km
#4 good for a few
 
To go faster, definitely doing some port work will help, but be sure to read up on how to do it, you can mess up a cylinder by going too far with it, and you can kill your bottom end torque by giving too much intake and exhaust duration, but there's a good happy medium where the engine will make excellent torque with lots of power up top... read up on it and ask a lot of questions before doing any cutting.
Shaving down the head or installing a high compression head is another way to gain some good power, and the stock exhaust is very restrictive on these, drilling extra holes into the end cap will get you a good power and torque increase, but getting a good expansion chamber pipe will give the best gains.

Boost bottles are a waste of money, and high octane fuel can actually slow you down if it's not needed, remember, the octane number is it's Resistance to burning, not it's ability to burn so realistically you want to run the lowest octane fuel your engine will run on without any signs of detonation. If you shave down the head or get a high compression head, then you might need to run mid grade or premium, but with the un modified stock head, 87 octane is plenty enough, these things have a pretty low compression ratio in stock trim so it may even gain a mph or so by running the regular 87 octane, just remember it may need more after modifying the head, and will definitely need higher if you get a Fred head or a Puch hi hi head.
 
I got a bottle boost......it's a waste of money...I can't notice any increase in performance at all. I should say that I also don't notice any decrease in performance either. Since I got it on already and drilled into my intake I just left it there but I won't do the bottle boost thing again. If you want more top end speed on the cheap, just get a smaller tooth rear sprocket, but you will sacrifice hill climbing ability.

Davezilla Thanks for explaining that. I've been using 87 octane E-10 because nobody sells ethanol free gas here, but I've been mixing with opti-2 at 100x1, unmodified stock slant head, SBP expansion pipe, Dax F80 engine, Dellorto Clone (RT) Carb and a 40 tooth rear sprocket. I top out at 29mph on the flats at WOT. I should say that I have an old school steel frame 80s Peugeot 26" Mountain Bike with a steel rack on the back and with the tools I carry the bike weight is 68lbs, I weigh almost 200 lbs. I was thinking of jetting down because I have a little 4 stroking but it's not really bad. Do you think this top end speed is slow given my setup? I've never tried porting but I do have a dremel tool. Where can I read more about how to do it right?
 
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Sounds slow? It might be the 200 lbs. Iam 155 lbs. And my stock motors Useally go 55km (35mph) with a 44T sproket.
I would try shaving your head down a millameter or so. Before trying porting. Anyway Goodluck!
 
Robbie said:
Sounds slow? It might be the 200 lbs. Iam 155 lbs. And my stock motors Useally go 55km (35mph) with a 44T sproket.
I would try shaving your head down a millameter or so. Before trying porting. Anyway Goodluck!
Click to expand...

Yeah, those extra 45 lbs difference in our weights is a pretty big difference, maybe 7-10mph right there! I'm 6'1"and I weigh about 198 lbs fully dressed and wearing the helmet. I've never had much fat on me even though I'm old now, haha. I would say my total weight (me, the bike, and everything else) is about 265 lbs going down the road, give or take. I should say that my expansion chamber has about 19inches of pipe between the exhaust manifold and where the chamber starts to get fat, it gives me a lot of low end torque but I was thinking if I reduced this distance I might get some more top end. I might try shaving the head some too. To be honest, going super fast is not really a big objective for me but I would like to know how to properly port one of these things.
 
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