Thread: how to increase compression on a 2 stroke?

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Ok, I like to ride bicycle a lot, and my current bike is very neat.. not in the best cosmetic condition, but it's solid.. it's a late 60's GrantSport Easy Tour 26", sold from W.T Grant when they were still in business.. being a low end bike, it might be worth $5 or so, not collectible like an old schwinn.. it was a 3spd but the 3 gear axle was replaced with a single gear, and the old pull type dérailleur does nothing.. easy bike to pedal going on the level but due to no gears, hills arn't easy.... searching on craigslist for a new truck I found that bike-moped kits are made ( was in the auto section ).. 48-66CC 2 strokes with manual clutch and pedal start... searched Ebay and found the kits for $129 for a '66CC kit.. specs list 6.0:1 compression and 6hp ( seems logical for a 2 stroke ), which will deffinetly haul me up the hills, or at least assist... but how do I get more compression and power?.... there listed at 40 MPH top speed on a 26", so I'd like to hotrod it to go 60 if I can...


yes, I know I'm asking how to hotrod a moped

60 Mph on a bicycle with skinny ass tires and terrible flimsy little brakes?
eek:

You got a death wish or something??

Take the 40 mph and live to enjoy it. Actually 40 might even be a stretch.

I know, really don't want 60 MPH.. the main reason for wanting a little more power out of it, is I live on a very large hill, probably 60* incline and it's about 1 mile up.. with the ignition and fuel off and some decent compression, I should be able to descend down the hill using the brakes very little, and then the engine should be able to take me up the hill...


I'll have to see how it does first, because really.. I'v pedeled up to 30 MPH down hill, and that's pretty fast on a bike for me.. 15 MPH would be just right I think

Wowzer Zowzer!!

I'm with Bob!

That said, I used to race the daylights out of go-karts when I was a kid. Homelite and McCullough engines that we would squeeze 20-25 horse out of. The compression ratio is fairly easy to raise by shaving the head as you have no valves to worry about. Thinner copper gasket does the same trick.

A word of caution - the spark plug clearance is critical and you need to check before you mill the head - Also bear in mind that these little buggers run hotter than the hinges on the gates of hades and will burn a hole in the piston in a heart beat. If you're going to raise the compression, back down one heat range on the plug and go a notch richer on the mixture and use a good two-stroke oil. I like RedLine or Honda HP. We raced Suzuki and Kawasaki motocross at 50:1, but rebuilt the top end every other race. The sponsor had a fresh motor in the truck (it was a nice truck - complete machine shop inside) ready to go and rebuilt between motos at the track You probably need to stay at 32:1 for what you're looking at.

Have Fun

P.S. Update the brakes on the bike and send a picture.

I'll deffinetly send an update with a pic.. probably change the brake pads out with a bigger unit from a mountain bike.. I'v got the wheels off right now, and I'm putting brand new tubes and tires on...

factory oil spec is 16:1 for break in and 25:1 after.. if I find it needs more go power, I'll do some milling... maby run an aftermarket exhaust pipe for the low end... parts for these bikes are cheap enough... exhaust pipes: $20 carbs: $20 new engines: $90.. list goes on and on, and theres not much over $200...


here is a completed moped conversion bike, from a pic on Ebay
http://img.auctiva.com/imgdata/9/7/2...4482846_tp.jpg

while doing some searching on a forum for these bikes, and found that high compression slant heads are available for them.. sparkplug is slanted 45* and the chamber is smaller... $13... hotrodding this thing will be easier than I thought

Well--besides top fuel and prostock type engines we have been into karting -----your package as sold is probably pretty well optimized for what its purpose is---biking as on flat ground---higher compression in itself won't be a lot of help altho some porting changes would---porting is like camshaft changes not about the size of the port but how the vertical diminsions effect inlet and exhaust---just like cam changes tho, it really effects the rpm level where hp/torque occur

if you want to climb a hill you should be looking at adding to the low rpm range that will be happening closer to the top of the hill, not max rpm----

I found 50 tooth sprokets for $20, probably order 1... factory has a 41 tooth sprocket... because it is the low end grunt I need... if this 1 goes good, and I deem them pretty fun to ride. Maby I'll get a Schwinn Stingray chopper and really gear that 1 for speed

would a boost bottle help? I understand the theory behind how they work. and there advertised to increase torque, but would it really help?

I don't even know what a boost bottle is.... but I hope you'll report how this project works out. I'm really interested, I just might do the same thing.

Originally Posted by 65ny

I don't even know what a boost bottle is.... but I hope you'll report how this project works out. I'm really interested, I just might do the same thing.

boost bottle is a bottle that has the same volume ( within 2cc ) of the engine size.. a 2 stroke makes compression on the down stroke also, and when the compression is made a 'wall of air' is created obstructing the intake mix a bit on the up stroke. the boost bottle is mounted above the carb/ intake and the fitting is threadded right into the intake.. when the compression air comes out, it has a place to go and it smooths out the mixture.... this is all theory that goes behind them anyway.. weather or not there are true gains IDK...


www.zoombicycles.com sells the kits with the high compression slant heads arleady installed.. I would have gotten there kit had I known it had those parts on it, but when I ordered mine, I still knew little about them

here is the bike sort of finished.. it's all done now ( needs tweaking ) but this pic doesn't have the chain shortened, clutch hooked up or tensioner installed.. still needs the tensioner modefied.. the rear chain stays angle in where the tensioner goes, so I have to twist the tensioner to accomadate that.. pulls the chain off the way it is.