cheap 66cc engine mods

Boost bottle, nope!

Change down to a 34 tooth sprocket and you should get close to your 40mph or definately 35 mph top with a 38 to 30 cruise speed depending on your set up.

Boost Bottle in my opinion is a joke. There are a few that swear by them, my barometer is to look at the factory engines, they are gone. They made a tiny amount of power but only on reed valve motors and only at a RPM we will never see. NOS would just burn the engine up as fast as you pushed the button. I only have one 66cc engine and I am not fond of it. It is a 48cc with a cylinder kit installed so it uses the small bolt pattern and no other top ends will interchange. I do porting on all my engines and so the 66 got the treatment, it is OK but like I said I am not fond of it. The 36 tooth sprocket might be a bit of a chore for that engine. My sprocket of choice is a 39. I am making them so the only way to get one is from Kings sprockets, they will custom make anything. Have fun, Dave
another Idea. http://motorbicycling.com/f13/stock-carb-mod-1494.html

porting helps a lot. on the intake, dremel out as much as you can to match the intake port on the engine. be careful not to go overboard. the engine port is bigger than the welds on the intake. while you're grinding away, get up inside of the intake manifold and smooth out the casting burrs.

the exhaust can get the same treatment, but again, there's not enough material to match the port exactly, so just do as much as you can.

pay attention to your spark plug's color till you get that dialed in.

make sure your bike's tuned up. good tires, straight wheels, no loose parts, greased bearings, etc. will help. the less rolling resistance that motor has to push, the faster it'll go.

as far as sprockets go, it depends on your weight and where you ride.

i'm 135 and i've got a 32 sprocket. works great on the flats, but bogs on steep hills. i can get an average of 37mph.

i had a 36 which worked great overall, and it averaged about 34.

nos and boost bottles are just gimmicks, don't waste your money. buy a tuned pipe instead. (haven't tried one myself, but everyone else swears by them.)

whenever you're adding a part, tuning something up, or modifying something, do it one piece at a time. that way you'll know what actually works for you and what doesn't. it'll also help you find problems. if you do ten mods at once and your bike stops running, you've got ten times the problems to figure out why.

despite what people say, don't expect much over 35mph, unless you're willing to spend money and tons of time fine tuning it. everyone likes to believe they're getting more out of their cheap little engine than they really are. (including me)

Have done:

36 tooth sprocket- Big increase and still has good accelleration- a light rider may get by with even smaller- 34 or 32

Smoother, more narrow tires- if you're riding on the road and not dirt or gravel, and want some more speed- non-cruiser tires are essential- I got some smooth tread 1.175 blackwall tires for $10 each at a bike shop- not only much less rolling resistence and so more speed than knobby 2.25 beach cruiser tires,

a more confortable ride with less vibration- knobby tires aren't meant to go very fast.

In fact the new tires made such a difference, that I ended up putting an even narrower one- a 27 x 1 1/4 with an alloy rim, on the front end for even BETTER rolling and less weight- and I put a campagnolo road brake on to fit with it- which is really a better and lighter brake than the cruiser's cantilever

Haven't done, but probably will-

new carbs are out- a slick racing carb thats a little expensive, but largelly sold out
and a new stock 66 carb for half as much- see both at spookytooth where both are sold out for now. I think they are supposed to start shipping with kits soon, so double check if you order any more kits.

The carb has been the weak link I think.

Pirate bikes makes a nice looking ported carb billet which is a larger alloy intake pipe- not much money and may try that with a different carb someday.

Good luck

Dave, I thought I heard you say you were not fond of your 66cc engine, twice.

I have found speeds up to 35-40 mph attainable by making sure the engine is broken in, properly set up and tuned and then turning the throttle to full and waiting for about a minute to pass.

Joe I did say that twice! Oh well I have not run that engine in a while. I get it out to ride with my wife walking every night but it has been out of fuel for a long while. I have a 30 tooth sprocket on the thing and it is too small, I just wanted to see how it would do. Actually for just rolling along on the flat it is fine and it would get good fuel mileage. It takes a lot of slipping to get it going, I guess if I raised the compression a little and made the transfer ports larger it might be able to top out with that sprocket, I wonder what the top speed would be? I always take my engines apart before I run them and this one the crank was rusty and dirty inside, looked like the parts lay outside for a while before it was assembled. I guess that turned me off to the little thing. OH well, have fun, Dave

PS: Maybe I am not fond of the rust, Fond (I did it again) LOL

c'mon joe, you just pedal off the line like you're in a race, trying to pull the holeshot. then it cuts down the time it takes to get up to speed to like, uh, 45 seconds...

I did bust a crank on a Next bike- I was trying holeshots (pedal only) and I really did break the crank where it was "attached" to the sprocket. I welded it and added a Bike Bug after that.

buddy of mine broke one of those old black one-piece ashtabula cranks (which i always thought were indestructable.) the crank arm snapped right in half when he landed a jump, and he impaled his leg on the broken half still attached to his bike.

luckily, he didn't skewer anything that couldn't be fixed, but he got some serious stitches, and there was a blood red line leading away from that jump for a week.

now back to your regularly scheduled topic...

Could anyone please tell me where I can get on of those smaller prockets? Does it new to be a 9 hole like the original? Please help.

My stock 66cc with the stock 44 rear will go 39mph(not downhill but probably wind to my back). I have found that once these little engines are hot they will pull 30+ with enough room.

oh and you can get those sprockets from here

psprat496 said:

Could anyone please tell me where I can get on of those smaller prockets? Does it new to be a 9 hole like the original? Please help.

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You can get them from just about any vendor anymore. I would not recommend going down past 40T if you have any hills or weigh over 200#.

A 36T is almost too much here (slight hills, 185#) with a well sorted engine. Top speed doesn't increase much, but the cruise rpm is lowered.

I will also add, (said it a million times) that when you start lowering the number of teeth on your rear sprocket, you are not going to have an infinite increase in top speed....that is determined by horse power, not the size of the rear sprocket. You can EASILY overgear a small engine such as we ride with.

I did get the billet intake-about $14 from pirates and Creative engineerig, and for thecost it's one of the best things you can do- eliminates the weird carb performance-

I reamed it out a little further- there's not much sense in porting the motor it would seem if you use the stock intake- that's still gonna be the smallspot in restricting flow-

I haven't ported the motor and don't think I'll have to- I've got a good cruise speed now and can go about as fast as I want to- got an electric speedo- (for like$3 on ebay!)but haven't tried it out yet

also got a 66 carb, but haven't tested since weather got cold.

the poo-poo pipe has it down to moped sound level which I REALLY like- but I had to cut it and run it under the bottom bracket- and take off the kickstand, which doesn't work well with 27' wheel anyway-

I am 150lb, my bike weighs about 35lbs and the kit should weigh about 25lbs right? I have slight to large hills in my area. What is recommended, 36T or 40T? Or even 34T??? Thanks.

I would either stay at the 44T or go to a 40T at the smallest.

bradentonmotorbikes said:

Okay, so I have just recently (3 months ago) installed a bicycle motor kit,
Its a 66cc and its past its break in, but im only getting about 27mph out of it.
Is there any inexpensive ways (under $75) to get it up to like 40 mph?
Also, do the NOS Kits and boost bottles from Boost Bottle Industries work well

Also, i figured this bit of info might help
I live in florida, my biggest hill is my driveway

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yep i run a 36 tooth and get 42 to46 on the straits !!!!! stay away from boost bottles!!!!!!

Claims of this type of speed are taken with a LARGE handful of salt. 46mph? What's the source of proof? Or, as they say- "Downhill don't count."