Hello, looking to do 30mph.

[kodex]

Hi,

I finally got my 2-stroke cruiser working after many, many hours of trial and error. It runs well now and I have an absolute max speed of 25 mph (it feels like it's gonna fly apart!) I can cruise at about 21mph pretty comfortably, though. Anyway, I'm thinking that I'll put a boost bottle and a smaller rear sprocket on it. Will this likely get me to my goal of 30mph cruising? And what would be a good sprocket size to try, as I am currently at a 44T?

Thanks,
Steve

 

[richirich]

ive got to say, and im sure youll get the same from a few others , when it comes to the upgrades , get an expansion chamber and a 40 tooth sproket. about the boost bottle- that is a touchy subject on the forum. i have one and i could say that it really did not produce any noticable power but it did help cut down some high speed engine vibration.

 

[rohmell]

I believe every tooth reduction in sprocket tooth count gives you 1 mph additional, so a 36 tooth sprocket should give you 33 mph and a 32 tooth would give you 37 mph.

 

[KCvale]

Just for future reference, always say exactly what motor you have ;-}

As richieRich said, an expansion chamber is the way to go for the most bang for the buck.
An Iridium spark plug if you buy your X-chamber from SIckBikeParts.com too.
I made a page with my take on pretty much everything you can do to these 2-smokers here KC's Kruisers - Motorized Bike Forum

Note about X-chambers...
Beware the one-piece 'Fat Boy' pipes. I have yet to make a bike one of those worked on without the end hitting the BB and they even state 'some bending may be required' to make it fit. Ya right, they don't bend pretty for me.

I like the SickBikes pipes but they can be a challenge to install on many bikes so I have used a couple of these one-piece pipes from Zoombicycles.

 

[darkhawk22]

If you are able to top the engine out (i.e. sounds like it is about to fly apart) then most likely the smaller sprocket is going to do wonders but you will lose torque and hill climbing capability will be reduced. With the smaller sprocket you will be able to go faster before the engine hits the max. rpm range.

 

[KCvale]

When it comes to gearing you can bend it anyway you want but it is still a single fixed gear ratio.
You can sacrifice low end for more speed, or high end for more torque, but the only way to really get the most overall performance is with gears.
I've been Gear'n for a Year now and never looked back ;-}

 

[Werner Keggenhoff]

just cahnged last week from a 44 t to 36 love it. HAvent gps'd it yet but engine doesnt scream anymore, less vibration and noise. did loose a little bottom end but well worth the sacrifice. Next Sb pipe and a Dax carb and shifter kit

 

[nightcruiser]

Hi,

I finally got my 2-stroke cruiser working after many, many hours of trial and error. It runs well now and I have an absolute max speed of 25 mph (it feels like it's gonna fly apart!) I can cruise at about 21mph pretty comfortably, though. Anyway, I'm thinking that I'll put a boost bottle and a smaller rear sprocket on it. Will this likely get me to my goal of 30mph cruising? And what would be a good sprocket size to try, as I am currently at a 44T?

Thanks,
Steve

What kind of motor and carb do you have? A standard GT5 should be able to do right around 30MPH without any mods once broken in and tuned properly.
When you say it feels like it wants to fall apart at 25MPH do you mean the motor or the bike?
IMHO I would work on tuning your bike properly before you start mod'ing it.....

 

[ducedave]

run it for 300mile on 24/1 then 32/1 oil gas re-jet correct ports and manifold to match then get the up grades

 

[nightcruiser]

run it for 300mile on 24/1 then 32/1 oil gas re-jet correct ports and manifold to match then get the up grades

I agree completely. It makes no sense to start mod'ing a motor before it is broken in and tuned properly to start with. It takes AT LEAST 300 miles to break these motors in, I have been told by others that have built quite a few bikes that it takes more like 500-800 miles to fully break in a motor.
Running break-in fuel mix is gonna effect the way she runs, and the way the carb needs to be tuned, so it doesn't make much sense to starting mod'ing or even tuning the carb too much until you have run through all your break in fuel and are running a standard 32:1 mix.
Since your goals are all attainable with a stock motor I would tell you to just chill a bit and keep putting miles on the bike until you are all broke in, then tune the carb to your 32:1 mix and you should be able to go 30-35MPH with no problem.....

 

[happyvalley]

Hi,
I finally got my 2-stroke cruiser working after many, many hours of trial and error. It runs well now and I have an absolute max speed of 25 mph (it feels like it's gonna fly apart!) I can cruise at about 21mph pretty comfortably, though. Anyway, I'm thinking that I'll put a boost bottle and a smaller rear sprocket on it. Will this likely get me to my goal of 30mph cruising? And what would be a good sprocket size to try, as I am currently at a 44T?
Thanks,
Steve

A good idea to keep an eye on safety upgrades on the bike if needed as well Steve, brakes, bearings, etc become more stressed when looking to push top end. Wheel revolutions on a 26" bike @ 20 mph is +/- 260 rpm, jumps close to 400 rpm @ 30 mph, 520 @ 40 mph.

 

[kodex]

Alright, I suppose I should break-in the motor properly before moving any further with the upgrades. I'm current;y running with a 16:1 gas/oil ratio, and it seems like this is actually too much oil. Would I see a power improvement when I switch to 24:1 on my next tank?

A good idea to keep an eye on safety upgrades on the bike if needed as well Steve, brakes, bearings, etc become more stressed when looking to push top end. Wheel revolutions on a 26" bike @ 20 mph is +/- 260 rpm, jumps close to 400 rpm @ 30 mph, 520 @ 40 mph.

Certainly. I repacked my wheel bearings with high-temp grease, and my breaks are pretty good.

 

[iflyos]

Alright, I suppose I should break-in the motor properly before moving any further with the upgrades. I'm current;y running with a 16:1 gas/oil ratio, and it seems like this is actually too much oil. Would I see a power improvement when I switch to 24:1 on my next tank?



Certainly. I repacked my wheel bearings with high-temp grease, and my breaks are pretty good.

You will see a performance increase when you change to 24:1. At 16:1, you are actually running the engine on less fuel, and that means there is less energy available to convert to "go-power"

I may be new to the forum here, but I have run small 2 strokes for many years on my RC planes, from the old Zenoah 23cc engines to my current favorites, Desert Aircraft 100cc and up. The break in process is something of a ritual with all owners, and everyone does it a little different...but if done properly, you will see gains for quite a while in power. I have had engine running at my final mix of 40:1 for as much as a year before they really "woke up" so to speak. Don't forget to keep a close eye on the engine when you switch to your 24:1 mix, you will more than likely need to adjust your mixture..

Tim

 

[nightcruiser]

Alright, I suppose I should break-in the motor properly before moving any further with the upgrades. I'm current;y running with a 16:1 gas/oil ratio, and it seems like this is actually too much oil. Would I see a power improvement when I switch to 24:1 on my next tank.

16:1 is a LOT of oil, Grubee says to use 18:1 for break in and most people in the forum will tell you to use even less. I ran 2 gallons of 20:1, then one gallon of 24:1, then moved to the final mix of 32:1. I was getting about 130MPG so that makes about 400 miles of break in fuel I ran, but never as much oil as 16:1.
I would tell you to move to 20:1 mix and see how she runs on that.
How many miles do you have on the motor with the 16:1 mix so far?

 

[biknut]

Hi,

I finally got my 2-stroke cruiser working after many, many hours of trial and error. It runs well now and I have an absolute max speed of 25 mph (it feels like it's gonna fly apart!) I can cruise at about 21mph pretty comfortably, though. Anyway, I'm thinking that I'll put a boost bottle and a smaller rear sprocket on it. Will this likely get me to my goal of 30mph cruising? And what would be a good sprocket size to try, as I am currently at a 44T?

Thanks,
Steve

All you need is a 40T sprocket to do 30 mph. My little 50 will do 30 all day and sometimes up to 33. The only difference between mine now and when stock is, a MM shorty manifold, a 40T sprocket, and a modified stock exhaust. + a 68 jet. You don't need the manifold, but you di need to open the exhaust a little, but no need to go crazy.

Here's how it runs, enjoy


China Girl and Proud of It - YouTube

Fastest Motor Bicycle in Farmers Branch. - YouTube

 

[kodex]

All you need is a 40T sprocket to do 30 mph. My little 50 will do 30 all day and sometimes up to 33. The only difference between mine now and when stock is, a MM shorty manifold, a 40T sprocket, and a modified stock exhaust. + a 68 jet. You don't need the manifold, but you di need to open the exhaust a little, but no need to go crazy.

Here's how it runs, enjoy


China Girl and Proud of It - YouTube

Fastest Motor Bicycle in Farmers Branch. - YouTube

I gutted my exhaust so that there is nothing inside it and drilled two 3/16
holes in the end cap. Is this a what you mean as far as opening the exhaust? And is there any place to find an expansion chamber for less than 60-70 dollars, and where is a good place to buy a sprocket?

I have taken in all the input so far, btw; much appreciated.

 

[nightcruiser]

All you need is a 40T sprocket to do 30 mph. My little 50 will do 30 all day and sometimes up to 33. The only difference between mine now and when stock is, a MM shorty manifold, a 40T sprocket, and a modified stock exhaust. + a 68 jet. You don't need the manifold, but you di need to open the exhaust a little, but no need to go crazy.

Here's how it runs, enjoy


China Girl and Proud of It - YouTube

Fastest Motor Bicycle in Farmers Branch. - YouTube

30MPH all stock should be no problem, really, you shouldn't have to do any of that mod'ing to hit 30MPH.... I can do at least 35, I weigh just over 200lbs, I got a stock 66cc GT5, stock sprockets, exhaust etc. By stock I mean no major mods, just an NGK plug, quality wire and boot and carb tuned up well, thats it... My spedo recorded 36.8MPH once, flat land with no wind, that was before I developed this wikked wobble in my rear wheel which slows me down a bit. Lately top speed is between 29.4-31.8 on a bad day, 34.8 on a good day....

 

[Pilotgeek]

Don't fall into the false claims of many people on here with bone-stock china motors hitting 35+ with a 44t sprocket. Their speedometers are wrong. It just doesn't happen. The gear ratio with a 44t sprocket and 26" wheel simply don't allow it. Often, the 26" preset is not correct on digital speedometers, and mechanical bicycle speedometers are often not intended for such high speeds and don't have a linear curve, so as you get faster, the speedometer keeps getting less accurate. Also, don't fall into any rumors about "drilling your muffler", just tune your jet to the pipe and you'll have the same effect but much quieter and with a better torque curve and higher efficiency. If you want a tuned pipe, get a tuned pipe instead of a drill.

As far as hitting 30mph, I cruise at about 25-26 and top out at 30 with a stock non-cat exhaust, NT carb, 40t sprocket, and matched ports. Verified with a GPS, accurate speedo, and car.

 

[2door]

Let's not turn this one into a "I can go faster than you" argument. Keep the discussion going but no fighting/name calling/hair pulling or eye gouging.
Tom

 

[KCvale]

One thing I have noticed after a couple of dozen 2-stroke Skyhawk builds is some motors seem to simply just flat run stronger right out of the box.
It was a 2010 66cc SKyhawk with NTS carb and it just flat flew and still does.
Would it hit 30? No speedo on it but I know what 25 MPH feels like and it was faster than that.

One other thing about break in MILES, it's not the miles, is the hours of operation.
12 hours of light break in use (300 miles at 25MPH) should be fine at 25:1, and you don't have to be riding it. I routinely take a new build around the block and then just let it idle out back for a couple of hours at a time with periodic revs a few times before I start putting real miles on it.