Hello, looking to do 30mph.

Pilotgeek said:

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.

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I set the wheel size on my spedo, its accurate. I guess I will have to put my gps on my bike and take a ride to prove it to you, but I already know I can hit 30MPH no problem with stock stock stock....
I do agree with you about the tuning, I havent touched my muffler, all I did was tune the carb, I do have the performance CNS carb that WILL outperform the NT carb if tuned properly....

2door said:

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

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I got no argument here, no name calling. Just stating the fact that I can get 30MPH from a stock 66cc tuned properly....

KCvale said:

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.

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I have always heard for break in you should let the motor idle with no load for the first 10 minutes, then ride to break in for a couple hundred miles. I have also heard that proper break in requires a load on the motor, not just idling. I know everyone has their own break in technique, and there is no exact right or wrong way, so please do not take this as criticism of you method.
I have a 2010 skyhawk with a CNS carb and it just flat flies, like you said. I broke in as described, 10 minutes idle then couple hundred mile riding on break in mix.
I am glad you chimed in here and stated that you feel this bike went faster than 25, I know mine does. By the feel of the speed, by the reading on the spedo, by the way I keep up with traffic, all of these factors telling me that I can hit just over 30MPH. Plus, I don't get scared by speed at 25MPH on a bike, but I have been fast enough to feel it is TOO FAST since I put this motor on the bike.
Maybe you guys that don't hit this speed need a better bike? I have a high quality mountain bike not a cheap Chinese cruiser, cost $550 in 1988 new, maintained like new until this day. My bike does not slow me down, until I developed my wobble in the rear wheel, which DID slow me down a bit. I think a lot of people use pretty crappy bikes for these projects. Also, I do not use a chain tensioner, so that drag is gone on my bike, which can be pretty significant depending on the chain angle and how tight it is etc.

I thought I originally had my speedo set correctly. I set it up with the 26" wheel preset, and was happily cruising along at what I thought was 30mph. After trying it with a gps and noticing I was about 4mph under what I thought, I measured my wheel circumfrence in milimeters and entered that into the speedo. Now my gps and speedo say the same thing, and now I know that it feels like you're going way faster than you really are on a motorized bike.

Pilotgeek said:

I thought I originally had my speedo set correctly. I set it up with the 26" wheel preset, and was happily cruising along at what I thought was 30mph. After trying it with a gps and noticing I was about 4mph under what I thought, I measured my wheel circumfrence in milimeters and entered that into the speedo. Now my gps and speedo say the same thing, and now I know that it feels like you're going way faster than you really are on a motorized bike.

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If the temp wasnt in the 40's here I would strap on the GPS and verify the accuracy, but I'm not into freezing my knuckles off... I just checked the 10 day weather and there is a slight chance we might hit 60 degrees in the next 10 days, I will ride if it hits around that temp, and will take my gps with me...

I hear ya. We've got a scorching high of 50 today in Northeast Wisconsin. I honestly don't doubt a bone-stock 44t could do 30mph if it came from the factory with a moderately well balanced crank and was well tuned. I'm mostly nitpicking the guys who claim 35-40mph on a 44t. I kinda gotta chuckle a bit at those. Didn't mean to derail the thread with a speed argument, I gotta learn to shut it sometimes =\

Pilotgeek said:

I hear ya. We've got a scorching high of 50 today in Northeast Wisconsin. I honestly don't doubt a bone-stock 44t could do 30mph if it came from the factory with a moderately well balanced crank and was well tuned. I'm mostly nitpicking the guys who claim 35-40mph on a 44t. I kinda gotta chuckle a bit at those. Didn't mean to derail the thread with a speed argument, I gotta learn to shut it sometimes =\

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Its all good, the topic here is about speed...
My bike does on average 29-31, regularly, which I think is fairly average for a well tuned bike (many people attain this I believe, and that is why I chimed in to tell the originator of this thread to break in and tune motor before he starts mod'ing if all he wants is to hit 30MPH). On those few days when my spedo hit 34-37 I could tell the difference in speed above the average 29-31, so I am fairly sure it was accurate. I can't hit that speed every time I go out for a ride, but at one point I did. I have made so many changes to the bike and motor over the summer, and the carb tuning, I think when I hit that top speed the the carb was tuned rich and I was having rough low end ride. I have since tuned the carb to have a really nice smooth low end which seems to have taken a little off the top end. The highest speed I have seen since the latest tuning was 34.8 on the tail end of a 2 mile run on a perfectly flat brand new asphalted road. Again, when I was hitting that speed I could feel the difference from the average 30MPH....

After reading through this thread I have to agree that you need to get your engine well broken in before starting major mods, small mods like port matching and cleaning up the intake and exhaust can be done while doing a build. The best thing to do is to tune your mixture as good as you can and get it broken in. I tried the 16/1 on my first build but have since went to 24/1 for break-in, a well tuned stock engine will run fairly well.

Greg58 said:

After reading through this thread I have to agree that you need to get your engine well broken in before starting major mods, small mods like port matching and cleaning up the intake and exhaust can be done while doing a build. The best thing to do is to tune your mixture as good as you can and get it broken in. I tried the 16/1 on my first build but have since went to 24/1 for break-in, a well tuned stock engine will run fairly well.

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I guess my idea of stock might differ from some, by stock I mean not changing parts to aftermarket stuff basically. (besides the plug, wire and boot, which I think everyone should upgrade) When doing my build I cleaned up the intake and did a small amount of port matching where I could see it would be benificial. The way I see it that stuff is not really a mod, it is finishing the job of manufacturing the parts, which they really don't do before they ship out from china... A lot of the parts are pretty rough when they leave the factory, a small amount of finishing work can be done on your own to smooth out some of those bumps they left in the parts for you....

I agree, but alot of people just put these kits on a bike as they come out of the box. Thats where the luck comes in, some run o/k as is but most will run better with a little detail work.

I have to agree that it is very critical to clean up the engine from the factory with slightly better components and port matching. I think that is probably the best place to start. I'm not sure if I just have a dog of a motor, but I regularly spin it up to 7200rpm and all I get is about 30 with a 40t sprocket. Then again, working at a snowmobile repair shop and having to often fix people's blown up crap, I tend to try to stay on the safe side and back off the engine when it sounds like it's revving a little too high for its own good.

Pilotgeek said:

I have to agree that it is very critical to clean up the engine from the factory with slightly better components and port matching. I think that is probably the best place to start. I'm not sure if I just have a dog of a motor, but I regularly spin it up to 7200rpm and all I get is about 30 with a 40t sprocket. Then again, working at a snowmobile repair shop and having to often fix people's blown up crap, I tend to try to stay on the safe side and back off the engine when it sounds like it's revving a little too high for its own good.

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I think it takes a lot of fine tuning on SOME of these motors to get them running at top performance, others are lucky and get ones that perform great right out of the box. Besides cleaning up the parts that are sent out rough from the factory, tuning the carb is essential. Because there are so many factors to consider when mounting a motor most carbs end up not getting installed level, this begs a float adjustment even if it was sent out adjusted properly from the factory...

I'm with nightcruiser
I have a 48cc gt2b sky hawk and stock just ngk plug and wire.I pull the black little hose on the right side of carb and it ran great check it with a gps it said 26mph and tires were 40psi with could be aired up to 65 but bumps are not so bad at 40psi,that's with a tensioner.I since have got it too 28mph float adjusted and jets.It also has a 44 teeth sprocket.

Pilotgeek said:

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.

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I thought your statement about "false claims" was a bit harsh but the weather has been to crappy to ride, so... It hit a whopping 60 degrees today so I strapped my GPS on my bike and took it for a (very chilling) ride. I am glad to report the spedo on my bike was 100% accurate when compared to the GPS all the way up and down the speed range, actually, the few seconds it was off I found it lagged the gps by 1MPH.

Today my top speed was 33.3MPH as you can see from the picture of my GPS... I purposefully took any terrain with even a slight decline at less than 20MPH so I wouldn't screw up the statistics. The speed was attained on a smooth flat asphalt road, the bike is NOT running anywhere near it's peak performance of earlier this summer. The rear tire has a bad wobble now and I had been doing some fiddling with the carb and it is not tuned for well for top end right now.

Recently (on a warmer day and longer ride) my bike spedo recorded 34.6MPH (with the same setup I am riding right now), my previous top speed recorded was 36.8MPH, all done on the same stretch of road as above. The 36.8 was attained before the rear wheel wobble became an issue and the carb was tuned a bit better for top speed then.

I have a STOCK Grubee 2010 SkyHawk 66cc kit (from GasBike.net), running the sprocket that came with the kit and the motor has all stock parts, but I will list the things I have done that differ at all from the kit:

NGK plug
Quality automotive wire and boot
Cleaned out extra material from inside intake at elbow
#41 Chain
Metal Throttle grip
Eliminated chain tensioner by adjusting motor position
TUNED CNS CARB

Thats about it, pretty much stock other than some durability upgrades, certainly no "performance upgrades" on my engine (maybe next season!). Did I mention that I TUNED THE CARB? LOL I have done a LOT of fiddling with the carb, really happy with how she runs after I got the carb in the right ballpark. I am still fine tuning it, right now my low end ride is super smooth but top end is a little limited. I KNOW I had been going a LOT faster than I went today in the past because of the sound and feel of the ride, I had the carb tuned up for top speed earlier in the summer. Over the winter I am gonna source an aftermarket air filter and will tune the carb again in the spring, hope to get her back to hitting the upper 30's again next season...

Does it sound like it's gonna blow up at that speed? The engine has got to be revving at over 8000rpm.

Pilotgeek said:

Does it sound like it's gonna blow up at that speed? The engine has got to be revving at over 8000rpm.

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No it does not. I don't know how you determined how many RPM the motor is doing at that speed, or what the maximum RPM of the engine is, but it certainly doesn't sound like it is revving into any dangerous territory. Speeds in the low 30's are common for these bikes, lots of people routinely achieve these speeds. I have read people say they commute on their bike and spend most if the time at WOT running with traffic at these speeds with no problems.
I don't know what kind of setup you have on your bike, but if you mod'd it right away assuming you couldn't get these speeds with the stock parts you have made a wrong assumption, if you have not mod'd your bike and can't get speeds into the low to mid 30's then you have room for improvement if you do some fine tuning....

8000 is a high estimate, but it's nearing that with a 44t.
http://motorbicycling.com/f48/i-calculated-my-gearing-speed-25142.html

I could easily get low to mid 30's with my bike. I would use a 36t sprocket. I have about the same tweaks as you, but with an NT carb and a milled head. I have the torque and can max out my rpm's with the 40t. I just don't trust the frame and other components above 30. You'll notice my original argument is not about whether or not it's possible getting low to mid 30's, but the people who claim an out-of-the-box stock motor will hit 35-40.

Biknut and a few others around the forums have calculated what the RPM of the motor has to be for a given gear ratio. Maybe what sounds like a good rpm to you sounds too high to me. I have a full-bearing engine, and I'd rather not have one of them blow out at high rpms. The bushing engines are a little more tolerant of high rpms. If your engine has the power, why make it have to put up with higher rpm's than it needs to? I know my bike is running well, I deal with 2-strokes all the time in a snowmobile repair shop.

I have no problem with you getting your speeds. Obviously, you know engines and can tweak them to get that speed. But your engine is not stock in the sense I was originally talking about. Sure you have stock parts, but they're tuned and perfected. Bone-stock is basically take it out of the box and run it. And some are claiming 35-40mph bone-stock with a 44t sprocket. *Those* are the people I don't believe.