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2 Stroke Bicycle Engines & Kits 2 stroke engine kits need careful installation and setup, find out how from our professionals here!

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  #11  
Old 07-26-2010, 12:17 AM
jamrhein jamrhein is offline
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Default Re: are 2 stroke engine kits the same?

So far this is my 3rd bicycle motor kit. The first one was stolen with a set of bolt cutters, as it was locked up outside, and I never got to finish breaking in that motor, of which I paid $170.00 for including S & H. Although, even so in the short time I had it, I travelled probably 100 miles, and either the CDI or magneto failed, probably due to overheating of the motor. I bought this motor local, from Pirate Cycles, right here in Massachusetts. After replacing the blown electrical part, the motorbike was stolen.

The second motor, I bought from California from "Boy Go Fast" and I ran it over 20 mph during the break-in period, against the manufacturers recommendations for a short time, and noticed the motor wasn't breaking in properly, as the performance was starting to decrease noticably, so I filled the gastank with 16:1 2-stroke pre-mix, locked it by chaining it to a tree in my backyard, and figured I'd let in run of of a full tank of gas twice, so I could guarantee I didn't drive it over the recommended 20 mph to finish off the break-in period. The motor ran thru about half the tank of gas before it stopped running for some reason. I restarted the motor, and tried to get it to run thru the other half a tank of gas. It died again before running out of gas, and I wasn't able to get it to run since. It looked identical to the motor I bought from Pirate Cycles, made in China, as well, so I figured it must be a common problem and suspected the same ignition electrical problem. Since there was no repair manual available for purchase, with the ohms specifications, and/or other testing procedures for the CDI box and the Magneto coil, I purchased both and installed them, along with a new spark plug although the motor still wouldn't start, even with a spark present.
I tried squirting ether starting fluid in the carburetor. I also took out the spark plug, and squirted a small amount of 2-stroke oil into the spark plug hole, to seal the rings, in case it had too low of a compression to try to get it to start in this manner, which always works, but didn't in this case either. It should have started in one of these manners, althogh it didn't. The compression tested around 60 psi, which seemed low, but should have started anyway. The motor wasn't completely broken-in yet, although that could have been normal at that stage; again with no availability of a repair manual, I had no way of checking it against manufacturers specifications.
So I gave up on this motor, and ordered a new motor only, not the whole kit.
I ran this motor meticulouly under 20 mph for a 20-mile round trip after I first installed it. It seemed to be running kind of hot after the first 10 miles, so I turned around, and drove it home trying not to drive it anymore than possible 'til I figured out the problem.
I had a 16:1 mix of gas in the tank, although when I looked at the clear fuel line, there was no hint of color due to the color of the 2-stroke oil mix passing thru it, and I figured somebody around here may have dumped some straight gas unmixed into the tank leftover from mowing the lawn, thinking they were doing me a favor, not realizing it requires a 2-stroke mix; but the gas in the tank did have a hue of green color in it, obviousy being in such a larger concentration compared to the thin fuel line.
Also, I was using some cheap 2-stroke oil, Itasca, of which I never heard of, that I bought from a supermarket instead of an auto parts or hardware store; and it's possible the cheap oil could have contributed to the problem, but I'm not sure.
I added some more 2-stroke oil and gas to the tank to bring the gas mix down to around 12:1, which helped, a bit, but the motor developed a very noticable piston rap, over the next few days, meaning the piston to cylinder clearance was so excessive, the piston was actually slapping around in there instead of just sliding up & down, as it should; which causes the piston knock or rapping sound, and also causes premature destruction of the motor if not fixed.
So I decided to tear open the previous motor I still had laying around, the one I gave up one, and measured the piston to cylinder clearance in 6 different locations; of which varied from .004 inches to .015 inches, which is clearly unacceptable. Normal clearance for similar motors is .001 to .002, although, again, no manufacturer's specs available for comparison.
I emailed customer support and they were guessing the catalytic converter, which is an upgrade used in my kit from the non-upgrade standard muffler, may have been causing the motor to overheat.
It seems mostly unlikey to me, since the cat. converter is a straight-thru design; in that there is no restriction of the flow of exhaust gases as it passes thru it. And since it's long, I would imagine it would act as a heat sink, drawing heat away from the motor instead of back to it. Although, it was odd that I noticed the cat. converter didn't smoke one bit on this new motor, as it did on the previous motor, which is weird and somewhat seems like it seemingly could be running so hot that it's burning up all residual unburned 2-stroke oil-in the form of smoke, in the similar manner that it does to unburned gas, as it was made to do.

These motors don't seem too reliable, although maybe they are if they are broken-in properly, of which I haven't be able to get to that point with these first three.

Has anybody noticed such similar problems? Are there much more reliable motors available that break-in easy and don't have this problem and have some type of longevity to them? All three of these were the 66/80cc made in China motors.
I'd like to stick to the highest displacement unless the smaller, say 48 or 49cc motors have the same power. And is there a better way to break-in these motors, which will run fine thereafter for a good longevity?
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  #12  
Old 07-26-2010, 03:35 AM
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GearNut GearNut is offline
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Default Re: are 2 stroke engine kits the same?

Break in the engine with 20:1 pre mix ratio. Use a quality pre mix oil made for motorcycles. Opti2, Amsoil, or Maxima brands come to mind.
Do NOT use pre mix oil made for outboard engines they are water cooled and have different requirements than air cooled engines.
Do not be afraid to go over 20 mph for SHORT bursts, like 100 yards or less, once in a great while.
It will actually help break in the piston rings better and faster.

Ride the engine for 15 minutes or so and then let it cool down completely, a 1/2 hour minimum.
I would ride it for 5 minutes and let it cool down. Then 10 minutes and cool down. Then 15 minutes and cool down, ect.
Long trips on an new engine will kill them if you do not let them cool down frequently.
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  #13  
Old 07-26-2010, 05:58 AM
Bikeguy Joe Bikeguy Joe is offline
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Default Re: are 2 stroke engine kits the same?

16:1? 12:1?!? That can cause a lean condition (fuel to air) and can cause other problems as well.

24:1 is really too much oil, but I recommend running a tank at 24:1 then going to 32:1 or even 40:1 for the next couple hundred miles. Always check the plug when you make ANY changes and see what the engine is doing mixture-wise.
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  #14  
Old 07-26-2010, 08:54 AM
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stuartracing stuartracing is offline
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Default Re: are 2 stroke engine kits the same?

What is the deal with these people who think that breaking in a motor without actually riding it is going to work....Met one dude who strung his bike up in a tree and let it run through a tank of gas to break it in.....It don`t work that way....Ya have to put a load on it.....Ride it brother....I`ve had 4 of these and to tell ya the truth,I never worry about breaking it in....I just take It a little easy at first to get it dialed in and then go out and have fun with it....My motors all worked great.....
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  #15  
Old 07-26-2010, 09:52 AM
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Default Re: are 2 stroke engine kits the same?

The rings don't seat in proper without a load.
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  #16  
Old 07-26-2010, 03:36 PM
jamrhein jamrhein is offline
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Default Re: are 2 stroke engine kits the same?

Quote:
Originally Posted by Bikeguy Joe View Post
16:1? 12:1?!? That can cause a lean condition (fuel to air) and can cause other problems as well.

24:1 is really too much oil, but I recommend running a tank at 24:1 then going to 32:1 or even 40:1 for the next couple hundred miles. Always check the plug when you make ANY changes and see what the engine is doing mixture-wise.
The recommended mixture of gas to 2-stroke oil by the manufacturer is 16:1 during the break-in period, to ensure the internal parts of the motor are lubricated properly. A higher ratio of fuel to gas such as 24:1 or 32:1 means the new engine is getting less oil to lubricate the new motor, and more of the chance of ruining the new motor due to lack of adequate lubrication.
Not only does oil lubricate the motor, it also cools the motor, of which is an air-cooled motor, and needs all the cooling it can get during break-in, unlike water-cooled motors, as there is a lot more friction inside the cylinder, until the cylinder reaches a slippery, shiny surface, with less friction, and thus doesn't need the extra lubrication and cooling as a non-broken in, new motor, which hasn't achieved that slippery/shiny surface, which can run on less oil, for more horsepower.
A lean gas to air condition is controlled by the carburetor, not the gas to oil mixture.
Some carburetors have an air mixture adjustment screw for controlling the richness/leanness of fuel/air mixture, although mine doesn't.
Other than that, the only other ways of controlling the air/fuel mixture are to change the size of the tapered needle jet, which controls the air/fuel mixture during mid-throttle use; and change the main jet size, which controls the air/fuel mixture during full throttle use.
Also the choke can be applied partially during running application, to make the air/fuel mixture richer, which in turn will also allow more gas/fuel mixture to enter the motor in relation to the air entering it, and will help cool and lubricate a new motor for break-in purposes.
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  #17  
Old 07-26-2010, 07:27 PM
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Default Re: are 2 stroke engine kits the same?

Given the carburetor jetting remains constant, not altered, a 16:1 ratio will run leaner than a 32:1 ratio due to the fact that the oil mixed with the gas affects it's specific gravity. In other words 16:1 weighs more than 32:1.
At any throttle position, 16:1 would allow less fuel through the same jet than 32:1.

16:1 can be lean and 32:1 can be rich if the jetting is not set appropriately for the fuel/ oil ratio being burned.
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  #18  
Old 07-26-2010, 07:36 PM
Bikeguy Joe Bikeguy Joe is offline
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Default Re: are 2 stroke engine kits the same?

Quote:
Originally Posted by jamrhein View Post
The recommended mixture of gas to 2-stroke oil by the manufacturer is 16:1 during the break-in period, to ensure the internal parts of the motor are lubricated properly. A higher ratio of fuel to gas such as 24:1 or 32:1 means the new engine is getting less oil to lubricate the new motor, and more of the chance of ruining the new motor due to lack of adequate lubrication.
Not only does oil lubricate the motor, it also cools the motor, of which is an air-cooled motor, and needs all the cooling it can get during break-in, unlike water-cooled motors, as there is a lot more friction inside the cylinder, until the cylinder reaches a slippery, shiny surface, with less friction, and thus doesn't need the extra lubrication and cooling as a non-broken in, new motor, which hasn't achieved that slippery/shiny surface, which can run on less oil, for more horsepower.
A lean gas to air condition is controlled by the carburetor, not the gas to oil mixture.
Some carburetors have an air mixture adjustment screw for controlling the richness/leanness of fuel/air mixture, although mine doesn't.
Other than that, the only other ways of controlling the air/fuel mixture are to change the size of the tapered needle jet, which controls the air/fuel mixture during mid-throttle use; and change the main jet size, which controls the air/fuel mixture during full throttle use.
Also the choke can be applied partially during running application, to make the air/fuel mixture richer, which in turn will also allow more gas/fuel mixture to enter the motor in relation to the air entering it, and will help cool and lubricate a new motor for break-in purposes.
There is so much wrong with the above statement, I don't even know where to begin.....so I won't.

Apparently, you read the instructions that come with some kits, in which case you should have known better than to believe part of them (16:1).
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  #19  
Old 07-26-2010, 07:39 PM
Bikeguy Joe Bikeguy Joe is offline
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Default Re: are 2 stroke engine kits the same?

GearNut is correct.
So is Goat Herder.
jamrhein....not so much.
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  #20  
Old 08-01-2010, 11:07 AM
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talltommy46 talltommy46 is offline
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Default Re: are 2 stroke engine kits the same?

I'm a new guy on these pages.. But, just had to add my 2c on this topic... Bikeguy Joe, and the others are absolutely right! No question! I have 30yrs of racing dirtbikes under my belt, MX, Offroad, and some RR too.. 90% on 2stroke engines.. I can jet a 2stroke by the feel sound and smell.. Have a stable of vintage racebikes, most run at 12-13.5 comp ratios and VP Racegas at 50:1 mix... Mmmmmm, love the smell of premix in the morning! Yes, go with the 24:1 mix for breakin and 30:1 for reg use... After ya get it fine tuned(jetted), then move up to 40:1, and rejet again... Remember every mod, will need a rejet..
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