Power cutting off at high rpm

Karl Snarl

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Wouldn't that be the equivalent of putting back the cap?
No, soda can has a bigger opening than a stock exhaust. With the cap of, your running a bit lean from the sounds of it. An with it on, you could probably drop a few teeth on the back sprocket to help reduce, do not eliminate it though you want that extra fuel, the 4 stoking. A little 4 stroking on a 2 stroke will happen, it's just how these engines run. If you don't have a little, you are to lean and the life of the motor will be reduced. You may get 2000 miles out of it as it slowly wears away, but you could have gotten 5x that when the a/f mixture is correct. While yes slightly less power, but what's more important, the power for a short while, or the longevity of the engine. Only you can decide that, it's your ride. I would try messing with the needle a bit and if not, rejet the carb to suit the engines new needs without a cap.
 

Datboi

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No, soda can has a bigger opening than a stock exhaust. With the cap of, your running a bit lean from the sounds of it. An with it on, you could probably drop a few teeth on the back sprocket to help reduce, do not eliminate it though you want that extra fuel, the 4 stoking. A little 4 stroking on a 2 stroke will happen, it's just how these engines run. If you don't have a little, you are to lean and the life of the motor will be reduced. You may get 2000 miles out of it as it slowly wears away, but you could have gotten 5x that when the a/f mixture is correct. While yes slightly less power, but what's more important, the power for a short while, or the longevity of the engine. Only you can decide that, it's your ride. I would try messing with the needle a bit and if not, rejet the carb to suit the engines new needs without a cap.
Sorry I'm not getting this, you want me to cut the bottom of a soda can, and slide it on so the exhaust fumes come out from the top of the can (from the opening where you drink?)

If so, its the same size roughly as the hole in the original cap...

Perhaps y'all got bigger soda cans than we do here in the EU, i know you guys definitely have bigger soda bottles, 2l soda bottles aren't really a thing here.

Cant i just add holes to the original cap?

Make a hole, try, make another, see how it performs until i achieve what i like?
 

Datboi

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I just looked up the sound of 4 stroking.thats exactly what i have when im near top speed at full throttle
 

Karl Snarl

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I just looked up the sound of 4 stroking.thats exactly what i have when im near top speed at full throttle
Your good then, you can listen to some of these guys and jet leaner, but if it was me, I like my engines to last. Lean might be mean, but it sure wont last that long. My highest mileage engine has around 4500 on it. At full speed with no hill, I 4 stroke, an that is how a 2 stroke should act if you plan on keeping it a long while. At the most, I would drop the needle down a notch and call it good. You have to understand that a 2 stroke does not run like a 4 stroke engine does. That 4 stroking you are getting is the fuel needed to climb an incline or pull a load. When the load is not there, it will 4 stroke. That is just the beast of these engines. If you eliminate that extra fuel, you are now running lean, when you really need the extra fuel to keep the engine cool. I know a lot of you guys call all these engines junk and swear they break down all the time. I seem to never have a dead engine laying around, all mine just keep going and going. An they run with 4 stroking on the top end at full speed if I am on a flat, just how they should run when there is a light load.
 

Datboi

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Your good then, you can listen to some of these guys and jet leaner, but if it was me, I like my engines to last. Lean might be mean, but it sure wont last that long. My highest mileage engine has around 4500 on it. At full speed with no hill, I 4 stroke, an that is how a 2 stroke should act if you plan on keeping it a long while. At the most, I would drop the needle down a notch and call it good. You have to understand that a 2 stroke does not run like a 4 stroke engine does. That 4 stroking you are getting is the fuel needed to climb an incline or pull a load. When the load is not there, it will 4 stroke. That is just the beast of these engines. If you eliminate that extra fuel, you are now running lean, when you really need the extra fuel to keep the engine cool. I know a lot of you guys call all these engines junk and swear they break down all the time. I seem to never have a dead engine laying around, all mine just keep going and going. An they run with 4 stroking on the top end at full speed if I am on a flat, just how they should run when there is a light load.
thank you,

if this is caused by richness in the main jet, why does it not happen with the end cap on? opening up the exhaust SHOULD make everything leaner right? also why do i have so much more power with the cap off? i know 2 strokes an expansion chamber to increase compression, now i should have less compression (because of less backpressure) so less power but that's not the case

so there is no harm caused by prolonged full throttle 4 stroking? (expect the oblivious wear and heat that comes with keeping a 2 stroke at peak rpm)

would going leaner increase top speed or would it still top out at the same speed?

for tuning, is the plug-chop actually accurate? i see so many mixed thoughts about it. my ducati monster and bmw f650 are perfectly jetted (dyno) and the sparkplugs look very lean (pretty much completely white)

so i'm wondering how accurate it can really be, some say due to fuel additives and cleaners it's not reliable like it used to be back in the day.

also can a plug chop be done with a rich oil-gas mixture? i'm still using the recommended break-in period mix, i'm wondering if the extra oil would make the plug chop reading even more inaccurate.



sorry for all the questions!

i build this bike around 1-2 years ago and after using it for a while i just left it there with no time to work on it.

however i'm motivated to get back on this project.... i'm planning on making tons of improvements

disc breaks, saddle with shock absorber, spring-tensioned chain tensioner, and a bunch of other stuff

then perhaps i wanna work on performance a lil bit, what are the biggest performance mods on these engines(especially cheap ones, not planning to spend a lot as i trash this bike off-road and have tons of fun with it)?
 

Karl Snarl

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thank you,

if this is caused by richness in the main jet, why does it not happen with the end cap on? opening up the exhaust SHOULD make everything leaner right? also why do i have so much more power with the cap off? i know 2 strokes an expansion chamber to increase compression, now i should have less compression (because of less backpressure) so less power but that's not the case

so there is no harm caused by prolonged full throttle 4 stroking? (expect the oblivious wear and heat that comes with keeping a 2 stroke at peak rpm)

would going leaner increase top speed or would it still top out at the same speed?

for tuning, is the plug-chop actually accurate? i see so many mixed thoughts about it. my ducati monster and bmw f650 are perfectly jetted (dyno) and the sparkplugs look very lean (pretty much completely white)

so i'm wondering how accurate it can really be, some say due to fuel additives and cleaners it's not reliable like it used to be back in the day.

also can a plug chop be done with a rich oil-gas mixture? i'm still using the recommended break-in period mix, i'm wondering if the extra oil would make the plug chop reading even more inaccurate.



sorry for all the questions!

i build this bike around 1-2 years ago and after using it for a while i just left it there with no time to work on it.

however i'm motivated to get back on this project.... i'm planning on making tons of improvements

disc breaks, saddle with shock absorber, spring-tensioned chain tensioner, and a bunch of other stuff

then perhaps i wanna work on performance a lil bit, what are the biggest performance mods on these engines(especially cheap ones, not planning to spend a lot as i trash this bike off-road and have tons of fun with it)?
You are getting more power, because it is breathing better. You are not really looking for " back pressure", but an acoustic wave. The wave is what stuffs the fuel back into the chamber, adding to dynamic compression. When you took the pipe off, you reduced the " back pressure", allowing it to breathe better. Allowing more exhaust gases to escape and not to be stuffed back into the chamber, reducing the available fuel to burn. By opening it, its running better, because it can push those gases out, and stull draw in a good charge, because there is less stopping the fresh mix from bottle necking. You will have a lower dynamic compression, but with more fresh fuel, it helps to make more power.

Prolonged 4 stroking will just foul the plug and build up a bit of carbon. The engine will probably stop running from the fouled plug, long before any of the carbon become a problem in the cylinder.

Leaner doesn't mean more speed, you will still have the same top speed. Your speed is determined by your gearing for the most part. An that will not change if you have more power, you will just have more ability to climb inclines.

No one does a plug chop correctly anymore. It is called that, because we used to actually chop the plug in half to read it. Now people just look at the color on top for the most part. Which is only half the story.

Your ducati and beamer are 4 strokes, an most likely liquid cooled. A liquid cooled engine will never see temps an air cooled engine will see. The cooling system allows them to run leaner without damaging components, because it is the heat that kills it. The cooling system takes away the heat faster and more of it, than just blowing air across some fins.

Even with extra oil, you should still get a nice cocoa color. You are not trying to burn the oil, just the fuel. The oil exits as a high temp vapor and some liquid, carrying away carbon and debris from combustion. Extra oil will help make more power, by sealing the rings better and helping keep it cooler by reducing friction. As long as your fuel to air ratio is correct and the right plug temp range, your plug will still look good, unless you like to idle a lot, then it will foul out from all the extra oil.


Never be sorry for asking question, it's why we are here. We want you to learn, grow, and smile while riding your MB. So please, feel free to ask all the questions you need to get going and understand your engine. No one here will ever knock you for asking questions, it's a sign of being intelligent.
 

Datboi

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You are getting more power, because it is breathing better. You are not really looking for " back pressure", but an acoustic wave. The wave is what stuffs the fuel back into the chamber, adding to dynamic compression. When you took the pipe off, you reduced the " back pressure", allowing it to breathe better. Allowing more exhaust gases to escape and not to be stuffed back into the chamber, reducing the available fuel to burn. By opening it, its running better, because it can push those gases out, and stull draw in a good charge, because there is less stopping the fresh mix from bottle necking. You will have a lower dynamic compression, but with more fresh fuel, it helps to make more power.

Prolonged 4 stroking will just foul the plug and build up a bit of carbon. The engine will probably stop running from the fouled plug, long before any of the carbon become a problem in the cylinder.

Leaner doesn't mean more speed, you will still have the same top speed. Your speed is determined by your gearing for the most part. An that will not change if you have more power, you will just have more ability to climb inclines.

No one does a plug chop correctly anymore. It is called that, because we used to actually chop the plug in half to read it. Now people just look at the color on top for the most part. Which is only half the story.

Your ducati and beamer are 4 strokes, an most likely liquid cooled. A liquid cooled engine will never see temps an air cooled engine will see. The cooling system allows them to run leaner without damaging components, because it is the heat that kills it. The cooling system takes away the heat faster and more of it, than just blowing air across some fins.

Even with extra oil, you should still get a nice cocoa color. You are not trying to burn the oil, just the fuel. The oil exits as a high temp vapor and some liquid, carrying away carbon and debris from combustion. Extra oil will help make more power, by sealing the rings better and helping keep it cooler by reducing friction. As long as your fuel to oil ratio is correct and the right plug temp range, your plug will still look good, unless you like to idle a lot, then it will foul out from all the extra oil.


Never be sorry for asking question, it's why we are here. We want you to learn, grow, and smile while riding your MB. So please, feel free to ask all the questions you need to get going and understand your engine. No one here will ever knock you for asking questions, it's a sign of being intelligent.
the monster is air cooler, but i get your point, besides 4 strokes use oil to cool so running lean isn't nearly as much of an issue as on a 2, and i'll tell ya what with fuel prices right now, i'm running my carbed f650 lean for sure:ROFLMAO::ROFLMAO:

i knew people actually cut their plugs, but it tho you could still get a more or less accurate read not cutting it.

you think i can get a more or less reading by not cutting it? i'm guessing the "plug chop" is the easiest/most convinent way to go about tuning mixture on these engines?


i tho more oil reduced power! why do ppl run their mopeds with very very little oil on purpose? (like vespa's for example)
 

Karl Snarl

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the monster is air cooler, but i get your point, besides 4 strokes use oil to cool so running lean isn't nearly as much of an issue as on a 2, and i'll tell ya what with fuel prices right now, i'm running my carbed f650 lean for sure:ROFLMAO::ROFLMAO:

i knew people actually cut their plugs, but it tho you could still get a more or less accurate read not cutting it.

you think i can get a more or less reading by not cutting it? i'm guessing the "plug chop" is the easiest/most convinent way to go about tuning mixture on these engines?


i tho more oil reduced power! why do ppl run their mopeds with very very little oil on purpose? (like vespa's for example)
Besides cocoa, the plug strap says heat( should be in the middle to the curve of the top/flat part where the spark jumps too, the ring on the bottom of the threads say oil.


I have no idea why people would run a scooter lower on oil, maybe better materials, but if they jet correctly, more oil is a benifit to around 16:1, I recommend no more than 24:1 if you are not racing.
 

Chainlube

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The exhaust cap has a tube welded to it that extends up inside the muffler, by eliminating the cap with the soda can you get rid of one other path that the exhaust gases has to follow.
 
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