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How to make a 2 stroke more like a 4 stroke?

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I know I'm going to get weird looks for this post but hear me out for a bit. I'm 5'5'' and weigh 130 lbs. I have ridden both 125 2 strokes and 250f's. Loved how light the 125 felt everywhere felt like a bike. I never was very fast on it though. Then I went to a 250f and it made a night and day difference. The only problem I had was it was about 20-40 lbs more than my 125 and because of the rotational mass It felt like a hog everywhere. Now I'm looking to buy a bike again. I will be doing lots of technical stuff (rocks riding, steep stuff, hard packed etc.) and some motocross tracks, out here though the tracks bake and get super hard packed. That is the reason I want to go back to a 4 stroke, not having that peak of power allows me to stay on it without sliding out too much. I just hate the weight. So I'm considering the 2014 yz250f because on a 4 stroke I want efi.

 

Here is where I want to know is there ways to make the bike as close to a 4 stroke as possible? I know a fww will make a difference but how big of a difference? I'm considering two bikes, the 2012-14 ktm 250sx and ktm 200xc. It seems like the 200 would be my best bet but if it still has too much of a spike in power where i will lose traction in the hard packed stuff then I may have to go 4 stroke. So what other mods can be done to get as close as possible?

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No 125 is going to have the power delivery like any 4 stroke. A 250 or 300 2t will pull more like a 250f, but nothing like a 450f.

 

That being said, I ride a 2001 CR125, and these were pitiful from the factory. I definitely have learned a lot about waking up a 2 stroke in the past 3 years building it. A 38mm carb (many 125s have one stock), aftermarket reeds, and proper jetting made some of the most noticeable changes. I definitely prefer the power delivery of my 125 over a 4 stroke, its just my preference. And I'm not biased, I also owned a yz250f on top of my 125, I sold the 250f because I never wanted to ride it.

 

Bottom line, if your looking for low end tractor like pull you need to buy a 4 stroke. The newer hondas are small and light, but don't expect to own a 2 stroke that feels like a 4 stroke, they are just different machines.

 

Hope this helps.

Edited by dan2581
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Yes it can be done. Kind of.

2t Trials bikes are kind of this way.

High high compression. And a lowered exhaust port would get you close.

A custom pipe would get you even closer.

and a enormous flywheel weight will get you the rest of the way.

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No 125 is going to have the power delivery like any 4 stroke. A 250 or 300 2t will pull more like a 250f, but nothing like a 450f.

 

That being said, I ride a 2001 CR125, and these were pitiful from the factory. I definitely have learned a lot about waking up a 2 stroke in the past 3 years building it. A 38mm carb (many 125s have one stock), aftermarket reeds, and proper jetting made some of the most noticeable changes. I definitely prefer the power delivery of my 125 over a 4 stroke, its just my preference. And I'm not biased, I also owned a yz250f on top of my 125, I sold the 250f because I never wanted to ride it.

 

Bottom line, if your looking for low end tractor like pull you need to buy a 4 stroke. The newer hondas are small and light, but don't expect to own a 2 stroke that feels like a 4 stroke, they are just different machines.

 

Hope this helps.

im not looking at a 125, i know it would be impossible on one. I was talking 250 or 200

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You will like the KTM 200. Awesome bikes. Add an autoclutch and dialing the power valve back should get you going in the right direction. Also, make sure your suspension is setup for your weight and take the time to dial it in.

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Yes it can be done. Kind of.

2t Trials bikes are kind of this way.

High high compression. And a lowered exhaust port would get you close.

A custom pipe would get you even closer.

and a enormous flywheel weight will get you the rest of the way.

so doing all of this wouldnt that hinder reliability and such? If it does would it make it less reliable than the 250f as in more rebuilds with less hours costing about what doing the top end on a 250f every 60 hours would cost me? so in reality it wouldnt even be worth it?

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You will like the KTM 200. Awesome bikes. Add an autoclutch and dialing the power valve back should get you going in the right direction. Also, make sure your suspension is setup for your weight and take the time to dial it in.

suspension is always my number 1 mod; at 130 lbs stock suspension just doesnt work for me. it makes a world of a difference when i get it sent out.

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you know,

it doesn't have to be. less reliable, my buddy runs his trials bike on 91 some times but, sometimes it will ping, and sometimes he runs it on 50/50 pump/fuel

the high compression ratio will help the power before it comes on the pipe making it smoother when it does and adding some tractorabillity.

 

 

i dont think it has to be less reliable, maybe the higher compression will be harder on the piston and rings but i dont see it being any worse that someone who pins/revs the shit out of the bike

but if you do it yourself,

a top end on a 2 stroke costs nothing compared to a 4 stroke.

 

what id do.

look at some port maps for trials bikes. and use a timing calculator to come up with the degrees of duration (this will vary with rod ratio)

look at the port timing on your bike calculate the duration. you want to get the exhaust duration down between the mx and trials spec

 

you may be able to machine the amount necessary right off the bottom of the cylinder and stack head gaskets,

or, have copper piece made and use it as a center, and put the top and bottom pieces from the oem mls gasket on it.

or if possible you could live with the resulting squish clearance

or the cylinder head may even need to be re machined

the transfers should be raised back up to O.E.M. height or possibly slightly higher

something not so nice here the bottom of you transfers are now lower than the top of the piston >:(

 

get a rad valve or v force (im not sure which ones better any more)

 

figure out just how high you can raise the compression ratio

 

find someone who really knows what they are doing and what you are doing to build you a pipe

 

get the heaviest flywheel anyone has ever put on the bike.

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Forget about all that trials bike crap. ADD A REKLUSE AUTO CLUTCH!!!! I put one in my RM 250, and it works a lot like a 4 stroke now. Click it into 2nd, or 3rd and pretty much leave it there.Pretty much climbs anything, can tractor through some nasty shiit, and powers up whenever you need it

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you know,

it doesn't have to be. less reliable, my buddy runs his trials bike on 91 some times but, sometimes it will ping, and sometimes he runs it on 50/50 pump/fuel

the high compression ratio will help the power before it comes on the pipe making it smoother when it does and adding some tractorabillity.

 

 

i dont think it has to be less reliable, maybe the higher compression will be harder on the piston and rings but i dont see it being any worse that someone who pins/revs the shit out of the bike

but if you do it yourself,

a top end on a 2 stroke costs nothing compared to a 4 stroke.

 

what id do.

look at some port maps for trials bikes. and use a timing calculator to come up with the degrees of duration (this will vary with rod ratio)

look at the port timing on your bike calculate the duration. you want to get the exhaust duration down between the mx and trials spec

 

you may be able to machine the amount necessary right off the bottom of the cylinder and stack head gaskets,

or, have copper piece made and use it as a center, and put the top and bottom pieces from the oem mls gasket on it.

or if possible you could live with the resulting squish clearance

or the cylinder head may even need to be re machined

the transfers should be raised back up to O.E.M. height or possibly slightly higher

something not so nice here the bottom of you transfers are now lower than the top of the piston > :(

 

get a rad valve or v force (im not sure which ones better any more)

 

figure out just how high you can raise the compression ratio

 

find someone who really knows what they are doing and what you are doing to build you a pipe

 

get the heaviest flywheel anyone has ever put on the bike.

Pretty much sums it up, I would just add it doesn't need "high high" compression as bumping msv with the correct designed head helps a lot. Just found the higher the compression ratio the shorter the crank big end bearing life. Although I wish I would have been using the Motul 800 back in the supermini days.

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Pull the head, put some valves in the cylinder, replace head, kickstart the bike as hard as you can, then pull out your wallet.

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Any 200+ 2 stroke can be tamed down to be a fantastic all around bike. Almost nothing you do to mellow out a 2 stroke takes away any of the fun.

 

Add flywheel weight, g2 throttle tamer, on some motocross 2 strokes retard the timing slightly and have the suspension setup for you. Stock pipes have great all over power on most bikes, so start with stock then add a pipe when you feel you need some more power.  

 

A kdx 200, ktm 200, 300, or yz250 are all incredible off road bikes that can handle all the riding you described when setup to do so. A 125 can be better, but they are much more tempermental engines and only make really good power high up in the rpm. a 200 or larger will have more grunt in the bottom to help in the technical sections as well as the hp to pull the high rpm for the occasional motocross track

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Why would you want to make your bike slow and boring?

 

 

:smirk:

Haha ya I've been told, but it's no fun trying to get traction on hard packed stuff when the rear wheel is just spinning!

 

you know,

it doesn't have to be. less reliable, my buddy runs his trials bike on 91 some times but, sometimes it will ping, and sometimes he runs it on 50/50 pump/fuel

the high compression ratio will help the power before it comes on the pipe making it smoother when it does and adding some tractorabillity.

 

 

i dont think it has to be less reliable, maybe the higher compression will be harder on the piston and rings but i dont see it being any worse that someone who pins/revs the shit out of the bike

but if you do it yourself,

a top end on a 2 stroke costs nothing compared to a 4 stroke.

 

what id do.

look at some port maps for trials bikes. and use a timing calculator to come up with the degrees of duration (this will vary with rod ratio)

look at the port timing on your bike calculate the duration. you want to get the exhaust duration down between the mx and trials spec

 

you may be able to machine the amount necessary right off the bottom of the cylinder and stack head gaskets,

or, have copper piece made and use it as a center, and put the top and bottom pieces from the oem mls gasket on it.

or if possible you could live with the resulting squish clearance

or the cylinder head may even need to be re machined

the transfers should be raised back up to O.E.M. height or possibly slightly higher

something not so nice here the bottom of you transfers are now lower than the top of the piston > :(

 

get a rad valve or v force (im not sure which ones better any more)

 

figure out just how high you can raise the compression ratio

 

find someone who really knows what they are doing and what you are doing to build you a pipe

 

get the heaviest flywheel anyone has ever put on the bike.

Thanks man I appreciate the advice!

 

Forget about all that trials bike crap. ADD A REKLUSE AUTO CLUTCH!!!! I put one in my RM 250, and it works a lot like a 4 stroke now. Click it into 2nd, or 3rd and pretty much leave it there.Pretty much climbs anything, can tractor through some nasty shiit, and powers up whenever you need it

I've always wanted to test a bike with a rekluse, how are you liking it? 

Any 200+ 2 stroke can be tamed down to be a fantastic all around bike. Almost nothing you do to mellow out a 2 stroke takes away any of the fun.

 

Add flywheel weight, g2 throttle tamer, on some motocross 2 strokes retard the timing slightly and have the suspension setup for you. Stock pipes have great all over power on most bikes, so start with stock then add a pipe when you feel you need some more power.  

 

A kdx 200, ktm 200, 300, or yz250 are all incredible off road bikes that can handle all the riding you described when setup to do so. A 125 can be better, but they are much more tempermental engines and only make really good power high up in the rpm. a 200 or larger will have more grunt in the bottom to help in the technical sections as well as the hp to pull the high rpm for the occasional motocross track

thanks for the advice!

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Why would you want to make your bike slow and boring?

 

 

:smirk:

I was thinking this very thing as i was reading through this , Buy a cr500 and take the brakes off  :ride:

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With your size, a KTM 200 XC will take you anywhere you wanna go, especially for hard enduro stuff.  But be warned, you won't like it at all on a motocross track because of the suspension.  I refuse to take my KTM to a motocross track.. did that last summer and looked/felt like a goon.  Had no confidence if my wheels left the ground lol.

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On a ktm 200 xc you dont need to do the porting thing. Its already done right from the factory. This bikes find more traction than 4 st. On the 200 you have also the option for a flywheel. This and jetting are the only things you need.

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No 125 is going to have the power delivery like any 4 stroke. A 250 or 300 2t will pull more like a 250f, but nothing like a 450f.

That being said, I ride a 2001 CR125, and these were pitiful from the factory. I definitely have learned a lot about waking up a 2 stroke in the past 3 years building it. A 38mm carb (many 125s have one stock), aftermarket reeds, and proper jetting made some of the most noticeable changes. I definitely prefer the power delivery of my 125 over a 4 stroke, its just my preference. And I'm not biased, I also owned a yz250f on top of my 125, I sold the 250f because I never wanted to ride it.

Bottom line, if your looking for low end tractor like pull you need to buy a 4 stroke. The newer hondas are small and light, but don't expect to own a 2 stroke that feels like a 4 stroke, they are just different machines.

Hope this helps.

Good advice ;) except for the part where you said a 2T 300 pulls nothing like a 450. Ever been on a freight train that can wheelie? The last time a crf450 pulled along side of me it got eaten...

Edited by Fattonz
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Good advice ;) except for the part where you said a 2T 300 pulls nothing like a 450. Ever been on a freight train that can wheelie? The last time a crf450 pulled along side of me it got eaten...

 

I strictly meant power delivery. Obviously 300s are fast as hell, same goes for a 500 2t. For the most part with a 2 stroke its always gonna pull hard up top, the larger bores do have insane low end for a 2t, but not the same feeling as cracking the throttle on a 450 and it pulls like crazy. In my experience 450s pull really hard everywhere (minus WOT), but its not like a 2t when you hold it wide open and it just keeps going faster and faster until you top out in that gear.

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