2 stroke technique

Did a super quick google search the other day and landed on an old thumpertalk thread. It had some pretty good info. Maybe i can go find it again. I learned 2 main things. 

1. Consistent speed on some 2 stroke motors can be harmful. Because you will be at a high RPM but with low throttle input. Which means low lubrication. Its a valid point. You could be screaming 5th gear but only 1/2 throttle to maintain it. 

2. The RPM you ride at will determine jetting. At high RPM the gasoline and oil do not have much time to attach to the metal. So you have to run a much richer mix. It was a foreign dude with bad spelling who made a really long post. That dude taught me a bunch. Could tell he knew his stuff. 

 
Correctly jetted you can pin it.

if you can’t it was not correctly jetted

49 cc ported race engines running 13000 rpm pinned 

running one L shaped piston ring

The more cc’s the easier  it is to get it right

Btw Bonneville 49 cc speed record 134 mph

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This post is fun to read. 

.......

A properly jetted 2/ with the proper oil mix should be able to run indefintely at high-rpm. And a 2/ engine will functionally see much less fuel mix at high-rpm, not more. The important factor is not the amount of fule you may be pumping thru the engine, but the amount of contact time that that fuel mix has with the moving parts it needs to lubricate. While you may indeed dramatically increase fuel consumption and therefore believe you are putting more lubricant in the engien, the fact is that at high rpm, that fule mix is transitting thru the engien so fast that it has little time to deposit the needed lubrication on the moving parts.

That's one of the reasons there is no set-in-stone oil ration for 2-stroke motors. It is all related to rpm/piston speed. The fuel/oil requirements for a 125cc GP road race engien capable of sunning over 15,000rpm and never dropping below 11-12,000 rpm is going to be entirelly different than, say a 250cc trials bike that spends most of its time below 4000 rpm. Its also why an 85/125 dirt bike needs a higher oil ratio than does a 250/500 dirt bike, though ridden on the same track. Its about the rpm. The amount of time the fuel mix spends traveling thru the motor at 3000 rpm allows for a greater contact time and hence more oil depostion than that same engien running at 12,000rpm.

THrottle position has little to do with it, so long as each portion of the metering system is properly adjusted/jetted. The throttle position realy only matters in relation to the corresponding rpm it produces. If an engine has the fuel mix ratio blended for sustained high-rpm flat-out running, than running it at a partial throttle at a lower rpm is going to increase your changes plug fouling, gumming up a ring, etc, though with modern oils, they are pretty tolerant of being run with too much oil for a given rpm range. That's the problem with pre-mix fuel ratios, it is one set ration that you are running thru that engines at all rpms. You need to determien your pre-mix ration based on engein size, type of use , and rpm range that the engien spend most of time in. A CR125 being ridden on the trails doesn't have the same pre-mix needs as a CR125 flattracker.

SO as long as you preperly jet the 2-cycle and run the proper pre-mix ration, sustained flat out full throttle running could be kept up indefintely.

Try reading up on a fellow named Gordon Jennings and some of his works.

 
Having had more 2 strokes than I can even count over the years I never really read that much into it. 2 Cycle engine s are so simple, inexpensive and easy to fix/rebuild. I'd just ride them how I wanted to. Fixed whatever broke. Replaced broken parts with better stronger parts when possible. A blown up/burned up 2 cycle engine was always a great excuse to make improvements and more power. My fav has to be 250 Hondas. They were so easy to improve on and make loads more power. 

 
Kevin said:
impropper oil ratios or wrong jetting is what causes failures typically not high rpm specifically. thats just when you happen to find out theres an issue since the oil ratio and jetting are more critical at high rpms.

look at other 2 stroke engines like weed eaters, outboard boat engines.. which i have a 2 stroke outboard on my eliminator daytona and i run that thing pinned for miles at a time when i head up river to topock.
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Agree. They can be held wide open. It’s about tuning 

 
Crusty said:
Two-stroke motors are not meant to be revved at constant high RPMs. 
 

On the gas off the gas on the gas off the gas… and constantly shifting gears to hit those peak RPMs.
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Sorry bruh, this is an incorrect statement... If built correctly you can pin it to win it everywhere you go

 
On a properly jetted/ tuned 2-stroke you can duct tape the throttle wide open and just use the clutch and have zero issues. I wouldn't recommend it but you could

To lean and it will go boom

To rich it will bog down and fall off the pipe..

If you hurt yours you need to figure out why and what you hurt.

 
So, can of worms time....

In the dunes, what's everyone run oil mixture wise?  Failures/issues?  I'm generally at 40:1, which lines up with the label on Motul 710 (25-50:1) or Motul 800 (25-33:1 for racing, decrease to 40:1 for "normal use") that I run.  Zero issues/failures, but not like we're running the bajeezus out of these...  I tried 32:1, but was getting clouds of oil smoke and dribbling out of the tailpipe, so pretty sure that's a bit excessive for our riding.   40:1 still needs the plug cleaned every trip on the daughter's Eton 90, but since I'm not mixing separate cans for every bike, it'll do.  

What I hate is some oil companies say to only use manufacturer-specified instead of what they engineered it for (looking at you Maxima).  Yeah, I'm not running 20:1.

 
Rockwood said:
So, can of worms time....

In the dunes, what's everyone run oil mixture wise?  Failures/issues?  I'm generally at 40:1, which lines up with the label on Motul 710 (25-50:1) or Motul 800 (25-33:1 for racing, decrease to 40:1 for "normal use") that I run.  Zero issues/failures, but not like we're running the bajeezus out of these...  I tried 32:1, but was getting clouds of oil smoke and dribbling out of the tailpipe, so pretty sure that's a bit excessive for our riding.   40:1 still needs the plug cleaned every trip on the daughter's Eton 90, but since I'm not mixing separate cans for every bike, it'll do.  

What I hate is some oil companies say to only use manufacturer-specified instead of what they engineered it for (looking at you Maxima).  Yeah, I'm not running 20:1.
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40:1 is a good mixture.

20:1 is too lean of a fuel mixture, yes plenty of lubrication but not enough fuel.

If your two smoke is set up correctly, pin it and have fun.

 
Cookie said:
40:1 is a good mixture.

20:1 is too lean of a fuel mixture, yes plenty of lubrication but not enough fuel.

If your two smoke is set up correctly, pin it and have fun.
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Agree.  More of a jab at some of the oil companies out there.  1981 ATC 250R manual says 20:1 pre-mix, which is just plain stupid with modern oils. :biggrin:

 
Orange_R said:
Sorry bruh, this is an incorrect statement... If built correctly you can pin it to win it everywhere you go
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Yes, that has been clarified here :lol:    ....I think my Dad was just trying to avoid messing with the jetting or me hurting myself... :lmao:

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Cookie said:
40:1 is a good mixture.

20:1 is too lean of a fuel mixture, yes plenty of lubrication but not enough fuel.

If your two smoke is set up correctly, pin it and have fun.
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I always ran 32:1 with Castor/C12 or Sunoco Purple. They always ran sooooo good :lol:  

 
Rockwood said:
So, can of worms time....

In the dunes, what's everyone run oil mixture wise?  Failures/issues?  I'm generally at 40:1, which lines up with the label on Motul 710 (25-50:1) or Motul 800 (25-33:1 for racing, decrease to 40:1 for "normal use") that I run.  Zero issues/failures, but not like we're running the bajeezus out of these...  I tried 32:1, but was getting clouds of oil smoke and dribbling out of the tailpipe, so pretty sure that's a bit excessive for our riding.   40:1 still needs the plug cleaned every trip on the daughter's Eton 90, but since I'm not mixing separate cans for every bike, it'll do.  

What I hate is some oil companies say to only use manufacturer-specified instead of what they engineered it for (looking at you Maxima).  Yeah, I'm not running 20:1.
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All my 2 strokes are all 40-1 mixed if they are jetted for that mix they run great never fouled any plugs unless i was jetted rich.

 
77charger said:
All my 2 strokes are all 40-1 mixed if they are jetted for that mix they run great never fouled any plugs unless i was jetted rich.
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Daughter tends to let it idle for long periods, not much I can do with the mix to fix that. :biggrin:

 
It warms the cockles of my heart when I see a little kid running Castor .   There is hope….
 

Cr500.  40-1   Banshee 35-1  seems to work well  

I really like Amsoil burns very clean.

It was developed to help prevent carbon buildup and seizing of power valves

When I pull a head off I am always amazed how clean the piston is and no signs of poor lubrication anywhere.

The bottle recommends up to  50-1 that scares me a bit.

good stuff

DE3BDDDE-37B7-4015-B642-D46791712883.jpeg

 
All of my 2 smokes were 32:1. I used to run Yamalube but then switched to SuperM. My step dad ran Golden Spectro but I was never a big fan.

 
I read Interceptor is more for cold weather riding. Looks like it has a snowmobile on the bottle. Was going to try Dominator. 

Anyone have more info about them? I agree doing 50:1 is hard mentally. Most likely do 42:1. Always ran yamalube at 40:1.

 
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