tuning small 2 stroke engines

flatyre

flatyre

Active Member
hey guys I need some advice on tuning my 150cc 2stroker. I'm still in the middle of the basic fabricating stage but for space reasons I need to work out what type of air filter I want now. I want to fit either a cone filter or a pancake job, but don't know how these will effect the bike. The original bike didn't have much power to begin with, and I'm hoping to modify the exhaust off something like an RD to fit the bike. (currently has a guzzi silencer, don't ask!) anyway I don't know all the science behind engines and hope some of you guys can help. Will I need to change the getting in the carb, and/or the mixture screws? is there a basic calculation used to work out cc x filter+jets+exhaust=improved performance? I don't expect to make any real power gains, its more to do with not sacrificing what little power I have to achieve the look I want, if that makes sence? cheers
 
2 strokes are much fun to play with and fairly easy to get more power from. we're talking about expansion exhausts, porting, reed valving,...

what bike are we talking about by the way?
 
flatyre said:
I need some advice on tuning my 150cc 2stroker.
Click to expand...

You have opened a can of worms with that request!

To do a good job with a two-stroke you need to have some understanding of the process. One of the best sources of information is Performance Tuning in Theory and Practice - Two Strokes by AG Bell. If you can't find a copy online or digitised, send me a PM and I can probably help out.

jungalist said:
what bike are we talking about by the way?
Click to expand...

As a wild guess, I would say it's a MZ TS150!

Crazy
 
You guessed it jungalist! 150 cc of pure comuter crap. I'll have a look for that info stroker crazy. Cheers guys
 
http://3cyl.com/mraxl/manuals/bell/performance-tuning-graham-bell.pdf

http://3cyl.com/mraxl/manuals/jennings/twostroketuner.htm

http://3cyl.com/mraxl/manuals/jennings/chambers.pdf


Happy reading! ;)

IMO start with a pipe, it will make the biggest power improvement without sacrificing too much bottom end, if you are still not satisfied, porting and bigger carbs but take it easy on the porting, a little goes along way. ;)
It's not too difficult to extract another 50% more power from an old 2 stroke.
 
Whatever level of modification you do, read this - also by Jennings:

http://www.strappe.com/plugs.html

A new well engineered pipe will provide more results than anything else as far as alterations go. All engine changes require a re-tune of sorts. Changing one thing requires reassessing everything else. Generally, there are always trade offs making changes. It is easy to get substantial power increases, but equally easy to have an unpleasant or even unusable machine. Especially on a small engine. You might be able to get 70% power increase, but all of it comes in at 9,000 rpm and the thing grenades if run past 9,500 rpm. Only fun for a short time and not very practical. Start with an expansion chamber and as large an air cleaner as possible. Adjust the jetting and timing accordingly. There is no especially practical formula to determine these things. It is cut and try and making changes based on evidence. Start with stock timing and 4 jet sizes bigger than stock, then follow Jennings's guide carefully. It works very reliably. Expect more power at high revs with less down low as a trade off, but most engines respond pretty favorably to this level of modification. Don't underestimate the importance of getting your 2 stroke timed and jetted properly. It takes a lot of time and dedication, and NOTHING will make as large a difference in how strong or reliable your engine can be. 2 strokes are incredibly sensitive to ignition timing compared to 4 stroke engines. Recommend you leave everything inside the engine alone, as it is very easy to greatly reduce engine lifespan, reliability and drivability. And those changes are permanent. good luck!
 
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