mini-stroke advantages

[elitedio]

Fortunately these little engines don't run much below half throttle. Not sure where the article was plucked from. If you change the main jet you will change the upper range from well below the 3/4 mark. There is overlap that can make or break your day.

If you are running an expansion chamber you will have to have some too rich conditions. The pipe causes the mixture to vary depending on the rpm separate from the throttle position.

The two stroke air cooled engine is in great part fuel cooled. Having lean jetting is not an option. Having even the fastest jetting is what is needed depending on the application, something a bit richer will help the engine live longer.

I am running the 28oko and set mine up so that it four stroked on full throttle then leaned it 5 at a time till it carburated fairly clean.

The more that I know about jetting the more I realize that I don't know.

[Wheelman-111]

Greetings:

Yup, it's an awful lot of Trial-and-Error, and pulling the carb off several times a day can be a PITA. I drop the bowl fuel back into the tank, then take the carb into the privacy of the Boudoir for Ministrations. When the error is rich, no harm. Be careful of dropping more than one size at a time. You could overshoot, misinterpret the engine's raspiness for four-stroking, and the next size drop will be the last. Shoot for 125 compression and no more. From Someone Who Now Knows...

Now You Know...

F4PMP3.jpg (213.85 KiB) Viewed 2299 times

Funny how it's right where the plug sits. Hmmm...

[Fishman43]

What is four-stroking when tuning the jets?

[Wheelman-111]

Greetings:

"Four-stroking" is the characteristic sound made by a 2-stroke that's only firing every other stroke - hence, the name. Instead of a smooth "Hummmm", it blubbers. The mixture has to be way rich (or occasionally WAy, WAY Lean...) for it to happen.

[custom_x]

how do you get rid of 4 stroking? my dio at full throttle with 28mm carb bogs out when i return it to idle then back to full,what the is my problem ?is that four stroking .what can i do to fix this.jet are 142 main 58pilot

[evilone]

I don't know your complete setup but them jets sound a little on the high side for a 28mm oko.

I've been going throught the same thing on my build, someone recommended a 145 main and it was way too much, then bakaracer recommended me to start at a 138 main with the 52 pilot. Last summer i ran a 55 pilot and 138 main but have a different setup now. You can start there and go up on the main till it does 4-stroke then drop back down. I personally trust plug chops (the 1mm ring at base of porcelain) over running rich.

[elite_dub]

"Four stroking" means your air to fuel ratio is too rich.
Four stroking is this >>.. when you near top speed the engine goes from a smooth high pitched ziiiiiiiiinnnggggg tone... to a lower pitch rougher tone... and the engine acts like it is choking, like it would like to go faster... and sometimes it WILL go faster if you close the throttle a little bit.

IF your engine is doing this... and the air filter is clean... remove the filter and test ride it again... if it goes faster and "four-strokes" less.. then you need to lean it out with a smaller main jet.
http://www.youtube.com/watch?v=0wzph3hL6EE

[evilone]

Great video Jay, very helpful!