Expansion Chambers

Thanks for the info! That makes alot of sense, i rebuild my shifter kart engines so im pretty formiliar with assembily/disassembily and how they work. I also have friends that still have tools to ballance cranks and shim them in the case if need be. Im happy with it for now, but i really appriciate the info on the reeds, and mods, that answered 90% of the questions i have and it would be cool to see a couple of pics of those newer emgines, they arent the ones on the 1st page by chance are they? Those looked pretty good.

And one more quick off topic question, what kind of oil and what ratio do you run?
I was going to run cheap oil but i can get it in bulk so im running maxima kart oil because these little 66cc motors are some what similar to kt100 yamaha kart engines (both aircooled and run hard). I mix rich compared to most and 28:1 but i think 32:1 would be as lean as i would want to go. I thought about running motul but it is really pricey.

Thanks for the help, - austin

I used castrol for decades. It's very good stuff, even for you throttlemad Aussies with your MadMax heritage and endless straightaways.
But I also know there is simply no better oil than a good full synthetic. Cost would be the only reason I would stop using it.
But that being said, it's a chinagirl. I doubt you will notice anything different regardless.

I think it really depends on jetting, i run my shifter kart at 20:1! But the jetting is way leaned out, i would have to ask a friend on that but i think the 40:1 would be ok, you can always try leaning it out and check it using a "plug chop" if you are formiliar with that.

Im still new to jetting two strokes but i do know that you should have a golden color to the plug, some oils can leave different colors i think.

The oil ive been using is called maxima formula k2. It comes in a purple bottle and its 100% synthetic. It recomends ratios ranging from 24:1 all the way to 60:1 depending on jetting. I always have mixed at 32:1 and ive never had a failure. But i have less than 100 miles on the china motor so i cant really tell if its right or not. My plug is black but that is from the break in. Im not sure of the numbers off the top of my head but i believe the karting oils dont burn as clean because the kart engines run really hard (the aircooled engines run really hot) if you google the oil above and the motul 2t karting oil, they are my two favorites for these motors cause they can get pretty hot.

My friend and alot of people swear by castor 927 but like my motul oil it is pricey

Theon said:

Finally finished of the KTM pipe for my 'Dual Suspension Roo'.

Click to expand...

Nice!, sorry for the late reply, ive been really busy at school.

So i ran it once without the element, and i gained alot of my bottom end back. Because my pipe has such a large diameter, i think the speed carb is limiting the amount of air being allowed into the motor. I picked up a k&n waffle style filter that should help alittle but i havent tried that yet, i have to modify the intake so it will fit in the frame

Do you have any experiance with running a slightly larger carb? I want to try and maintain as much bottom end as possible so i think a reed will help and it should help with keeping the fuel in the combustion chamber. I found a cheap atv carb that has a opening of 18mm where it mates to the intake manifold and 15mm at the slide. I might have better luck with slightly porting the intake/speed carb but i dont think you could open it up enough to see a improvement.
Also, does intake lenght make a difference? I know on larger engines it does.

And i know this is off topic, but i run 110 vp, is there anyway to advance the timing on these, or would that just make them run hot, and i also have been running a e3 plug which seems to run hot already so i should probably leave it alone.