H E L P! Calling all 2-stroke mechanics!

[Louis Angel]

OK guys, I am at a loss as to why I am having engine failure!!!
If you have the knowledge and the time, please check out my
blown 50cc engine video and leave any thoughts / suggestions
either here or over on my channel. Thanks!!!!
.
https://www.youtube.com/watch?v=w_JiUejfHWQ

[Mudflap]

Can't watch your video with my current internet connection but I'll be glad to help if you feel like writing about your problem. I was a professional 2 stroke mechanic for many years.

[BARLOW]

ok, i know you asked for a pro builder, and i am not ... but i have built a few 2 stroke engines, and got all my tech info from a yamaha dealer and former racer. he told me the first thing you need to do if you make any change that requires a larger jet (and you have done at least 3) do not use the factory oil injector ... the pump is set to mix to the factory jet only and when you go up in jets, you go up in fuel:oil ... going up in fuel:oil will make a 2stroke scream, but it will also shorten the life of all the moving parts, so you may want to check the end play of the rod to be sure the rod bearing is not past its lifespan as well ... if it were my 2stroke, i would remove the gear from the oil pump, and mix it to factory specs ... as a side note, he told me to never trust the factory injector even on a stock bike, unless it is a polaris, they are the only ones that got it right

[Louis Angel]

ok, i know you asked for a pro builder, and i am not ... but i have built a few 2 stroke engines, and got all my tech info from a yamaha dealer and former racer. he told me the first thing you need to do if you make any change that requires a larger jet (and you have done at least 3) do not use the factory oil injector ... the pump is set to mix to the factory jet only and when you go up in jets, you go up in fuel:oil ... going up in fuel:oil will make a 2stroke scream, but it will also shorten the life of all the moving parts, so you may want to check the end play of the rod to be sure the rod bearing is not past its lifespan as well ... if it were my 2stroke, i would remove the gear from the oil pump, and mix it to factory specs ... as a side note, he told me to never trust the factory injector even on a stock bike, unless it is a polaris, they are the only ones that got it right

Well sir, that sounds exactly in line with what my theory was!
It makes since , , , really.
100 miles on hopped up engine after going up 2 times on main jet, then BOOM! ( well, more like, screeeeeeeeechhhhhh!!!!! ) motor seized.
New motor, 1 mile , same seizure!
It haaaassssss to be starving for oil Me'sa 'Tinks!!!!
.
Piss on that pump!!!
I will mix my OWN for this next go around and see what happens!
:-D
.
Thanks!

[Jay In Milpitas]

I watched your video. You mention jetting changes but unless I missed it, nothing about spark plug readings.

Good observation on the piston scoring in relation to the head/cylinder studs, but that's only coincidence. Because of the geometry of the piston casting, that is the way it expands.

It's indicative of overheating, not lack of oil. It's quite possible that air is being drawn in somewhere, i.e. crack in the carb mounting system, failing crankshaft seal on the magneto side.

If you have gone up in jet size and the plug still reads as lean as it did before, that confirms the air leak.

Good luck.

[BARLOW]

I watched your video. You mention jetting changes but unless I missed it, nothing about spark plug readings.

Good observation on the piston scoring in relation to the head/cylinder studs, but that's only coincidence. Because of the geometry of the piston casting, that is the way it expands.

It's indicative of overheating, not lack of oil. It's quite possible that air is being drawn in somewhere, i.e. crack in the carb mounting system, failing crankshaft seal on the magneto side.

If you have gone up in jet size and the plug still reads as lean as it did before, that confirms the air leak.

Good luck.when dealing with 2strokes, you have 2 ways to be lean(to much air, or not enough oil), and both will make it hotter, but from what i have learned over the years with 2strokes, lean from air does not make them run as well as the op said it was running, but lean on oil will, but i have been wrong before (just once many years ago :hehe:), and looking for an air leak is always some good advice

[Mudflap]

Too much oil in the fuel will make the engine run leaner (hotter), not cooler. The more oil in the fuel, the slower it will flow through the jets.

[Louis Angel]

Too much oil in the fuel will make the engine run leaner (hotter), not cooler. The more oil in the fuel, the slower it will flow through the jets.

So, install larger jets?
Factory was 74 ( IIRC ) "stage 2 kit" from scooterworks came with an 85, After air pod filter I installed a 92 ( or maybe a 96???? I forgot. A 90-something ) but I still have a 102 and a 118 on hand that can go in.