3.sccoters all the same issue

[mybad]

Hi guys I have 3 2 stroke scooters , 2 kymco super 8 2ts and a sym jet 50 eco. All the same 2 stroke engine and all take off with tons of power then lose power drastically . I stop and take off again and they take off fine again . How could all 3 have the same issue . I have rebuilt the engines ,new pistons and rings , same issue , new carb same issue, new plugs , new reeds new gaskets , changed exhaust, I have tried everything so far except the crank seals . Does this sound like the issue to you guys ? And i cant find the seals for sale . Only full bearing kits and indent need bearings and have 3 scooters to do . Anyone have this issue before ? By the way even when I swapped to my malossi 73cc BBK it still did the same thing . Its driving me crazy . Because my sym was a rocket before this issue came from no where and now with the 2 super 8 2ts doing the same thing I'm baffled . All are 2015. So I'm leaning towards the seals being bad . But would love some opinions. Thanks guys .

[Zino]

Can you post up video .
A pic of a well used plug would also be helpfull
It might just be as simple that you are over jetting each of the scoots .
Jetting mistakes are quite common a notch rich is ok ,Way too rich at wide open and you load with fuel and fall on your face .

Bad Seals only happen once in a great while so to happen x 3 at same time is unlikely

[Zino]

When was the last time carbs were cleaned ?
I have to clean 2 carbs this weekend after sitting over the winter .

[lunatuck]

It's gotta be main jet and/or outside temperature related. I wonder if you tuned slightly lean last summer, and then in the spring with colder weather you're more lean. This would probably be exaggerated with a pod filter if you're using one. Or you're main jets could be a little clogged from oil sitting if you haven't started them regularly. 

[103stroker]

I have a 2003 kymco cobra, 49cc 2 stroke. Same engine as the super 8 if im not mistaken. When i first got it it didnt run so i took off the air box, and the factory carb. I cleaned the carb and put it back on, without the airbox. Started it up, idled mint, would rev up on the stand, sounded healthy, but as soon as i put the tire on the ground and went to ride with a load on the engine it would fall flat on its face.
If i let it idle again for a second it would “reset” and be able to rev up again until it got load on it and then fall on its face again.
i put the airbox back on and it had al the power it was lacking before
I later came to realize that not haveing the factory airbox inplace caused it to run super lean.
So my question to you is are you running the factory airbox? And if you are maybe try upjetting

[mybad]

Thanks for the replies . Bought 3 new carbs . All do the same after cleaning the originals many times , changes spark plugs numerous times with NGKS . Has stock airbox now and also tried pod filters. Cant find the right jet kit . I just got another kit in today and again wrong jets . I'm lost . Also got another new carb today but doubt it will make a difference . One of the super 8s still has the stock carb so I'll swap that out soon but doubtful it's the issue . Tried with stock exhaust , stick unrestricted exhaust and my leo Vince and even took the packing out of the leo vince and same thing falls flat on its face after taking off quick. No bog. New gas , new oil . Frustrating as hell . Also they all start immediately and idle perfect and accelerate perfect then fall on there face until I take off again .

[103stroker]

Are you sure the fuel you are using is good?

[ThaiGyro]

Too many changes and something (info) is missing. Can you go back to the setup you had when all was working well? Just a point of old man tuning reference...we keep a log of every tiny change to any engine, drive part or whatever. We don't even assume that a part is marked correctly. Main jets are often not the size of the stamp, or not stamped on occasion. Carb bodies are often not round or the throttle plate has too much gap.

Hard to say what it is from afar...my first guess is as above members have written. Try to compare your original carb pilot jets/settings to the new ones. Look at your everything magnified. If all three fall on their face, it seems as if is in transition from idle to pilot or pilot to main.

Swapping pipes and other super critical parts is not going to help you. Start over if you can.

[mybad]

The issue was on the 2 super 8s always like that even stock . The sym jet 50 evo just all of a sudden did it . 1 super 8 is completely stock . Only thing I can think of is they are 2015s and sat so thinking it's a good chance it's the bearing seals leaking air . Dried out from sitting .

[aeroxbud]

Might be time to do a leak down test. At least you will be able to rule out a leak somewhere then.

[103stroker]

X2 on the above advice. One other thought, i would try troubleshooting the totally stock bike first, to take all the other variables such as mods off the table , make sure your getting proper fuel flow to the carburetor, check float level in your carburetor(tech section should have a tutorial), also make sure that you have good ground to your engine/ignition system/coil and frame.

[ThaiGyro]

Apr 22, 2021 11:00:26 GMT -5 mybad said:

The issue was on the 2 super 8s always like that even stock . The sym jet 50 evo just all of a sudden did it . 1 super 8 is completely stock . Only thing I can think of is they are 2015s and sat so thinking it's a good chance it's the bearing seals leaking air . Dried out from sitting .

I guess that I would not agree.  Three of anything nearly never act the same...especially two strokes.  All three with three identical seal leaks?  No way, assuming the installation was as it should be....and all seal journals were the same.

I am not trying to be an arsehole...but you are missing something that is blocking our ability to help.  I am quite simple.  One plus one plus one must equal three.  Thus you have done some act of tuning that made it that way.

The probability of three "equal" units mysteriously choking?  Astronomical.