ATC 70s worth the 90 or 125 upgrade?

[DesertRider]

I have a 82 and 85 waiting to be brought back to life. I never owned one not even when I was a kid. Should I just go for the updated engines? Or will the 70cc engine due for for two grown adults (wife and I)?

[ps2fixer]

I rode my dad's atc70 a bit, on flat land / sand it didn't do bad, the top speed was limited based on power rather than reving out with such a heavy body on it. If you're not a speed demon, which the atc70 isn't really in the first place, then the factory setup isn't bad. If you have a lot of hills around you, re-gearing or an engine swap will help tons.

If you run across a atc90 or atc125m parts machine that runs, it might be worth while keeping the engine in the original machine unless the rest of it is really trashed, but that is purely my opinion, I ride some pretty ugly machines lol.

[jb2wheels]

I weigh quite a bit more than a 70.

A stock motor will pull me around with no issues on pavement and hard pack but really struggles in anything soft.

I put a $100 88cc kit on my stock TRX70 and woke it up enough to be fun on sand trails.
I had a 125cc engine in another TRX70. That was better. And it had e-start and reverse.
A already have a 125cc e-start 4 speed manual clutch engine for my next 70 build. Will go in this ATC (the TReX is already rebuilt and sold):

214033

For putting around the campsite, 70cc is OK. Otherwise, I would upgrade.

[Racer-X]

Yes it is sooo worth it. 70cc's will only be any fun on a hard flat surface. If you're only 60lbs its plenty but for an adult its not going to cut it in my opinion.

[briano]

I absolutely love my atc 70 with a China 110 motor in it. No modding to the frame, converted to pull start, and using the stock 70 exhaust. It will move my 250 pound butt around quite well, although I want to play with the gearing to get more speed out of it. I've built 3 other 70's, one with a stock atc 110 motor, one with a piranha 140, and another with a pretty well built atc 110 motor. The little China 110 is my favorite out of them, and the only one I have left out of 21 atc 70's that I've owned over the last few years.

[SSLS1]

Go with a bigger engine for adults as the stock 70 is just adequate and the old style points/condenser ignition is not as nice as the modern CDI in the Chinese motors. I have a Piranha 90cc in my ATC 70 and it's a riot for adults. I have the 90 primarily for the auto clutch as my wife is not comfortable with a manual clutch. The 90 pulls wheelies in 1st and 2nd easily and 3rd with a decent yank on the bars. I will likely add the TBOLT race head with 114cc high compression piston this summer which is said to pull harder than a stock 125cc motor. Should be fun with the auto clutch transmission.