ATC 70 engine question

[az350x]

Anyone out there with engine know-how, I need some advice. My kids' '85 ATC 70 runs kinda crappy. I just swapped the stock exhaust for a cute little Supertrapp. It ran crappy before the exhaust swap, and still does. I'm considering putting a new 20mm Mikuni ($60), a new pod-type air filter, and redoing the top end on it.

Here's the question-
Should I

a) hone the cylinder and re-piston and re-ring it with stock size
b) bore it ever-so-slightly and go with oversize piston/rings.

What's it cost to bore a cylinder? I'm assuming the cylinder is virgin, although I don't know for sure...

Anyone with advice, please let me know...

Thanks!

[Nuthinspecial]

If it were mine I would go with choice A .......provided someone hasn't already been in there. ;)

[dads]

Try cleaning the carb.

[az350x]

Carb has been cleaned/rebuilt. The engine just bogs down at mid/high end...

[secluded]

you think i could be the gearing? is there a high and low range? if so it might be in high??

[az350x]

Originally posted by secluded
you think i could be the gearing? is there a high and low range? if so it might be in high??

70's don't have dual range, and this thing falls on it's face even when you rev it in neutral.

It's drivin' me NUTS!!!:fire:

[Mr. Richard]

ok, here we go ,,, first get a timing light and a battery, fire it up and check the timing , should fire right on the F mark on the flywheel, since they have no advance timing is imortant.... make sure that you have good fuel flow out of the tank before the petcock, make sure that the nylon screen behind the petcock is clean , the pilot jet is so small on these 70's that it doesn't take much to plug them up. when its all back together turn on the gas ,open the bowl drain to see if you have good fuel flow . now is is starving for fuel or is it loading up??? maybe the choke butterfly is stuck, there spring loaded maybe the spring is broke too,,, or drity air cleaner ???? let me know

[az350x]

Thanks, Kasey. It'll probably be a couple weeks until I can mess with it, but I'll try checking the timing first thing. I've got a Clymer's manual for it, so it shouldn't be a problem. I've never replaced the points in this thing, and I've got a couple sets on hand. How would I know if they need replacing or not?

[Mr. Richard]

if you got em and a flywheel puller change them!!!! i would . might as well eliminate a possible problem right off the bat,,,,,,,,,,,