Atc70 spitting

[ivan-083]

Hey guys
I have a 74 atc70 that was a basket case it’s been up and running now for a few years and it didn’t have the original carb with it. It’s missing the standard air box.
I brought one of these expensive 90$ after market carbs here in Australia and it seems to idle fine I had an original carb I brought but it wouldnt run right with it.
When I give it throttle in 1st gear it’s fine and I can hit the throttle quick and fast.
Once I hit 2nd and 3rd I find if I hit the throttle quick it starts to spit and big down a bit but if I do push the throttle slowly it seems to be running good.
The needle clip is on number 5 and won’t run good on the other clips which I’ve tried?
Any ideas? Go up on a jet size? Or try and put on the original air box? (Will need to get a new carb rubber to try this).
Any ideas? I’ve heard the 70 don’t run right without the original air box?
Thanks


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[shortline10]

I would change the points and condenser just to be sure your good their .
Worn points will give your symptoms .
You can also try choking the carburetor when it starts to act up , if it needs a little choke then the main jet is to small .

[ivan-083]

I would change the points and condenser just to be sure your good their .
Worn points will give your symptoms .
You can also try choking the carburetor when it starts to act up , if it needs a little choke then the main jet is to small .

Shortline
I will get a carb rubber and put on the original carb and airbox hopefully next week! If that doesn’t work I’ll check the condensor and points! Thanks


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[ivan-083]

I would change the points and condenser just to be sure your good their .
Worn points will give your symptoms .
You can also try choking the carburetor when it starts to act up , if it needs a little choke then the main jet is to small .

Shortline
I wrapped the after market air filter with a double layer of foam! It’s running much better now and when I hit the throttle quick it doesn’t bog down anymore!
I know it’s a 70 much I think it could have a bit more power? Maybe put the clip from position 5 to 4 and see or maybe a bigger main jet?


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[350for350]

You're on the right track. It's jetted too lean. It may not be just the main jet either. I'm not saying that you need to put it all back to stock either. You need to adjust the current fuel set up to the mechanical set up. Once you get it jetted right, it should have more power.

[ivan-083]

You're on the right track. It's jetted too lean. It may not be just the main jet either. I'm not saying that you need to put it all back to stock either. You need to adjust the current fuel set up to the mechanical set up. Once you get it jetted right, it should have more power.

Thanks 350! Got it in the ball park today, just a bit more tweaking! It seems to have good power now, but I know it’s only a 70 and my other 70 has a 125 in it and I don’t have anything to compare it with!
Plus Iam 74kgs and they are kids bikes too ha ha ha ha! Idles much better now and I tightened a manifold bolt that was loose.
I’ve got a few jets arriving soon and I can try that too