Hey!
first post, but I have a 1971 AT1. I can get it to start and it will run for about 5-8 seconds then shut off. So far it has only started w choke on, and it dies faster when I turn off the choke, and also hasn’t gotten warm enough to really tell if it’ll run w choke off. Increasing throttle kills it too. 

runs on pump gas (and oil).  So anyway, where should I start?  I can buy a cheap $35 mikuni carb off amazon and see if that fixes it, but don’t want to chase parts either. 

71AT1 video link . Also put as attachment to this post. 

Have you cleaned the carb, verified jets and float level? 

Greetings from Tennessee  

I’ve cleaned the carb, yes. But one (maybe the only one) of the jets’ that was deep down had the slot all stripped up, and I couldn’t get it out. All other parts were removed and cleaned.
 And blown out w air. 

 

It sounds like you are describing the pilot jet is stuck and that's the most likely culprit for the issue you're having. 

I might have a good used original carb body cheap if you can't get the jet out and need to replace the body...  aftermarket carb is generally not the way to go.  

Ok thanks. I guess I’ll pull it apart and see if I can get that jet out. I might take you up on that spare carb if I can’t get this working. 


- on the carb there were two adjustment screws that are spring-loaded. The idle speed screw and the throttle screw. One of them is larger l, near the center driver side and can be adjusted by hand or slotted screwdriver. the other is smaller, near the driver right side and needs slotted driver to adjust.  Any idea which is which? And how many turns out from bottomed?  My manual doesn’t differentiate them but says idle 1 1/2 — 2 turns out for the idle screw. 

Factory manual is available in Tech Library here.

Larger central screw is idle stop screw.  No "turns" spec...  you use it to set the idle speed. 

Smaller screw towards rear is idle air and spec is generally 1.5 turns out from lightly seated. 

Leave the throttle shut with choke on & don't touch it until it settles down.
But that's on a good carb, not yours.
You could hand choke it over the carb mouth varying the hand as it improves & will accept throttle.
I'd say the pilot is blocked but seeing it won't come out without problems i'd pull a strand out of your wire brush & poke it right through & out into the venturi, that'd work except there's also an angled hole in the forward end coming off the pilot drilling, ya might get lucky then blow it through again. Also think i'd raise the slide needle "by lowering the clip".
But bottom line might be the main jet.
Its in the side mount on the bowl. Remove it from its holder & look behind it plus through it as everything 'except pilot & choke' comes through the main jet.
Also the choke "fixed jet" in the bowl cavity may need poking--look down with a light, it's small.
Re-thinking, wire brush might be too big for the pilot jet but just be careful. If all else fails then a new cheap Chinese carb will fix it. Uhh--did i say that. Here's mine lol.

Don't give up, here are some pix of where you could poke about with some thin softish wire and maybe a little vinegar (it can eat aluminium if left too long) (you may want to check that the very old filter hasnt exploded and is blocking the air )

Great pic there RVR, Expand up totally clear. Can see right in.