I have a AT1c with a CT2 topend. It was rebuilt about 5 years ago by a good engine builder in town.

The last year I have had running issues. I clean the carb really good and blow it out with high pressure air, but it seems my pilot jet keeps getting clogged or a passage gets clogged. I drained the old gas and refilled with fresh 91 octane and seafoam. It ran great right after cleaning the carb. Now the bike has sat a week and it doesn't want to run without the choke. Once out of low rpm it rides great.

I used a piece of wire to even clean the pilot jet on the AT1 along with letting it soak in B-12 chem tool for a few hours.

I'm at wits end with the carb. Should I try a new one?

Run the carburetor dry every time you put the bike away. Turn the petcock off and let it idle until it stalls and then turn the key off. I hope that helps.?

Run dry or drain your carb. I always run non-ethanol in my bikes, last month my son took out my street bike and topped off the tank with E10. The bike sat for 2.5 weeks. Last night he went to take it for a ride and it wouldn’t idle off the choke then eventually fouled the plugs. I walked him through the process of dropping the float bowls and removing the pilot jets. Both were plugged. After cleaning the pilot jets and putting everything back together it ran perfect. Today he had the pleasure of draining the fuel tank and refilling it with non-ethanol fuel.

Question is do you think its blocking with dirt of some sort rather than old fuel residue. if i'm reading it correctly it's been in semi regular use for the last year so would have had semi regular fresh fuel. Are yo removing the pilot jet to clean it. Takes a very small wire through it depending on size. I'm having a similar issue with my 250 which i'm starting to think is crank seals as takes about 20 kicks to cold start but is good when warmed up & runs good all day & thinking bad seals get wet & work a bit better than when dry. In my case the fixed choke jet in the bowl was half restricted but not fixed my problem. I'll try fresh fuel first as does lose its igniting ooomph over time--terrible fuel we have here. Anyway, if your pilot is getting blocked then there should be signs of dirt sitting in the bowl. Maybe look further up top at the fuel cock filter & in the tank. I've yet to prove my seal theory but could be your problem too, if cleaning pilot didn't work this time.

Might check your pilot jet for blockage which will cause it to not idle with the choke off. the pilot jet is the smaller than the main jet and inside a tube below the needle and seat if you hold the carb with the spigot which faces the cylinder end up.

make sure the idle air adjustment is 1 1/2 turns out from closed or less. if this screw is turned out too many turns it will lean out the idle circuit too much and at the very lest it will run poorly with the throttle at the idle position.

Like RT325 said you might also have some dirt or rust from the tank getting into the carb and plugging things up?

In any case, it doesn't sound like replacing the carb would be the fix.

My tank was lined a few years ago. Acid dipped, then lined/coated.

I run a small see thru fuel filter just to catch any crap. Is there a better fuel filter to catch everything to prevent issues?

Small particles of brownIsh rust on the bottom of your float bowl can pass through "just about" any inline fuel filter. What happens to the pilot jet is a film that drys and forms a solid bubble only penetrable by a wire. It's like plaque. Every so often you just need to go through your fuel system instead of changing your engine oil. Your engine oil will outlast five fuel tank and carburetor cleanings.

This is so true. When I was having carb trouble my float bowl was full of this very fine material, all the while using one of the clear filters (which would be full of larger stuff after a few weeks!)......once I removed the old tank liner (photo #1) and relined it did I eliminate the fine material that was hiding in the tank. It is evil stuff! Now my clear filter is clean and I have checked the carb/float bowl since lining the tank and all is well. Make sure your tank is CLEAN.

Is there anywhere to get a new flange mount carb for these old bikes? I wouldn't mind going to a bigger MM carb either.