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I have an old JD AMT 625, given to me by my dad. It starts and runs well, but only if you leave the enrichment circuit open for what seems like eternity. I'm planning on re-gifting it to an elderly lady for her gardening needs and want it to run well.

My question is, what causes this requirement of the AFR? Is it low compression? The engine has a new from JD carb, and other usual maintenance complete. Is there a method to get it running better?

I'm a HD mechanic and am much more versed in $100,000 diesel engines. Small carb engines often get the best of me...

I’m sorry but what do you mean by enrichment circuit? As please supply us with the model and serial numbers off the engine.

Enrichment as in choke. Some carbs restrict air some add fuel. Either way it's to alter the stoichiometric ratio of fuel and air

Thank you. I’ve been working on and teaching small engine repair for 50+ years and I’ve never heard the choke circuit referred to as enrichment circuit. Learned something new today. Please post the model and serial numbers for your engine and a description of the problem. Different carbs do it different ways.

A choke and an enrichment circuit are two different things. A choke restricts air intake and an enrichment or tickler circuit adds fuel. Many motorcycles use enrichment for starting and don't have any type of choke butterfly. They both do pretty much the same thing but they do it very differently.

Any adjustments on that new carb? A lot of the newer carbs are jetted pretty lean to keep the EPA happy, users are not so happy sometimes.

Prior to Fuel Injection on Harley's, they used a CV carb (Constant velocity) it had an enrichment knob to pull out for cold starts.
It allowed raw fuel into the carb ventruri to aid in start up.