My Holley 3310 had been running great lately after I tweaked it using an AEM air fuel ratio gauge. My idle circuit was just over 14. This morning I was taking a cruise and noticed the idle readings were way too lean (over 16) and the car had a stumble. Driving it home there were not issues running lean only when I stopped. My idle is about 850 - 900. I re adjusted the mixture screws out about 3/4 of a turn each and I am now back to around 14 at idle. What could have caused the sudden change? I have been cruising in the car for about a month and a half with it running great. The weather was on the cool side last night and this morning...any thoughts ? I am still learning about carbs.

My bet is weather conditions.

if it still likes the new position check for a vac leak
also bowl level,vac adv can, pcv,or brake booste rmight have changed
14 to 16 is a fair bit of difference unless there are some real big weather issues and would tend to go back to norm
since driveability went to crap a ex leak can probably be ruled out

Thanks..I'll check my vac hoses and connections.

I had a similar problem and it ended up being my accelerator pump needed adjusting. Plus when cold it was a pain to keep it running until it got up to temp. I had to pump the throttle as it was running for a few seconds.

But any vacuum leaks will run it on the lean side.

Gary..cool air is denser and requires more fuel to maintain an ideal a/f ratio.The efi crowd utilize intake air temp sensors for this reason.

Thanks for the feedback guys. I checked over all my vac hoses and acc pump. Everything looks ok. I guess I'll just take it cruising and see if it acts differnt on a hot day, which are fading quickly here in NJ.

Could be some debris in the metering block.

Could be some debris in the metering block.

Yeah I was planning to take it off and soaking it, maybe clearing anything that could be causing me issues. Thanks

Barometer was over 30 (30.4 highest I saw saturday night), air temp was in the 50s. My other car was a little lean too, had to go up a jet size for racing Saturday.