350 High Inconsistent Idle

[captainwhisker1]

Hey guys, I'm having some trouble with getting my 350 to idle right.

It's a '76 4 bolt block with a really recent complete rebuild. 1405 Eddy carb, 2101 Performer intake, 462 heads, Lunati .420/.442 lift cam, gear drive, and long tube headers into a 2.5 inch stainless exhaust. It has maybe 200 miles on it and ran really well, then my issue started only about 50 miles ago.

My issue is, when the truck is out of gear it idles roughly at 800-1200 rpm, but when I drop it into gear, it drops to 600 rpm (what I'm aiming for) and is pretty smooth. Before my issue started, the rpms would barely drop (maybe by 100) when I put it into gear. It's also stalled on me 3 times today already, every time it was in gear. It runs really well with throttle applied, good power, it's just the idle acting up.

The fuel pump is maybe 4 years old, the carb hasn't even seen it's first birthday yet, The carb was dialed in before the problem flared up, so I don't think it can be a carb issue. I even messed with the idle adjustment a little after I got home but it didn't seem to help. I haven't noticed or heard any vacuum leaks, but I haven't got it tested. The only other thing I haven't checked yet is the ignition system, which is still the original HEI system that came with the truck. Could this be the problem, or do I need to be looking elsewhere?

Any input will be appreciated. I had a video but it says it's an unsupported file type.

 

[Edelbrock]

I would check for vacuum leaks with a smoke gun (you can make one very easily using a cigarette). Maybe the vacuum line to the trans? Also, I would toss another carb on there just as a test. Are you sure your fuel is good? No water in the tank or old fuel? Ya, check the timing for sure, and make sure the distributor hold down is not loose.

 

[captainwhisker1]

I would check for vacuum leaks with a smoke gun (you can make one very easily using a cigarette). Maybe the vacuum line to the trans? Also, I would toss another carb on there just as a test. Are you sure your fuel is good? No water in the tank or old fuel? Ya, check the timing for sure, and make sure the distributor hold down is not loose.

Smoke gun was one of my first thoughts, I'd like to try and get that done soon. Fuel is good, I drive it frequently so it gets filled about once a week, I also try to put treatment in it once a month. I would try and throw another carb on but I don't have another one that's in useable condition. Thank you!

 

[legopnuematic]

Might give a quick check with a wrench on the intake and carb mounting bolts, I've had them loosen up a little (or the gaskets settled/compressed some).

 

[Ricko1966]

A quick squirt with carb cleaner well usually find a vacuum leak quick and easy. Hey @legopnuematic remember last week when we were talking about installed vacuum gauges. He'd know now if the vacuum level had dropped.

 

[PrairieDrifter]

Electric choke? Check choke adjustment.