Carb question

[Mrturner1]

On an Edelbrock 650 AVS, barely a handful of hours since rebuilt, what would make the idle in PARK go up about 200-300 rpm while warmed up, and drop back down to normal after I give the throttle a stab, and then almost immediately creep back up again? Only does it while warmed up as far as I can tell so far.

Idle screws are turned 2 1/2 turns out currently, no idea if that's a good spot, it's just where I started. Pretty new with carbs

[long67]

Those arent idle screws they are air fuel mixture scews,adj them to where motor is running smooth,idle will change when adjusted.Set idle with sngle scew on throttle lever.

[jdalexa84]

The factory setting is 1 1/2 turns for the idle fuel/air mixture screws. I have the same carb on my truck. Does your fast idle screw need adjusted

[geezer#99]

Your idle is too high!
The mechanical timing is just starting to add more timing. More timing means a higher idle. When you blip the throttle the weights pop back where they belong momentarily, then start swinging out slowly speeding up the idle again.

[Mrturner1]

Originally Posted by long67

Those arent idle screws they are air fuel mixture scews,adj them to where motor is running smooth,idle will change when adjusted.Set idle with sngle scew on throttle lever.

That's what I meant lol see I am new

[Mrturner1]

Originally Posted by jdalexa84

The factory setting is 1 1/2 turns for the idle fuel/air mixture screws. I have the same carb on my truck. Does your fast idle screw need adjusted

Haven't messed with the fast idle screw yet

[Mrturner1]

Originally Posted by geezer#99

Your idle is too high!
The mechanical timing is just starting to add more timing. More timing means a higher idle. When you blip the throttle the weights pop back where they belong momentarily, then start swinging out slowly speeding up the idle again.

Ok here's my diagnosis, tell me what you think. The cam I put in calls for a 2500rpm stall at the minimum, 2800-3000 is probably better. I think my converter is to tight and that's what is fighting me on tunin this puppy. For the sake of getting the truck driveable and out of the garage, I grabbed a B&M 2200-2600rpm "white box" stall converter. Not sure it works that great because when Im stopped in PARK and put the truck in gear, it immediately lunges forward like the converter is tight. It also drops from an 800rpm idle, to 400-500rpm when put in gear. It's not AS bad as the stock converter with that Lunati 285 cam, but it's still pretty bad. The white box converter was only 140 bucks so I won't be torn if I have to ditch it. Wanted to throw this out there in case the problem could be more than just the carb.

[geezer#99]

What's your initial timing?
And what's your timing at 800 rpm?
You might just be starting the mechanical at 800.

You shouldn't have that much drop when in gear. 150 rpm would be normal.

[Mike C]

Sounds like mixture screws too lean. Richen them up and turn idle speed screw down.

When you stab at the throttle it puts the extra shot of fuel from the accelerator pump in, then when that extra fuel is burned it's too lean again. So richen the mixture screws should raise the idle, so lower it back to correct spot using idle speed screw.

Obviously, this is in a perfect world and nothing else is out of adjustment.

[Mr Handy]

first thing I would do is check for vacuum leaks, pulling down 400 rpm in gear with a 2200 stall is a bit much. Also check the pcv setup and make sure it is hooked up properly and you don't have a bad pcv. Also if you have power brakes make sure the booster is not leaking.
Then I would set timing, and finally set idle mix on carb. I like to use a vacuum gauge and tach.

The fact that it is pulling down so low in gear makes me think leak/pcv problem. My old 283 did the same thing when the PCV went bad causing bad idle in gear and started burning oil.

[67 chevelle]

fast idle cam ,on passenger side under choke