Can't bring idle below 1000

[jeff74]

I refreshed a 1996 vortec engine and installed it in my '71. Today was the first time I took it for a good drive, when it's warmed up the idle was around 1000 and wouldn't go any lower with the adjustment screw backed out. Quadrajet 4MV

The carb had a good cleaning and rebuild kit and I put in brass bushings on the primary shaft only, the secondary seemed fine.

I was reading on here for ideas and this is what I've tried so far...

Blocked off the pcv line and brake booster line , no change
Checked the mechanical advance action, it returns to normal on its own. I didn't check the timing.. it was set at 10 or 11 btdc the other day

The other vacuum ports on the carb are plugged, I don't have the vacuum advance hooked up at the moment. I'm going to convert to manual choke , but for now I have the choke linkage held in the hot position.

Anything else before I pull the carb ?

Thanks

This is what she looks like today.

[truckster]

I would start with verifying the timing, then go to the idle mixture screws. The idle speed screw is after that.

[jeff74]

Originally Posted by truckster

I would start with verifying the timing, then go to the idle mixture screws. The idle speed screw is after that.

Thanks
I forgot to mention that I set the idle mixture the other day, I ended up with both around 3.5 turns for max vacuum. First time I've done it that way

Yes I definitely need to recheck timing

[mr.mud1]

Originally Posted by jeff74

Thanks
I forgot to mention that I set the idle mixture the other day, I ended up with both around 3.5 turns for max vacuum. First time I've done it that way

Yes I definitely need to recheck timing

i always tune the carb with a vacuum gauge for max vacuum.did you disconnect the throttle to see if it'll idle?maybe your throttle isn't let it return?

[dmjlambert]

Also check that fast idle cam and adjustment screw is working and adjusted. That's an additional idle adjustment thingy.

[jeff74]

Originally Posted by mr.mud1

i always tune the carb with a vacuum gauge for max vacuum.did you disconnect the throttle to see if it'll idle?maybe your throttle isn't let it return?

Yeah, I disconnected the linkage, there is some slack in it.
Forgot to mention that, too

[jeff74]

Originally Posted by dmjlambert

Also check that fast idle cam and adjustment screw is working and adjusted. That's an additional idle adjustment thingy.

Thanks
I need to double check that, I believe it's kicking down all the way. I actually adjusted the fast idle up a touch today because it's just a handful of degrees above freezing

[geezer#99]

Since you had the primary throttle apart maybe you didn’t get the plates both back in perfectly. One could be hanging up on the bore.

[jeff74]

Originally Posted by geezer#99

Since you had the primary throttle apart maybe you didn’t get the plates both back in perfectly. One could be hanging up on the bore.

I'll have to check that, you could be on to something, it did feel like the throttle stuck a bit when I was messing with it... I mean, pulling it towards closed

[Dan-K]

Vacuum leak ?

[jeff74]

Originally Posted by Dan-K

Vacuum leak ?

Maybe, I've checked all of the ports, but today I pulled the carb and the mounting bolts were just barely tight. I guess the gasket has squished down a bit, it's a thick one with plastic washers, I think it came with the rebuild kit. The 2 screws on the bottom side were not so tight as well, the lower gasket is fairly thick , maybe 1/8"

I didn't run it today, the next few days are supposed to be warmer.

I took a pic of the primary, this is as closed as it goes, the transfer slots form squares ( or maybe slightly less than squares). The fast idle mechanism is fully out of the way.
Should they close more than that?

[geezer#99]

Put a flashlight on the top side so you can see fitment of the plates in the bore.
Should see light evenly all the way around.
Check shaft movement side to side while checking with the light.

[HotWheelsFan]

Bottom of the carb looks great, air/fuel mixture screws look normal, and the square slots are normal.

You mentioned refreshed the engine... Is cam timing correct? Maybe off a tooth? Did you double check the distributor timing yet?

Did you match the carb rebuild gaskets with the old ones during rebuild?

Bob

[jeff74]

Originally Posted by geezer#99

Put a flashlight on the top side so you can see fitment of the plates in the bore.
Should see light evenly all the way around.
Check shaft movement side to side while checking with the light.

It's not perfectly even, but I don't know if it's enough to cause a problem. There doesn't seem to be any side to side movement. Should there be a little?

Should the plates be able to close to completely cover the slots?

[jeff74]

Originally Posted by HotWheelsFan

Bottom of the carb looks great, air/fuel mixture screws look normal, and the square slots are normal.

You mentioned refreshed the engine... Is cam timing correct? Maybe off a tooth? Did you double check the distributor timing yet?

Did you match the carb rebuild gaskets with the old ones during rebuild?

Bob

I did replace the timing set, dot to dot, pretty sure checked and checked again but I can't seem to find a picture of that..
I took a picture of just about everything else..

I rebuilt the carb a couple of years ago, I hope I matched the gaskets..
It's running really good otherwise, cold starts, hot starts , all good so far

I'll run it again tomorrow and check the timing, and make sure the mounting bolts are tight enough, I'd like to try that before I take it apart to check out the alignment of the plates

[geezer#99]

Originally Posted by jeff74

It's not perfectly even, but I don't know if it's enough to cause a problem. There doesn't seem to be any side to side movement. Should there be a little?

Should the plates be able to close to completely cover the slots?

You’re good if no side to side.
I’m not sure on the slot coverage.
Your plates look well placed.

What’s with the long screws on the secondary plates?

[jeff74]

Originally Posted by geezer#99

You’re good if no side to side.
I’m not sure on the slot coverage.
Your plates look well placed.

What’s with the long screws on the secondary plates?

Thanks
I think those screws are just what I had when I put it back together, I probably botched the stock ones..

[geezer#99]

Better make sure they’re staked in place.

[jeff74]

Originally Posted by geezer#99

Better make sure they’re staked in place.

Yeah, I'll see what I can do, I used high strength loctite, but I know what you mean

[jeff74]

I checked the timing today, its still right around 10, dwell is at 30-31.
The carb mounting bolts are snug with a 1/4 ratchet.

It'll idle now at 750-800, I'm happier with that. I can definitely kill the engine by turning in the mixture screws, it seems to like 3-1/2 to 4 turns and vacuum is almost 19 inches (2300 feet elevation)

This is with the idle speed screw backed out, that's as low as it goes. I've watched a couple videos saying to set the transfer slots to "squares", that's pretty much what they look like.
It would be nice to get the idle down a little more.

[geezer#99]

Is your distributor vac pot hooked to manifold or ported?
Hooking it to ported would slow idle down.

[jeff74]

Originally Posted by geezer#99

Is your distributor vac pot hooked to manifold or ported?
Hooking it to ported would slow idle down.

Oh, I didn't try that , the vacuum advance still disconnected. I briefly connected it to manifold today and the idle increased. I didn't realize ported would slow it down.

Something for tomorrow.. thanks

[jeff74]

Originally Posted by geezer#99

Is your distributor vac pot hooked to manifold or ported?
Hooking it to ported would slow idle down.

I think I misunderstood, you meant from manifold to ported, not from no connection to ported.

It was disconnected, so I think that's as low as the idle will go