Fresh engine won't idle

[Seff]

Car: 72 Cutlass
Engine: Olds 380 stroker 9.5:1, roller cam, Ebrock performer RPM intake, stock 7a heads with 2" intake valves and a bowl blend port job. HEI off a 403 Olds connected to ported vacuum, set to 19 btdc initial timing.
Carb: 17057253 rebuilt for the old engine, a stock '71 Olds 350 8.5:1. I've just fitted it with an electric choke.

Symptoms:
 - Engine won't idle, but will run at 2500 RPM on the top step of the fast idle cam.
 - On the second step it runs, but stumbles.
 - Off the fast idle cam it dies immediately.
 - The GEN light remains on even at 2500 RPM, and the electric choke is slow to open, if at all. (suspect the field terminal is loose, will re-tighten).
 - Backfires up through the carb when cranking.

I suspected that the idle mixture was too lean for this engine, so I turned the screws out - no effect. Haven't moved ATP, but that should't hamper idle quality.

[77cruiser]

What are the specs on the cam? Was the cam degreed? Did you check for vac. leaks?

[Seff]

The cam was degreed by the builder. Didn't check for vacuum leaks, but I'll hook up a vacuum gauge.

[Cliff Ruggles]

Pretty hefty cam for the little Old's 380 at 9.5 to 1 compression.  The carb will need idle system modifications to make it happy at low rpm's, but that is a nice carb for what you are doing.  I use a near identical Pontiac unit on my 455 over 550hp.....Cliff

https://www.youtube.com/watch?v=6zVdoLR-VzM

[Seff]

That's a cool video for sure!

I double checked, the final calculated CR was 9.3:1, not 9.5:1. Sorry for the confusion and misinformation. Originally and ultimately the engine is built with EFI in mind in conjunction with a TKO 500 and a 2.56 rear, which is what the cam choice is based upon.

I have the book, is here a recipe in it that describes the idle system modifications needed? It's back at my shop, so I can't check it at the moment.

Thanks.

[Seff]

My engine builder says to specify that it's a 221/228@.050 on a 112lsa. That shouldn't be so extreme?

[Seff]

Chased vacuum leaks today, every intake bolt got tightened about a quarter turn. Still rough idle.

[carmantx]

Like Cliff said, you are going to need idle circuit modifications to get a proper idle without nozzle drip.

[Seff]

Well, I have two carbs, so I might as well. Can you tell me what kind of modifications, or what page of the book shows this kind of modification?

[Cliff Ruggles]

I would read the chapter on how they work, then go to the high performance chapter for specific guidance. 

Bigger than stock cams reduce signal (engine vacuum) at idle and low rpm's and require minor idle system modifications so the engine can get enough fuel from the idle system to make it happy.

I'd look at recipe #3 for idle fuel, for what you are doing.

If you haven't done so I would also install one of our kits, and I can supply tuning parts, jets, metering rods and PP spring, plus sized idle tubes for what you are doing.

I'd also make sure that you blocked off the vacuum supply to the choke housing when the E-choke was installed, or there is a vacuum leak at that location. 

Also vacuum test the pull-off, and time it.  It will need to fully release in less than 2 seconds for what you are doing.  We have quick release pull-offs available as well...tks.....Cliff

[Seff]

Gotcha, will start reading.

Have a HP kit in one of the carbs already, rods and jets as well. Sadly can't remember which.

Choke housing is NOT blocked off, just sucking air. Will fix that immediately. Or are you talking about the port at the rear of the air horn?

Choke pull-off will be checked.

Thanks!

[carmantx]

Choke housing itself.  The hot air choke pulls air/vacuum from the carb body.  When converting yo electric choke, that vacuum passage needs to be blocked.

[Seff]

Welded shut an old tube for the choke vacuum, car runs much better at high rpm. Will try recipe #3 on the 77 carb now.

[Seff]

For reference, it's 74 jets and D4 primary rods.

[77cruiser]

What's the cranking compression?  Let us know how it turns out with the other tweaks.