Carburator Tuning

[CABilly]

Well, I finally took possession of my dad's old Capri. He put a 5.0 in it and it has an Edelbrock 1406 electronic choke carb. He had it tuned by a guy who knows his shit and they fixed all the vacuum leaks and got it running great.

On a cold start it idles at a nice 800 rpm. It's a 5-speed so it doesn't have to kick down any.

But when it's good and warm, it wants to idle around 1400-1500. It's like the electronic choke is programmed backward. Blipping the throttle doesn't drop it. Sometimes it will come down, but it really just seems to be happy idling way too fast.

So, do you guys who know this stuff think it's more likely a new vacuum leak or something to do with the choke? Or something else? My only experience with carbs and chokes is running the manual choke on my bikes. There's not really much thinking required for that..

 

[kingmoochr]

Disconnect it and see if it changes?

 

[CABilly]

That's a good idea. I'll try that tomorrow

 

[Caddywumpus]

Spray carb cleaner around the carb boots. They could be cracked

 

[littlebeast]

don’t have any experience with automatic chokes, but considering how they work, sounds like a spring issue. older vehicle - do they corrode?

 

[CABilly]

Could be I guess. It was all new and garage kept but I’ll poke around tomorrow.

It’s just weird to me that it’s fine until it warms up.

 

[littlebeast]

Could be I guess. It was all new and garage kept but I’ll poke around tomorrow.

It’s just weird to me that it’s fine until it warms up.

it actually makes sense. electrical resistance increases as heat increases. i still think it’s the spring.

 

[TheRobSJ]

It’s been many moons since I’ve had to do anything with a carburetor. But the cold start sitting at 800 and then warm being at 1500 sure as hell sounds like they choke is functioning exactly the opposite of how it’s supposed to.

I googled that model Edelbrock and it looks like the power and ground on the choke are simple spade terminals. Very easy to connect them wrong.

Not sure what’s going to happen when you disconnect it. It may be spring loaded to stay closed, in which case it will stay at 1500rpm no matter what. Also not sure what happens if you reverse the leads connected to it...but it sure seems like that makes the most sense. Are the wires going to it different colors?

 

[Abacinator]

Should be easy enough to pop the air cleaner off and look at the choke plate to see if it's behaving the way you suspect.

 

[ontherearwheel]

FWIW, the way the choke plate works is to restrict airflow which decrease the air enough to achieve proper A/F ratio needed to start the because colder air is denser.

If the plate is closed when the motor is warm......it is gonna run rich and you will smell it.

To check the choke is wait until the motor is cold. Remove air filter to see if the choke plate is closed and by how much.

Just turn on the key......do not start the car. As the choke element heats up, the choke plate will open up.

The black housing the wires are connect to is used to adjust the cold opening. The screws can be loosened, the housing rotated to change the opening.

The choke on motorcycle carbs are not chokes, but circuit enrichers. When pulled on, this allows more fuel to flow through the carb to help starting in cold weather.

 

[augustiron]

The choke on motorcycle carbs are not chokes, but circuit enrichers. When pulled on, this allows more fuel to flow through the carb to help starting in cold weather.

All good until this part. Then your new bike bias is showing.
Many older bikes have actual choke flaps on the carbs. Think up to about the 80s

 

[Beanzy]

Dang. This carb doesn't look complicated at all. Lol. But it sure is purty.

 

[augustiron]

I don't know if it applies to this carb, but on a Quadrajet i recently rebuilt and tuned, you had to depress the accelerator one time before cold starting it.
This was NOT to squirt gas into the intake, but to reset the throttle linkage back onto the fast idle cam for a cold start.

As the engine heated up, the electric choke also pulled the fast idle cam back to the "hot" setting, and it stayed this way as the car ran and was shut off and slept until the next start. If you did not tap the pedal before cranking, the choke flap and fast idle would still be at the "hot" position.
YMMV

 

[CABilly]

Thank you all so much for your thoughtful input.

My dad made the 30 minute drive to come help me troubleshoot it and my first idea seemed to work. A few spritzes of carb cleaner all around seemed to do the trick. I felt bad he made the trip just for that :facepalm

 

[ontherearwheel]

FYI........I’ve always heard and use the carb cleaner trick. Then, one day I was researching possible causes for some codes. One possibility being intake gaskets.

To help verify that the intakes gasket were leaking, this guy took a small bottle of water, poked a small hole in the lid and sprayed water along the intake and head as the engine was running.

I did the same thing, and could hear the water being sucked in, and then watched as steam came out the exhaust and the engine stumble.

It was way easier to control the stream of water then spray cleaner under pressure.

FWIW.......

 

[msethhunter]

It's not an "electronic choke", it's an electric choke. I'm not sure how you could set one up backwards. It's a coiled up spring that coils tighter as it gets hot, and the choke opens (turns off). But like someone else said, disconnect it and see what it does.

Those carbs aren't to hard to tune, but you need to start at the baseline setup, and go from there. IMO, I would disconnect the choke, make sure it's open, and get it warm. Set the idle, while it's warm, about the 8-900 rpm. Then, while it's still warm, set the choke up. Download the instructions for that carb. They're pretty good, and will walk you through the setup.

Edit: Here, read this. It's stupid simple.

https://www.edelbrock.com/mwdownloads/download/link/id/69761/

 

[Jalopyshoppe]

FYI, disconnecting the choke will ensure it never pulls off. That bi-metal spring will hold it closed. There are 3 screws that hold the plastic cap down. You loosen them and wind the spring tighter to take the choke out of the equation.
Your fast idle sounds like you could have the vacuum advance connected to manifold vacuum instead of port vacuum. That would make it idle high due to advanced timing when warm.
It's easy to visually check that the choke flap is open when the car is warm. You do need to manipulate the throttle to let the spring pull the choke off. That's what the blip is for. The spring sets it closed and there's a stop that falls into place. It will hold it closed until you blip the throttle and release the tension. That link above should explain it.
Carbs are not voodoo. They're easily tuned mechanical devices that require logical thinking, patience, and methodical procedure.
Cool car, good luck.

 

[aminalmutha]

All good until this part. Then your new bike bias is showing.
Many older bikes have actual choke flaps on the carbs. Think up to about the 80s

Dunno about "new". There are 30+ year old bikes with enrichers rather than chokes. I think early 80's is about when chokes went away.

 

[augustiron]

Dunno about "new". There are 30+ year old bikes with enrichers rather than chokes. I think early 80's is about when chokes went away.

1980s and younger are "new" bikes :afm199

 

[Sharky]

Spray carb cleaner around the carb boots. They could be cracked

Carb boots on a 4bbl?