Ideal 1985 5.0 Air fuel ratio

[Stang1985]

I’ve read a few articles with various info. What is the ideal afr at idle and under full throttle? Car has a Summit 650 carb, Edelbrock performer intake, and BBK off-road h-pipe with unknown mufflers. Any insights are greatly appreciated as I try to get a couple more drives in before the great white north has it parked for 6 months.

[richpet]

Idle with my FiTech, cold (coolant temp 77).

When warm (over 170°) it runs 14- 14.5 at idle.

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[Two86fiveoh's]

Full throttle 12.5-13:1. Idle, 14.7 is ideal but I've found these 5.0's like it a bit on the rich side. 14:1 should give a nice idle without burning your eyes.

[Bentley]

What do you do with your car?

[Stang1985]

Full throttle 12.5-13:1. Idle, 14.7 is ideal but I've found these 5.0's like it a bit on the rich side. 14:1 should give a nice idle without burning your eyes.

thank you, my numbers are way off. I’m at 10.6 at idle and can only get to 13.0 with the screws almost all the way in and it idles at 1100. Would reducing the jets fix this? First carb I’ve messed with.

[Stang1985]

What do you do with your car?

Enthusiastic driving driving from time to time, not a street/ strip car.

[Stang1985]

How do you like the FiTech system? How was the install?

[emerygt350]

That is odd. Stuck float? Too much fuel pressure? Jets too large? Makes me appreciate my CFI....

[richpet]

How do you like the FiTech system? How was the install?

I'm liking it. Had some initial frustrations and component problems, but all seems to be sorted. Car has awesome throttle response, makes great power, and gets decent mpg (at least a bit better than a carb).
I just like never having to mess with a choke, etc., and it starts right up every time regardless of the temperature outside.

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[Two86fiveoh's]

thank you, my numbers are way off. I’m at 10.6 at idle and can only get to 13.0 with the screws almost all the way in and it idles at 1100. Would reducing the jets fix this? First carb I’ve messed with.

1100 rpm idle, is the throttle shaft binding holding the butterfly's open? Check for vacuum leaks as well, although if there's a vacuum leak it's minor with your AFR so rich.

Manual or electric choke? If it's electric, try adjusting it. That may be causing both the high/rich idle.

When I still ran carburetors, I always deleted/disabled the choke. They always irritated me, so I ditched em'. EFI is sooooooo much easier to tune and much better power/driveability.

[Bentley]

So you have a stock street car with an intake on it?
First thing your Carb is too big... Go down to a 500 CFM....

[Two86fiveoh's]

Agreed the 650 is a bit too large, but it leaves room to grow if he decides to do future mods. The 650 can be jetted/tuned to work with his combo.

[Bentley]

Agreed the 650 is a bit too large, but it leaves room to grow if he decides to do future mods. The 650 can be jetted/tuned to work with his combo.

You can never tune out the additional CFM's of air with a too large a carburetor.....

[emerygt350]

ummmm... the air does not make it rich, you just put smaller jets in it. The car only pulls what it pulls. The carb may not be operating optimally but it should not be show stopping issue.

That said, carbs are cheap, a 500 would be easier to tune on a stock motor.

[Stang1985]

Yes the car has a stock engine aside from the intake and carb. I recently purchased it with the 650 and it ran rich and fouled the plugs. I’ve been able to get the afr somewhat close to what is recommended, but if I get on it, it will buck at 2000 rpms afterwards. If I drive normal, there are no issues. It’s still showing around 10.9 at idle. If I rejected it, what would you recommend? It should have 69s right now.

Thank you to everyone who has been sharing knowledge.

[Drivunn]

I just went thru this this week after putting a Holley 4777sae dbl pumper 650 on my 331 stroker. Started real rich in the 10/11s. Dropped primary jets down 3 sizes with little effect. Read on one of the forums that it might be the secondaries needed to be opened more or possibly change the power valve. Since I felt I was just guessing at stuff decided to ask my mechanic to check. In two hours of alternating carb work with quick runs, the biggest improvement came from adjusting the secondary opening using a screw midpoint under the passenger side of the carb. Had to remove carb given manifold/fuel line routing. As I recall they opened it up to 2/3rds of a turn. That got us into the mid 12/13 range at idle. We played some more and basically ended up near standard primary jet of 64 and 73 on secondaries. Left the power valve alone. The primary shooter was weak at 29 so we upped to 34 to resolve an off idle bog. So go try the secondary screw next and then redial in the jets again. Double pumpers usually run rich since they are performance carbs so I’m happy at 12.5/13.5 idle and got to 14.1 at cruising rpm’s, never more than 14.6 on acceleration.