More carb tuning problems.

[scottj]

Originally Posted by Humbucker

Actually, it's 5 sizes up.

To fill you in better, I had the Ford crate 392, 430hp engine. I put AFR 185 heads on and a Victor Jr. intake. Those are the only changes I made.

Before that, the car ran perfectly. Very strong and streetable. This was on 71's in the front and rear of the carb. I'm thinking 73's in front and maybe 74's in rear to start with??

Perhaps the 76's I put in on Wednesday was waaaay too much.

I keep coming back to this major jetting change. If the carb was correct with 71s before then it should be correct with 71s now. Drivability may not be perfect because of changes to the signal strength but, unless you modified the carb the jet requirments wouldn't have changed. I would put it back to what JET Perf had in it and call them.

[Humbucker]

I was under the (perhaps misguided) impression that making a significant upgrade in power and airflow would require one to jet up a bit.

Don't get me wrong. I'll certainly and happily submit to superior knowledge, but was I just mistaken? You're not the first to mention this. A couple local guys suggested I stay the same and see what happens, while a couple others suggested upjetting.

I just figured morre airflow would require more fuel, thus more jet. What am I missing? Thanks for taking the time with this, too. Much appreciated!

[scottj]

Originally Posted by Humbucker

I just figured morre airflow would require more fuel, thus more jet. What am I missing? Thanks for taking the time with this, too. Much appreciated!

You are correct- more airflow does require more fuel and that is exactly what a carb does. The more air that goes through the carb the more fuel that air draws with it. Once the ratio (jetting) is correct the carb will pull the correct amount of fuel based on airflow.
For what it is worth, I switch carbs between 600 hp and a 800 hp engines and I don't have to change anything.

[JLC800]

What size shooters are you useing?
If they are 32s, your OK there. Then try an 8.5 Power valve.
Sounds like you are experiencing a bog or hesitation off idle.
This should eliminate the momentary lean condition from idle to the mains.
Jim