hey guys i just put smaller jets in my edelbrock 750 carb. it was running rich and got horrible gas milage, so i put a smaller jet in it and a slightly smaller rod then wut i had in there cause i had the biggest one in my kit. ok well my question is- I have tuned the carb to my best doing the max rpm deal and it smells a tiny bit but stumbles nowhere or anything, seems to idle consistant within a 150rpm range, but i think i can go leaner so how do i tell if i am to lean? thanks guys

 

look at the spark plugs, black is too rich, tan is too lean, you want them looking pretty clean...just a slight tint...

 

If the car still has good drivability after leaning out the primary jetting, it is not likely too lean.

The best way to tell is to install a O2 sensor on the exhaust and
a A/F ratio guage in the car.

14.7:1 is the chemically idea ratio and best for emissions with the current emissions devices. ( egr, catalytic converter etc)
but is not the best A/F ratio for best fuel economy at cruise.
Something around 15:1 to 17:1 is better. Exactly how much leaner youwill be able to tune your motor to will depend on a lot of things. Like cylinder to cylinder fuel distribution among other things.

Keep leaning out the A/F ratio at cruise by installing "smaller"
jetting. that means a smaller jet and a rod with a larger cruise step diameter until it starts to not drive right ( surging @ part throttle cruise) Avoid full throttle testing for now as having it too lean at full throttle can damage your motor.
Also be sure the motor is fully warmed up before deciding
if the drivability is ok or not.
When you get the jetting leaned down for good cruiseing gas mileage,, having the choke hooked up and working will become much more critical and nessessary for cold motor drivability.

When you get to the point of leaning out the jetting where it starts to stumble and surge while cruising, or you hear any detonation (pinging),,, THAT IS TOO LEAN.
Now install jetting that is a little richer until the drivability just comes back. Now you are close to optimum.
Note: leaner jetting will burn slower and want more ignition timing AT CRUISE!!. This is where tailoring the VACUUM ADVANCE
comes in.

Remember the full throttle jetting of your carb is not that far off
if at all with the stock jetting. So now you need to install a rod/ jet combination that will give you the jet area that is best for cuising with the rod down in the jet and best for power @ WOT with the rod up. "Power Mode".

What jetting / rods do you have in the car now?

And what color Power Step Up Springs are installed?

Of course if you'd change the cam you'd have half the battle won. You will not go slower!!!

DO NOT F***K with the secondary jetting and do not operate at full throttle while tuning the primaries!!!! For Now...

 

Well it was a 750 manual choke so it was set a little richer form the factory, but i put a .110 jets in it and orange springs and i can't remember exactly wut rod rigth now. i will have to go to the garage and check.

just ran out side and i have a .068x .047 metering rod in it right now. I was runing the stock jet and i had the biggest metering rod in my kit in there to lean it oiut and it did help but i just couldn;t get it perfect

 

Buy a set of #1458 rods .075x.037 (they are not in the tuning kit for the 1407).

Use these rods with a .107 to .110 primary jet, blue springs,
and .107 sec jets.

Be sure timing is set accuratly for 32 to 36 deg total mechanical
at high rpm and plug the vacuum advance into "ported vacuum source".

Buy a manual choke linkage kit ( about $10) and install it so you'll have good cold engine drivability with your new "Leaner Jetting"

 

Unfortuatly the combination of .068x .047 rod with a .110 jet is about the same as the stock .071x.047 rod and .113 jet
at cruise. It is slightly leaner at WOT.
You want to concentrate on the Part throttle cruise tuning first.
try the .075x.037 rod with a .107 to .110 jet and blue spring.

Edelbrock should have included the .075x .037 rod in the kit.

 

well i did out an electric choke on the carb so nothing to worry about there. with this combo and having it jetted and tuned right wut kind of gas milage do u think i can get out of it? about 10 out of the peddle? I don;t do much highway driveing so that doesn;t mater much to me

 

I would not expect great mileage out of it in the city.

Especially with that camshaft. It's just not efficient in the rpms
that use use to cruise in the city. But you can improve it by tuning.
Your mileage will depend a lot on your driving habits.

A heavy foot will $$$cost ya$$$