Put new quadrajet carb on 400, (my mechanic). running way to rich. told me he put a 750 but i need a 650 because the heads on the motor are not correct for a 69 400 330 hp motor. sd they are from a less agressive 400 motor. Motor was out and resealed. sd he noticed then. Does that make sense? I like my guy and he has dome a lot of work. Has a good reputation. The previous carb was period correct numbers matching for a 400. Ran well. he sd the base was bad and it was probably re- jetted.
anyone have thoughts on this mystery. I cant pull apart yhe motor at this point.
Second; Is this thing running rich at idle or cruise or both? Is it burning your eyes? Are there any drivability issues, stumble/hesitation, bogging down under heavy throttle, stalling or hard starting.
What's the ignition timing? Initial and total?
New Qjet from where? Do you know the calibration, needles and seats?
Need full motor specs, at least cylinder head and block numbers. Camshaft would be nice as well.
Let us know, otherwise we'll all just be spit balling.
Don’t worry. You’ll get the carb tuned. I’m guessing your running rich at idle and low rpm cruising. The secondaries are vacuum actuated, so that shouldn’t be issue. You won’t use the full capacity of the carb.
It could just be a float adjustment.
But, I could be wrong...
I'm a hobbyist. Not a professional. Don't be hatin'!
There's qjet guys and then there Holley guys because you can take them out of the box and they work pretty good. Sounds like your mechanic is of the later persuasion. 750 is not too big for a 400. A few years later they were installing 800s on them. I ran an 850cfm Holley on my 350 at one time. It ran like a raped ape. Truth is your motor pretty much decides how much fuel and air it can use regardless of carb size. If you want your car to run right with the carb you have you will have to find someone that knows how to tune your carb properly. If that's not an option buy a Holley 750 and be happy with how it works out of the box. Or better yet spend $2K on a new fuel injection setup and never think about it again.
