Carb Help 440 GTX

[Blake67GTX]

Hi, I have a 67 GTX convertible that I'm trying to get running for the summer. I've worked on it on and off thru high school and college and now have some money and time. I could definately use some help. It has a relatively fresh rebuild with less than 1000 miles. Anyways, I'm having trouble with it idling and at WOT. It seems that the 850 Double Pumper w mechanical secondaries may be too big and a 650 vacuum secondaries is worthless. But to start things off, its a 440 .030 over with the factory mopar hp heads, 10.5:1 compression, 1.5 MP hydraulic rockers (stock valve train), headers, 292 dur/509 lift purple shaft cam, Weiand Team G single plane intake. 727 Torque Flight w 2500 stall. BUT, unfortunately the 8 3/4 still has 3.23 gears and that too will be changed soon. It is a 67 GTX, so if I'm not mistaken it weighs approximatley 3700 lbs. With the 850 cfm Double Pumper mech.sec., the car wouldn't idle worth a crap and was hard as hell to start. The timing was off. Fixed it. Runs like **** still. Pulled off the Holley, put an edelbrock 650 vac. sec. Starts up fine, idles okay, WOT is pathetic and obviously starving for fuel. When floored, its pops and hesitates... Please help, I'm somewhat new to this and could appreciate some wise advice. What type of carbs and what range of sizes should I be looking for? What could be compromised and what can be gained? Thanks...

 

[Meep-Meep]

Hey there. First off I'd go over all the basics and make sure everything is in spec. Ignition system including advance curve (approx 34 deg @ 3 KRPM with vac advance disconnected), plugs, double check firing order, voltage to the coil, fuel pump delivery, vacuum leaks, compression, float level, etc.. Then make sure whatever carb you will use has the factory jet settings and power valve. In my experience carbs are quick to be blamed for problems but rarely at fault.

 

[Blake67GTX]

Alrighty...I will check those items. Hopefully, it will get me closer to the problem.Thanks...

 

[moparstuart]

welcome

 

[dantrap]

if you had any backfires you may have damaged the power valve on the 850. Or the carb is to fat. I used to run a similar setup with 87 jets all around. Check your float levels, fuel pressure and idle mixture screw settings. You can try setting them at 1 1/2 turns out from the seated position as a start. If its an old carb it may need to be cleaned and rebuilt. On the big 4150s I have used in the past they all had .060" holes drilled in the primary side throttle blades to help air flow at idle with the blades closed. There is so many things you can try, but we could be typing for hours. Take your time and triple check everything, as described by Meep Above. Good luck.