[70 RR]

I have a 70 Roadrunner 440/6 w/4 speed and 4.10 gears. When l really get on it, the motor bogs and there is a slight hesitation. After a second or two of this, the motor seems to get caught up and runs like hell. I have checked the timing and set it to 12.5 btdc. The holley carbs are new with an Eldelbrock aluminum manifold, E Street aluminum heads and a little hotter than stock cam. Also Mopar electronic ignition, new Accel wires and new Champion RC12YC plugs. Any thoughts? Thanks.

 

[70 RR]

Hey dana44,

Thanks for your input. A friend of mine mentioned to me the "total timing" of 38 degrees. I will experiment with your suggestions this weekend.

70 RR

 

[70 RR]

I was thinking about that last night and couldn't remember if I had added that or not. You or your friend know how to figure that out, right? The butterfly portion of the rotor shaft that is part of the mechanical advance has a number stamped on it, which is either 14 or 17. Double this number is the mechanical advance available, so 28 or 34. From there the 28 is best so you can have (or should have) no more than 10 degrees at the crank, so you should back yours down just a few degrees, kind of hard on the starter at this point, especially when warm, and then the heavy and medium springs under there will make it nice and smooth, especially with those 4.10s in the rear. Oh, and too much advance tends to have a history of both bad gas mileage, and broken pistons, so not worth pushing it.

My friend has way more knowledge on this subject than I do. I ordered a couple of the vacuum spring kits and will consult with him on the rest. I hope to get on it this weekend, I will give you an update as soon as I do. Thanks again!

 

[70 RR]

There's also a bleed hole on the wall of the venturi of outboard carbs. This hole is drilled into the vacumn signal port feeding the diaphram that the spring pushes against. If that hole size has been changed it will impact the opening point of the secondaries. Check it for dirt.

My carbs had the second strongest spring (brown) in both the front and rear carbs. I swapped those for black springs and the car ran perfect. Would you suggest putting the brown spring back in the front carb, or leave well enough alone. By the way, I appreciate the help!