400 Big Block running issues
It's an under the hood type, I think that the psi might be getting a little high during high rpms...
Tank venting = unknown.
Not checked the sock pickup in the tank, could that be blocked?
Cheers
Jon
If you are able to repeat the problem with full throttle runs I would be willing to bet one of two scenarios. I'm not really familiar with the Holley carbs, someone help me out here, I think it may be possible that at WOT you are dumping enough fuel on the plugs that they are getting fouled, making it run like **** and tough to start back up, after you get it started, it could be clearing them after some running.
I bet it's either that or it's gobbling all the fuel out of the float bowls and starving at the top of 3rd gear, then the pump has to catch up.
Once you KNOW your carb and timing are correct, if it still does this same thing, I bet the pressure is dropping to the point where the float bowls are out of fuel at the top of 3rd gear. The first things I would look at would be to make sure the floats are set as high as you can get away with on that carb, pull the sending unit out of the fuel tank to check the mesh sock to be sure it's not gunked up. If it looks good you will want to get a new gasket for it anyway, the gasket likely came out in pieces. Make sure the fuel line hasn't been crushed somewhere on the bottom of the car. The tank should be vented to be sure when the fuel level is dropping it doesn't try to stop the flow of fuel with vacuum - picture dunking a glass in a full sink of water, turning it upside down, and pulling the bottom of the glass above the level of water in the sink, the water stays in the glass until the top of the glass clears the level of water in the sink. I know the tank is different from '68 to '73, but they may have had a similar setup, mine had a 2nd line from the tank that went up to the engine bay (this part I know for sure), was somehow hooked into a charcoal canister (I think, it's been years since I dealt with it) that I think was tied into the vacuum system on the engine. I removed all that and added a breather filter to where the 2nd line tied into the tank.
Those are the possible scenarios I would try to eliminate first, hopefully this helps.
Good luck! Please keep us posted on what you find.
- Steve
