Here's the deal. I have a 78 Ranchero with a mostly stock 400M that has 130k original miles and I don't believe it has been serviced (top end rebuild, rings, etc). Doesn't smoke or anything, just feels generally down on power. It has a Weiand 8010 dual plane manifold and an Edelbrock AVS 650cfm carb.

It performed well when I first got it, but a bit rich at idle. Anyway, I had the dizzy loosened for some reason, and lost my timing setting. Also replaced the plugs wires rotor and cap. I couldn't see any timing marks on the damper, only because there's a thick coating of oil and dirt. I cleaned it up a bit and found a chalk mark that was at I think 16° BTDC, and I couldn't get ahold of the PO, so I set initial timing at that. Ran like crap, would start stalling at anything more than 1/4 throttle. I had experienced that before with my El Camino where the dizzy was stabbed in probably two notches off, and it ran severely retarded. So I advanced it a bunch, and it ran better, so I concluded the damper rubber had slipped, and have been timing it off that since then.

I've been timing it with vacuum, and aiming for 18-21 inHg. I've tried multiple settings of idle mixture and timing, but still had ill results, stalling at high RPM WOT. A few days ago I realized it may have been a bad fuel pump, so I replaced it. Whatever settings I had when I replaced the fuel pump, it ran well, didn't starve and ran strong all the way through the range in every gear, but still felt down in power, and the plugs read lean still. So I adjusted the timing some more, and it started starving of fuel again. That either means something is clogged (in-tank sock filter, fuel lines, or something in the carb), or the timing is really wrong (likely advanced?).

I just set the timing back to the 16ish° of initial timing, but haven't had a chance to test it out yet. I will in a bit, but does anyone have any insight? I'm waiting on the adapter for my fuel pressure gauge, so it'll be a few days.

p.s. I hate that I have such a low post count and I'm already asking for technical advice. I'm a member of a few other forums, and that was always a pet peeve, so bear with me. Mainly because they never introduced themselves and never made any contributions to the forum. But I've done one of those so far

 

Okay so I hooked up my fuel pressure gauge, got 5.5-6 psi on the gauge (gauge is notorious for calibration being off) when the engine was cold and the fuel filter was still full. After running it a bit, I'd get some starvation at high RPM WOT, but the fuel filter was still about the same and as well as the pressure. After another 15 minutes of running I got home, and the fuel filter was empty and the engine was lugging slightly, and the pressure was about 4.8-5 PSI.

Maybe a tank venting issue or in-tank fuel filter?

 

The pressure is about right for a Carter. However, you said the filter is empty but you still have pressure? That sounds like vapor locking. You don't show your location (go to User CP to add that), but it is certainly the time of year for that. And, the ethanol in the gas makes it even worse. So, check to make sure your fuel line isn't running against the block or close to the exhaust.

Another possibility is a cracked or otherwise bad fuel line. I had one on an 82 that was so bad it would leak gas through the side of the hose when sitting, and pull air through it when running - which killed the pump's vacuum so it couldn't pump. And, that usually stalled me on the side of the road after about 15 minutes of driving.

 

Yes, after about 15 minutes of driving after the engine is up to temp the filter will start emptying, but I'll still have roughly 5 psi.

I'm in Hawaii, so it's hot year round, but it's been unusually hot recently. my fuel line from the pump is routed up the front of the block through a hard line, then over the valve cover to the carb. I am familiar with vapor locking and in my experience (with old bikes) a venting problem caused it. Do our fuel tanks have a vent, or is it in the gas cap? I may end up dropping the tank, and if there's a vent tube on the tank, I can inspect and service if needed. One thing I did notice is that when in filling up the tank, it likes to spit out gas when it it's about half full, and I can hear it "draining" into the tank then it's ready foe more fuel. this sounds like a venting issue, yes?

 

The tank vent runs up the passenger's side frame rail to the vapor recovery box that sits below the battery. From there, in stock form, a hose runs to the carb via a solenoid to pull the vapor out during operation.

One way to check for a vacuum on the tank is to pull the tank's fuel fill cap, which isn't vented. Either run it that way or pull it after the problem develops to see if you hear air rushing in. But the problem of filling the tank is just a poor design that was changed in later years.

 

Thanks Gary, I'll check the tank vent and vapor box. I don't have the stock carb.

I believe I had a slightly kinked fuel line near the carb, and putting a hose clamp around the kink helped a bit. The air cleaner still pushes down on the rubber hose near the fuel inlet. I have the Edelbrock banjo bolt/chrome line/filter kit, as well as some AN fittings for the hard line and running a pressure gauge. That will take care of any kinking under the hood.

I'll also check the gas cap when I can.

Been working on the Vette suspension all weekend along with being on call all weekend. Fun stuff.

 

Alright I checked, and since the Ranchero is based on the Thunderbird, not a truck, there's no room for vapor canisters under the battery. I checked from the tank, and the only vent there seems to be one that goes to the filler neck.

 

So, if the vent is to the filler neck, then you have to run a vented cap. Are you? If not it will pull a vacuum on the tank and the engine will die. Try driving without the cap?

 

I don't believe the filler cap is vented. I'll double check everything though.