I'll apologize in advance for the long post. I recently rebuilt the extremely abused Super Six in my Gold Duster (She showed signs of being run extremely hot and without oil pressure a few times by her previous owner.) The original plan was to top it off with a Motorcraft 2150, but the adapter plate wouldn't seal completely on the back of the carb so I substituted a Holley 2210c off of a 1975 International 304. It fired right up and ran well, with a surprising amount of power, but had a massive, engine killing, dead spot off of idle and was overfueling severely. I figured it was the carburetor so I found a Carter BBD that wasn't worn out near as bad as my original BBD and rebuilt it. I slapped it on and got the car running again. It would accelerate ok but was completely gutless. After a few miles the throttle shaft loosened up and it developed a vacuum leak which wouldn't allow it to idle. I swapped back to the Holley, checked high and low for vacuum leaks, tuned the accelerator pump, and tweaked everything I could. The overfueling is fixed and the dead spot is a lot smaller now but still enough to render the car undrivable to anyone else but me. It seems like it isn't pulling enough vacuum to correctly operate the distributor. Any and all help would be greatly appreciated, I'm about at wits end with this engine.

I take it you've replaced the jets with something a bit richer, and not sure how you addressed the power valve. A 304 BB Binder engine has a very different calibration than a slant. I had a 266 BB and a couple 345's. Beasts of a different era. If it's out of the group of smogger engines from the mid seventies, it may be very tough one to tune.
Check with Charlie and see if he still has a line on NOS Holley carbs. Dan had some BBD's at one time, not sure if that source has dried up though.

CJ

Edit: The jets for the 304 were 53's IIRC. If the carb was off a 345, they were bigger.

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Thought about rebushing the throttle shaft in your BBD? A kit is readily available for that. Just search for "rebush" or "rebushing" by using the search function. It's bound to turn up.

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82 D150-225/727
02 Dakota-3.9/5 speed
87 GMC C7000-8.2 Detroit Diesel/5+2

I actually haven't done a thing to the power valve and the jets are stock. It shows signs of being rich but nothing too bad. The carb is definitely from a smog era engine. At best it pulls 17" Hg from the mainfold source and 10" Hg from the the ported source underneath the bowl on the front of the carb, 5" Hg from the ported source on the side. Once the car gets rolling it's fine, anything above about 1300 rpm it runs good, pulls strong, and accelerates beautifully. It's just that intial burst of air that does it in.

As far as the Carter goes, I have thought about rebushing the throttle shaft, but I just can't justify spending any more money on it at the moment. It is a combination of a early 70's 318 carb and the original slant six carb modified to work and rebuilt by the book. It ran, but it was pedal to the floor on most hills and was hard starting on a warm day.

Well, it's not the carburetor that's been giving me issues. I got a good carb off of a running engine and slapped it on her. Still the same problem. I don't know what's wrong with it. Pulled the intake and inspected it for cracks, checked for leaks. Nothing. It's sucking exhaust from somewhere, is my best guess. I'll run a compression test this week, but I doubt it's the head that's leaking.

What year engine/head?

It is a 1977 engine

Leaky EGR valve or blown EGR valve gasket or hidden crack in floor of intake manifold.

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Too many people who were born on third base actually believe they've hit a triple.

Thank 'ya Dan. The EGR has been long gone. It has a block off plate and the gasket didn't show signs of leaking, but I might try tapping and plugging the hole in the intake. I think I'll still run a compression check though. It had been run extremely hot cooking all the gaskets hard, but I'm not sure how prone these engines are to warping or cracking heads...

I ran a compression check and everything was within specs, installed a new intake gasket, plugged the egr, capped the pcv, and eliminated all possible sources of a vacuum leak. Same problem. I messed around with the timing and found it ran its best (while kicking the living daylights out of the starter) at 30+ degrees over tdc. It didn't run quite right but it didn't spark knock either. This engine seems like it is missing something. Ignition possibly? Maybe it needs its egr system? Or it just doesn't have the potential to carry the vacuum it needs... I've never seen anything quite like this. It seems like it has some inherited problem and possibly has never run quite right... I just don't know...

"Plugged the EGR" wouldn't help if you have a crack in the floor of the intake manifold, which you may not be able to see.

"Capped the PCV" is a large step backwards, not forwards.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

The pcv isn't an issue it made no difference one way or the other. I've seen and run engines before without them hooked up, never made a difference just let them vent into the engine bay. The way it runs no longer suggests an exhaust infiltration into the intake, this problem is deeper in the engine.

Yeah, it does. Put it together correctly -- the PCV is a good thing, not a bad thing. Capping it off is a bad thing, not a good thing.

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Too many people who were born on third base actually believe they've hit a triple.

OK. Let's get back to square one.

You rebuilt the engine. What exactly did you do? Be thorough with the description of the parts used, and what was done.

Did you surface the intake/exhuast stack? New studs etc...
Did you follow the FSM for tying the stack together once things were rebuilt?

You were running a BBD. What precipitated the decision to take a big block International carb and slap it onto a 225 cubic inch slant six? The air bleeds on that carb are not going to behave well with a small cubic inch engine. A slant is not going to behave the same with regard to vaccuum or flow rates.

See if Dan has any NOS BBD's in his goodie pile. That may be just the ticket. Not a plug and play due to age, but with a quick rebuild coupled with adjustments should rule out the carb problem.

Your in the midwest, so it's unlikely I'll be in the neighborhood until November, then I'll hang out with 'Zilla, 'cause he's really fun! (And has been known to let me drive his fast cars.)
Got any slanter's in the area that can help this guy out?

If he was in, say, western Oregon, we'd be on it. Long drive for us though.

CJ

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Thank you Ceej. The rebuild wasn't initially intended but when I pulled the engine out to fix a bad rear main seal shortly after buying it I found cam bearing material all over the inside of oil pan. I installed federal mogul main, rod, and cam bearings. Cleaned up the cam, rebuilt the oil pump, polished up the cylinder walls, new gaskets, rings, timing chain, adjusted the valves, your basic rebuild. Everything was federal mogul or fel-pro, timing chain was a cloyes. Brand new ignition, plugs wires, cap, rotor, and vacuum advance. All borg-warner, and autolite parts. The factory exhaust was replaced with 2 1/2 od pipe.

For the intake the studs are original, the intake hasn't been surfaced, but when I pulled it out this last go around the gasket showed no signs of leaking. The egr had been wiped out prior to my purchasing the car. Someone had cut and beat out the wheel and flap inside the exhaust manifold and replaced it with a bolt and made a block off plate for the intake. For the intake stack everything was installed and torqued to Chilton's standards during my rebuild.

For the carburetor(s) situations, the factory bbd had a badly worn throttle shaft, I blamed all of the engine's problems on this during the first drive home. During the rebuild I looked for a Motorcraft 2100 or a good replacement in the junkyards and that's were the Holley came in. According to other online posts its calculated cfm was slightly smaller than the bbd. It was a good carburetor and it functioned correctly after a thorough rebuild. The stumbling problem made itself known on the first drive with the rebuilt engine. I figured it was the carburetor. Searched a few more junkyards were I came up with a 318 carb that someone had modified to run on a slant. I took the throttle plate off it and put it on the my slant bbd and rebuilt it. It ran but it wasn't right. Took it off and put it to the side. Put the holley back on and tuned it. It fixed some issues but still no luck. So I got a new Summit bbd on loan from a friend and the problem is still there. Pulled the intake checked everything, all the gaskets, the compression of the cylinders, timing, nothing seemed out of place. Put the intake back on it with new seals and played with the timing. Tried a rebuilt Motorcraft carb, still the same problem.

The timing is now set at about 22 degrees, with the Motorcraft carburetor on it. This is the combination the engine as a whole seems to like the best. The hesitation is the smallest its ever been, but it is at a certain throttle position, no longer just off idle and it won't recover from it unless you let up on it or mash the pedal down. Everything I do helps it, but nothing cures it. The initial point were it starts keeps getting pushed back, but the stopping point of the hesitation has remained stationary. All I've been doing is just chasing it around trying to isolate it. Like I said earlier it seems like its "missing" something. It runs too well before and after the hesitation to suggest a major issue.

I wish I knew if it had this problem before, someone swapped that engine in for some reason. I'm starting to think it was for the wrong reason, not to put a good engine in but to pull a good engine out.