So I've got a 77 with the 20R and in tank electric fuel pump. Carb was rebuilt, starts up fine and idles perfect but i'm getting gas leaking from where the top plate and carb base bolt together. Gets wet in the areas marked in red on the first pic and on the second pic you can see the fuel soaked gasket above the fuel window.

This is with fuel half way in the window so it's not overflowing due to the float.

Main question is without a return line on the carb, when the float closes the needle what happens. Does the pump just keep pumping against it? Almost seems like it is then starts to leak.
I have seen posts talking about a fuel return valve?

 

And here's the truck in question. It had a weber so i'm trying to go back to stock for smog purposes

 

Did the problem start after the new tank and fuel pump went in? Does it show the saturation while at idle, or after curb revving, or driving?

when the float goes up, inlet plugs the fuel has no where to go up back up the same tube it came in or overflow the bowl so w a single hose inlet and outlet, my gues is...the fuel pump is likely connected to a fuel pressure switch which is also linked to emissions control circuit board. assuming this is the case, if the original fuel pressure switch is removed or disabled, it could explain the prob. Just thinking outloud. I have an 80..has inlet and outlet. I have all the emissions connected and running well now but had to learn a lot about the emissions switches and controller and all the switches that turn on and off for various conditions....there are a lot of dependencies and various conditions the controller deals with. unfortunately it u mess w one of the relays or switches it usually has an undesirable effect.

 

It came with a Weber and i'm going back to stock for smog purposes. Freshly rebuilt carb, didn't replace the tank/fuel pump.
Does it all the time while running or idling.

Yeah I know about the emissions but haven't seen that there's any kind of pressure switch. I do know the fuel pump is operated through a relay that gets a signal from the oil pressure sensor. The fuel pump only runs while there is oil pressure (cranking or running).

The repair manual does show a fuel relief valve in the tank, which I have but maybe it's not operating correctly? I'll have to pull it and check

 

#1 on the diagram

 

Do you have the pinout of the emissions control box? it should be on the wiring diagram. I would check that to see if there is anything that is switching on or off fuel pressure. Just a thought. I will look thru my 80's manuals tonight and see if anything else stands out to me.

 

I don't the manual I have (Haynes) doesn't show it

 

FWIW I also put a rebuilt stock carb on my '78 (same setup as your '77). The carb was pro rebuilt but I also had leaks in the exact areas you did, as well as a leak at the fuel inlet fitting. This started about 1K miles after the install. Turned out that the cover screws on either side of the fuel inlet had loosened up, as well as the "banjo bolt" for the fuel inlet itself. Snugging those up solved the problem. Each of those screws took about half a turn until they were "firm". The fuel inlet bolt was more like 3/4 of a turn loose. I also checked the rest of the cover screws & found two more that weren't exactly "firm" so tightened them as well.
Don't overdo this because if you torque them too much, you can strips out the threads in the aluminum carb body. yikes.

I replaced my in-tank electric fuel pump 5 years ago, but left out the relief valve, as it didn't seem to be functional anyway. I haven't had any problems with the relief valve not being there. Interesting that you say the truck had a Weber on it when you got it. Did it also have a fuel pressure regulator in the fuel line? Those Webers are well known to not like fuel pressure above 3 PSI or they tend to flood. The stock Toyota pump is rated for 5-8 PSI. If there is an old in-line fuel pressure regulator in there you might want to see what it's set for.

 

The weber did not have a fuel pressure regulator, but from the way it was running I think it needed one. I did check for that thanks.

I think I got it fixed but now need to do some fine tuning. Starts and idles perfect, drives fine at low speeds but sputters pretty bad when you punch the gas.

Took the cover off and the two sealing surfaces weren't exactly clean so I went over it again and got rid of all the old gasket. Thinking maybe it wasn't sealing all the way even though it was just small bits left over.
Also pulled the fuel pump and the fuel relief valve. Think the valve might have been gummed up, blew some carb cleaner and some compressed air through it while plugging one side and got it to operate.
Re-adjusted the float bowl level as well I was a little off.

 

Good work. Make sure your vacuum/mechanical advance on the distributor is working & moving freely, and has a good engine vac source. I use the "bent port" on the passenger side of the carb, the one pointing towards the front.

 

Would you happen to have some pics of your stock carb linkage? Think something is iffy on mine and want to see how it's all supposed to be setup

 

I do not have any static (still) pictures of the carb linkage setup, but I do have a video up on Youtube where you can see most of it here:
Extra Info. In going over (and over again many times!) the throttle rod linkage from the pedal to the engine, I've found several problems areas. Most of these are due to age, wear, dirt & grime & lack of lubrication.

1. Rod Ball-Ends. There are 4; 2 on the long rod in the engine compartment near the firewall, & 2 on a short rod near the gas pedal. The ball-ends on the long rod were worn & sloppy, causing a very erratic idle character. I fabricated a new rod with some threaded rod & 2 new ball-ends. It made a bif difference in the idle quality. The 2 ball-ends on the short rod were ok, probably due to them being inside the cab. I imagine that the ones underhood caught more dirt & grime that acted like an abrasive inside the joints over time.
2. Gas Pedal Pivot Rod. This rod sits in a stamped & formed sheet metal bracket, & "hinges" thru 2 holes in that bracket. I found some play or "slop" on this rod. I removed this bracket & rod assembly & disassembled it. I found grooves worn into the rod from where it had been in contact with the bracket holes (This issue will come up later). The holes were still round & no "oval-ed" from wear. No new replacement parts are available. So the best I could do was weld some new metal into the grooves, then grind & sand it back to perfectly round. This worked to remove the "slop" in the assembly.
3. Throttle Rod Hinge. This is the larger black piece, mounted on the firewall near the carb. It's there to supposedly allow the rods to move with any engine movement. This piece on mine currently has 2 problems. The lesser one being that the rubber grommets that the two bolts that go thru it to attach it to the firewall are petrified (hard). The larger problem is it has the same issue as the Gas Pedal Pivot Rod Bracket. This is (sometimes) allowing the carb Bellcrank rod to move back a bit too far, closing the carb's butterfly valves in the base too far at idle position. This sometimes causes a difficult hot start, with the carb "blowing back" large amounts of fuel vapor out the air cleaner. I have not fixed this yet, but have just been oiling or greasing the hinge near the pivot points, which helps it some.
Solutions to this problem? Possibles I've come up so far are:
A. Do a repair on it like the gas pedal pivot rod (remove, weld & grind/sand the original rod), which will be difficult as the hinge rod is peened into the bracket (have a look at yours, you'll see what I mean), OR
B. Remove original hinge rod & replace with new rod of same diameter & length & re-peen the hinge to hold it (same problem), OR
C. Cut the peened ends off the bracket to remove the original rod, replace with new rod of same diameter but longer length so I can drill holes in each end of the rod for washers & clips to retain it in the hinge, OR
D. Try to find a lower mileage unit from a '75 to '78 RV version of the truck. The RV's always have less miles than the pickup*, so their parts are usually in better condition & the hinge is less likely to have those grooves worn into it.
(* I've had good luck with this from YodaJims, with a gas tank, an exhaust manifold & a fuel sender.)

Frankly & in hindsight, I think it might have been better and easier to just replace everything with a later '79 & up throttle cable system. That's what I get for being a slave to originality.

 

Awesome that helps a lot i'll go through and check everything.
Does this look right at the carb? Circled was bent and tweaked for some reason so I pulled it down but not sure how it's supposed to be set.

 

I couldn't get a pic of mine with it being on the truck and that part being towards the rear, but as near as I can see that looks OK. That lever on mine is in the same orientation. That bottom tab looks to be roughly "in the same plane" as the carbs bottom surface, if you know what I mean. No idea what it's for tho.
Here an overall pic of my carb. Keep in mind this one has been de-smogged so there are less than stock number of vac lines. But it does run this way and pretty well.

 

Hmm ok thanks for the information and pic. That tab looks like it's connected to the arm on the secondary but it's vacuum actuated right? So not sure what it does.

 

It does look attached to the vacuum secondary in the diagram but I don't know for sure if it has anything to do with that or not. I never got that far into understanding all of this carb's particular quirks.

 

Ok thanks looks like mine's close to that maybe still slightly bent.

 

I have a'74 (18R-C engine) & a '75 (20R) and they served me well, but both had intermittent stalling/no power problems that were fixed by removing a very small plastic screen just inside the fuel inlet. It's about 5/16" high and 1/4" wide, it filters the gas just before it hits the needle & seat. I have no idea why they installed this, there's an in-line fuel filter that is many times larger, and many times EASIER to service, it (the gas filter) is just before the fuel pump (on the 18R) and about on the same area on the other. I don't think you can access the screen through the inlet, (but maybe...) I removed the top of the carb, remove the float, and unscrew the needle & seat assy from under the top, it will be sitting right inside.