Mark L

From what I understand, the location of the start of the return line (at the fuel pump or closer to the carburetor at the fuel filter) is not model year dependent. It was changed at a certain serial number. The Authenticity Guide indicates return line at the filter is usually seen on later '64 models.

I called Myer's Studebaker Parts. They currently don't have any, but they make up another batch when they run out, so they'll be making more next week and sending one to me.

I appreciate everyone's help. I'm definitely missing the return hose nipple with the .043 orifice. The one I installed is a standard nipple for a 1/4 inch inside diameter return hose. The inside diameter of the nipple is probably too large and allowing too much fuel to bypass back to the tank. I checked my shop and parts manuals. The 0308-8 group of parts is for the return line, and one nipple p/n 1558295 is listed, but there's no other description, and the parts are not illustrated. Is p/n 1558295 the correct nipple I'm looking for? I'll call around to see if I can find one. If not, I imagine I can make a brass plug to fit inside a standard nipple and drill a .043 hole through it.

My Avanti is an early 1963 model with the return line coming off the side of the fuel pump. R1204. The "T" fitting was still installed on the side of my pump. The port for the return line was plugged with a NPT pipe plug. I didn't remove the T from the pump since the line to the carburetor was still attached. One of my suspicions was that the return line needed a restriction somewhere to maintain adequate flow to the carburetor. I mentioned I installed a check valve in the return line. I suspect the rhythmic nature of the problem may be from the fuel pump developing enough pressure in the return line to overcome the cracking pressure of the check valve. My theory is: the engine runs fine while the check valve is closed, but once it opens, the fuel flow back to the tank is unrestricted and causes reduced flow to the carburetor and the rough running. Once the pressure in the return line drops off, the check valve closes and allows fuel to resume flowing to the carburetor until pressure builds up again, then the cycle repeats. Yes, it caused the car to buck between proper acceleration and poor acceleration as the cycle repeated itself. About one half to one second of running poor before switching back, then one half to one second of running well before switching back again. As long as I drove it easy, there was no problem.

Is the restrictor listed as a stand-alone part in the parts catalog?

I don't think they are the original. Is the restrictor in the fittings at the pump for the return line? What is the inside diameter of the restrictor?

I have a copy of the shop manual, so I'll be consulting it. The current filter has a solid metal housing, so I can't see the condition of the filter without destroying it. I'm going to replace it to be sure it's clean. I'll cut the old one open to see what is inside. The return line was capped off long ago, based on the patina of the plug and the poor condition of the hose. The maintenance receipts I have show the fuel pump was replaced within the past 15 years or so, but no reason as to why, or why the return line was capped off when it was replaced. It might have been the "solution" to this issue. Before I restored the return line to the original condition, it was running fine. That's why I want to test the output of the pump. It may have sufficient capacity under load with the return line capped off, but insufficient capacity under load when the return line is connected.

Thanks, A0136. This is very helpful. Today I was talking to a fellow gearhead about this where I work, and he suggested I install a fuel pressure gauge and measure the output pressure under various conditions to help troubleshoot the problem. These numbers will help.

Thanks. I had heard there were differences between the pumps, but I don't know what they are. A few weeks ago I got the return line reconnected at the pump where it had been capped off in the past, and I installed a check valve in the return line at the tank, and replaced all the rubber lines. The test drive to fill the tank was fine. This past Saturday I drove the Avanti to a SDC chapter meeting, and it was really struggling. I punched the gas pedal to leave a four-way stop, and the engine bogged down repeatedly in a rythmic kind of way. It was fine on flat ground, but I couldn't accelerate going uphill like it was starving for gas. It was about 75 degrees on the way to lunch. On the way home, I didn't have any problems. Both the ambient temperature and the engine were about 5 degrees cooler going home. I'm just wondering if the pump is going bad, not the correct pump, or something else I should check. This photograph will help. I also have a '62 Lark Daytona with a 259, so I'll compare the two pumps.

What are the differences between a "standard" mechanical fuel pump for a Studebaker V8, such as a 259 or 289, versus a mechanical fuel pump for an Avanti R1 289? Is the flow rate and/or output pressure higher on a R1 pump to accomodate the Avanti's fuel return line to the gas tank?

I didn't do any work on the gas tank itself, so I can't give any advice on that. Neil Loughlin posted a series of videos on You Tube where he works on an Avanti. In one video, he describes the steps he completed to remove and clean the gas tank. That may be useful for you. The fuel hoses are pretty basic stuff. The vent hose is the most difficult due to its route. It goes through a rectangular channel and up into the right pillar between the rear window and the right vent window (directly opposite from the filler neck in the left pillar), makes a 180 degree turn, comes back down through the channel into the gas tank compartment, then goes down through a hole in the tank shelf in front of the right side of the tank. It apparently has (or should have) a clip that holds it up in the pillar. The hose passes through two holes going up through the channel and another two holes going back down. In a nutshell: I cut the ends of the old hose that were visible below the channel and pushed it and the clip up into the pillar. I will remove them in the future when I remove my interior for restoration. I'll put the clip on the new hose at that time. I straightened out a wire coat hanger and fed it through the inside of the new replacement hose. I tied an additional piece of aircraft grade .032 stainless lock wire to one end of the coat hanger wire. The coat hanger wire was sticking out one end of the hose, and the .032 wire was sticking out of the other end. The junction where they tied together was crimped tight to fit through the interior of the hose. I bent the end of the coat hanger into a hook and fed it through the holes in the channel so that it formed a guide for the hose. I beveled the end of the hose to make it easier to pass through the holes in the channel. I put some oil on the outside of the hose at the beveled tip to help it get through the holes. I put some oil inside the hose to make it easier to remove the wire once the hose was installed. I pushed the hose up through the forward holes in the channel while I was holding onto the coat hanger wire where the wire came out of the rear channel holes. The hose went up through the holes, was forced to make the 180 degree turn by the wire, and came down through the rear holes (after a lot of pushing and coaxing). When I saw the hose coming back out, I grabbed it with a pair of needle nose pliers and pulled it down the rest of the way as I fed more hose up into the pillar. Once I was sure I had enough hose to connect to the vent tube, I pulled the wire all the way out of the hose, cut off the beveled tip of the hose, and clamped the hose to the vent tube. I then adjusted the amount of hose in the pillar to make sure I had a tall loop that was higher than the filler opening on the left pillar. I then fed the hose through the hole in the bottom of the tank shelf. It took three tries to be sucessful. Adding the .032 wire and lubricating the hose were the two things I learned between the start and end. Ok, I guess that was a pretty big nutshell.

Earlier this week I replaced the plug in the T at the fuel pump outlet with a nipple, replaced all the rubber fuel hoses including the tank vent hose, and installed a check valve in the return line to the tank. I did not install the ball valve I purchased. I would have had to engineer a place to install it, which would have taken longer than the time I had available to work on it. The car had already been sitting on the driveway for the last month under a cover, so I needed to get it fixed and out of the weather. I should probably write a technical article for the Avanti magazine describing how I replaced the vent hose. I looked in the article index that was printed in the 2024-2025 member directory, but didn't see anything that described how to do it. That was the most difficult and time-consuming hose to replace. When I finished, I refilled the tank with 5 gallons of gas and leak-checked all the lower hoses. I then drove to the gas station to top off the tank to verify all the upper hoses were not leaking. Everything was dry. Now I just need to install the bulkhead and rear seat.

I'm also following the dual master cylinder portion of this thread. My Avanti only has the single master cylinder. Question: Does the Avanti already have a proportioning valve since it's front disc/rear drum, or will I need to add one if I convert to a dual MC?

Tonight I ordered a motorized ball valve for the supply line from the tank to the fuel pump, a check valve for the return line to the tank, and some Sidewinder mandrel-formed hoses. I'm also going to get a fuse, an inertia switch in case of an accident, and a toggle switch for under the dash. My plan is to run a wire from the ignition circuit to the ball valve, with a fuse, the toggle switch and the inertia switch in series with the ball valve. The particular ball valve I ordered is designed to remain open as long as its energized with a minimal power drain to keep it open. It's designed to automatically close if there is a loss of power. That way if any one item opens the circuit (ignition off, fuse open, inertia switch open, or toggle switch open), the valve will cut off fuel to the inlet of the pump.

I was able to quit work a little early today and found the problem. Since this is an early build car, the fuel return line to the tank comes off a T on the outlet side of the fuel pump. The port where the return hose should have been connected was capped off, and the hose to the return line was open. The entire output of the pump is going to the carburetor, and the fuel return line is acting like a tank vent/overflow. I spent the rest of the day's light siphoning as much gas as possible out of the tank and making sure the lines to the engine were drained. I'm going to replace as many of the rubber fuel hoses I can reach, and install a fuel barb on the T at the pump and get the fuel return line working again.