Talk Morgan Forums Morgan Sports Cars Morgan Three Wheeler & Super 3 M3W Fuel Pump Replacement

What you are referring to is the fuel rail I believe which connects the two jugs injectors fuel system. The little return line dumps the excess pressure back into the system. I see now, thanks.

You can't be turning the pump on and off. There is no accumulator to maintain the pressure when the pump is off. The bucket that the fuel pump sits in is to insure there is no fuel starvation when the fuel tank levels are low and the fuel is sloshing around. That is why the fuel return is dumped into the bucket. Walro recommends that a new fuel pump installation should start with 1/2 tank of fuel. They want the fuel pump wet and primed when it first starts.

So, here is how the fuel goes: starts at the pump, goes to the connection on one of the injectors, crosses through the short hose to the other fuel injector, then returns to the fuel filter. Why the fuel filter at the end of the loop? because inside the fuel filter is a pressure regulator that maintain the 58 psi fuel pressure in the loop. The only section of hose that is not under pressure is the fuel return line, beyond the pressure regulator, that dumps the unused fuel into the bucket where the fuel pump resides.

Thank you for the explanation Kolvites.

Thanks for the clear explanation! I wasn't aware that the return fuel was dumped back into the pump pickup bucket. Makes sense, but I wonder if that may be a contributor to the suspected heat-related pump failures?

If the fuel is "over-heated" by its trip past the engine then returned directly to the pump pick-up location, it stands to reason that over time with a hot engine on a hot day, that heat could build up faster (in the fuel going through the pump) than one might expect of the larger volume of fuel in the tank. If so, it may help explain why insulating the lines near the engine is reported to help with pump life.

I think the pumps are failing because they are cheap crap. There are a lot of manufacturers copying the old Walbro pump design. My OEM pump didn't fail after 4,000 miles, but I replaced it with a new Walbro anyway.

I took a failed pump apart... donated by Bill Fink of Isis Imports. One of the brushes had failed, most of the brush had crumbled with only a pinhead size portion making poor contact with the commutator. It was obviously a low mileage pump. The commutator was in good condition as were the bearings. There was no sign of over heating. I'll post some pictures when I figure out how to do it.

I will put a thermocouple into the fuel pump bucket to see how hot the fuel actually gets. I don't think over heating of the pump is the problem. The fuel is in contact with the hot injector bodies for a very short period of time. The fuel is constantly circulating through that area. With a fuel pressure of 58 psi in the fuel line loop, vapor lock is an impossibility.

If anybody has a failed fuel pump they want to send to me, I'll take it apart to see what failed and report.

Al Kolvites
1548 Brandywine Rd.
San Mateo, California 94402

This was the conclusion of Bill Fink (Morgan Guru), he believes that the return fuel is heated by the engine with the fuel line being too close and in contact with the engine. In tank fuel pumps can be very sensitive to heat which is why it is advisable to keep fuel tanks with these types of pumps at least half full. Bill's solution is to locate the fuel line away from contact with the engine and sheath it.

Agreed. I also don't think that hot fuel or vaporisation is an issue. Not had any fuel problems since replacing the original pump with the Walbro...... fingers crossed.

What a great thread with some truly knowledgeable people responding!

Top tips from the TM posse once again. The collective knowledge on this forum never ceases to amaze.

Long may it continue.

Very helpful. A good reminder that quality is always better than cost in the long run.