I know of one car that was fuel level in the tank sensitive. It operated great below 1/4 tank or so. Above that fuel level there was an issue. Car was acquired without the cigar hose present.

I suggested over some objections that the cigar hose was needed. The objections where that the only function was noise reduction. The fuel level operational problem was then gone when a new cigar hose was installed for the tube.

If the fuel pressure is normal. The relief valve will always be open or at least 95 percent of the time. There are fierce hydraulic pulses inside the injection pump.

The cigar hose being of softer rubber mitigates their severity. That is also a reason to compare a really old heat baked cigar hose especially in the southern states with a new one. If the cigar hose has become hard of course there will be no difference with substitution of a solid tube for it.

There may also be no apparent differance with the hose being soft and substituted with a stiff hose. I would want to know the operational pressure in the base of the injection pump if that was the case. It may be below the opening pressure of the relief valve. A simple test may be to look for fuel returning to the return line.

Their are some issues in this area as well. Some euro cars with the same euro injection pump where manufactured with and without the cigar hose. We got a diferent injection pump in north America. I never researched that to find the reason and do not know if it is mentioned anywhere or not.