TR2/3/3A Electric fuel pump questions.

[tinman58]

I have a TR3 with a supercharger. (Moss Motors ). While out on a drive thru the hills on Saturday the TR felt like it kept wanting to run out of gas. It would spit and sputter for a bit as I would pull over and after a few moments it would be back to normal. After about 70 miles of this %^$# I made it home. The fuel regulator is set at 4.5 . Today I hooked up a fuel pressure gauge in line between the pressure reg. and the Carb. At idle 4.5 Normal acceleration 3, under hard acceleration it would even go down to the negative side as I would let off it would climb very slow. I do not know much about the electric pumps. I do know that they either work or don't work. This one works but not good enough or am I doing something wrong or ??????

 

[TR3driver]

How much is the pump producing? Sounds to me like either the pump or the regulator can't keep up with the flow required. (Although unless you have more than one pump, the negative reading says to me that your gauge is wrong.) The reason I ask about pump pressure is that regulators require a certain amount of pressure drop in order to deliver their rated volume. Checking pressure at the pump outlet would also tell you if the problem is the pump (or in front of the pump) or the regulator.

Another concern would be if you have installed a paper element filter in front of the pump. If so, I would try changing the filter first, as the paper may have absorbed water causing the pores to close up and not pass enough fuel. (Actually, if it were me, I'd remove the filter entirely or substitute with a screen type. A paper filter only belongs after the pump.)

 

[tinman58]

Randall
I have the clear cleanable filter and I have cleaned it . Right out of the pump I get 5 PSI. No kinks or other obstructions in the line. Can I install a higher PSI pump to accommodate the fuel required to keep the 4.5 PSI at the carb?
P.S. I called Moss tech support but no call back yet.

 

[TR3driver]

Which regulator do you have? If the pump is holding it's rated 5 psi at full throttle, then using a larger pump isn't going to help. I think you need a higher pressure pump or else one that does not require a regulator after it. Several of the racers have reported that using a regulator at all in combination with a float valve can cause problems. Also worth double-checking on the regulator specs, whether it has enough return line and so on.

Did Moss switch away from using the SU HS-8 carb on their blower? 4.5 psi seems like a lot for an SU.

Might also be worth hooking up your pressure gauge on the pump inlet side, to see if it's pulling a vacuum against something. I had some serious fuel delivery problems on my TR3, evidently caused by body shop dust settling in the bottom of the line from the tank. (I specifically asked them to block off the tank entrance during the painting process, but they didn't do it.)

 

[tinman58]

I have the regulator that came with the blower. Also it is the SU HS8 carb. 4.5 is the recamended pressure from Moss. I am getting 5 PSI right at the pump, but not under load. I think I will get a fuel pressure gauge to mount on the dash to keep a watch on things. A drove the TR to a show last night and had no problems. I will go for a longer and faster drive this morning.

 

[tinman58]

Problem solved! The electric fuel pump was bad. I thought that a fuel pump works or don't, Talked to Blaine at Moss and thought it was rare for the pump to be intermittent . After installing the new pump I ran the TR down the HWY 4 bypass at 100 mph, for as long as I could stand it, (about a mile) No hesitation or any problems.
Thank You Randall for your help.