[Mgs] Intermittent fuel problem- 1974 MGB

[wkilleffer at epbfi.com]

Hi everyone, 

The car's a '74 MGB with an 18GK engine, HS4 carbs, SU fuel pump, Pertronix ignition. May or not make a difference, but the pump's less than two years old, and I haven't run up many miles since it was replaced. 

I've posted on here a few times recently about some fuel issues, and they continue to baffle me. The most recent issue is quite frustrating as it seems intermittent. 

Recently, I installed a new fuel tank in the car, and replaced the rubber line from the pump to the metal line, and the rubber lines under the hood, and the fuel filter. I've also replaced the anti-run on valve, oil pressure switch, all the lines under the hood associated with the ARV and evaporative system, the rubber fuel inlet collar, and the rubber lines for the vapor separator in the boot. 

After doing all this at first, I had to take the carb float bowls apart as the grosse jets had become clogged. Got that rectified and everything seemed ok at first, but then after some driving, the car started running like it was getting fuel starved, and I noticed what looked like some black chips in the fuel filter. I unhooked all the rubber fuel lines and and pump, and then blew compressed air through the line back to the pump. All seemed well for a short amount of driving, but then it bogged down again, got flooded when I tried to start it, and fuel ran out the ARV. 

I took the carb bowls apart again, and figured out that the rear carb's grosse jet was stuck open. I cleaned it, got it to work properly, and checked the front one as a precaution. All was well there, so I checked the junction for the evaporative line in the rear fender, and it was clear. No sign of any rust residue at all. I then took it for a test drive of maybe 30 minutes without incident. 

Today, I felt confident enough to drive the car to visit my folks, who live about 20 minutes from my house. All seemed well until I was about halfway there, and I started getting the symptoms of fuel starvation. Thankfully, I could pull into a parking lot to figure it out. I noticed that there seemed to be more of those small black chips in the fuel filter. I unhooked the fuel line from the carbs and switched the key on, and it was pumping a jet of fuel about every 2.5 seconds. I put the line back on the carb and started the car. It ran, and the fuel pump seemed to bang away like a hammer if I revved the engine up above around 1200 rpm. That didn't seem normal, so I looked under the hood, and the fuel line into the fuel filter nearly came off in my hand. It looked like the clamp had it on tight, but it wasn't. I made an adjustment, started the car, and all seemed well, so I motored away. 

Trouble is, I had two more incidents on the way. My father looked at things and said that it appeared that the fuel lines could be coming apart from the inside, and that maybe I should get new fuel lines and a new filter. He also wondered if I could be sucking air, but I showed him how I'd tightened all the fittings, almost to the point that I was afraid of rounding off nuts and bolts or stripping threads. I showed him the ground in the trunk and how it was clean. We went and got a new length of fuel line and a filter, and I put them on the car. 

Now, here's the odd part: I took the battery cover off and had a look at the pump from that angle since I could see the end of it near the battery box. I then checked that connection and discovered that the terminal was loose. A check of the ground terminal on the pump found that it was ok. I used a small wrench to tighten the nut on the + terminal and plugged it back in. I really expected to hear more clicking from the pump when I started the car, but it was functioning. 

After a few hours, I drove home, and came sooo close to making it home without incident. But it did it again, acting fuel starved right outside my neighborhood. I managed to limp it home. 

I really thought the problem was solved when I found the loose power connection. I tried running it without the fuel cap, but this didn't make a difference. It's late and I'm tired, so I'm not sure what else to say except that the intermittent nature of this is making it very frustrating. 

It's been hot and muggy here, and I wonder about vapor lock, but that's not supposed to happen as long as fuel is flowing, right? 

Needless to say, any advice would be appreciated. 

Thank you, 
-William 
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