MGB Stalling and then restarting after 4-5 minutes

Hi folks, Been away a while but just getting back into driving the '67 B. On my second tank of gas since the spring and she stalls after driving a while, generally 30-40 minutes. It's happened the last three times I took her out, once with a full tank, once almost empty and once in mid full range (I guess I'm a glass half full guy after all!). Haven't changed the fuel filter but it looks ok, I overwinter with a full tank of 93 octane, some dry gas and some Moss product that is supposed to minimize water in the newer gases, same routine for last 4-5 years. She loses power, and sputters to a stop. Sit a few minutes and fires back up. I recall reading a thread about vapor lock, but that was usually immediately after a fill up and in hot weather. This has happened in all weather. Noticed one of the SU's was a little low on fluid, but not enough to impact the delivery of fuel which is what this feels like. Contemplating emptying the tank and looking for schmutz that may have accumulated over the winter, I haven't driven it more than 10 hours total all summer. Any ideas anybody?
Thnaks,
Mike

Welcome home, Mike!!

Some build-up of crud on the float needles and seats would be my first place to look. After that, check fuel delivery from the pump. If it is an SU and the pump is degrading it can run fine for a while, then heat up and malfunction. If you can run the thing to the point of failure THEN check pump delivery immediately, you may get a better indication.

Good luck and report back!

Thanks Doc, Hope you and the Rose are doing well, it's been a while fer sher. In laws moved away from your neck of the woods so haven't been able to get down to see you again. Anyhoo, I had the pump rebuilt to solid state in Jan 2012 by Dave Dubois so I don't think it's the pump and I rebuilt the carbs my self at the same time with one of Joe Curto's kits, so I think that's ok. However I do suspect that the needle on my front carb doesn't fall all the way down and close because the pump will click after it stops (upon turning the key on) about every 3-4 seconds, leading me to believe the carb is still calling for fuel even after the initial fill. But your suggestion of floats and needles offers the path of least resistance, so I'll check that first and report back. By the way I''ve already checked the tire pressure, so that's not the cause!!!
Mike

Mike - before you go too deep in the fuel pump, the next time the problem occurs, remove (or just loosen the filler cap for the fuel tank. The vent in the cap could be clogged, causing a vacuum to form in the tank. If that doesn't cure the problem, then see the article Fuel Delivery Troubleshooting Guide in the SU Fuel Pump Articles section of my Homepage, linked in the signature block below.
Cheers,

Aw Jeez Dave, I've already pulled the engine and tranny and rear end!! The only problem with that advice is that I have to go for a ride and every time I go for a ride she stalls, but more importantly I am more concerned that she either won't restart or will stall multiple times on the way back home. I will start however with a close inspection of the cap, I dearly hope that's it.
Thanks!

Dave I don't know if you can make it out, but the vent hole is at 9 oclock, and is inside the ring created by the pressure of the tightening of the cap. The hole is clear, but cap fits so tightly and the hole is so close to the "pressure ring" that the amount of venting provided is certainly minimal. I have enlarged the hole a little in an attempt to determine if the gasket might have been fused to the inside of the cap, but that's not the case.

Mike - Best way to test it is to leave the cap lose (or even off completely if the tank is not completely full) and see if the problem goes away.
Cheers,

I don't know enough about MG's, but I've seen on a number of GM carb cars that people insist on running premium fuel instead of the recommended regular will foul out plugs much quicker and get similar affects. After stalling and the plugs dry out, it will run fine again for a while before stalling again. Replacing the plugs will return it to what they are used to, but the ultimate issue is the fuel grade. It is always best to run the fuel rating that engine was designed for. Premium doesn't mean better. May be worth a shot to run a lower fuel rating on a tank to see what happens. You'll generally smell some gas when this happens since you'll be blowing unburnt fuel out the tail pipes.

Hope you can track down the issue.

Mike said:

By the way I''ve already checked the tire pressure, so that's not the cause!!!

Click to expand...

Don't overlook those muffler bearings!! :smirk:

I didn't consider the cap... try running with it off. Good call, Dave. I'm still going with gunk buildup on the float needle and seat. The ethanol fuels are a real problem. Where the air/fuel interface in any carb occurrs, the stuff tends to condense moisture and a green-blue gummy crud is the result. I am currently in process of rebuilding the carb on a pal's pressure washer with the very same issue.

If Dave rebuilt the pump, that likely isn't the problem.

DrEntropy said:

If Dave rebuilt the pump, that likely isn't the problem.

Click to expand...

Can't really add to this with ideas except to not that "that likely isn't the problem" can blind us to the #1 maxim of LBC work. Never assume. Don't ask me how I know

So here's the result of first test drive with loosened gas cap, which is tough to to do since the '67's have the internal locking slots and the cap is either on (tight) or about to fall off. So I placed it on the spout entry held in place but loosely with packing tape. 28 miles into the drive, she sputters to a stop. I hear a little whining coming from my Powerblock located in pass leg area, I'll deal with that later. I immediately tried to restart it with cap completely off to no avail. Waited 5 minutes, turned key just enough to start fuel pump and it was clear that there was no fuel between the pump and the carbs as it took about 8-10 seconds ( or 2-3 times as long as normal) before the clicking stopped. Started immediately and ran for the duration of the trip home. I think there must be schmutz at the intake in the tank, when it gets blocked, the pump sucks as much as it can, the carbs use all available fuel and she stalls. I wish I had looked at the filter before restarting the fuel pump, I bet it would have been empty. Next step is to drain the gas tank through a screen and see what falls out. As a result of Mathrin's post, I pulled my plugs and found that while they are a perfect cocoa color, one of them was set at .22, while the other 3 were at the desired .33. Glad I checked, I run the 93 or 94 Octane because it doesn't ping at that level.

hmmm... I revise my initial WAG. You may have a tank issue BUT(!) did you hear the pump run on the "immediately tried to start it" part?

no , I didn't pause between key positions ,went right from oh shoot, gotta pull over to gotta jump out and remove cap to gotta jump back in and turn it over.

Instead of running a loose gas cap, put some cellophane over the spout, hold it on with and elastic and poke a hole in it.

I don't think that there is any further need to run with the cap off since the problem came back with the cap loose. I think that you are correct MIke, the filter screen on the end of the pickup tube is probably getting clogged with loose debris in the tank - particularly since the pump had to run longer than normal to fill the float bowls after running them dry.
Cheers,

I actually wonder whether you are overheating the pump? Logically, clogged should be clogged - so, if you wait five minutes for the line to "refill" you shouldn't be able to drive any more than it takes to empty the line again - you shouldn't be able to drive home as per a previous post (I assume that if it is clogged, it stays clogged - or even to the point of slowing flow) If on the other hand it isn't clogged but sludge, it would still flow but could clog the pump - which overheats and shuts down - and after 4-5 minutes cools enough to re-start and keeps running if the clog has passed? Just a thought

would lack of suction allow particulate matter do drop away from pick up after the four or five min allowing a restart untill enough matter clogged again?

If a clog occurs on the inlet side of the pump, it will cause the pump to get hot. If the clog is tight enough to cause the pump to over heat to the point that it stops entirely, it will take longer than 5 minutes for the pump to start working again and will also cause permanent damage to the pump, in the form of burning out the internal swamping resistor, which in turn causes greater arcing at the points resulting in rapid erosion of the points.

"would lack of suction allow particulate matter do drop away from pick up after the four or five min allowing a restart untill enough matter clogged again?"
Yes, this is a definite possibility if there is sufficient debris in the fuel tank to accumulate around the filter screen on the pickup tube in the tank and then fall away once the pump stops running. The tank should be checked for sizable debris to cause this scenario as normally the filter screen is a fairly course filter, meant to stop rocks and small birds from being pulled into the pump. The SU pumps and carburetors are relatively immune to the fine rust particles that often form in a fuel tank.
Cheers,

I have cleaned out the tank as best I could, I siphoned the majority out through the filler spout and using cheesecloth as a strainer found no particulates. I then emptied the last of the fuel through the drain plug and there I found a gelatinous substance in the straining cloth. I alternately flushed with clean gas and then I would blow out the tank using a compressor until there was no more of the substance, I would guess I got most of it. It dried up to a fraction of it's original size once in the air, but I could see where it could represent a mass of maybe 1/2" were it gathered together. If it were suspended in the gas I could see it being sucked in against the filter and as it was the consistency of "hardened" silicone I could see where it would fall away from the filter once the pump shut down. I also changed the fuel filter and upon opening the fanned filter found a lot of grit for lack of a better word. I'll be taking her out today or tomorrow and we'll see what's up at that point. One thing that concerned me was that my gas gauge showed a half a tank, but I nearly filled two 5 gallon cans. So a new gauge may be in order as well, I pulled the sender unit and cleaned it up and regreased the connections while I was in there.
I am concerned that the filter is too large to stop the gelatinous substance based on Dave's description of small birds and large rocks, I'm thinking I may have a rubber fuel line that has collapsed internally, that may be the cause for the grit in the filter also.

So a test ride has taken place, but only a couple of minutes then back in the garage to look for leaks etc. The whining from my Advanced Autowiring Powerblock turned out to be the fuel pump relay!!! So my question is could the relay be heating up and then shutting down until it cooled off enough to power up again? Didn't notice the whining when driving prior to the shutting down, but did notice it when trying to restart unsuccessfully. Just now jiggled the relay as it was whining and it stopped whining, (boy if it were that easy on other whining one might hear from time to time!) so I'm hoping it is the relay and not the entire buss arm or whatever they're called. any further thoughts?
Looked over the fuel line front to back, no old rubber except for the 2" piece right under the transom and fore of the crossbar, but that feels solid and there's very little rubber seeing fuel anyways as the metal pipes are about 1/2" apart. I changed out the fuel lines while the pump was being rebuilt. Missed that little section as it was painted when PO painted the chassis.