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MG MGB Technical - Car shutting off

Hello! New 1965 MGB Roadster owner here. I have the following problem: after warming my MGB in the morning I drive approx 2 miles and then all power is lost. The motor dies and if I give it two minutes I can start up and drive for the rest of the day with no reoccurrence. This has happened 3 times and ive owned it for 3 days. This only happens within 20 minutes of a cold start. The fuel pump seems to be making it's usual working noise and when this occurs there is gas is my fuel filter.

Any ideas?

Thanks and I look forward to your help!

Edm Miranda

Assuming it is really a 65 with the electronic tachometer and not a late-registered 64 with the mechanical rev counter, what does the tach do when the engine dies. Don't do *anything* before looking at the tach, i.e. the momentum of the car (assuming you *are* moving at the time ...) should still be spinning the engine with the ignition on i.e. you haven't switched off, dipped the clutch or knocked it out of gear.

If the tach is still registering then the problem is either HT, fuel, or just possibly the condenser gone open-circuit. Any break in the ignition LT circuit or the condenser going short-circuit will cause the tach to stop registering instantly.

Also look at the ignition warning light at the same time, if that is glowing and the tach has dropped than you have lost the 12v supply through the ignition switch.

The coil is a prime cause of this when it has the original rivetted spades, these work loose, later coils had threaded studs and nuts.

It doesn't sound like it is fuel pump from the filter still being full, but in practice the filter can be anywhere between almost full and almost empty and not have any effect on running. If it *were* the pump when you switched on again immediately before it started and ran normally, the pump would chatter away like billy-oh for a few seconds to refill the empty carb float chambers.

A good diagnostic of HT when it has stopped and won't restart is a timing light. However most 12v clip-on timing lights probably won't trigger and flash when cranking because the system voltage is too low, unless you power it from another battery or vehicle. The old-fashioned neon timing lights that simply go in series with an HT lead *will* show you whether there is HT or not. No flashing in the coil lead indicates it is the coil or ignition LT that is at fault, flashing on the coil lead but not on one or more plug leads indicates a faulty cap and/or rotor. Modern rotors except from specialists are notorious for premature failure these days, as are condensers, and caps aren't much better.
PaulH Solihull

First of all, you couldnt get better advice than Paul has given you above if you paid for it. Second, welocme to MGB owbership, they are one of the best cars ever anytime IMHO ,good choice, and if it's your first MG also welcome the worldwide Octagonal family .
The 2 miles sounds a bit fuel pump, Jane and I did something similar in our car once. We were just going out locally hood down and I pressed on despite losing the fuel gauge (I think from memeory). We got about 2 miles before the car splutterd to halt with less and less power until zero, this usualy tells you its fuel.
To complete the fun Penn School Minibus which we had just passed in a blast of straight though exhaust and a wave (Jane works there part time) then came chugging along full of schoolkids. This proved to be a 3 way bullet connector rusted though, found quite quckly as I could walk home for a meter, the other fault was on the same circuit so the car gave me fair warning I now carry a cheap analog meter in the boot. When you turn on the ign first thing does the pump chatter until any overnight evapouration in the float chambers has been filled up? If not you are setting off on what remains in them just dont pass anyone you know if you dont want to get embarresed 2 miles down the road:-). As Paul notes when you restart if the pump chatters away before slowy tailing off to a stop your float chambers have emptied . Its possible that the few road bumps plus switching on and off are just enough to restart it. I put a transistorised one on to avoid this, Paul will tell you not to, but I'll let him tell you his reasoning. Has the car been converted to -ve earth reason I ask is if it is ign then this give you lots more choices in electronic ones to avoid the problems with components noted above.
Stan Best

Thank you Paul and Stan! I'll be starting her up today and I'll watch for these signs to better answer these questions. May I ask, does HT stand for high tension as in high voltage electrical installations?

Yes, this is my first MG. I am quite happy with the car so far! The MGB has a brand new engine, transmission and hydraulic shocks and so much more. The fuel pump is the one item the seller told me he had no gone through but was generous enough to includ a rebuild kit and a "how to" YouTube link.

The only other concern I have are high RPMs of nearly 5000 at registered speeds of 65mph. Is this normal? Also, as I was waiting through thanksgiving bay bridge traffic she stared to heat up to 200+ deg F. Luckily traffic broke and I was able to get her going and in a flab, cooled down. I know theres a new radiator and oil cooling system. Any thoughts?

Thanks do h teat advice and warm welcome! I am enthused to be a part of he team!

Edm Miranda

Yes HT is the spark plug end of the ign circuit. Pauls comments are leading you towards seeing if there is an intermittent open in the 12v side that provides the LT current. (Electronic tach drops to zero even with engine stll spinning) then is there something stopping the HT (high tension) side.
Stan Best

Sorry missd the RPMs ? The B is 22 MPH/1000 rpm in o/d top and about 18 in direct so about 3600 is what you should be seeing worst case. Does the car sound stressed, like its really buzzing or does it pull strongly as though its in the meaty centre part of the torque v rpm graph? This is probably a tacho problem if so.
Stan Best

Great, thanks! Sorry about all past/present/future typos, iPhone + big thumbs=horrific grammar.

The car seems to start stressing, rattling above a reading of 65mph.

Any thoughts on the rapid heating I experienced?

I'd like to also reach out for advice on interior: panels, seats, carpet, trunk carpet set.

Also, for floor pan, rocker rust would you suggest rust repair kits (Por-15) or replacement body pieces?

Thanks a million.

Edm Miranda

If it is a brand new engine 5000 RPM is not good for it. Try to keep it to under 3000rpm for the first 500 miles and 4000rpm for the next 1000 miles. Then get an oil change.
It may be overheating because the engine is still tight.
c cummins

Eric. As Stan notes, if the tachometer and speedometer are reading accurately, 5,000 rpm at 65 mph indicates a problem. Normally, a slipping clutch.

As to the over heating, it is not uncommon for the cylinder head temperature to rise when stuck in traffic after driving at high speed. Once again, it is necessary to know if the old gauge is reading correctly to actually know if you are running temperatures this high or not. But, 200 deg F is not that high under the circumstances you describe. Your water/anti-freeze mixture raises the boiling point of the solution as does the radiator pressure cap. Thus, the boiling point would be over 243 deg F when running pure water and the 7 psi radiator cap that was standard (from memory) on your car. Add in some amount of anti-freeze and the boiling point is increased to a higher temperature. Thus, noting to worry about right now.

Find out what is causing the problem with the engine turning an indicated 5,000 rpm at an indicated 65 mph, then worry about the temperature problem.

Les Bengtson

Update: I have been choking while giving plenty of warm up time and Im happy to report that for the past three cold starts I haven't had the shutting down problem. I'll keep an eye on it.

As for the RPM's, Les thank you for the helpful feedback. Seeing as the transmission was recently rebuilt, I doubt it's the clutch. The clutch seems to operate perfectly. I drove for about 30 minutes down the coast and I'm simply not believing the tach. The motor doesn't seem to be stressing that much nor winding. And simply revving a little and Andropov light made the RPMs jump 1500. Is there a simple diagnostic I can run to see if the unit is faulty?

Edm Miranda

Sorry for all the typos. Heres this post again (take two)

Update: I have been choking while giving plenty of warm up time and Im happy to report that for the past three cold starts I haven't had the shutting down problem. I'll keep an eye on it.

As for the RPM's, Les thank you for the helpful feedback. Seeing as the transmission was recently rebuilt, I doubt it's the clutch. The clutch seems to operate perfectly. I drove for about 30 minutes down the coast and I'm simply not believing the tach. The motor doesn't seem to be stressing that much nor winding. And simply revving a little at a stop light resulted in the RPMs jumping up and down 1500. Is there a simple diagnostic I can run to see if the unit is faulty?

Edm Miranda

Eric - pick up a diagnostic tach/dwell meter at your local auto parts store and use it to check the reading on your tach. My bet is that your tach is reading high by as much as twice the actual rpm. Cheers - Dave
David DuBois

The MGB has a very clever choke system. Fully out it enriches the mixture for starting, Then once it has run for 30 seconds up to a minute or two (depending on how cold it is) You can push it in until its on the fast idle cam only, here the engine wont stall but you are not washing the cylinder walls with excess fuel. You can always tell someone who knows the cars when they start from cold and you hear them do exactly this. The fuel pump may be feeling better for being used regularly but they are a service item.
MGBs do not like queues, some people fit electric fans, others inc me fit the Moss fan shroud but as noted above your car was in no danger of boiling.
I found the idea of getting the Poliburo interested in sports cars rather than an ice free port on the Indian ocean a really fascinating concept and was looking forward to seeing where that one went, sorry to see it was just a typo.
Stan Best

A slipping clutch is easy to diagnose, the revs will vary wildly as the throttle is rapidly pressed and released but the actual speed will vary very little. Do this in 4th though not 1st!! Clutch slip will occur in 4th before any other gear. Blipping the throttle when stationary causing the tach to jump 1500rpm seems quite normal to me, but it does depend on how much you pushed the accelerator of course, and it doesn't take much. If it is *erratic* though, rather than simply going up when you press the throttle and dropping again when you release the pedal, then it is quite possibly caused by the same fault that is causing the engine to cut out. MGB distributors should have a very flexible brown cloth-covered wire under the cap between the points plate and the distributor body. If this is missing or broken then blipping the throttle causes the manifold vacuum to change, which twists the points plate, which can cause a break in the ignition circuit. 25D4 distributors with the spade connection on the side of the distributor have a second wires like this, between the spade and the points themselves.

I don't know about MGBs not liking queues, temps *will* go up stuck in traffic on a hot day but it has a very wide 'normal' range on the gauge, unlike modern cars which seem to show exactly the same reading (once warmed up, I hasten to say) no matter what. Later (than 1965) gauges have 'Cold Normal Hot' markings rather degrees F or C, and the Normal section ranges from about 120F to 212F. These cars have run in desert states from inception with no cooling problems. What many describe as 'overheating' is nothing more that showing a higher temperature under more arduous conditions, if it isn't steaming or losing coolant it isn't overheating. If it does, or the temp gauge consistently goes to the top of the gauge under what should be 'normal' conditions then there is something wrong that should be fixed, auxiliary cooling shouldn't be needed. This could be anything from some issue causing the engine to generate more heat than it should, or the cooling system not to get rid of it, or simply a faulty indication.
PaulH Solihull

Well, I figured out it was my fuel pump. I successfully rebuilt it and reinstalled. This seemed to have an effect on lowering the tach reading, is that even possible?

The seller suggested a new thermostat for any over heating.

I calculated my mpg and arrived at 21 mpg. That's vastly different than the 27-30 I was quoted. Any ideas?

Next is interior kits and body work. I'm trying to decide between Por-15 rust restoration kit vs floor pan and rocker welding.


Edm Miranda

Anything is possible! Strictly speaking no, but if operation of the pump was causing fluctuations of the 12v supply to the tach then it's possible that was affecting the reading. Highly unlikely though.

27-30 mpg is what I've seen for Imperial gallons, USA gallons will be proportionally less. But if I got 27-30 from my 4-cylinder I'd be horrified. I get low to mid 30s even on route-map runs where you are typically making turns all the time and going up and down the gears. On long cruises I have seen over 40mpg. I've had 34mpg more than once out of the V8 on long cruises (but also 10 mpg knocking around town).

Paint is no substitute for steel as far as rockers/sills are concerned, or anywhere else really. If there is any perforation when prodded with a spike it needs cutting out and replacing.
PaulH Solihull

Well, as I said, I rebuilt the fuel pump, reinstalled and last night I drove all over the city. But this morning was particularly cold and now my fuel pump is not working all together. No noise, dry fuel filter, NOTHING.

I already checked the electrical connections, they're connected. I suppose next is a meter test?

Any ideas out there?
Edm Miranda

Indeed, a meter test. Measure between the insulated spade the white wire is connected to on the end-cap and a known good earth, you should see 12v. If not check the white wires in the 4-way bullet connector by the fusebox where the rear harness joins the main harness.

Also measure between the uninsulated spade on the pump body by the set of screws that hold the two halves together and a good earth, and you should see zero volts. If you see voltage check the earth connection which should be on a rear number plate bolt.

If you see the correct voltages on both the problem must be internal. If you can hear the pump click once each time you tap the white wire on and off it's spade with the ignition on then either the diaphragm isn't moving far enough to throw the points open, or they are short-circuited somehow, possibly if there is a spike on one of them. If there is no click but there is a small spark then the diaphragm or points are jammed. If no spark either then the points or the solenoid winding are open-circuit.
PaulH Solihull


It looks like Paul just included the suggestion I was going to make. Yes, check to see if your license plate is tight.

C R Huff

Thank you for all the great advice. I ordered a brand new mechanical SU pump. Heard too many negative comments about the solid state.

Keep 'em on the road!

Edm Miranda

Thank youth everyone fir the helpful advice! I went ahead and ordered a brand new SU mechanical fuel pump. I've heard questionable things about solid state.

Next it's onto cosmetics. Anyone out there hadgood experiences with Victoria British? I'm looking to purchase their floor pan (rh) for replacement of my rusted one.

Also, my 1965 mgb came with a stow away and foldable convertible frame (no top) is this stock? Will a non stow unit work? Any suggestions for brand.

Edm Miranda

The attachments for the three types of hood frames are identical, but you must have the matching frame and top or the fit can be very poor. The packaway or optional early folding were used until 1970, then an improved folding from then. It's difficult to describe the difference between the two folding types, the attached images from Clausager may help, early abopve, later below.

PaulH Solihull

This thread was discussed between 26/11/2010 and 01/12/2010

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