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MG MGB Technical - Hesitation....dies...back again

Hello,

So, the other day my 73 BGT fired right up as normal, but, upon driving a few minutes down the road, hesitated a bit, but then came back to life. Close to home, I swung around and put it in the garage for a few days.

I checked it out yesterday, as the symptoms seemed fuel related. I started by swapping out the fuel filter, as it needed doing, thinking something might have been blocking the lines.

I fired her up again, and took her out for a drive, noticing the same symptoms again. Again leaning towards something in the lines, sometimes a good drive will pass it through.....but after about 10 min at freeway speeds it hesitated and died again.

This time I had turned the key off the minute it happened, as I wanted to observe the fuel level in the filter. Seemed very low.

Turned the key, the fuel pump clicked away and pressurized the system, and off I went home again.

What do you all think? I truly believe it to be fuel starvation. Cap, rotor, and wires are good, and it is electronic ignition, which, in my experience, when done simply dies.....does not go back and forth.

My thoughts would be:

-Replace all rubber lines in case of delamination inside??
-Before tightening the lines, run the fuel from the tank end to the end just before the filter into a jam jar to clear out any potential bits.
-Maybe pull the carbs and see (not sure where abouts) something might be swirling around, settling, and blccking something.

Any other ideas? The fuel tank was new and sealed back when I restored her 15 years ago, but maybe after 80K miles and the years the sealant is coming loose (was told it was good for life though?).

Thanks,
Julian
Julian Dufour

Firstly the level of fuel in the filter is no guide to anything, it can be completely full, completely empty, move from one to the other at different times, and have no effect on running.

If you suspect fuel flow issues then remove the feed pipe from a carb and direct it into a container. Turn on the ignition and it should deliver *at least* one Imperial pint per minute, and in practice more than double that, in a continuous series of pulses with minimal bubbling.

However if turning the ignition back on shortly after this problem occurred, and the pump chattered away, that implies the pump had stopped working allowing the float chambers to empty. Sticking points can cause that, or any poor connections in the 12v or earth connections.

Then again it's possible something is blocking the strainer in the tank, but I'd expect the delivery check to reveal that. It's very unwise to internally seal a tank with the fixed pickup used before 1977 as the strainer can get blocked. From 1977 the pickup including strainer can be removed with the level sender.

"Good for life"? Life of what?

Take a logical and step-by-step approach to diagnosis rather than swapping stuff willy-nilly.
Paul Hunt

Paul,

Thanks for the input.

As far as the tank coating goes, it was done 15 years ago, and recommended by the shop restoring the mechanicals on the car. By "life", I suppose they meant that I would not have to worry about the tank rusting out ever. Not sure about the coating loosening up though. Anyway, it was just a thought, and until this point has been alright.

I think it is related to the fuel pump end of things, but will try your test for fuel quantity/minute.

After looking for the receipt for the pump I bought in 09, it appears that I bought a standard pump with points, not the new solid state version (that's why I did not think about sticky points).

Can the points be easily removed if necessary and cleaned? I do see Moss sells points separately.

Anyway, before I even go there, I have a backup generic solid state pump with the correct PSI that I carry with me, and will quickly put that inline to see if the problem disappears after following your fuel test and checking electrical connections.

Thanks!
Julian
Julian Dufour

Julian - To expand on Paul's suggestion of checking the fuel delivery. Use a quart jar, marked at 1 pint (US measures), disconnect the fuel line from the carburetors and turn the ignition on and measure how long it take to produce a pint of fuel in the jar - should be 25 second or less.

Regarding the sealer that was applied to the tank - I used some of the "good for life" stuff and it failed after about 20 years, turning to jelly and coating (and gluing) the valves in the fuel pump and the needle valves in the carburetor float bowls. What wasn't taken into account when applying the 'good for life' sealer was that the fuel formulation was changed over the years and the 'good for life' was not resistant to today's fuel formulation. I would suggest that you put some of your fuel into a glass container and let it evaporate, then see if there is any residue in the container - if there is, it is time to get the stuff removed from the tank and the fuel lines.

I would also recommend that you clean the points in your SU pump. I suspect that living in Colorado, you probably put your car into hibernation during the winters - if so the points should be cleaned each spring when you get your car ready to drive. I don't like just dragging some sand paper between the points as is often suggested. See the procedure in the article, Cleaning Points in the SU Fuel Pump section of my Homepage at: http://homepages.donobi.net/sufuelpumps/ Cheers - Dave
DW DuBois

A couple of testing ideas.
Try with the filler cap off / loose, you may have a vacuum build up in the tank. Running OK for a while then dying is a typical symptom.

Testing the pump long term (i.e. 10 minutes or more) is difficult with a jar. What I have done is to use a fuel resistant plastic tube, run from the carb end of the fuel line back to the tank. You can run the pump all day, this way. Using clear plastic tubing also allows you to see if there are any air bubbles coming through.

Herb
H J Adler

Tried the jam jar test.....and it failed! After 10 seconds of pumping, it just stopped. Then, after another 25 seconds, it started again......then stopped.

So, I pulled the pump out and took a look at the contact points. They were a bit dirty, but otherwise good. So, I cleaned it all up, gave them a very light sand with 400 grit, and put it back together.

30 mile journey later.....problem solved!

Thanks,
Julian
Julian Dufour

This thread was discussed between 20/09/2015 and 22/09/2015

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