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MG MGB Technical - running problems

my engine seems to die going up hills, and if i release the thorttle for a few seconds then re-apply the problem goes away, but not for long as it returns only seconds later.

do my carbs need balancing?
d buck

It could be that fuel is not getting through.Check the carb float levels, chambers & valves for dirt & Fuel filter for blockage (if fitted). Have you checked that the timing advance/retard works as the engine speed changes with a strobe light?
R J Collier

Sounds like a fuel delivery problem. The engine is working harder and the fuel has to be lifted higher so you get fuel starvation. When you back off the fuel "catches up" but only for a short while when you accelerate again. Check the whole system from the pump to the carbs including any filters and flexible sections.

John
John Tampkins

ok i figure maybe my pump is playing up again.
i have recently fitted a new set of contacts and it appears to be working ok. however i may take the advice of a previous thread.

i had a fuel leak on the small jet tube from the bottom of the float chamber that was fixed last night, with the installation of a new tube.

should i remove both floats and see if the floats are operating properly?

the fuel lines should be ok and i can't see any leaks.

if not should i remove the pump and try turning the contacts round to adjust the pumps throw?
d buck

I'm not an expert on fuel pump adjustment, but it sounds like this is the first thing to check.
Fuel delivery can be checked by disconnecting the fuel
pipe before the carbs and getting someone to turn the
turn the engine on whilst you catch the petrol in a comtainer, but be carefull!!
Its easy to check the float chambers just three screws
on the top of each.Check floats for petrol leakage inside.Check that the fuel level in each chamber is the same.The chambers may need cleaning out if you dont have a fuel filter.You may also need to fit new gaskets on reassembly so buy these first!
R J Collier

i do have another pump with me but its off a 1971 GT that was negative earth. my car is a 1967 roadster that is positive earth [still]. is there any issue in changing them over. i spoke to my dad and he was half sure that pumps cannot be interchanged.
d buck

If both fuel pumps are both original, they are designated positive or negative earth and to my knowledge not interchangable.Later replacement pumps
could be dual polarity. Personally if you have had
problems before,I would replace it with a new one, but
others on this forum may be able to tell you how to fix an old one!
Robert
R J Collier

The fuel pump should deliver at least 1pt per minute into a container at the carbs, with little or no bubbles.

All electronic i.e. pointless pumps can only be used on the correct polarity, but these were never standard on the MGB. Using these on the wrong polarity will not work at all at best, or destroy the electronics at worst. Later factory pumps are polarity sensitive in that they have diode quenching of the points. These are protected against reverse connection causing any damage, but the points quenching function is reduced so you will get accelerated wear, but the pump will work. Earlier pumps had capacitor points protection and can be used on either polarity. the changeover point was about January 1977, but of course you could have a later pump on an earlier car. The earlier 'safe' pumps have a stepped end cover, the later polarity sensitive pumps have an end cover without the step.

You can interchange 67 and 71 pumps with impunity.
Paul Hunt 2

Paul
I stand corrected if earlier standard positive and negative fuel pumps are interchangeable.
But I understand that modern replacement fuel pumps with points are dual polarity, and modern electronic
pointless replacement fuel pumps are of dedicated polarity.
It is a question of correctly identifying your pump.
I don't know how many 67 cars would have an original pump!Robert.
R J Collier

Robert - there may well be dual polarity, electronically quenched, points pumps available, but they would be after-market units not OE, and I have to say they are something I have not heard of before. Have you got any references or links?
Paul Hunt 2

Paul
Burlen tell me that their AM (aftermarket) fuel pumps with points are are dual polarity. It seems that fuel pump identification is complex and from your & my information and Burlen's I have come up with the following

1/OE pos earth (Interchangable see above)
2/OE neg earth (interchangable see above)
3/OE neg earth 77 on (neg earth only)
4/AM pos/neg (Burlen Points After market AZX 1307)
5/AM pos earth (Burlen P'less electronic AZX 1307EN)
6/AM neg earth (Burlen P'less electronic AZX 1318EP)

If you go into Burlen systems www.burlen.co.uk and then Parts Store, the above part nos can be used
Robert.
R J Collier

interesting, now all i have to do is survive the 14mile journey home
d buck

Are there any hills on the way ?? Good luck!!
Robert.
R J Collier

D Buck - Remove the end cover of the pump off of the 71 MGB and look at the area under the cover. If it has a black cylinder with a red and black wire coming out if it, then it is a polarity sensitive pump. If it has a capacitor (two uninsulated wires coming out of either end of a cylinder), then it is not polarity sensitive and can be used on either a positive or negative vehicle. If it has the black cylinder with red and black wires, the wires can be reversed to make it a positive ground unit. See my Fuel delivery troubleshooting giude at: http://www.custompistols.com/cars/dave/ddFuelDeliveryTroubleshooting.htm
for information on how to troubleshoot your problem. Good luck - Dave
David DuBois

Just noticed I mixed the part numbers up for Burlen electronic pointless fuel pumps!
AZX 1307EN is negative earth
AZX 1318EP is positive earth
These dont seem to be listed on Burlens website, but are stocked both at Burlen & Moss under these parts no's
There is also an electronic conversion kit availiable.
Robert
R J Collier

ok i had the car towed by the RAC. used my mums land rover defender today - slower than the mg hence i was late.

the spare pump i have has got a black capacitar with an insulated red wire and an insulated black wire. hence i pressume it is polarity sensitive.

so i won't use that pump by try and fix my original pump. cheers
d buck

AZX items have the diode and are polarity sensitive. I'm guessing here but I suspect that for the 1/OE and 2/OE items the 'pos earth' and 'neg earth' refers to the cars they were originally fitted to, and as such they are interchangeable, as they have capacitor quenching. These have always been interchangeable. From 77 on the factory pump was an AZX1307 with diode quenching and so would be negative earth only as they say. Their 4/AM is the puzzler, it quotes an OE part number (AZX1307) without any prefix or suffix to indicate a copy, but the AZX1307 is for negative earth only. If it truly is dual polarity then it is an aftermarket item and as such should have a suffix or prefix to the original part number. Their 5/AM sounds like a copy of the original factory pump for 77 on negative earth cars, and the 6/AM another copy for positive earth cars, both with diode quenching.
Paul Hunt 2

Hi Paul
1,2 & 3 are from the information you gave:-
1&2 are the stepped cap dedicated + or- but are interchangeable at the expense of accelerated wear due to the points quenching function being reduced.

4,5 & 6 Are Burlen parts numbers.
The parts numbers quoted are current numbers which have superseded the OE parts numbers. Ignore the AM, that was my designation for Aftermarket!

If you look on the burlen website (or phone them!) you will see that AZX 1307 (pump with points) which is for now suitable for both + OR -, AZX 1307 has superseded AZX 1318 which was + only pump with points & obsolete due to AZX 1307 now being dual polarity.
Cheers Robert.
R J Collier

Paul
Forgot to add that 5 & 6 are both electronic pointless pumps. EN is neg earth & EP Positive earth.

d.buck.
Sorry to hear about the tow truck! Let us know how you
go on with your pump!
Robert
R J Collier

I can't make head nor tail of the Burlen site. There is no menu item for pumps, and putting 'pump' in the part name search comes up with nothing, neither does entering any of the 1/OE etc. numbers you give above. The AZX numbers do work, but it says the AZX1318 positive pump superceeds the AZX1307 negative pump, which is hardly correct. It also seems confusing to give a fully electronic pump the same part number as an OE points pump, but that is just a matter of opinion. If 1 and 2 have a stepped cap they are capacitor quenched and hence *not* polarity sensitive, unlike the diode quenched points type.
Paul Hunt 2

Hi Paul
Don't want to labour the pumps point, I agree that the Burlen website info could be better, a phone call to Burlen (or Moss) would clarify that the AZX 1318 +ve pump has been superceded by AZX1307 which is a dual polarity points pump which was my original point - that some replacement fuel pumps could be dual polarity.
The fully electronic pumps use OE part no's but end in EN or EP to distinguish the polarity.
Cheers Robert
R J Collier

This thread was discussed between 23/02/2006 and 26/02/2006

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