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Fueling
#1
Jonahmgb Graham Jones
West bromwich, West midlands, UK   GBR
Hiya everyone .
Just got my 1979 rubber bumper mgb through the mot .
No mechanical problems just a small hole needed welding in the floor pan.
Now I'm using the car it runs fine from cold.
But as it gets warmer it starts to miss under acceleration to the point where it
Cuts out completely .
When you wait five minutes it will restart.
All of the ignition side as been replaced and a new fuel filter .
My feeling is its a fuel problem perhaps fuel pump ?
Any help would be appreciated .
Ps when stationary the car revs fine .

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RAY 67 TOURER Avatar
RAY 67 TOURER Ray Marloff
Fort Bragg, CA, USA   USA
1967 MG MGB "My Girl"
The first thing, that I would do, is check the point gap. That is if your distributor has points. Since these parts were replaced recently, it's possible that after running in, the gap is now off. RAY

rocannon Avatar
rocannon Platinum Member Frank L
Inconveniently located in the wilderness, OK, USA   USA
1967 MG MGB GT "GT From Hell"
1980 MG MGB "Restored By Photoshop Inc."
Also symptom of failing coil.



;-\

TANSTAAFL !

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misterfox Avatar
misterfox Bryan Lever
Beachwood, OH, USA   USA
1972 MG MGB "Gone, But Not Forgotten."
1973 MG MGB
1974 MG MGB
Fuel filter? Some years ago, I had a clogged fuel filter limit my speed under load. Not an MG. Though.

Is your fuel tank able to 'breathe'? if not - a vacuum in the fuel tank will impede fuel delivery. If the car stops on it's own - and you remove the gas cap - is thate a bit of a whoosh of air being drawn into the tank? DON'T DO THIS IN TRAFFIC!

Are you able to test for spark? Ray may be on to something.

I'm sure more answers will be along shortly.



Member - NAMGBR, Emerald Necklace MG Register


Murphy's paradox:
Doing it the hard way is always easier.

pshipley Avatar
pshipley Silver Member Paul Shipley
Kelowna, BC, Canada   CAN
1980 MG MGB
Sure sounds like tank venting problems. My '80 had this problem initially due to a crimped tank venting hose in the trunk. Like Brian said above, you'll likely hear a sucking noise when you loosen the gas cap, and it should start right up after you've run the fuel pump again.

I did just have a similar problem with a bad ground to the fuel pump, but it was far more intermittent than what your problem sounds like.

Jonahmgb Graham Jones
West bromwich, West midlands, UK   GBR
Had the day on the car .
Drilled the filler cap,fitted new fuel filter ,checked the points all ok.
Rechecked the timing all good .
Ran the fuel pump with the line at the carbs off plenty of fuel coming through.
Still got the same problem runs great from cold but splutters under acceleration when warm.
If you are slow with the accelerator no problem but try putting your foot down and it splutters and backfires.
Only things I have not replaced are the coil and distributor.
Any ideas .
One thing I have just thought of is I might try replacing the old ht leads one by one.

misterfox Avatar
misterfox Bryan Lever
Beachwood, OH, USA   USA
1972 MG MGB "Gone, But Not Forgotten."
1973 MG MGB
1974 MG MGB
Sputtering, etc on hard acceleration, but 'OK' on slow acceleration - Oil in the dashpots?

I forgot that once - and the car ran like poop. I had one of the dampers work loose - essentially the same as no oil - the car ran like poop.



Member - NAMGBR, Emerald Necklace MG Register


Murphy's paradox:
Doing it the hard way is always easier.

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Nicecar Avatar
Nicecar Gary (ex "Harv") G
Victoria, BC, Canada   CAN
1980 MG MGB "Red On Red On Red"
"hard acceleration" problems can be a faulty dizzy condensor. Learned this years ago c/o Dick Moritz.

Jonahmgb Graham Jones
West bromwich, West midlands, UK   GBR
Thanks for that .
I know this question as probably a dozen times .
But what oil would you use in the dash pots 20w50 ?

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benhutcherson Avatar
benhutcherson Gold Member Ben Hutcherson
Louisville/Frankfort, KY, USA   USA
1970 MG MGB
In reply to # 3733389 by Jonahmgb Thanks for that .
I know this question as probably a dozen times .
But what oil would you use in the dash pots 20w50 ?

That's one of those things that will be argued to the end of time.

Here's the run-down...

SU's official oil(that's freakishly expensive but comes in a neat looking bottle) is SAE 20. Marvel Mystery Oil, Automatic Transmission Fluid, and 3-in-1 electric motor oil(blue label) are all about that same weight.

MG specified 20W-50, and that's as good of a choice as any.

John Twist likes 90wt. gear oil, which at carb temperatures is close in viscosity to 20W-50(but probably a tiny bit more viscous). SAE 30 motor oil will also get you in the same ballpark. I've gone as high as SAE 60 motor oil. The acceleration did seem a bit "punchier"(heavier oils enhance the accelerator pump effect of the dashpot) but it may have also been my imagination.

wbacall Walter Bacall
Canyon Country, CA, USA   USA
If its a single Stromberg car, it will run just as you say, if it does not have the original air cleaner assembly fitted.

RAY 67 TOURER Avatar
RAY 67 TOURER Ray Marloff
Fort Bragg, CA, USA   USA
1967 MG MGB "My Girl"
For '79, a home market B would have still been fitted with twin HIF4 carburetors. RAY

Jonahmgb Graham Jones
West bromwich, West midlands, UK   GBR
Put some 90wt in the dash pots .
Transformed the acceleration . .
Not cut out when warm since so hope it was related or the holes I drilled in the cap may
Have cured the problem .
Thanks for all the help and sugestions .
Anyway the suns out and I'm off to play.
Been a biker for 40 years but I'm getting into this mg thing

Jonahmgb Graham Jones
West bromwich, West midlands, UK   GBR
Hiya all .
Took the mg out today (a warm day)
The problems back when the car gets warm about 12o'clock on the
Temp gauge the car starts to miss fire and splutter
Till the point where it just cuts out .
Wait 5minutes then you can restart it then the same happens again.
Managed to limp home .
I have removed the fuel pump and cleaned the contacts and reset it .
Only thing I haven't replaced is the coil .
Any suggestions .....?

neil stern Avatar
Florida, Naples, USA   USA
1980 MG MGB "My Tomato"
after all you have done did you replace the coil Sometimes they dont go out Also you say it backfires Someone said condenser Could be But did you change the cap If they have a crack and they get them sometimes It will backfire

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