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How would you diagnose this problem?

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How would you diagnose this problem?
#1
oily-hands Avatar
oily-hands Owen Frankland
Stockton on Tees, Cleveland, UK   GBR
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1937 MG TA "Numbum"
1971 MG MGB GT "The Bruise"
Just for grins here's the problem I had last weekend. It's fixed now, but I know there will be differing views on how to diagnose & fix it. What's your method & why?

Stock engine apart from electronic ignition. Car was running fine all day until about 50 miles from home. It started to run rough and lose power. I stopped and checked for obvious things like loose plug leads but nothing amiss. I carried on and the problem gradually got worse but we made it home. Could still maintain 70mph but it took longer than normal to get there. No obvious smoke. Temperature went up but only by a needles width.

Have at it. grinning smiley


Member of The International Society of Luddites (Unrepentant Chapter).

Take the time to understand what a part does and how it does it, then you'll have a better understanding of how to fix it when it goes wrong. Beats the scattergun approach every time.

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Re: How would you diagnose this problem?
#2
the omega man Avatar
the omega man phil wilkins
staffordshire, Stafford, UK   GBR
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1973 MG MGB GT
Silt in float bowl.ht leads broken down.fuel pump problem.new plugs required.new water pump required,alternator not charging properly.cell down in battery.bad earth connection.hows that,nailed it.

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Re: How would you diagnose this problem?
#3
dipstick Avatar
dipstick Kenny Snyder (RIP)
La Center, WA, USA   USA
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1941 Ford N-Series
1958 MG MGA 1500 Coupe "Rosie"
1970 MG MGB GT "Pat's GT"
1971 MG MGB "Gifted To Me"    & more
Coil failed. Did I win?


Be safe out there.
Kenny

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Re: How would you diagnose this problem?
#4
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raglits Steve M
West Midlands, Tipton, UK   GBR
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1972 MG MGB GT "Betsy"
Distributor clamp loose?

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Re: How would you diagnose this problem?
#5
lil.red.roadster Avatar
lil.red.roadster Bernie Anderson
Marshfield, Gloucestershire, UK   GBR
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1970 MG MGB MkII "The Beasty"
What sort of electronic ignition?

Bernie


Bernie

"discere mutari est"

Wiring Diagrams: http://www.advanceautowire.com/mgb.pdf
Paul Hunts very useful site: http://www.mgb-stuff.org.uk
Manual for download: http://www.geomatique-liege.be/MGJP/DocumentsPDF/MGB_Workshop_Manual.pdf
UK MoT guide: https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/518634/mot-inspection-manual-for-class-3-4-5-and-7-vehicles.pdf
Some basic guides: http://www.howacarworks.com/

1970 Roadster (First Reg July 10 1970). Std exhaust (Bell SS) AFAIK rest is bog standard

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Re: How would you diagnose this problem?
#6
herkdriver Avatar
herkdriver Gold Member George Pelech
Powder Springs, GA, USA   USA
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1963 MG MGB "Maggie"
Probably not the electronic ignition-they usually fail outright.
For the HT leads, start and run in a dark area-look for arcing or, look for ash colored marking on the leads themselves
For the floatbowls, turn ignition on, let the bowls fill, turn off, remove the covers and see if they are equal. If you have a fuel filter, probably not silt in the bowls

My bet-HT leads

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Re: How would you diagnose this problem?
#7
termglr Avatar
termglr Terry Allen
Lexington, GA, USA   USA
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1949 MG TC "Devlin"
1962 MG MGA MkII "Alison"
1967 MG MGB GT "Bridgget"
1968 Land Rover Series IIA "Monty"    & more
The condensor

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Re: How would you diagnose this problem?
#8
Cornfgl Avatar
Cornfgl Graham Cornford
Bellville, TX, USA   USA
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1974 MG MGB GT V8 "Goose Poop"
If you are running SU,s did one of the dampers come unscrewed, or out of oil in the damper?

I hope that it was not as expensive as Phil's diagnosis where he metaphorically threw all sorts of parts at it.

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Re: How would you diagnose this problem?
#9
riley1489 Avatar
riley1489 Gold Member Bruce H
Great White North, QC, Canada   CAN
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1953 Jaguar XK120
1959 Riley 1.5 "King George"
1973 MG MGB
Owen,
The ultimate fix is not to venture out further that 49 miles from home. winking smiley

My guess, heater valve dripping onto distributor?

Bruce


Life's most persistent and urgent question is, "What are you doing for others?"

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Re: How would you diagnose this problem?
#10
LaVerne Avatar
LaVerne LaVerne Downey
Fruita, CO, USA   USA
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1954 MG TF "Green Hornet"
1969 MG MGB "The Beater"
1979 Triumph TR8 "Turd 8"
Fuel delivery would be my guess..based on a slightly rising temp indication (weak mixture)...not a head gasket as apparently it was an easy fix.

Could have been a plugged filter, stuck float, split line, or even as simple as the damper cap working it's way out. Just my initial guess.

Had there been no rise in the temp I would have looked at the electrical system.

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Re: How would you diagnose this problem?
#11
ErnieY Avatar
ErnieY Ernie Y
Albatera, Alicante, Spain   ESP
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1976 MG MGB GT
Sounds like a mixture problem (running weak can cause the temperature to rise) so a blown inlet manifold gasket or perhaps a split servo take off pipe ?

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Re: How would you diagnose this problem?
#12
Sinewave Avatar
Sinewave T. Keith Vezina
Kenner, LA, USA   USA
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Check for loose plug wires, then oil level in carbs, then check fuel pump output, then blocked exhaust.


T. Keith Vezina
British Motoring Club New Orleans
1976 MGB, 1976 MGB Trailer & 1978 MGB V8

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Re: How would you diagnose this problem?
#13
JuancarlosMGB Avatar
JuancarlosMGB Juan Carlos Perez Velasquez
Madrid, Madrid, Spain   ESP
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1974 MG MGB GT "El Cherada"
1978 MG MGB Racecar "El 81 De Carrera"
1995 Honda Civic "Beasty Boy (Race Car)"
1999 BMW Z3 Coupe "BATMOBILE"
If your ignition system is ok, my guess would be a clooged overflow port. I had that problem once with exactly the same symptoms.

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Re: How would you diagnose this problem?
#14
barry s Avatar
barry s Barry Stoll
Alexandria, VA, USA   USA
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1972 MG MGB GT
1974 MG MGB
1976 Triumph TR6
1980 MG MGB
I'm with Bruce, heater control valve. Otherwise electronic dizzy which I know nothing about except that I'm stuck on 'points'.

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Re: How would you diagnose this problem?
#15
MGJared Avatar
MGJared Jared W
Paradise, CA, USA   USA
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1971 MG MGB GT
1973 MG MGB GT
a vacuum line has become disconnected causing the fuel mixture to lean out and your engine to run rough. Causes loss of power and increased heat.

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