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Carbs again

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Carbs again
#1
  This topic is about my 1974 MG MGB GT
Bighair Andrew Bates
West Midlands, Streetly, UK   GBR
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1974 MG MGB GT
Help needed. I took off my carbs. They are HIF4s. I cleaned them so they are spotless with carb cleaner. They were dirty and varnished. I replaced the main jets and the smaller jets, re assembled and topped up the dashpots. Now it runs rough on low revs and I need choke most of the time. I assume they are running lean?
One thing that baffles me is that the front carb gets warm whilst the rear is freezing cold!
Any help appreciated.

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Re: Carbs again
#2
HiPowerShooter Avatar
HiPowerShooter James Booker
Lake Winneconne, WI, USA   USA
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1973 MG MGB
Ensure both carbs are getting fuel and they've been properly balanced.


"One test is worth a thousand expert opinions"--Alvin "Tex" Johnston...Boeing test pilot.

"Who do you think you are? I am."...Pete Weber

73 MGB. Tires: Round, black, hold air. Oil: Sometimes old, sometimes new...always slippery. Oil filter: Yellow, usually full of oil. Carbs: 2 SU HIF. Distributor: Yes. Headlights: Not that bright but bright enough. A bunch of other stuff most cars have but not really important enough to itemize. Oh, wait...it has a cool sounding exhaust with stickers on the chrome tips. Really slays the ladies...


Attachments:
Bentley HIF.pdf    2.16 MB

SU idiot guide.PDF    1.5 MB
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Re: Carbs again
#3
Fogliner Avatar
Fogliner Mark Vanherd
Port Clements, BC, Canada   CAN
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1974 MG MGB
Remember to loosen one of the linkage clamps on each linkage to separate the carbs before trying to balance the airflow or adjusting one will directly effect the other which is not what you want.

What does the "piston lift" tell you. Use the lifting pin on each carb in turn and see what it's doing. Rich/Lean?

Regards

Mark

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Re: Carbs again
#4
Wray Avatar
Wray Gold Member Wray Lemke
., SC, USA   USA
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1956 MG MGA
1958 MG Magnette ZB Varitone
1973 MG MGB
1974 MG MGB GT    & more
Sounds like the front carb is not passing fuel. Check that the needle is free and the float level is set right.

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Re: Carbs again
#5
Bighair Andrew Bates
West Midlands, Streetly, UK   GBR
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1974 MG MGB GT
You've just made me think. The front carb when I took it apart was dirty and glazed. The rear one looked white and furry. I have taken the feed pipe off from front to rear. It was clear. What else could stop the flow to the rear one?



Edited 1 time(s). Last edit at 2015-07-29 03:59 PM by Bighair.

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Re: Carbs again
#6
Wray Avatar
Wray Gold Member Wray Lemke
., SC, USA   USA
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1956 MG MGA
1958 MG Magnette ZB Varitone
1973 MG MGB
1974 MG MGB GT    & more
If the front carb remains warm then it seems that it is not passing fuel to the engine, whereas the rear carb, which gets cold, is.

Fuel is getting to the rear. It must not be getting through the needle/seat to the manifold on the front carb.

You'll probably have to pull them off, take the cover off the bottom, and make sure the float needle is free.

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Re: Carbs again
#7
Bighair Andrew Bates
West Midlands, Streetly, UK   GBR
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1974 MG MGB GT
So just to clarify, if the rear carb is cold then it's getting fuel? The problem could be the front one? All the parts are brand new.

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Re: Carbs again
#8
Wray Avatar
Wray Gold Member Wray Lemke
., SC, USA   USA
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1956 MG MGA
1958 MG Magnette ZB Varitone
1973 MG MGB
1974 MG MGB GT    & more
The fuel evaporating, when it's being pulled through the carb, will cause it to be cold. Based on the front carb being warm, that's where I would start looking.

You could confirm by starting the car, then shooting a bit of starting fluid into the front carb. If the car starts running smoothly for a few seconds then the front carb needs some attention.

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Re: Carbs again
#9
Bighair Andrew Bates
West Midlands, Streetly, UK   GBR
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1974 MG MGB GT
You lot are very clever. See if you can spot the fault on the front carb after taking the bottom off! It now runs. Just fine getting to do.


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