MGB & GT Forum
Carbs again
Posted by Bighair
Topic Creator (OP)
Jul 29, 2015 02:28 PM
Joined 8 years ago
16 Posts
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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.
One thing that baffles me is that the front carb gets warm whilst the rear is freezing cold!
Any help appreciated.
HiPowerShooter
James Booker
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Jul 29, 2015 02:43 PM
Joined 9 years ago
7,787 Posts
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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...
"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
Jul 29, 2015 03:33 PM
Top Contributor
Joined 13 years ago
2,298 Posts
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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
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
Jul 29, 2015 03:52 PM
Top Contributor
Joined 22 years ago
17,547 Posts
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Topic Creator (OP)
Jul 29, 2015 03:58 PM
Joined 8 years ago
16 Posts
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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.
Edited 1 time(s). Last edit at 2015-07-29 03:59 PM by Bighair.
Jul 29, 2015 04:08 PM
Top Contributor
Joined 22 years ago
17,547 Posts
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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.
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.
Topic Creator (OP)
Jul 29, 2015 04:52 PM
Joined 8 years ago
16 Posts
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Jul 29, 2015 06:25 PM
Top Contributor
Joined 22 years ago
17,547 Posts
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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.
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.
Topic Creator (OP)
Jul 30, 2015 08:21 AM
Joined 8 years ago
16 Posts
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