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MGA Swapping Carbs MGB to MGA

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ronzet

ronzet

Jedi Knight
Offline
LBC Fans,

Is it possible, <span style="font-weight: bold">or even worth the effort</span>, to swap out a set of H4 carbs (and manifold) in an MGA 1500 for a set of HS4s from an MGB??

I was hoping for a little bit more power and thought that this might be a quick way to do it... :rolleyes:

By the way, I have found the other emotion faces that I was complaining about.... :square:
 
Re: Swapping Carbs MGA to MGB

Steve,

Thanks for the note....

This is the on-going saga of the head gasket/overheating adventure...

It appears that I will need to replace (or do much more of a rebuild) on my MGA's H4s and thought I might spend the money elsewhere to better advantage...

I have a good set of HS4s on my soon to be dismantled '66 B and thought that I might swap them... I might do it anyway just to see what happens...

I am getting SOOOO good at tearing them down and putting them back together... :rolleyes:
 
Re: Swapping Carbs MGA to MGB

Ron, I just replaced a set of H4s on my Magnette with MGB HS4s. The throttle linkage was the only hurdle to really overcome. Other than that, you must use the MGB intake manifold, but its a direct fit.
 
Re: Swapping Carbs MGA to MGB

JeffS,

Thanks for the advice and anecdote.

I have an MG Club cruise this Saturday and I want to take the A. I will swap out the carbs and manifold tonight and see what happens!! :thumbsup:
 
Re: Swapping Carbs MGA to MGB

JeffS said:
Ron, I just replaced a set of H4s on my Magnette with MGB HS4s. The throttle linkage was the only hurdle to really overcome. Other than that, you must use the MGB intake manifold, but its a direct fit.
Click to expand...

I take it you are now the proud owner....
 
Re: Swapping Carbs MGA to MGB

Power is identical. What made you think that two SUs of identical throttle bore size would show any different?

Reliability in the old days wasn't as good - the cork gland washers in the jet head were prone to leaking and the flexible style jet used on the MGB was more reliable.

Today, with modern washers made from better material than cork, leaking is much less of a problem.

Unless you happen to have a newly rebuilt set of carbs for MGB, I wouldn't bother switching, just rebuild the MGA carbs and enjoy.
 
Re: Swapping Carbs MGA to MGB

billspohn,

<div class="ubbcode-block"><div class="ubbcode-header">Quote:]Power is identical. What made you think that two SUs of identical throttle bore size would show any different?
[/QUOTE]

Whew, Bill, I think that is called a 'terse' statement.. as in 'WHAT WERE YOU THINKING, STOOPID?'
grin.gif


Actually, I had thought that the HS4 had a larger bore than the H4...(that is 1.75 vs 1.5) I now stand corrected.... I have been enlightened and elucidated.... :yesnod:

SOOOOOO, OK... I took the carbs off last night. I had rebuilt them when I was rebuilding the engine. The forward one appears to be working fine. HOWEVER, the piston on the aft carb sticks. In other words, it does not demonstrate a smooth action and binds in the bottom 1/3 inch of its travel both upward and down...What is most perplexing is that when I had airflow balanced the carbs they seemed to be working properly???

I think, unless someone has any thoughts about it, A new piston and cover is in order OR just buying a pair of new or professionally rebuilt ones...Any suggestions?

Comments are welcomed...
 
Re: Swapping Carbs MGA to MGB

One other note...

I stood there pondering the removal of My HS4s and manifold from my B to intall on the A... After much thought, I decided that It just was not worth the effort. :wall:

Following the advice tendered by Bill, I am sticking to the path of rebuilding or replacing the H4s in the A and leave the B alone. Alone, that is, until I tear it apart to rebuild it. :thumbsup:

Thanks for the help... :cheers:
 
Re: Swapping Carbs MGA to MGB

Are you sure you put the pistons and covers back together in their original positions?
 
Re: Swapping Carbs MGA to MGB

They are rather sensitive to alignment and will bind...

Test lift the piston while tightening the 3 screws.
It should fall with a soft thud.

If you need a piston and/or chamber PM me.
I have many extras....Free.
 
Re: Swapping Carbs MGA to MGB

Steve and WhatsThatNoise,

Thanks for the comments.

I did keep the piston/covers as matched pairs. After 40 odd years I am sure they are like an old married couple... a matched set...

I have tried your suggestion, to no avail. Actually, neither of the pistons fall with a thud, slight or otherwise...so I may have a bigger problem that just the aft carb.

On the aft carb, I can slide the piston into the chamber and feel a slight resistance as I move it in the lower portion. Is a little burnishing on the piston and chamber in order, or ill-advised?

WhatsThatNoise, if all else fails, I will take you up on your most gracious offer and PM you.

It does not look like I will be taking the A on the Club Run on the morrow after all... :cryin:
 
Re: Swapping Carbs MGA to MGB

When disassembled and turned upside down...

Mine takes about 1 second to fall.
(no oil and dashpot plunger in place)
Parts006.jpg

Parts007.jpg

There is no perceptible side play between the piston and the chamber so I'd be careful about polishing the surfaces.
 
Re: Swapping Carbs MGA to MGB

Quick SU nomenclature note-

The number, 2, 4 or 6, refers to the bore size in number of eighths of an inch over 1 inch.

A "2" (HS2) would be 1 + 2(1/8) = 1.25.

A "4" (as in H4 of HS4 or HIF4) would be 1 + 4(1/8) = 1.5.

A "6" (HS6) would be 1 + 6(1/8) = 1.75.
 
Re: Swapping Carbs MGA to MGB

Yes and H6 has 4 mounting holes instead of 2...

In case you thought about using your existing manifold.

You have to be an artist to make a H6 look like a H4

Not saying you can't....You just have to be really motivated.

[cough]cheater[cough]
 
Re: Swapping Carbs MGA to MGB

Gentlemen,

Thanks for the information.....

I will try the drop test this evening....stopwatch in hand... :wink:

And, WhatsThatNoise, thanks for the time and effort providing the photos... :thankyousign:

While I am at it.. I have this old Holley 4 barrel....I wonder if I can make a manifold....NAW :crazy:
 
Re: Swapping Carbs MGA to MGB

Ron, remove the needle from the piston and refit it and see if the drop is suddenly the way it should be.

If so, you just need to centre the jet as it is rubbing the needle (which of course only takes place near the bottom when the needle dimension is largest).
 
Re: Swapping Carbs MGA to MGB

Bill,

Thanks for the suggestion. I will reseat and see if that makes a difference.

As I said somewhere in an earlier post...

If we had any sense or were relatively sane we would be driving late model Miatas.. Operative word here is DRIVING... :wall:
 
Re: Swapping Carbs MGA to MGB

ronzet said:
Bill,
If we had any sense or were relatively sane we would be driving late model Miatas.. Operative word here is DRIVING... :wall:
Click to expand...
That's why everybody needs at least 2 LBCs
grin.gif


I'm currently down to one...But
I can justify that.
On account of it being rather reliable lately. :sick:
 
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