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MG MGB GT V8 Factory Originals Technical - Factory V8 carburettors
|A few years ago, when I had a 1.8 MG BGT, amongst other modifications I replaced the 'poppet valve' butterflies for plain ones in the SU carbs. This made a fair bit of difference to throttle response, and pull at the top end. |
Does anyone know if the carbs on a '73 Factory V8 will also have poppet valves? I'm guessing they will, but I'm struggling a bit to see down the chambers! Has anyone else removed these?
Also, the car came with some K&N filters. I've not tried fitting them, as I've not got a pair of richer needles, but I'm guessing they make quite a difference. Are they really noisy, though? Are there any other problems with them (running in hot weather, for instance?)
I might wait until a few fingers grow back before attacking the carbs: I spent 6 hours (is this a record?) changing the gearbox mounts this weekend, and it was perhaps the most unpleasant job I've ever tackled on a car! I'm sure I did these on my old 1.8, but I don't remember it being quite so impossible...
|Yup, mine have those decceleration valves|
Has anyone else removed them?
|Darren - I threw the SUs away years ago but I am pretty sure the original factory HIF6s had plain butterflies.|
The K&Ns should help a little with richer needles but both are marginal unless you have had your heads modified and a hotter cam fitted.
.....Sympathize over the gearbox mounts (worth doing) but wait until you have to replace the starter !
I have changed my butterly valves to plain ones. You can solder the poppet valves closed or get another plain pair.
Replacing the starter is 100 times easier with tubular headers!
|mh never noticed them before, they might be there.. I have to remove front crossmember to get at engine mounts ... (it took a "specialist" 4 hours to put the engine mounting bolts back on)|
Anyway this is child play
rover 2000 inboard rear discs
you need swivel joint fingers to work on them
one caliper leaked, took it off 4 hours - stipped it and fitted a rebuild kit - complicated caliper or what! 2 hours back on - yep still leaking - waiting (since start of Aug) for exchange units - cant wait... al least all the wings unbolt...
|From the factory service manual, the carbs came with the valve. You can swap them out with any SU 1 3/4" carb throttle plates ie. TR3,4, MGC, etc.|
|My 75 has them and were sticking open when warming up from below zero, giving an 'idle' of 2500 rpm. I soldered them shut being the quickest and simplest way to cure the problem and without introducing others of butterfly seating etc.|
For the most difficult job on an MGB changing the roadster windscreen glass gets my vote, and the GT is bad enough.
|My 75 V8 has them|
|Oh and my manifold and carbs are off of a '73 so I know they started life with the valves. If yours are missing, its the work of a PO.|
|Many thanks, I shall order some new butterflies!|
The biggest problem as I saw it was that the poppet valves are a huge obstruction to the airflow at wide-open throttle. I haven't based this on any tests, but it seems like common sense when you see the size of the things.
It would be interesting to carry out a before and after dyno test, but that would be a bit expensive. I certainly noticed a difference with my 1.8.
|The poppets can be broken off and removed then the openings soldered shut by laying the poppet against a piece of stainless or aluminum and soldering from the other side to get a smooth surface.|
This thread was discussed between 07/09/2004 and 14/09/2004
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