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MG MGB Technical - Advise please


The engine up the front of my kit-car is an '76 Morris Marina but is essentially the same as the 3-bearing MGB for the issues I'm needing advice on if you would be so kind.

The engine was rebuilt nigh on 15k ago and has been running without air-filters since, apart from some blue-smoke on start it appears to be running ok (although I appreciate the damage probably done). I've finally got the finances & source to get a scoop made which will allow the fitment of some pipercross air-rams & socks. But I have some questions which I can't get answered from searching google and the archives here (not many people are stupid enough to run without filters ;)).

1) When I put the filters on for the first time I'm expecting that there will be an increase in air-flow (it currently has some mesh on so the filter should allow easier breathing, but not by a massive amount one presumes). As I understand it, this will weaken the mixture - will this be an issue for driving the car the 40miles home as damaging the engine is concerned?

2) I'm planning on getting the car set-up by people who know what they are doing as I expect the mixture & therefore needles will needing changing (see above) but rather than get them to set the whole car up using "old" components would it be advisable to do anything to the carbs (i.e. change the jets/floats etc), if so what?

Thanks for the advice.

Stefan Carlton 1


I would expect a 'proper' filter to reduce the airflow slightly, which will tend to cause a rich mixture. Running a little rich for a while shouldn't cause lasting damage, though it might cause some carbon build up.

I'm not sure what you mean by 'socks', but am suspicious that these will not provide adequate filtering for normal use either, they might be more appropriate for races.

I would get the other tuning (ignition timing, tappets, etc) sorted before you take it for the carbs to be tweaked. I would also have the compression measured, to get an idea of how much bore / ring wear there is.


You didn't even mention which carbs you have! Adding air filters will be no cause for concern to take the car on a 40 mile drive. Depending on the carbs, there are a few things you can do for better perfomance. Let us know more details, and we'll be here to help!
Jeff Schlemmer

Hi, sorry - it's always the little things that I forget about.

The carbs are twin HS4's ( with some fine mesh across the mouths. It's been driven like that for 13k miles or so.

The filters I've got are Pipercross air-socks,, I got them as I hoped they might fit without any body modifications, alas they don't hence needing to cut wacking great holes in the bonnet. They'll be fine for use as I've seen umpteen Cater-field's etc using them.

With regards to the set up, I'm going to be asking them to set the whole car up (timing, point gap...) as whilst as I can do it, I can't do it well.

When you say check for piston ring wear, is that wise when I can't afford to fix the engine yet ;) I don't want to make myself worry about something else.


Stefan Carlton 1

Stefan, I'd try standard red springs and rich number 6 needles.


This thread was discussed between 20/06/2005 and 21/06/2005

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