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MG MGB Technical - HIF4's CO off scale

Hi new to MG ownership having bought a 75 BGT
Had heaps of cash spent on a body rebuild but nothing on the engine shows 91k
have checked the carbs out and tried to tune them up as per the book and advice from this board
I have managed to tune them by ear and using the pin lifter as am indication for mixture setting
having satisfied myself with the resultant running of the engine I put my exhaust meter up the tail pipe which went up to 4.5 then shot off the scale as I watched it/
Engine appears not to burn oil when running and has pleanty of pull on the road.
I suppose the next stage is to replace the needles and jets as they are an unkown quantity.
I can say that the needles are ACD standard for the 75
18v847F engine acording to Haynes.
Am I going in the right direction to get the CO down?
C J Bryan

C J

Have you checked the spark plugs? They should be light brown normally, if the mixture is rich they'll be sooty black.

I serviced my carbs (HIF4s) a few months ago with the SU kit from MGOC. I also replaced the bimetal jet adjusters, after problems with the engine cutting out when hot. I'd replaced the standard needles with AAA type previously, as I'm using K&N filters. Anyhow, after servicing the engine runs much better doesn't cut out even in heavy traffic, and spark plugs are normal.

While servicing the carbs I compared new and old jets, the difference was suprising.

So I'd recommend a carb overhaul, but do check the ignition system is upto scratch and timing correct as well.

Good luck.

Steve
75 Jubilee BGT
Stephen Lee

Steve

Thanks for the advice will check the plugs and I am going to check the dwell again timing spot on with strobe at 10deg
I expect I will go down the route of servicing the carbs with the kits you mention at least I will know what state they are in then.
C J Bryan

CJ,

Before anything else, I'd give the car a full tune up. Replace all tune up parts including spark plug wires, air filter and fuel filter. Since the car is new to you, you have no idea how old all of this stuff is. (It wouldn't hurt to check compression while you have the plugs out.)

Then adjust valve lash, dwell and timing.

Then after all of this other is done, adjust the carbs.

All of this other stuff affects the carburetor performance. Since all the other parts of the system have hard and fast settings, they can be adjusted independently. The carbs don't have that luxury. Their setting relies on the rest of the system to be doing it's part.

Congratulations on the new 'BGT. I know you'll love it.
Matt Kulka

Hi Matt
Thanks for the advice, I was thinking the same and will attend to it as soon as I get the time from work.
Had a Morgan 4/4 prior to the B and fettled that no trouble, sold that to a guy in Germany but really missed it so when the B turned up I couldn't resist it. Always wanted one some 30 years ago, finally got one. The wife likes it as well, she was not so keen on the Morgan.
C J Bryan

This thread was discussed between 07/10/2003 and 08/10/2003

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