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MG MGB Technical - Spark plugs & K&N cone filters

1972 MGB twin SU, HIF i think. Wondering what would be the best type of spark plugs, i seem to run a little richand have a hard time adjusting the carbs, i lean them out a little and she hesitates low down ( i take it its left to lean on the screw on the side of the carbs.Would a hotter plug work?
Plus
I love the look of the K&N cone filters but can't see any easy way of attaching them to the SUs.

Thanks in advance for any answers
Gerry Lodge

For what is it worth...

I had Champion RN9YC in the car, and just changed to Autolite AP 63 Platinum.

Car starts the same, but it typically just fires right off at slightest tic of starter, and gas mileage is still terrible.

No noticeable power change either.
R.W Anderson

R.W.
What was the problem with the original plugs, any low end fouling ?
Gerry Lodge

Original plugs were put in about Apr 07, replaced them in May 10. Only 5,000 miles or so on them. One plug had a slight build up on angled electrode part, not stem electrode coming from ceramic center. (Boy have I forgotten technical terms.)

They were performing fine, didn't know one was getting a buildup.

The champion plugs were left over from an old Dodge Colt I had many many years ago, I was surprised to see they matched up for B.

I changed plugs to Autolite, solely because I had them on hand, and I was trouble shooting a hiccuping problem that appears to be more of an air mixture - vacuum issue.
R.W Anderson

A hotter plug would only work if they were fouling, and the correct plugs shouldn't foul anyway. There are so many faults that can cause mixture problems, some harder to spot on HIFs than HHs. You should do a full setup for air-flow and mixture from scratch and see if either carb has to be turned more than the other from the starting positions to get the correct mixture, or if on one of the carbs you can't seem to *get* the correct mixture.

Yes, HIFs are unscrew to weaken. I remember it as both mixture and idle screws have to be screwed in to get more fuel/rpms.
Paul Hunt 2010

Paul,

But the SU HS4 screw in (up) to lean, correct?
R.W Anderson

Correct. The HIFs are designed bassakward. RAY
rjm RAY

Hotter plug is a band aid for the symptoms, which may or may not work as the cause is left untreated.

Some things to check, in rough order:

1) ignition system performance and timing - worn dizzy? bad vacuum advance unit? bad coil / leads / cap / rotor?

2) carbs - worn SU needles? wrong needle profile fitted by a DPO? Air leaks?

Get these questions definitively answered or you'll never get her running as well as she could and you'll be chasing your tail. K&N's will help the engine breath a little easier and may need richer needles (YMMV - literally!), but you won't see much benefit without a port & polish of the head and some attention to the exhaust side.

And you won' see any benefit at all if #1 and #2 aren't right!

Good luck!!
Curtis Walker

Mixture is clockwise to enrich, anti-clockwise to weaken. The idle screw is clockwise to increase, anti-clockwise to reduce. Hence my comment of screwing them both in to get more. I didn't mention HSs, the poster asked about HIFs. Because of that I don't consider the HIFs are back'ards, it's the HSs that are. But even then if you consider that HSs are usually adjusted with the operator above, adjusting the jet from below, then looking down on it (with your X-ray vision or imagination) that is also being turned clockwise to enrich and anti-clockwise to weaken...
Paul Hunt 2010

Paul,

See, I had to "look" at this without x-ray vision; and my neck is sore from twisting around upside down to make sure I was looking up at the adjuster on the HS.

For more head twisting see my next posting/inquiry on timing.
R.W Anderson

Tongue in cheek, Bob :o) Also not so easy with head twisted round ...
Paul Hunt 2010

This thread was discussed between 24/05/2010 and 28/05/2010

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