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MG MGB Technical - Trying to Pass Ca Smog

Here's another Ca smog problem to lay on the members of the BBS. First a little history of the 'B. I puchase a '77 B off of Ebay from a auto dismantler in the Sacto area for under a thousand dollars. The body was in great shape but they (dismantlers) said it wouldn't srart. I tow it home, let the ignition dry out(we had a very wet spring this year, no hood/bonnet) and charged the battery. It started right up. Gave it a tune up, took it in for a pre-test, Failed at idle.
Numbers are;
Idle-HC 483 needs to be <220/ppm
CO 1.43 needs to be <2.00%
2500rpm- HC 121 needs to be < 180/ppm
CO .78 needs to be < 1.70%
I'm would be label Gross Polluter if I didn't have the Pre-test. Replace both the air pump (because as I checked it wasn't putting any air out) and the check valve. Try to lean out the ZS( more I read the achives, more I find out that they are a piece of junk).Took the car back in to be pre-tested again,
Numbers;
Idle- HC 570/ppm
CO 0.45%
2500rpm - HC 33/ppm
CO 0.17%
Again I'm a Gross Polluter at Idle( I just can hear all those jokes out there about being a gross polluter). I have downloaded EVERYTHING from the archives dealing anything with SMOG/EMISSIONS. From reading them the HCs go up when you lean the carb too far.
Now for the Question- When I enriched back do I just use the idle air regulator or the main needle and the idle air regulator? Thanks for your help guys, Pat
Patrick Majeski

Pat. My opinion is that you are too lean at idle. This results in your very low CO measurement(after further adjustment) and the even higher HC reading. You are inducing a miss because the idle is too lean and this is showing up as high, then higher, HC readings. Enrichen the idle mixture until it is showing about 1.9-2.0% CO and see what the HC reading is then. The fact that your CO and HC readings are good at cruise are a good indication that it is a simple idle mixture problem. Les
Les Bengtson

If it's really running OK, stuff some denature alcohol in it...read the post from last week...
P J KELLY

My experience agrees with Les'. Too lean a mixture will start to bring up the HC. Since your CO was within limits initially, put the mixture back where it was, and enrich it a little bit. Your CO will come up, but hopefully the HC will come down.

Retarding the timing will also lower emissions at idle. I've never done it on an MG, but my first stab would be to retard 5 degrees from the correct setting. You might be able to retard as much as 10 degrees from normal, but I wouldn't go beyond TDC. Naturally, you'll have to reset the idle speed screw to keep it idling. The car will run like a sick Yugo, but if set this way just for the duration of the smog test, you won't do any damage.

If you can't get it in limits yourself, contact British Automotive in Novato, or British Sportscar Centre outside Sacramento (a town called something Park if I remember right). Either should be able to help you. Both have web sites for contact info.
Matt Kulka

The idle air regulator doesn't do much.
I leave it almost completely closed. (If closed
completely, the idle can become lumpy for
some reason.)

Adjust the Zenith using the main needle only.
If possible buy or borrow a gunson's CO analyzer
to set the mixture to about 5.5% with the
air pump disconnected. After reconnecting
the air pump the CO should be negligible.

If your ignition is in good shape (wires, plugs
cap, rotor can contribute to misfire), I would
check your cat converter. The cat
significantly reduces HC and CO.
Also check the valve adjustment. Good luck,
and the suggestion about going to a British
car shop is a good one, and I've done so
in the past to resolve the smog problem.
Ronald

British Sportscar Centre is in Cameron Park, a short ride up US 50 from Sacramento. The phone number is (530) 676-7226.

Also take a look at your ignition wires/cap/rotor if they haven't been replaced already. High HC at idle is an indicator of incomplete combustion, which can be caused by either too lean a mixture as noted or an ignition system in poor condition.

Paul K

Heet
vem myers

It is possible to pass CA smog with a completely non-functioning (hollow) Cat converter, but by no means easy. The first time I had to smog my 78, it took a long ($$$) session with a local mg specialist using an analyzer. The next time I decided to bit the bullet and replaced both smog pump and converter and had no problems. Replacement converters seem to be fairly available these days from places like Kragen or Autozone though, and can make passing a lot easier.

You do need to get your basic mixture in zone, though, and it is hard to do without a exhaust analyzer.

If you get the mixture optimised and are still having problems, you can try testing with the valves adjusted a few thousandths loose (reduces valve overlap to cut HC).
Tom G

Unless there has been a change, cars 25 years or older are exempt from smog check in California. I have a 1970 MGBGT and have not had to have a check for years. Check with CA DMV. You might not have to go through all the expense.
When I did have to have smog checks, the mechanic at the smog station and I adjusted the carbs on the test machine until it passed. Needless to say it would not run very well and I had to re-tune before I could drive away.
Lee

Lee,
They have changed it now to 30 yrs. and older. Starting January it will be all '74s. Pat
Patrick Majeski

What idle rpm were you at?
Daryl

I was at 950rpm give or take 100 rpm the B's tach is a little off. Pat
Patrick Majeski

Pat,

I wish I knew more about this, but there are 2 ways that idle rpm can affect you at the smog test:

1. You have to get it down below the maximum that they allow - in Calif, I forget whether that is 1000 or 1200 rpm. Looks like you are OK here. Otherwise you already failed.

2. I think you need to be just below this max rpm for best emissions (this is where I am ignorant). If I am right, you might be able to increase your rpm a bit?

I'm surprised that your tach is off - did you test it against another one?

I had 3 shots at the test before my MGB passed. Idle rpm was the issue.

Daryl
Daryl

This thread was discussed between 28/09/2003 and 03/10/2003

MG MGB Technical index

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