How can I reduce HC emissions on a 308 Engine - even temporarily?

a temp fix is to lean the carbs out 1 or 2 turns

 

does you car have an airpump?

I have heard people would add peroxide in the gas tank but I don't know the full effects.

Try a couple of more turns. My old carb car was leaned out so much i sounded like it was going to stall

 

You refer to a valid idea, but have interpreted it in the wrong direction!

Try RETARDING your timing by up to 10 degrees. note that the US cars have dual points so you run 10 degrees retarded at idle. This will help a catalyzed car in two ways, one being by keeping the exhaust gas temp up to keep the cats lit off, and the way it can help you as well is by heating the exhaust pipes up more and getting what's known as "post-flame oxidation". i.e. burn off the remaining HCs in the exhaust! Note that this isn't the same thing as dumping fuel into your exhaust and melting it down...

 

Another option (although not that easy) is to advance the exhaust cams by ~14 deg of crankshaft rotation (7 deg of camshaft rotation) to the US spec which closes the exhaust valve before the intake valve gets too far open -- i.e., helps prevent the incoming intake (unburned HC) charge from "leaking" into the exhaust system during the overlap period when both the valves are partially open.

 

If you've got the carbs leaned out so that the CO really is low (1-2%?) then apparently the HC from combustion should also be very low. I've got a graph at work which I'll try and post tomorrow. If that's the case and your engine is, what you could say, of mature condition then maybe it is oil being sucked past the valve seals and rings. A compression test would show this.

However aren't there lots of 'miracle' coating liquids on the market that promise to help in these cases? Anybody got experience of these? It may be a fix for the test.

 

Specifically, the goal of retarding timing FOR YOU would be to benefit from the post-flame oxidation, sorry if I wasn't clear.

 

I'm not expert at this but I'm wondering...since you are SO close to the number needed to pass emissions, will different spark plugs or a hotter set of coils increase the burn just a little to get the HC down?

I'm amazed that such an old car needs to pass emissions in a country that didn't even require catalytic converters until about 15 years ago!

Birdman

 

In the US there are some high oxygen additives that can be used to get emissions down temporarily. Search the archives (probably the old ones) for 'emissions'. There are several very long threads that have many good tips.

Believe it's primarily alcohol, but could have another high oxygen compound. A couple of bottles in 1/2 or 1/4 tank should do the trick along with tweaking your timing.

I can't remember specific brands, but they're out there. If you can't find it in the UK, ask & we'll get you some.

 

Rubbing alcohol is your friend

 

My advice would be to take your car to a different MOT station.

Some of them are so used to modern cars, that they don't know how to get an older vehicle through the emissions test. The one I use is prepared to adjust the revs in order to get a good reading. It would fail at idle, but at 2000rpm it passes...while still falling within the range of revs allowed for "idling".

 

A too lean condition will often produce poor burn and high HC. A lot of Porsche guys here convert to Webers and keep going leaner because of the black smoke and hesitation, not realising that te opposite is required. try setting the CO about 4.0-4.5% and see difference. Also the retard a few degrees will also help. you may actually notice a better bottom end respose.

Cheers, Brian
relocated Brit.

 

www.passsmog.com

www.passsmogtests.com

www.autobarn.net/ch05063.html

www.protecusa.com/tbpuragas_emissions_test.htm

I don't know how good any of this stuff is, but they do have "satisfaction guaranteed". Luckily, I live in a state that doesn't do those kinds of tests!

 

There is this stuff called "guaranteed to pass" for sale at the local parts store. i haven't needed to use it, they guarantee it to bring your numbers to a passable level.

Also, make sure that the car in realy warmed up, a good half hour before testing!!!


good luck
Mike G

 

I talked to Mike at Pierce who has a (79) 308. Runs it with 52 idle jets. Passed emissions w/o the airpumps. If it will pass in CA, it'll pass in the UK.

As others have said, take some timing out at idle. See where that gets you.
Philip

 

I agree with the above and also suggest 100 octane racing fuel from union 76, it can help reduce emissions for smog test.

 

208 GT4 is right on the money with his suggestion. You need to find the right MOT centre, don't fudge the engine until it's absolutely your very last resort. You run the risk of running lean & damaging something (like a valve or piston) or getting the exhaust system so hot through spark retard you end up with a secondary failure somewhere else (like a burnt-out exhaust valve). If the car is running nicely leave it. Look in Classic Car Weekly for a morris minor/MG/Triumph specialist that does MOTs & take it there. They will know exactly how to "handle" classic cars.

Try this site, it may help you, you may not be doing the correct MOT procedure:

http://www.motuk.co.uk/manual_730.htm

And one last thing -- are you sure your particulate meter is accurate ? Just a thought...

Rob.