Thermoquad tuning to pass smog

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MrBelvedere2

MrBelvedere2

FABO Gold Member
FABO Gold Member
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Location
Sacramento, CA
Not an A body but I picked up a 78 Dodge camper van with a 360 and a thermoquad carburetor. When I bought it i was told it needed a rebuild so i rebuilt it with a kit, followed instructions and made sure all internal settings (float height, etc.) are where they need to be.

I took it to the smog shop and they said it won't pass emissions, putting out too much NOX. Does anyone have any tips to tune thermoquads for emissions standards instead of performance?

I would also like to see if anyone in the sacramento area could come by and help that knows thermoquads, this is my first thermoquad I've dealt with.

Thanks
 
The people’s republic of California has been trying to legislate our old cars off the road… did they give you a fixit ticket?
 
NoX means its lean. Are you running cats? Are you allowed to increase the RPM or do thy stick to spec? What about timing, can you deviate from stock at all?
 
I was under the impression that something that old in CA is exempt. What is the "tonnage?"

It might not be the carb at all, but rather timing too far advanced or modified/ missing parts that change the timing/ timing curve.
 
they will give you a ticket and make you go to a certified repair facility
 
Thermoquads by nature are lean. It the carburetor is right, it shouldn't be the issue. Retard the timing down to zero, idle it back up where it'll idle and have another go at it. I bet it'll pass then. AS LONG AS they are using the 1978 specs for it.
 
Thank goodness I've never had to deal with that but I would think that ignition efficiency would be huge to assist with the burn
 
I essentially got a good deal on it because the current owner just wanted it gone, I need it to pass to transfer the title and get tags....In California (even in a no-smog county) It has to pass smog to transfer the title. In California 1975 and older is smog exempt.

I played around a little with it yesterday it seems to have a vaccuum leak somewhere(cover it with your hand and it smooths out and raises RPM) I traced all the emissions lines and they all look good (not cracked or anything). I think it still might be a carburetor problem as it really seems to not run right no matter what I adjust.

I did the carb cleaner around intake manifold, carb base etc. and it all seems fine.

thanks for the information so far.
 
Carb may not be the problem, plenty of other 'bits' in the emissions system can fail.
 
I have not read all the comments sorry if redundant. NOX is a buy product of combustion temp. The carb if really lean can cause this but lean is the direction of smog fix these days and back then. The EGR valve is the direct fix for NOX on that engine. Also the cat but EGR is what you need to check into. Make sure it is opening and all passages are clear and open and that there are no air leaks, if it leaks it can suck in more oxygen cause leaner hotter combustion Temps. Also make sure that the mechanical advance has not been speeded up with a recurve. This will cause higher combustion temperatures at a cruise. Retarded timing will run your engine hotter but it runs the combustion temp down. Ca. Smog suck good luck
 
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