High HC ppms indicate unburnt or paritally burnt fuel in the exhaust. High CO2 indicates partial combustion of the fuel. This would lead me to the same conclusion of running too rich.
If you haven't done a tuneup then you need to do that first. (cap, rotor, wires, plugs, air filter, and oil change with new filter) when is the last time the O2 sensor was replaced? If it hasn't been done in the last few years, change that out too. Set timing to 8 deg. BTDC. See how that works out
Where did you get the new Cat? I bought one off of ebay that was part of the down pipe....it sucked as it had about half the necessary catalyst to pass. I bought a magnaflow cat (just the cat) that was rated "extra duty" and it worked like a charm. I have found that a cat is one of those products that you get what you pay for.
+1 on the cap, rotor, plugs, wires, air filter... A steady misfire will richen up the mixture quite a bit.
O2 sensor is extremely important. If it has failed, or is just slow responding, then your mixture will be off.
I'd add that you should make sure that you get the engine up to operatiing temperature and try to get the test done at a time of day where they can take it right in. This ensures that the cat has "lit off" and is working as designed.
Failed components in the carb can also cause a rich mixture, as will the choke being out of adjustment.
'88.5 Samurai JX, mostly stock
1) make sure its heated up good so you know the choke isnt on...
2) give it a good run on the freeway to get that cAt really hot they dont start working until they are.
3) if you do have the stock carb check and see if your mixture pin has been driven out, its on the pass side of the carb on the bottom. if there is no pin, somebody has adjusted the mixture.
4) do you have a check engine light?
its a magnaflow cat, so quality should not be an issue, and i had driven the truck about an hour in city traffic so it should have been plenty hot.
my engine was fuel injected, and my dad swapped the head for a carb'd head. he said they bolted it right on, along with the carb and everything. no idea about any adjustments to the carb.
this vehicle has had no problems passing emmissions in the past, but has sat for a while, and now has issues. it runs like a champ, and gets great mileage so it cant be too bad off right? i have the option of registering the vehicle in a county that does not require emmissions. i am thinking about just doing this since the vehicle runs so well, and will be exempt from emmissions in a couple of years. seems like a lot of money and trouble to do the tune up and any sensors that it might need when i can dodge the emmissions test altogether. but then again, i do like working on things........
If you bolted a stock carb onto a fuel injected engine without replacing the wiring and ECM, or if it is a non-feedback carb, then there is no mixture control from the ECM and the 02 sensor has no effect.
The mixture is probably fine for normal running, but way off for optimal emmisions. At this point, your probably better off registering it in a non-emmisions county.
'88.5 Samurai JX, mostly stock
x2 on what Vader said. If that vehicle passed smog previously with it's current setup then your emissions standards may have been less strict at that time. An aftermarket carb won't pass emissions in most states (wouldn't even pass a visual check) it's just going to get harder to smog it as time goes on, you should probably look at registering in another county.
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