Tips on how to pass the pollution test (PUC), after failing it twice

He told me that 80% of the BS3 and BS4 vehicles are failing the test due to some new updates.

BHPian V0rtex recently shared this with other enthusiasts.

Do you have any tips for passing the pollution test? My 2013 Honda Unicorn, which I use for local commutes and errands, just failed the pollution test twice. Six months ago, it passed with a CO level of 1.15% at idling RPM. Now, it recorded 3.17% (the emission limit is 3.00%). The bike was due for service and was running low on oil. The next day, I took it for service where the air filter and oil were changed, and the carburettor was cleaned and tuned. Instead of the recommended Honda 20W40 engine oil, I used 20W50 Motul engine oil. The mechanic also adjusted the idle RPM, increasing it from around 1.2k to 1.8k.

I read online that riding the bike hard for some time before the test might help remove deposited carbon. Following this advice, I rode my bike hard, hitting the rev limiter for several kilometres. I then took it to the pollution center again immediately, but let the bike cool down before testing. Whenever I hit the rev limiter on idle, it produced grey/black smoke. The pollution centre technician mentioned he smelled burning oil.

I tested again and got a reading of 7.15%! I was shocked. He told me that 80% of the BS3 and BS4 vehicles are failing the test due to some new updates by the Kerala government. Two other people with BS3 vehicles also failed the test, despite one having done complete engine work and service.

I’m worried that my bike will fail again if I retest. Do you have any advice?

Here's what BHPian vrprabhu had to say on the matter:

I had to renew the registration of my 2009 Gladiator and was apprehensive about the emission test. But, the bike sailed through the test a couple of weeks ago. In fact, I did the servicing (oil change, air filter cleaning & chain lube myself). Didn't clean the carb; instead, waited for reserve and then filled 500 Rs. worth XP95. Drove continuously for 50 kms at varying speeds. Hopefully, the carb is flushed clean.

Coming to your issue, I think the grey/black smoke from your exhaust indicates that there is oil leakage in the engine. Maybe worn-out piston rings?

And, check whether the air filter was really changed (not reused after blowing compressed air through it).

Any doubts regarding the fuel quality? If so, Jio pump quality seems better.

Hitting Rev Limiter is the Italian tune!! Don't know if it will work for a 150cc engine?

I think the unicorn has an exhaust scavenging port; get it checked for accumulated debris. Also, check the choke cable and its play as well as the condition of the spark plug. This will give an idea of whether the engine is running rich or lean.

BTW, how many kms has the bike run?

Here's what BHPian Jeroen had to say on the matter:

Once an engine is properly maintained the CO level on most bikes/engines/cars needs to be set separately. It’s part of tuning the carburettor!

They will tell you that on some carburettors it is not possible to adjust the CO level. But that is rarely true. On some carburettors, it is quite complex as you need to take it apart and reset it multiple times.

You are much more likely to have a low CO level with a properly warmed engine than a “cold” engine.

Good luck

Here's what BHPian omranga98 had to say on the matter:

Well, I had a stranger issue.

I took my Taigun for PUC but it failed since it registered 0% pollutant according to the device and if the result is 0%, the certificate would not be printed.

The testing machine was fine because it had just tested my Ignis and a Brio before me. Turns out it is a rather common issue that a lot of BS6 cars face (?) As ridiculous as it sounds, I tried the following day and it worked.

Here's what BHPian kozhissery had to say on the matter:

My 14-year-old Activa was always being maintained at the company showroom and I was confident that it would pass the test, alas it did not. The person asked me to give it to any local shop and not the company showroom as they don't change the required things. When asked about where to give it, they suggested almost all the local shops which repaired Activa. He even mentioned that to inform the service advisor that it failed the PUC test. I just took the activa to the nearest shop and mentioned the issue. He said most probably the spark plug/filter/oil needs to be changed/cleaned, so I asked him to do full service and get the PUC done (with additional fees).

I got back the scooter the next day with the new certificate and a bill much less than what the company showroom usually charges. Only the filter and spark plug were changed, according to him, the oil is in good condition.

In short, there would be shops who does the job of getting the PUC after servicing your bike too. One thing that I've noted is that now you have to give the accelerator to keep it in idle, or else the scooter will die.

BHPian V0rtex provided an update on the matter:

Guys, I just passed the pollution test! I took my bike to another pollution centre, and the folks there were very friendly and helpful. When they tested it, they found my CO level to be around 8% immediately and stopped the system. If they had continued for a bit longer, it would have registered my bike as "FAILED" in the system and prevented it from being tested again for another 24 hours.

They told me about a nearby mechanic and suggested I bring him over to tune the carburettor while they were testing. I went to the mechanic, explained what had been done, and as they started testing again, he began tuning the carburettor. Voila! My CO level dropped to 2.3%, and hydrocarbons dropped from 156 (which was still way below the 3000 limit) to just 10. I was truly surprised, as every other mechanic I consulted wanted me to do complete engine work.

I'm really relieved as I didn't want to abandon this workhorse. I would like to thank each and every one of you who tried to help me.

So, in short, if you fail the test, change the oil and spark plug, and bring the mechanic along with you while you test the bike.

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