Advice on carb tuning to pass smog. 1982 720 CA emission setup

[720_Daniel]

Hi folks. 

I've read a load of posts discussing using the carb screw to adjust O2/fuel mix. I'm not sure which way does what? 

I got a smog report and my HC's are in a decent range, but my NO was too high. I've heard that I can run it richer and increase the HC level but bring down the NO level. Which way is richer? Neither make the engine sound swampy like my old yamaha 2-stroke when I put too much oil in the gas mix as a kid. 

 

Thanks anyone. 

[datzenmike]

The idle mixture screw only affects the idle mixture. It has zero effect on anything when driving. Driving mixture in only adjustable by  replacing the jets inside the carburetor. It's unlikely they were changed so they are not an issue.

 

On a fully warmed up engine with correct timing and idle speed, choke off, turn the mixture screw in to lean and out to make richer. Start by turning one way or the other doesn't matter much. Idle quality will drop, turn the other direction till idle quality drops noticeably. There will be about a half turn where it idles smoothly between these two. Set roughly in the middle. Idle RPM may have risen so turn back down to spec. Continue this in and out adjustment to find the smoothest best quality idle and again, reduce the idle speed to specification. Do as many times as needed till you can't improve the idle quality and the idle speed is correct for the Z22.  

 

 

NO is produced by high temperatures inside the combustion chamber.

 

Make sure that both intake and exhaust side plugs are firing. If the exhaust side are not, replace the first fuse on the left side of the fuse box. Both plugs firing reduces the burn time when NO is produced.

 

Make sure the timing is correct for the Z22 under California specs. I don't have this but expect something like 3-5 degrees. Too advanced will increase the burn time when NO is produced.

 

 

 

 

 

 

[720_Daniel]

On 5/9/2022 at 7:07 AM, datzenmike said:

Make sure the timing is correct for the Z22 under California specs. I don't have this but expect something like 3-5 degrees. Too advanced will increase the burn time when NO is produced.

 

 

 

 

 

 

I checked the timing, it looked to be about 5 degrees BTDC. I adjusted just to see what happened, and when I moved it to ~8, the thing ran a lot smoother (at idle), so I left it there. Honestly though, the notch on the pull was very hard to see, so I marked it with yellow paint. It was hard to get in there, so my dab covered about 3 degrees anyways. All I'm saying is that I'm in the grey area of correct. I plan on going to the smog shop in the morning. 

 

I used an induction timing light with the clip around the 1st intake plug wire. I didn't read anywhere that you should use the exhaust plug, but I'm curious if there'd be any reason to. 

 

Advancing the timing increases the NO levels, and that's what I'm trying to reduce, so I think I've done the wrong thing. Is it better to go the other way and let the engine run rough for smog? 

 

[datzenmike]

All engines run smoother when advanced because they are all artificially retarded at idle. The reason for the retarded timing at idle is to reduce emissions. (at the expense of idle quality) If the specs say 5 then set at 5. Total advance when revved up is something like 32 degrees so yours will be 35 and that's not good for it.

 

You can use intake or exhaust for your timing as the both fire together.

[720_Daniel]

Awesome. Thanks. I can go fix this now. 

 

Last question, the little toothed gauge is really hard to read. Is the center of the gauge TDC, or is the right side of the gauge TDC? 

[datzenmike]

 

Zero is the tip of the top point. Each tip is 5 degrees. So counting the top point, the second one down is 5 degrees

[720_Daniel]

Damn. You are the absolute best. Likely the most helpful person on the internet. 

 

Now, I know I said last question... but... um. 

Somehow during the clutch change, I must've bonked out my wires for the oil pressure and engine temp gauges on the instrument panel. Do you know of any threads where people discuss the wiring for these gauges? 

 

Thanks again. 

[datzenmike]

Does the red oil light come on when you turn the ignition to ON? If no then probably the two wire plug has just fallen off the sender. The sender is above the oil filter on the side of the block under the intake manifold. Looks like this...

 

 

The temperature gauge sender is mounted in the intake near the thermostat and the top radiator hose.  Same thing the wire may be off.

 

 

[720_Daniel]

That's the ticket. Thanks. 

Smog guy's machine was down, but he's committed to helping me pass. 

[datzenmike]

Check the EGR is working. Under load, a proportional amount of inert exhaust gas is added to the intake. This just takes up space and the cylinder temperatures are reduced. High temperatures are what contribute the most to NO emissions.