Adjustable Main Jet and another carb Q

[toddster]

Following in Hanley's experience, I installed an oxygen sensor and a fuel:air ratio gauge, and use it to set the main jet mixture screw for a perfect 14.7:1 ratio at cruise RPM.

Darn you! An hour ago I didn't even know there was such a thing.
And now I sorta want one.

[ndutton]

Hanley's O2 sensor was pretty cool

[edwardc]

The MMI manifold makes this particularly easy to install. It has exhaust take offs at both ends (to accommodate V-drive installations), with a blank flange plate bolted over the unused port. This blank plate makes the perfect place to install the oxygen sensor because it's smooth and flat, so it's easy to drill and tap.

[Marty Levenson]

sensors

This is all news to me! So, both sensors are on the exhaust manifold? I find that confusing at first glance: I would guess the ratios change after combustion?

[edwardc]

It's simpler than that. There's only a single oxygen sensor. By measuring the amount of oxygen left in the exhaust gases, you can directly determine the ratio of fuel and air that was burned to create that exhaust.

[Marty Levenson]

O2

cool. Thanks.

[Wrsteinesq]

Now maybe I want one, too. I've got that exhaust flange our host sells with the 1/8" NPT threads for a backpressure sensor, but maybe it would work for an oxygen sensor? Any recommendations?

[Jim Booth]

Me too!

This ebay item 222026510913 seems to be a nice gauge, analog and digital display only $20! Ships from New Jersey instead of Hong Kong.

Specs are:
Input voltage: 0 to 1V
Display range: 20% to 10%.

NGK 21002 O2 1-wire sensor is only $16 on Amazon, but they don't say what the voltage is. It looks like a spark plug size tap may be required.

Also, is the plug that closes off the unused end of an original manifold "tappable" for the sensor, or do we need to install a Moyer plate?

Jim

[edwardc]

I used this O2 sensor

http://www.summitracing.com/search/?keyword=SUM-G2989&dds=1

And this gauge

http://www.summitracing.com/parts/CYB-7009/

Unfortunately, cyberdyne has discontinued it, and Summit Racing has exhausted their stock . It's too bad, as it was inexpensive and simple.

[Jim Booth]

I googled around and found it appears the O2 sensors make 1V, with 0.45V at the ideal air/fuel mixture. So for adjusting the carb, all we need is the sensor and a trip to Harbor Freight some day when their digital volt meter is free with any purchase. I have several of them already. While trying to find detailed spec on the NGK sensor I saw one place selling it for $12. So the plate and tap are the biggest cost, and really not that
much for a useful tool.

[edwardc]

One thing to keep in mind: The 1-wire sensors do not read accurately until they are up to temperature. Some of the fancier (and more expensive) sensors have a built in heater element.

I've liked having a dedicated gauge. A quick glance after every warmup assures me that all is well with the fuel system. Can't have too many gauges!

[tac]

Oxygen Sensors

For a good explanation of automotive oxygen sensors and fuel control, see:

https://en.m.wikipedia.org/wiki/Oxygen_sensor

https://en.m.wikipedia.org/wiki/Air–fuel_ratio_meter