Topic: 1978 CB750 Tuning with Wideband o2 and Digital Readout. (video)

[J.Webster Designs]

Hey guys and gals, I Just figured I would post what I have been up to lately with a custom build that we are doing for a customer. The bike is nearing its full completion and I am down to the final stages of road worthiness testing and tuning.

Equipment: I have recently picked up a Wideband O2 and Digital Readout setup to tune bikes with a bit more accuracy than doing the standard tuning practices.  The system uses an NGK O2 and can accurately read between 9.00 and 16.00:1 AFR with a response and accuracy of + or - 0.01 AFR. I am using a pitot tube style exhaust sniffer which I have extended with copper tubing to be able to reach into individual header pipes as well as avoid exhaust reversion pulling fresh air into the system and giving me falsely lean readings.

Bike: This build is a 1978 CB750 with a rebuilt stock spec top end and the stock PD carbs. The changes to the motor are K&N pod filters, a 4 into 1 header and a Cone Engineering Slip-on exhaust can. The current jetting in the carburetors is #42 pilot jets, and #120 main jets.


Here is a video of the current set up at idle with the choke out (on) in the beginning and the choke in (off) at the end. You can see that the bike still needs much more fuel at idle. This surprised me as most people are running #42 pilot jets in these PD carbs with pods and open exhaust and seem to be happy with the results. The testing here shows that setup is still very much lean at idle and especially at initial throttle opening. The Fuel Mixture Screw Setting in this video with #42 pilot jets is at 4 turns out just to get it to the low 14's at idle WITH the choke on!

I will post more updates and video as I tune the bike more. Feel free to comment!

Enough talking and more video right?

[flybox1]

Id be interested in seeing what this bikes idle chop plugs look like 

[Bodi]

http://www.movierotator.com

It works.

[brewsky]

Hook it up so you can ride with it working, and you will be in business!

[J.Webster Designs]

Brewsky, It is hooked up so that I can ride with it.

The 35s have been drilled out and put me a little too rich. So I am waiting on some #45 pilots to come in. I will do a follow up when I get everything back together. Might even be able to get some go pro footage of the wide band running while riding.

[brewsky]

Good deal!

I ended up making several passes at different throttle positions to dial mine in.

If you mark your twist grip, you can make a run at a set throttle position, allowing the rpms to vary from low to high. Then you can adjust the carb circuit corresponding to that position.

I would pull over after each run, and write down the max and min for that run.....if you can go-pro your runs you could save that trouble!

I found that generally as the rpms increased at a set throttle position, the mixture became leaner.

Here are my results in a spreadsheet:

[J.Webster Designs]

Liking the spreadsheet brewsky! Looks about in line with the results that I am seeing

[scottly]

The WFO readings need to be recorded at various RPMs. There will typically be a richer reading in the 5000-6500 RPM range than at 7000-9000, when the motor is making the most power. The A/F should be between 12.8-13.2 at that point.

[brewsky]

The WFO readings need to be recorded at various RPMs. There will typically be a richer reading in the 5000-6500 RPM range than at 7000-9000, when the motor is making the most power. The A/F should be between 12.8-13.2 at that point.

That is exactly what I observed on each run, and it held mostly true for the smaller throttle openings also.

All runs (all 45 of them) were made varying the rpms from approx. 2K to red line at the given throttle opening,

I started recording both max and min a/f readings for each run at first, but later just the highest reading.

I was shooting for around 14 at light load cruise, and mid to high 12's on WOT.

When I marked the throttle for the first time I was amazed how much of the time normal riding is at 1/4 throttle or less!

[bochnak]

I always wanted a wideband for this exact reason.

At 4 turns out, did you reach a peak idle RPM? I have a feeling you will need to bump the pilots 2-3 sizes larger from where you are at get the fuel screws at 3 turns out max.

Let us know the AFR at idle after fuel screw tuning (peak RPM).

[PeWe]

I would like one too :-)
A movable sensor to be plugged into each pipe.
4-4 means readings for each cylinder and detect a single lean cylinder, or rich. I had one cyl that ran too lean and leaner than the other. That can be expensive if not detecting it in time.

[J.Webster Designs]

Pewe, the setup that I put together utilizes a pitot tube style muffler mount that I extended to be able to reach into each individual header tube to be abke to do exactly what you were talking about. Let's me see what every cylinder is doing without having to weld in 4 O2 bungs.

Bochnak, the motor ran well at the 4 turns out on the #42 pilot jets.  It was suprising to me as I have heard numerous people running this setup with the same pods, unrestrictive muffler and 4 into 1 header reporting that it was running well and with a good AFR according to plug chops and butt dyno.

But I am intrigued whether or not most people are just tuning the top end circuit with plug chops and getting the slow speed circuit "acceptable." As Brewsky stated, it's surprising how much time you spend below 1/4 throttle while riding. With the idle at 14.00+AFR I would expect it to be easily at or above 16.00AFR at partial throttle. This would lead me to believe that most people with this setup (#42pilot, #120main, pods, 4into1 header, unrestrictive muffler) are riding around most of the time way lean.

I am happy with the investment in the setup that I put together as I tune many different bikes and this allows me to honestly know that they are operating in a safe mixture range. Plus... I can use it on all my 4 wheel rides too.

[flybox1]

But I am intrigued whether or not most people are just tuning the top end circuit with plug chops and getting the slow speed circuit "acceptable." As Brewsky stated, it's surprising how much time you spend below 1/4 throttle while riding.

+1!!!

[firebane]

Not really applicable to the W/B readings but how did you setup the choke to work like that?

[flybox1]

Not really applicable to the W/B readings but how did you setup the choke to work like that?

That choke pull knob is standard (at the handlebars) for the 77/78 bikes.  He just relocated it to a more convenient location.

[firebane]

Not really applicable to the W/B readings but how did you setup the choke to work like that?

That choke pull knob is standard (at the handlebars) for the 77/78 bikes.  He just relocated it to a more convenient location.

Yes I know. But he must have modded it to some degree cause that would be a very long cable being snaked around.

[brewsky]

Pewe, the setup that I put together utilizes a pitot tube style muffler mount that I extended to be able to reach into each individual header tube to be abke to do exactly what you were talking about. Let's me see what every cylinder is doing without having to weld in 4 O2 bungs.

 

I'm interested in your pitot tube design.

Is that a standard wideband o2 sensor?

Did you make up the pitot tube adapter, or did it come with the setup?

I'm kinda getting tired of welding o2 bungs into the exhausts!

[J.Webster Designs]

Brewsky - Check out the Innovate exhaust clamp. That is the pitot tube style sniffer that I am using. I then extended it using copper tubing to be able to get into the individual header pipes. The sensor is an NGK LZA08-H6 that I am using.

Firebane - As flybox1 stated, the choke knob is a stock relocated item. I did shorten the cable to be utilized well in that location.

[PeWe]

About the sniffer... It must have a long pipe sticked into the exhaust?
Like described here http://www.daytona-sensors.com/download/WEGO_Motorcycle_Sniffer_Tech_Note.pdf
This is for the Harley's, right?  Limitations: severe reversion effects will occur at part throttle.

I have ideas about an A/F gauge with logging like Wego III. http://www.daytona-sensors.com/WEGO3.html
A sniffer to measure each exhaust one by one. I use a 4-4 without diffusers.
I thought is should be OK to use a pipe with ID 1", lenght about 6" mounted into the exhaust instead of the diffuser. The description for an Auto sniffer will work?  http://www.daytona-sensors.com/download/WEGO_Auto_Sniffer_Tech_Note.pdf

I have diffusers out mostly.

See and log while driving.
I have had bike on dyno for mostly WOT runs. Different with normal driving with relatively low throttle lift.

[J.Webster Designs]

PeWe, Your diffuser idea may just work, however you may still run into air reversion problems due to the O2 sensor still being so close to the end of the exhaust.

The set up that I am utilizing is similar to the first link that you posted, however, It is designed a bit differently. The innovate sniffer that I modified has a hole in the bottom causing a low pressure situation that draws exhaust into the open hole in the front. The one that you posted relies on the positive pressure  of the exhaust to force itself into the tube.