Rebel AFR! - Honda Rebel Forum
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post #1 of 99 Old 09-03-2019, 11:44 AM Thread Starter
 
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Rebel AFR!

Guys and gals,


Today I am scheduled to receive the bike bullets and can finalize power and ground connections to my AFR gauge. To get a background and pictures of what I'm talking about, check out the below thread:


https://www.hondarebelforum.com/f18/...-122021-3.html


I decided to start a new thread because the following discussions are more appropriated under, "...Carburetor, Fuel System..." than it would be in the thread above.


My only target at this time to come from obtaining AFR data, is to improve the AFR under WOT conditions. I've had some time to think about this, and this is what I've come up with. From 65 mph to whatever top speed the bike may attain, the performance is dismal. Not unexpected though, as we are only given 233.9 cc's! I expect it runs leaner than optimal AFR at WOT. It seems it runs a lean at cruise speeds too, but personally, I'm OK with it because the mpg is so good. So, my efforts at this time are for WOT performance only. Any other data is good to know, but I don't intend to change it.

What I want to provide to the forum members here are at least the following things. Feel free to add to the list, and I will achieve those where possible. The below measurements to be done on my totally stock (at the moment) Rebel.


  • Cold and choked idle AFR
  • Warm idle AFR (no choke)
  • Cruise AFR (5th gear, from 30 mph to 60 mph in 5 mph increments)
  • WOT AFR (5th gear, from 55 mph to 80 mph in 5 mph increments)
Anything else?


7milesout

2016 Honda Rebel 250 - The "Piglet."
AFR sensor equipped and downsized to a 0.105" main jet.
The only changes so far.
Bought on 6/29/19 with 44 miles.
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post #2 of 99 Old 09-03-2019, 12:54 PM
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Looking forward to what you find.

Keepin' all the left over parts. Gonna use 'em to build another bike!

'01 & '09 Rebel 250, '06 Ninja 250, '89 VN 750
Putting your bike year and model in your signature helps others help you!
Here's how: https://www.hondarebelforum.com/f19/...re-121087.html
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post #3 of 99 Old 09-03-2019, 04:40 PM
 
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Ditto. Neat research project.

.

2016 Rebel 250 - - Black
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post #4 of 99 Old 09-03-2019, 10:00 PM Thread Starter
 
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Gaahohaaalie! (Like Gomer Pyle). You ain't gonna believe it, you just ain't gonna believe it! I would have told you were wrong if I hadn't seen it myself.

All you stock boys, we may have an opportunity here. But first...

The white wire is evidently not the optimal power source because when I turn on the HI BEAM the AFR gauge loses power. Easy enough to resolve because no wires were cut. Just have to break out the multimeter again.

I have not started doing my official testing yet, but I rode it with the gauge up and running. What an eye opener.

Choke idle is pig rich, but it's supposed to be that way so whatever. It's like 8.0 or richer ... my wideband sensor doesn't go richer than that.

Warm idle is a healthy rich. About 11.2. Both choke idle and regular idle are richer than what I've tuned the Scamp to. Nothing negative about that. Just how it is, from the factory. But a good learning lesson for me ... maybe I need to be a skosh richer on my Scamp.

Cruising, moreso at higher rpm, it is stratoshpherically lean. Near the lean limit of the gauge. Running 18 - 20 AFR at 45 mph and higher. Don't worry, I will have better defined numbers and maybe even a plot later.

But here's they eye opener. Bear in mind, my bike is new so everything is fresh. And with enough level ground the speedometer will get very close to 80 mph. So it is running right. But at WOT it is RICHER than optimal! Wow! I would not have believed this!

I wasn't on my testing grounds and so I could only pull 65 mph in 4th to hit max rpm at full throttle, but at WOT it starts out at like 9.0 AFR and at max rpm it hits only about 10.5 AFR!

So yeah, rich. Richer than 12.5 AFR. That means I'm gonna have to do some math (I have a spreadsheet already) and downsize the main jet. The opportunity is that 12.5 AFR will use less fuel, and will make more power! Will more power at 12.5 be noticeable? Dunno. That's what my testing will determine.

Also, what I believe is that the jet kits on carbjetkit help not with power, but smooths out power and improves driveability due to shimming the jet needle up. Which richens up the cruise AFR which woukd make it run more smooth. Because under certain lean conditions, it stumbles like it is running out of gas. I may shim the jet needle too later ... but before that I will tune the WOT AFR and see how that affects the performance.

Hope you guys and gals find this interesting, more to come!


7milesout

2016 Honda Rebel 250 - The "Piglet."
AFR sensor equipped and downsized to a 0.105" main jet.
The only changes so far.
Bought on 6/29/19 with 44 miles.
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post #5 of 99 Old 09-04-2019, 12:11 AM
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Very interesting. I put first generation (larger) jets in my 2009 when I began using a first gen foam air filter in place of the stock paper filter. The common thought was that Honda had used smaller jets in the second gen for better fuel economy/EPA guidelines, etc., but the bikes ran too lean. When I recently pulled my plugs to check valve clearance, they were very dark. Really need to do a high speed plug test, as that's more reflective of what they should look like.

Keepin' all the left over parts. Gonna use 'em to build another bike!

'01 & '09 Rebel 250, '06 Ninja 250, '89 VN 750
Putting your bike year and model in your signature helps others help you!
Here's how: https://www.hondarebelforum.com/f19/...re-121087.html
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post #6 of 99 Old 09-04-2019, 07:52 AM
 
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Wow. Interesting preliminary results.

My 2016 is all stock with now 800 miles or so on the odometer. So results for your bike should be very applicable to mine. Definitely keep us posted on final results.

2016 Rebel 250 - - Black
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post #7 of 99 Old 09-04-2019, 03:04 PM Thread Starter
 
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I had to leave this morning and go to my old man's house ... well, the hospital. He took an ambulance ride to the hospital this morning. So I'm spending another night tonight in the hospital. Suffice it to say, there will be no testing this evening. Too bad, the weather is so good right now.

I did some figgerin (sans the spreadsheet) and it seems to me I'm going to have to go way down on the main jet. So much smaller, I'm going to have to consider the size of the jet needle.

I'm assuming the jet needle parks in the main jet. So I'll have to make sure it will still fit. Does anyone know the size (diameter) of the jet needle? Or have one laying around that can be measured?

I'm sitting in the hospital now with my smartphone and gonna see if I can find how small a jet I can get.



7milesout

2016 Honda Rebel 250 - The "Piglet."
AFR sensor equipped and downsized to a 0.105" main jet.
The only changes so far.
Bought on 6/29/19 with 44 miles.
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post #8 of 99 Old 09-04-2019, 05:38 PM
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I can measure the length and diameter of a needle, but IMO, the taper on the end is probably critical too. Not sure exactly how to measure the taper. I cleaned a first gen carb a while back, and the needle that came with the kit was not the same size as the one it was supposed to replace.

Keepin' all the left over parts. Gonna use 'em to build another bike!

'01 & '09 Rebel 250, '06 Ninja 250, '89 VN 750
Putting your bike year and model in your signature helps others help you!
Here's how: https://www.hondarebelforum.com/f19/...re-121087.html
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post #9 of 99 Old 09-04-2019, 05:51 PM Thread Starter
 
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Maybe take a good close picture of it. Then measure the smallest diameter and largest diameter of the taper and the distance between the 2. That would be great and I did find small jets.

2016 Honda Rebel 250 - The "Piglet."
AFR sensor equipped and downsized to a 0.105" main jet.
The only changes so far.
Bought on 6/29/19 with 44 miles.
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post #10 of 99 Old 09-04-2019, 06:00 PM
 
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LOL, this has me thinking a servo motor attached to the mixture screw, oxygen sensor and a few $'s for computer board and parts, could make for a very simple ECU. Unlike EFI systems we don't have to worry about timing, knock, air intake volume, fuel pump, injectors.



How effective would real-time adjustment of the mixture work out, I have no clue....there's usually a reason why these things have not been done before!

1974 CB125S (purchased 1983, ate 2 crankshafts, sold 1984)
1986 Rebel 250 / N. California (purchased 2019)
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air/fuel results, air/fuel tests, fuel economy

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