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11K views 101 replies 8 participants last post by  VAReb 
#1 ·
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/f18/52mm-afr-gauge-mounting-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
 
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#4 ·
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
 
#18 ·
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.

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!

7milesout

This tracks with my experience out on the open road. I've been keeping a religious fuel/distance log for the past 5k miles, and while city/country riding returns a steady 65-70mpg (running a smaller rear sprocket) getting out WOT on the interstate returns closer to 50-55.
 
#5 ·
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.
 
#7 ·
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
 
#8 ·
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.
 
#9 ·
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.
 
#10 ·
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!
 
#11 ·
Here are the measurements from an (original?) second generation needle. All measurements in mm. Total length, 42.00, not including a small raised "button" on top of the needle cap. Thickness of cap, not including "button", 1.62. Diameter of cap, 5.90. There is a short uniform diameter "shoulder" that extends 4.19 below the cap and measures 2.90 in diameter. Below that, the needle is a uniform 2.50 for the first 13.0. From that point, it tapers down to 1.30 at 39.00 below the bottom of the cap. Below that, over a distance of approximately 1.00, the taper increases down to nothing.

This is probably clear as mud unless you have a needle in hand.
 
#12 ·
flitecontrol - You've disassembled a carb. Maybe you can answer this? At WOT, does the jet needle pull all the way out of the main jet?


I'm still in Chattanooga at the hospital with my dad. He had to stay a 2nd night, but he is doing WAY better. He'll go home tomorrow. But I'm not sure if I'm going to make it back home until late Sunday. I'm his short order cook for the weekend.




7milesout
 
#13 ·
flitecontrol - You've disassembled a carb. Maybe you can answer this? At WOT, does the jet needle pull all the way out of the main jet?
7milesout
Can't say. As much as I've tried to look, it's hard opening the carb, bending over to see, and still stay in my lane and operate the controls. :rolleyes::eek2::D:nonono:
 
#14 ·
Main Jet isn't involved other than it is the maximum fuel opening of the "High Speed System"

The "Needle Jet" diameter in conjunction with tapered needle provides transition between low speed/idle to intermediate system.. effects of needle jet taper off past 1/2 throttle and main jet comes more into play..

needle jet is held in place by the emulsion tube aka ("Needle Jet Holder" Honda nomenclature).. An important part, as it begins the processes of aerosolizing the fuel, as the needle rises greater amounts of fuel are aerosolized..
Main jet screws into bottom of emulsion tube..

The needle never pulls out of needle jet But does fully pull out of emulsion tube aka "needle jet holder"
There are performance emulsion tubes that enhance performance of some engines..

your AFR is dependent on more then static carb settings.. Altitude, Temperature, Humidity, etc. will also effect results at any given moment..
 

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#15 ·
Testing, Testing, 1, 2 ... 3?

Guys,


Below are sketches of the testing I'm going to do in addition to the data I'm going to check if I ever get to go home. But I made some sketches to describe the performance tests I want to do. I hope I can get these tests video recorded, both stock an with optimized main jet.







Tests:
  1. 50 - 65 mph Roll-On.
  2. Top Speed.
  3. Bunny Slope.
 

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#16 ·
Notice how our mighty Rebels pull the front wheel off the ground when hitting WOT in 5th.

This testing can get dangerous...
 
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#17 ·
Some data...

I did manage to get out on the bike yesterday. And got quite a bit of data. Not all. I didn't do any video recording as currently I have no way to do that. I do have a GoPro but I have not affixed it to my new helmet. I had my phone attached to the RAM mount, the AFR gauge zip tied underneath it (just cobbled it on, but it worked), and zip tied a stop watch to my left handlebar. So here's the data.



  • Choke (while cold) Idle AFR: Pig rich. 8.0:1 or less.
  • Idle (while fully warmed) AFR: 11.2 to 11.6. The warmer the engine the slightly higher.
  • Cruise AFR: I didn't get a chance to measure these. But they are lean to extremely lean.
  • WOT AFR: In 5th gear, they ranged from 9.0 (rolling on at 55 mph) to 11.5 at 70+ mph.
    • I had originally noted a highest AFR of 10.5, but it was a bit higher yesterday.
Performance Tests



  • Bunny Hill Roll-On from 55 mph: The bike gained up to 59 mph consistently. This may not mean much now, but will be relevant if my tuning improves performance.
  • Timed Roll-On (55 mph to 65 mph): I had 5 runs and this averaged 10.855 seconds.
    • I was originally going to do 50 - 65 mph, but in the course of trying to complete this testing, I didn't remember to start at 50 mph, instead started at 55 mph.
  • Top Speed 2.5 mile stretch: I hit 70 mph the first time, then 71 mph the next 3 times. Then I ran out of fuel on ON, and limped back home on Reserve.
What I did notice while pinning the throttle for ~ 2 minutes during my top speed run is that the AFR was higher than I expected. I would say it averaged about 11.5:1 (not 10.5:1). But that would quickly jump and vary from 10.5 to 12.5. So, I'm going to have to be careful tuning. That also tells me, that maybe I will make LESS improvement than I originally thought I could. All this testing was from gas pumped from an E10 tank. And other than equipping the bike with the AFR gauge, nothing has been touched.


I'm going to try to do some cruise AFR and WOT AFR, but that may require a video camera pointed at the AFR gauge and phone GPS speed to have reasonable numbers. So, I'm going to have to figure that out.




7milesout
 
#19 ·
The Piglet is sitting on empty right now. In order for me to tune optimally, I think I better top off with 90 octane no ethanol. And just do WOT high speed pulls. In that way, I can judge that with 90 octane no ethanol fuel, does the AFR at top speed go richer? Go leaner? Or stay the same from the 87 octane E10? I'll need this info to help select the all around best main jet.


Unfortunately tonight I need to make a run up to my father's house, just to break up his week of living alone. Thursday and Friday nights, I may have football games to go to. At least Thursday.




7milesout
 
#20 · (Edited)
Just as a datapoint for your top speed test runs....

I took my 2016/975 miles Rebel on the interstate today for the very first time. (Previous high speed runs have been on a divided parkway, but with 45-50 mph speed limits.)

I was just practicing, so was merging onto westbound, going up to the next exit, doing the clover leaf, and looping back on to eastbound to go back where I came from, and repeat 3 times.

Because of congestion and the short distance, I was not able to hit max speed. Each time I tried, I ran out of room and had to throttle back while the Rebel was still accelerating at a pretty good rate.

I was consistently hitting 75 mph, and there was definitely more speed left in it. I will be shocked if this bike won’t hit 80.

Flattish highway, wind not a significant factor (tested speed in both directions.) Totally stock. I do have a National Cycle windscreen, and I am running high-test gas (E10) with Seafoam added.

As a side note, I was very impressed with how nicely this Rebel cruises at 60-65 mph. After this test run, I am much more confident about doing some local cruising on the Rebel.

.
 
#21 ·
VAReb - At an indicated 75 mph on the speedo, it is doing about 71 to 72 mph. Just FYI. I have a "GPS Speedo" app on my phone. Very accurate, and a very large digital display (so easy to glance down and read). It's a worth app.




7milesout
 
#22 ·
VAReb - At an indicated 75 mph on the speedo, it is doing about 71 to 72 mph. Just FYI. I have a "GPS Speedo" app on my phone. Very accurate, and a very large digital display (so easy to glance down and read). It's a worth app.

7milesout
7Miles,

Good to know. I will have to look into something like that. What are you using to mount the phone, and where are you mounting it?

It will probably be a while before I head out far enough beyond the urban area to get a good top speed reading. The sprawl extends quite a ways...

.
 
#23 ·
Phone Mount...

This is my current set-up. I use the RAM mount to hold the phone and the AFR gauge (worth every penny). But during testing, it won't hold both. So I kind of clabbered the AFR gauge just below it, with zip-ties. It works well. I can see it real well.


This weekend I'm going to finish my stock carb set-up testing. Mainly I just need to do cruise AFRs and make a graph. Then I'm going to see if the 90 octane no ethanol gas makes any AFR difference at WOT at top speed. Just to help figure out the best all around main jet. Then I'll determine the main jet, and buy it, along with the next main jet smaller, and the next main jet larger.


When I go to change the main jet, I'm going to see if there's any way to shortcut the carb jetting work. I'm thinking that maybe it can be done on the bike. Take the 2 bolts out attaching to the intake, disconnect the cables and hoses as required. Loosen the hose clamp to the airbox, and then rotate the carb within the filter hole (with the clamp loose). Should have access to the bottom and top doing it like that. But we shall see. I've got a spot upon return to my house where if I turn the petcock OFF, by the time I get to my house it is stumbling and out of fuel. Making the float bowl nearly empty for servicing.


See my picture for my RAM mount setup, as well as the AFR gauge and stopwatch.




7milesout
 

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#25 ·
When I go to change the main jet, I'm going to see if there's any way to shortcut the carb jetting work. I'm thinking that maybe it can be done on the bike. Take the 2 bolts out attaching to the intake, disconnect the cables and hoses as required. Loosen the hose clamp to the airbox, and then rotate the carb within the filter hole (with the clamp loose). Should have access to the bottom and top doing it like that. But we shall see. I've got a spot upon return to my house where if I turn the petcock OFF, by the time I get to my house it is stumbling and out of fuel. Making the float bowl nearly empty for servicing.
7milesout
If you can just get the bowl off, you should be able to access the jets. Socket (Allan) head screws make it easy.
 
#26 · (Edited)
Completely Stock AFR Values...

I have completed the testing necessary for a completely stock bike. Check out the graph below. On Friday I went and got a tank full of Ethanol Free 90 octane. Then I went to the WOT test track to see what if any changes may occur with the E0 gas. Believe it or not, it was noticeably richer. It would not go leaner than 10.8 AFR.

Below is the results of the testing.


  • Choked Idle: 8.0 or richer (not a problem, the choke is working correctly).
  • Warm Idle: From 10.8 to 11.5 (richer than I expected).
  • Cruise AFR: See the plot below.
  • WOT AFR: See the plot below.
  • Bunny Hill Speed: 59 mph.
  • Roll On Average: 10.855 seconds.
  • Top Speed on Test Course: 71 mph.
A couple interesting things. Maximum lean condition seems to be about 50 mph (5th gear). Does this constitute maximum mpg? Maybe. Maybe not. Things are complex. Even though at 50 mph in 5th steady state cruising yields the leanest mixture, it also has higher drag due to increased engine speed, wind resistance (drag), etc. So I couldn't say 50 mph is the highest fuel economy. But certainly between 40 and 50 mph in 5th gear will yield the highest mpg.


After about 50 mph, the main jet begins to get involved. So even at 50 mph, a gentle twist of the throttle is going to get the main jet involved. So my guess is 45 mph should be the absolute optimal mpg. Because at 45 mph, a gentle twist of the throttle, like to pull small grades, may not involve the main jet, but certainly will involve the main jet less than what will happen at 50 mph.

As for the WOT AFR Curve. My goal is to elevate that curve (more lean) so that it a) it centers around the 12.5 line, b) increases performance at higher rpm / speed, and c) decreases fuel usage. And when I mention "increasing performance." I don't mean to turn the Rebel into a drag bike or road race bike. I mean, for the Rebel to perhaps not feel like such a dawg at 65 mph or greater.
 

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#27 ·
Great data!

One factor I am wondering about is how “break in” could affect some of the results. I bought my 2016 w/ around 430 miles on the odometer. It now has exactly 1k and I think I notice improved performance. I’m hoping that will continue as it gets fully broken in (maybe it’s there already?)

You bought your 2016 w/ only 44 miles on it! Have you run up the odometer yet enough to be confident break-in is complete?

.
 
#28 ·
You bought your 2016 w/ only 44 miles on it! Have you run up the odometer yet enough to be confident break-in is complete?

Mine has about 1,060 miles or so on it as of this morning. For the past 600 miles or so, it's mainly been just a test mule. As much time as I've spent at WOT (but maybe less than a lot of Rebel riders), I would have to assume it is broke in. Am I confident? I'm confident that with the use it has on it, if there's any break-in left, it would have to be minimal.


This morning, I ordered 3 main jets. My mathematically preferred main jet, a 0.102", and the next size smaller and larger. A (.100" and a 0.105"). It might be a few minutes until I get it installed. This weekend is my turn to a run to my dad's house.


When I get the optimal jet installed, and get the AFRs to the 12.5 zone, I will repeat all the tests. Crossing my fingers I'm not just wasting my time … that may be more likely than I think. :D
 
#29 ·
Okay, so we’re almost identical on the odometer. Let’s call it “broken in” then.

Another mpg data point to share. I’ve been adding fuel usually around 130-140 miles on the trip odometer, without going into reserve. At that point I usually add around 1.8-2.0 gallons. Calculating out to about 68 mpg, with much of the riding stop/go and under 35 mph - - not especially efficient riding.

Right now the trip odometer is at 148.5 miles, and I am still not into the reserve. I’m going to keep riding this tank until I need to switch to reserve.

Using your data on 45-50 mph being the most efficient travel speeds, I am confident I could get much higher mpg out beyond this urban environment.

.
 
#31 · (Edited)
Using your data on 45-50 mph being the most efficient travel speeds, I am confident I could get much higher mpg out beyond this urban environment.
VAReb - Even though somewhere in the 40 - 50 mph range should be the most fuel efficient, I recommend to all riders to sit back and enjoy the ride no matter the speed. Whatever speed is safest and suitable for the conditions, which should lead to the maximum enjoyable ride.


Because either in the optimal fuel economy range or not, the Rebel is very fuel efficient. I bought a Burgman 650 Executive, and gave up on it quickly because it was such a fuel hog. 47 mpg is the best I could do on it. I can almost do that with my Corolla. I think the CVT and the final drive are not very efficient. Sucker runs good and will do 100 mph, but, it is not nearly as enjoyable as the Rebel. I've rode all types. In the future I may find the biggest hulking Goldwing I can find, but for now, I'll ride around on the Rebel and love it.
 
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#30 ·
Not sure how, or if, it relates to this subject, but when I did my last valve check, the plugs were dark, indicating a rich condition. The last mile to the house is 35 mph, followed by a downshift to second, a turn into the neighborhood and less than 100 yards before I shift to neutral, turn off the engine with the key and coast into the driveway.

Today I did a highway speed plug chop. Was doing an indicated 55-60 mph coming up a long, gentle, hill, followed by about a 1/4 mile of level road at the same speed at which point I hit the kill switch and coasted to a stop. The plugs were white, like brand new out of the box white, which surprised me since I put larger, first generation jets in the carb. Current mileage is 18,221 and did an oil change this morning.
 
#32 ·
flitecontrol - I have to say, I've never been a big believer in reading a spark plug. My gut always told me they don't change in color quick enough to be clear enough on what's truly going on with a combustion event. Which is what led me to buying the wideband AFR for my Scamp. I had to replace the whole exhaust on that LA 360 anyway. So when I did, I bought headers, 2.5 inch pipes, ran that through a X-Pipe and Borla mufflers. I had a bung mounted on each exhaust bank. Boy, what an eye opener for me. I had been having the most difficult time cranking the Scamp prior to the new exhaust and gauge because I kept flooding it.


However, upon installing the AFR gauge, I found out quickly, that I was having a hard time starting the Scamp because … I wasn't giving it nearly enough gas! I wasn't flooding it at all! I learned that if there's one thing an LA V8 just loves, and that is GAS. I swear, it seems like I could fill the cylinders with gas and the sucker would fire right up. If it weren't for the AFR gauge, there's no telling just how --itty the car would crank and drive. And how poorly it would be carbureted. I would probably be in a constant state of aggravation with that car. An AFR gauge is a gift from God. Now the Scamp fires right up, and all except for one lean stumble off-idle, (which is a downleg booster Edelbrock trait), the car feels like it is fuel injected, and will melt the tires. That's why when I got the Rebel, I just knew I would have to put the AFR gauge on it. I had a local trustworthy shop do an alignment on the Scamp. And the tech came back and said, "there's one thing about it … that Scamp sure runs good." Had a Scamp load of friends ride with me to lunch one day and wanted to feel the power. One of them commented, "I didn't think it was going to pull like that." And the rest were all in agreement. I have learned a lot about Edelbrock carbs and tuning with an AFR gauge! Anywho…


If you were going 55 - 60 mph uphill, it stands to reason that main jet was largely involved in that. One thing I can note is that once the main jet is involved, the AFR tends to drop very linearly from the point the main jet first gets involved until the throttle is pinned. With a pinned throttle at 55 to 60 mph on the stock main (and all other stock stuff like filter and airbox), the AFRs will hit the 9 to 9.5 level (as shown on my plot). But if you weren't pinned it could have easily been 12.5 or higher … even to slightly above 14.7. There are lots of throttle inputs on the Rebel that run the AFR to a perfect condition. But what's a perfect condition? Depends on who you ask. The engine, the environment, me, you, will all have differing opinions. I like the fact that there are conditions the Rebel goes extremely lean. As long as it runs good. And I like the fact that the stock carb has the ability to completely satisfy both cylinders at max rpm and WOT. I was not expecting it, but the carburetion on the Rebel is able to quickly swing from super lean, to super rich. It can cover a lot of AFR ground.


As for why yours were so white? Dunno, never a big believer in that. Maybe your ride prior to your chop got the spark plugs really white and then your chop pull didn't change their color that quick (just speculation). I have not a clue. But one thing I can tell you, this AFR gauge doesn't lie. Will my tuning make much difference? Meh … maybe not. We've only 234 cc to work with. But any improvement in 65+ mph performance I'll take, especially if it will use a skosh less fuel in doing so.




7mileout
 
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