Tracking down AFR problem w/ WEGOIII

[fuzznut5197]

Well, I had typed up a pretty good reply on reversion, blow back, short circuit losses and lots of other goodies and it looks as if the "dog ate it". I gotta learn to do periodic saves while I "hunt and peck" on my replies, I guess.

Oh man, I would have thoroughly enjoyed that. It could've been a sticky! Something like: "What's going on between my Big Sucker and my Black Anodized End Cap?"

Ed, I didn't know that reversion was air (like fresh air). Is that the low speed gas mass exiting, leaving low pressure behind, which our atmosphere hates, so it shoves some 14.7 back up in there, but now it has momentum so it can't stop, and eventually winds up freaking out the carburetor?

Blow back, I had to look that one up! I must have a lot of it, with 60 degree intake closing 

Now I have to go look up "short circuit losses".

[ederdelyi]

Short circuit loss:

It is the percentage of fresh mass (intake charge) which "short circuits" or passes directly through the chamber and out the exhaust during the overlap period without being burned. This will vary with RPM and is a function of intake/exhaust tuning versus cam timing.

And you thought this thing was just a simple air pump? :>)

Suck, squeeze, bang, blow ... if it was only that simple!

[fuzznut5197]

Ok, got it. A certain pipe immediately came to mind, so here comes the useage in a sentence... 


On certain engines, the Thunderheader has a tendency to over-scavenge below the torque peak, causing short circuit losses.

Howszat??

[ederdelyi]

Works for me ... you gonna PM Bob about it? :>) 

[fuzznut5197]

No way!   

[choseneasy]

N

Works for me ... you gonna PM Bob about it? :>) 

Now THAT is funny!

[fuzznut5197]

I ran out of ideas, and winter was approaching, so I parked it and took the heads off to get worked on. Still don't know what's causing the problem. Is it the valvetrain? Is the electric compression release leaking at high rpm? Won't know until spring arrives, and continue with this "quest"

OK, spring ain't here yet, but it's close enough!
Bike is up and running, and tomorrow I will see if that lean front cylinder problem is still there. I am crossing my fingers that it will be gone, but we'll see. Here is the first WEGO log I just recorded, cold startup to warm idle, and then adjust the idle mixture. Startup with full enrichner (3500sec), enrichner off, throttle lock on (3550), throttle lock off and idling at 3800sec, AFR was at 12:1 so adjusted mixture to 13:1 (was adjusting between 3850 to 3950).

[fuzznut5197]

Baa, it's still there. 3rd gear run.

It has to be fake. The rpm line is straight right up to redline. That rpm line would fold over like a wet noodle if it was really lean. It pulls hard and consistent till redline, no signs of misfiring. I'm thinking that with this big cam's overlap and duration, I got the sensor too close to the exhaust port. The rear doesn't do it, but it's probably an artifact of what's going on in the y manifold intake.
I'll put an O2 bung further from the port.

[Evo160K]

Are you able to swap the o2 sensors, sort of verify it's not a sensor issue?

[fuzznut5197]

Are you able to swap the o2 sensors, sort of verify it's not a sensor issue?

I put the sensor on the rear pipe a couple of times and it works fine there.

All right, I give up. Welded a bung a foot downstream of the old bung, same result. This time I did a 4th gear run, starting at 48mph, 2700rpm, ending at 109mph, 6200rpm. 5.2 seconds between the two.

[ederdelyi]

Fuzz,
Didn't you see the same thing with the dyno sniffer setup? That would eliminate the O2 sensors and bung location from the equation, in my mind. Next thing to note, does the 3rd gear run look the same with the new bung location as the old one? It appears that the high speed run in 4th looks better than the lower speed runs and the dyno results you posted previously. If that is the case, you may have found that the airstream/low pressure extraction properties of the muffler/megaphone are helping to eliminate the amount of fresh air being pulled up the pipe ... odd fire engines with lots of overlap do strange things to the tuning pulses :>)

EDIT: Changed the gears ... how does a 2nd gear run look in comparison to 3rd and 4th? If speed does alter the results you may be on to something. The 4th gear run sure looks better than the others to me.

[fuzznut5197]

Fuzz,
Didn't you see the same thing with the dyno sniffer setup? That would eliminate the O2 sensors and bung location from the equation, in my mind.

Yeah but I'm at the point of trying anything.  I put the bung right where a sniffer tube would end up at, a little beyond the first major bend.

Next thing to note, does the 3rd gear run look the same with the new bung location as the old one? It appears that the high speed run in 4th looks better than the lower speed runs and the dyno results you posted previously.

They all look the same, 4th looks better because I changed the rpm scale on the graph. I can't really compare to the original dyno, as that was a completely different exhaust. 2nd gear? Can't do them anymore, it just wheelies. 

But I've noticed something. The AFR is not going off the scale anymore, like it was last year. The only change was head work. There is one consistency: it always screws up at 4,500 rpm.
According to PipeMax, this primary pipe's tuning is from 4,500 - 6,200rpm, peak at 5,700. If I move the cursor to the "center" of the bad afr "curve, it's always around 5,500. I't almost as if the bad curve is mirroring the pipe's wave tuning. Could it be yanking out fresh air/fuel at that point, perhaps with some help from the intake if there's a pressure peak at the intake valve? Or maybe the rear doesn't do it from having a trough at IVO.

[FLTRI]

Fuzz,
A couple questions:
1) Can you smooth the signal to get rid of some of the jitter/noise in the signal? That may help to better see the AFR trend. Maybe move the average by 10?
2) You got to admit that the AFR looks pretty good during decel @ 714-720secs. That simply doesn't make any sense from what should normally happen during decel....lean, not rich
3) AFR looks to be somewhere around 14.5-16.0:1 @700-708 secs at the steady T/P state 2000-2300rpm. Lean, right??
4) Upon acceleration @ 710 secs the AFR dips to about 12.5:1, then recovers and gets lean to the end of the acceleration run.

Overall looks lean during cruise and lean on acceleration except for the over evacuation of the exhaust, but gets to proper AFR during deceleration.
Just my observation, BWTFDIK? Right?

[fuzznut5197]

Hey Bob,

1- Naa, I can't smooth like in Winpep.

2- It doesn't make sense because I'm pulling the clutch in after the rev limiter hits, not spooling it down like on a dyno. After hitting 109mph, it would take a heck of a lot longer than 4 seconds to reach idle if the clutch was engaged.

3- I did steady state tests last year, ad it was fine. I don't think there's any valid steady state data on this chart. While in might be lean because it was only 45 degrees outside, that section you're looking at was a process of decellerating. I made the chart wider below so you can see what was going on. At 680 I'm in first, then you see the 2-3-4 gear peaks, the I'm deccelerating to get back down to 2,000rpm. Even though it looks like it's starting to accelerate at 705, the bike is still slowing down at that point.

4- Yeah, after the accel pump dip, there is the small window between 3500 and 4500 rpm where the AFR is correct.

Just my observation, BWTFDIK? Right?

A heck of a lot more than I ever will, that's for sure. 


So, if it's over evacuation, I could try to test that by introducing back pressure. Like 10 disks/closed end cap would plug this motor up good.

[fuzznut5197]

I'll do that test Wednesday, when it will be a scalding 60 degrees outside. I got to get this pipe painted now, with some nice BBQ black. Maybe that'll fix it. 

[ederdelyi]

At this point I'd consider trying a set of 2:2 pipes to eliminate the possible interaction of the 2:1. Also, have you looked at the burn pattern/plugs (use a magnifier to check the fuel ring, not the insulator color) on the front cylinder vs the rear? The rear still look good like it did before the rebuild?

Since the trend has been there on various incarnations of 2:1 exhaust and both the dyno and Wego have shown the same behavior I'm leaning toward the possibility of either some air bleed/emulsion tube mods or perhaps trying to pressurize the tank (Miks on big motors sometimes need a fuel pump as the float chamber is rather small), in fact, I knew a guy who used to make a spacer plate for the Miks float chamber to increase the capacity.

If we can establish the validity of the front cylinder actually going lean regardless of exhaust tune then it should be easier to zero in on the cause/fix. I have some other ideas, but until we eliminate some other things it makes no sense to even bring them up.

[fuzznut5197]

Hi Ed,

I do have the stock 2-2 head pipes with cycle shack mufflers, but I'm fresh out of O2 bungs. 

There is nowhere to do a plug chop around here without going directly to jail. I would have do that at the local drag strip. I didn't check the rear again yet.

I'll do some more runs Wednesday, but the bike is going on the dyno on Friday. If the HP curve looks normal, then...   ?

I did a bunch of stuff to the mikuni over the winter, whether it helps or not is unknown. The float was real sloppy and could induce foaming, so I tightened up all axis (except for Z, that would be bad!). And I "ported" the fuel inlet so the majority of fuel flows smoothly down the back side of the bowl, as opposed to spraying all over the float bracket. With a full tank of gas, there is a lot of pressure and flow through that huge needle seat. The main jet is 185, not the biggest gas sucker. The "emulsion" tube is solid, just pure gas flowing out the needle jet. I remember Bruce playing around with emulsion on a mik, and found that it just messed up everything. I could just put the G carb on there and see what that one does.

[Sonny S.]

Would be interesting to run data log on the WEGO during the dyno run.
15 sec. time / .1 log.

[ederdelyi]

Well, I gotta admit that at this point I'd have my DA setup on it and be checking EGT's as well as using a 5 gas :>) Considering what you have to work with, you need to verify the validity of what's being displayed. That's why I would be looking at whatever I had available to verify that the cylinder really is going lean. Those sensors are not perfect and can do some weird $hit at times, but the fact that both the Wego and the dyno setup show the same trend is a clue ... still not proof that both could be wrong.

BTW, a run on the dyno is about as close as you can get to a plug chop on the road/track. Got access to a bore scope to look at the burn patterns? IR gun for head temps? I prefer thermocouples and CHT gauges, but a gun is better than nothing.

[FLTRI]

Fuzz,
I can't get through all the data noise/misinformation here:


The first circled event goes from almost full rich to full lean in a very short order?
The second event looks to go to full rich during rpm acceleration and behaves normally, albeit rich, when shifts occur (throttle closed AFR goes lean).

Third event if that was not you closing the throttle for an instance (would look normal), the data there too is highly suspect.

Event 4, the AFR if the throttle is closed look pretty normal, lean. If so why would not the decel after the high rpm run also go lean as would be expected?

The AFR changes a lot (13:1 to 15.5-16:1) as with the last encircled event, but it is exceedingly difficult to look at such a long period of data in such a short graph. That is why I commented on the short period data in my last message the way I did...the data doesn't look like it is reliable.
Unfortunately it is difficult to better analyze this data because there is no T/P to coordinate the AFR data with since T/P should be what changes the AFR.
I have to say if the rear cylinder reads correctly and the bike runs really well, the data you are getting from the front cylinder, for whatever reason, cannot be relied upon for tuning.
JMHO,
Bob

[1997bagger]

I might be able to back up the inconsistency of the Wego3, I have been chasing roll-on detonation at 50-55 mph. Have been running individual cylinder data logging and making corrections per AFR logged chart, AFR is set @ 13.2 in troubled area and verified with Wego3 digital AFR gauge while riding in that area. Rattle is unsafe and timing is completely removed at roll-on area with PC3, problem is fuel map in that cell area has very little fuel added at 40% tp and a 0 right behind it at 60 % per Wego data chart with 60-80's earlier in the map running 13.5 and no problems.
Located exact trouble area (0 per wego) with tp and rpm and added fuel to 12.5 and eliminated detonation, the Wego3 system seems to have a loop hole or not accurate in some areas as 13.2 should work but very little fuel was being added to run 13.2 in that 50-55 mph acceleration area per data chart, can't be right.

[fuzznut5197]

Well, did more tests today and came to the conclusion that the lean O2 reading on the front cylinder at WOT "is just going to do that". The front works fine for idle, part throttle etc readings, just going to have to use the rear for WOT stuff.


The wave tuning is such that I probably have fresh A/F getting past the EV before it closes in the problem area. I tried plugging the exhaust up with 10 disks + end cap. Didn't show much. If this were a 2 stroke, a divergent cone would shove that A/F right back in there. 10 disks...





Now, before I get to the last chart, I have to post this one so you can compare the two. They are both with 28 disks, closed cap.





This next chart, I take the air cleaner off and install a 7"....      PVC pipe! I wanted to see the effect of altered intake tuning, so I used what was lying around. The ID of the pipe is 52mm, so it's not too far off from the carb's 48mm. A little OD sanding and it fit perfectly in the S&S bracket.




Well well, after the rich low rpm dip, I have a nice flat area of A/F that averages out to 13 :1. And while every other run before this started going lean at exactly 4,500 rpm, this one stays good until 5,700. So, because it doesn't seem to affect performance, I have to put this to bed.
I have been using these runs for another use also:  as a timer. Granted, 1/10 second intervals is not a lot of resolution, but it was good enough to show performance differences on these 3rd gear runs. If you have the space, 4th gear would be statistically better. I measured the time between 3,000 and 6,200 rpm:

10 disks, closed end cap       2.85 seconds
Plate with 1 7/8" hole           2.6 seconds
28 disks, closed end cap       2.55 seconds
Above, with carb extension   2.55 seconds
No disks                             2.45 seconds

So, no disks was the quickest, while 10 disks was naturally the slowest. The two with 28 disks were identical, but the power spread had shifted. I noticed when running the carb stack, that the lower end was weaker, the midrange very strong, and the top end a little weaker. Without the stack, the power was more linear. But as a whole, they got from point A to B at the same time. Neat-O!   


I have to post this, picture yourself riding down the road with this...   




I'll be back in 1 hour.

[fuzznut5197]

Sonny- I'll leave the wego on and running. It has to stay in there, I cant find a bung plug locally.

Ed- I noticed between my runs and the dyno, different points where the afr goes lean. The dyno one had a 28" long front primary, it's 40" now. More wave tuning effects?
Burn patterns? I had these heads off, the pistons looked exactly the same. Didn't see any indication of burning lean or detonation.

Bob- Don't know why you're looking at all the other stuff when my only concern was 100% WOT.
But your last sentence is accurate.

[FLTRI]

Bob- Don't know why you're looking at all the other stuff when my only concern was 100% WOT.
But your last sentence is accurate.

I only wanted to point out the inconsistencies I noticed in the entire recording throughout different TP, RPM etc. I regularly read this type of data for race teams and if I saw that much inconstancy it would not be considered reliable enough to make positive changes from. We only got a couple sessions prior to qualifying and the race to make changes and the data needed to be clean, without spikes and/or dropouts or we couldn't use it.
What really stumps me is how and why the O2 sensor sees so much air (phoney lean) @ high RPM/WOT when we know the exhaust is most reliable with out air (reversion, etc) getting into the mix.
If the lean reading came after the WOT run I would say there is simple data offset due to time lag from the RPMs to AFR, but it is lean reading during high rpm acceleration, then when you roll off the throttle it goes to normal reading (14.5ish), then a spike down to rich. I guess that could be just noise.

[fuzznut5197]

I only wanted to point out the inconsistencies I noticed in the entire recording throughout different TP, RPM etc. I regularly read this type of data for race teams and if I saw that much inconstancy it would not be considered reliable enough to make positive changes from. We only got a couple sessions prior to qualifying and the race to make changes and the data needed to be clean, without spikes and/or dropouts or we couldn't use it.

Yeah but with race data logging, there's not much variation in what's being logged. They're in a narrow rpm window, narrow speed window, etc. They're not riding on the street, dodging traffic and stopping for red lights.  . I can explain all those data points you pointed out, except for "you know which one".    I'll explain the first event you pointed out...

665- I am stopped, then slowly let out the clutch, the revs drop (670), and I ease the throttle to get moving- just a very slight rpm increase. And then...  Bam!, I whack the throttle open. You see a big shot of accel pump make it go rich, and then...   uh oh, I opened the Mikuni slide too much! Too big of a hole = no velocity = no fuel getting sucked out of the needle. I am lean, until the revs start building, velocity is picking up, fuel is starting to flow, and the AF starts returning to normal. That's all that was.

What really stumps me is how and why the O2 sensor sees so much air (phoney lean) @ high RPM/WOT when we know the exhaust is most reliable with out air (reversion, etc) getting into the mix.

Me too!!! I wish there was a dyno chart with AF of the same "build", just a crate 124 with a Mik48. I can't be the only one...