Jetting Update: Round 1..

[Blake]

Hey Everyone,

finally got settled down and was able to take a ride yesterday with my laptop hooked up to the afr meter and get some good readings.

first off...im running the "race exhaust" from Rick G that had 2 seperate 1.5" pipes(1 for each cylinder) and the stock flapper airbox and uni filter.

...also, for the front cylinder, last week when i was fiddling with the meter and laptop i was setting the idle mixure, and ended up having to turn the screw out a turn or so (dont remember specifically) to get it down to about 14:1...so its not too good of a "stock setting"

and also, i just want to make it clear that when i put this new exhaust on, it definately changed the flow characteristics and screwed with the jetting.  so dont take my findings as perfect for a stock exhaust setup.  

but here's the results:

(side note:  each pictures is a screen shot of the progam i use to log and review the data.  the big number on the top left is the air/fuel ratio, and also thers the RPM.  those numbers being shown are corresponding to the white line that goes through the graph.  i just selected a spot to make it a little easier to read.  as for the two lines.  The White line is the AFR graph with the cooresponding scale on the left.  The Blue line is the RPM with its own scale shown on the left too.)   ALSO, as you can see the graphs jump around a lot.  im still trying to figure out the logging so that i can get a smoother line (right now its logging at 100ms intervals).  but to figure it out pretty much just imagine a line in the middle of that graph and thats where its at.

pictures left in link form for those not on a cable modem.

Front Cylinder at Idle, with choke (after idle screw was turned)
http://filebox.vt.edu/users/bstoddar/Vision/AFR%20Graphs/front20idle%20choke.jpg

Front Cylinder at 7,000 RPM (stock jetting) - The section of line that the white line passes through is the 7000 section. also, 7000 is what i found to be about 1/2 throttle going up a pretty steep mountain stretch of highway.
http://filebox.vt.edu/users/bstoddar/Vision/AFR%20Graphs/front%207000.jpg

Front Cylinder 9,500rpm (stock jetting)  9,500-9700 is about 3/4 throttle.
http://filebox.vt.edu/users/bstoddar/Vision/AFR%20Graphs/front%20stock%209500.jpg


(full throttle discussion later after rear cylinder)

Rear Cylinder Idle (No choke)  As you can see, this is WAY lean (you want it around 13.5 at idle)   and this is with the recommended 2.5 turns out (or is it 4?..its whatever the reccomended "start point" is at.  thats what i set it at after dipping the carbs)  but as you can see, the idle is what makes me wonder how much of a difference the free flowing aspect of the new exhaust makes.
http://filebox.vt.edu/users/bstoddar/Vision/AFR%20Graphs/Rear%20Idle.jpg

Rear Cylinder 5,500 RPM (a little lean)
http://filebox.vt.edu/users/bstoddar/Vision/AFR%20Graphs/rear%205500.jpg

Rear Cylinder 7,000 RPM (little lean too)
http://filebox.vt.edu/users/bstoddar/Vision/AFR%20Graphs/rear%207000.jpg

Rear Cylinder 9,500 RPM (actually looks pretty good)
http://filebox.vt.edu/users/bstoddar/Vision/AFR%20Graphs/rear%209500.jpg



There you have it.  ok..now about for max throttle.  as i said, 3/4 throttle produced about 9,500-9,700 rpm.  as redline starts at 10,000 rpm i didnt really want to cruise at 11-12k rpm to find full throttle.  but i did remember a "trick" my auto mechanic neighbor told me.  If you run at full throttle (still accelerating) and let off the throttle about 1/8" turn or even a little less, if the mixture is lean, youll actually accelerate (which is what happened to me).  if your jetting is on, you should decelerate a little.  so my natural conclusion is that the main jet is a little lean.  maybe a size or two.


now to sum it up:

front cylinder:
idle: fine
pilot jet: size or two too lean
main jet: size or two too leanl

rear cylinder:
idle: WAY lean
pilot jet: size or two too lean
main jet: possible on..maybe a size too lean

now...  yesterday i went to the local dealership to order jets.  i ordered 130's, 135's, 127.5.  now, what i found out.  the pilot jets out carb uses are #60 (for 82) and 60's are the biggest you can go.  i talked to the guy and he said it MIGHT work to get a #60 with holes on the side of the jet (let a little more fuel in).  so i went ahead and ordered #60 pilot jets that have 1 hole on two sides of the shaft, and 2 holes on the other two sides of the shaft.  maybe itll make a difference, maybe it wont.  hopefully my main jet change will help some with the mid range.      I also asked the guy if i could just go down a size or two in the pilot air jet, and he said ideally you wouldnt want to, but if push comes to shove it might work.  so i might have to try that out. (have nothing to lose so i might as well fiddle with all the jets :)  )

hopefully my jets will get here either tomorrow or thursday so i can start changing jets out and see what kind of difference they make.

once i can get the carbs jetted with the stock airbox, im going to throw on the k&N's and change out the main jet to a 135 and see if i cant get a starting point to jetting for those.


Just thought id update.


Blake

[nvdranger]

:o well i have nothin to add b/c thats way over my head.  fyi the first hyperlink does not work, shows cannot find server.  great write up and good luck getting this stuff figgured out.

Ken

[Blake]

hmm..sorry about the links..

try

http://filebox.vt.edu/users/bstoddar/Vision/


under the folder "AFR Graphs"


hope that helps.


thanks for the comments..  this is definately a learning process for me, and just thought id share what i found with everyone else.


Blake

[silicon_toad2000]

If I rember rightly, when you change the air jets, the change has less effect at lower revs and more effect at higher revs.
so if you go a smaller air jet, the mixture enrichment will increase more at higher revs than it will at lower revs.
hope this helps.
have you thought of getting a set of jet drills and enlarging the jets yourself? problem is that you loose your reference points.

[Greenbee]

where can I get that program?

[Blake]

Silicon,

I was actually thinking i might have to go get a set of drills if this new pilot jet doesnt help richen up the mixture.  thanks for the thought about the air jet though, i never knew that.  



and Greenbee,

the program only works with the AFR meter.  its just a logging program a guy created so you can log on a computer instead of having to constantly look at the meter display while driving.

the program itself is $20 at http://www.devtechnics.com/tewblog.htm

the actual AFR meter, unfortunatly will set you back about $600 bucks or so depending on what option you get. http://wbo2.com/

the whole reason i bought the afr meter itself was that its a BIG help when tuning carbs, and with all the old carburated cars and bikes i have, its cheaper to buy the meter instead of taking them all somewhere to have them jetted ($200-$400 a session) .

but unless your doing some major jetting to more than just the vision, its not really worth the expense.

[rick_nowak]

the verymost recent edition of "Grassroots Motorsports" gives a review of several different wideband oxygen sensors.  very informative.

[jasonm.]

The stock #60 pilots should be fine for you. But going up on the mains will make it richer past 5000. Where the mains start to kick in. I suggest playing with the pilot airs first to get both the front and read readings the same. The #60 pilots can supply enough gas to kill the engine if the screws are turned out far enough. Also the opening of the flapper is adjustable. ON YOUR LINK> The rear does not look bad at higher rpm. And the front does not look to be off by much. ?On the charts ...Could the spikes be from shifting gears?

[Blake]

Hey jason,

before i throw in those different pilot jets im thinking of actually changing the pilot airs..

im not sure which cylinder it is..havent looked at the charts a while..but it really actually doesnt feel to be off by much....the mains maybe a size or two too small.. but it definately pulls like a horse.  the shop hasnt called me yet about the jets so im going to head there monday to go pick them up and hopefully figure things out.

as for the BIG spikes, thats me shifting down to get the rev's up.  you cant see it in those screen captures because i cropped it to get a better view, but the part that i look at is where the rpms "generally" stayed around the same place..

also... definately thanks for the flapper door adjustment..i never knew that.  think i may have to go take a look at it tomorrow.



also... Lucky wanted me to do a "cold engine with choke" check with the meter.. seems both him and i..on the front cylinder, it seems to warm up a LOT slower (header is warm and can be touched for a while..much slower than the rear)..  i completely got sidtracked these past couple of days, but hopefully tomorrow ill be able to do the front, and monday the rear (want a nice cold morning start).



Blake

[Cdnlouie]

Very interesting work you are doing Blake.  I can attest also to the slower front cylinder warm-up.  My Vision has stock mains and 135 rear and 130 front pilots.  I recently matched the front with another 135.  My Vision has run well for the last two years but I have wondered about the slow front start-up.  The front needs choke to come online, but the rear fires up without choke.  I am due for a carb sync, but intend to look further into this issue as I have some time to play.  I would be interested in any others who may have worked through this one.  It is certainly not a serious problem as it only requires a bit of choke and both fire up great, but it just intrigues the ever curious mind who likes to understand the things that elude the mortal man.

Great work,

Louie

[Lucky]

poor choke performance:
Check the passages marked in red in the pic below, these are the fuel feeds for the choke.  if you can apply air to the top hole maked "to feed hole" you should see bubbles come out the small hole in the bowl (arrow) this is the fuel feed for the pickup tube in the carb top that leads to the starter plunger.

the hole at the top left of the pic is where the fuel mixture goes after the plunger. it leads to the throttle plates. be sure all these are clear.  i've found the feed hole cloggs easily.

[jasonm.]

Blake, If you have '82 carbs ..you have #60 pilot gas jets. '83...#50's. It is so easy to change the pilot airs...try it if you want to. Also the low speed screw setting makes a difference higher up(rpm) than most folks are aware of. Hey, if you come to the Yamnkee Antique Meet in CT. I'll bring both my carb sync and digital tach. Except I don't remember where you live.

[Lucky]

So you'll bee there? cool!  
Blake is in Va.