Arctic Chat : Arctic Cat Forum banner

A/F Ratios for a 500

1K views 12 replies 3 participants last post by  spooln30 
#1 ·
Need a little bit of help finding out if my a/f ratios are ok or do I need to change something.
To start of its a 06 500i cat with two inch snorkel of the stock air box which has a UNI filter inside and I also have a moded stock muffler and the dynojet kit with a 148 main jet and the dynojet needle on the 3rd spot down all the other jets are factory. I borrow my coworkers wideband and im getting the following, also this numbers were archive under load riding down a trail*

Cold idle - 12.5.1

Normal operating temp idel -11.3.1

1/4 throttle - 12.9.1 to 13.1.1

1/2 throttle - 12.5.1

3/4 throttle - 11.9.1 to 12.1.1

Full throttle - 10.7.1

I also attach a picture of a brand new plug after riding to get the numbers above Thanx in advance for the help
 

Attachments

See less See more
1
#2 ·
if those are ratios you're reading while the engine has a load on it, your 1/4 and 1/2 ratios are close to perfect. it starts getting a little rich at 3/4 and full throttle though. to help that out drop the main jet size to maybe a 145-146 range and raise your needle to keep the 1/4 and 1/2 where it is.

Idle should be a little rich, starts better and runs better rich when cold. 11.6 to about 11.8 on idle is what I consider a sweet spot. keep in mind extended idle may start to foul a plug though. If it does, you can always close the pms a little or maybe reduce the pilot jet a size if needed. It's not that overly rich now though and is probably ok.

under full load, as flat as you can keep the ratios to around 12.8 to1 plus or minus 2 tenths the better off you will be for best power under load. Meaning hard acceleration.

it's normal and desirable for light load cruising to lean out to the upper 13's and low 14's as long as it's not over 14.7 to 1.
 
#3 ·
Thanx for the info Wyo I switch out the 148 to the 146 this afternoon and it just felt like a dog at 1/2 thru wot and every time i would let go of the throttle it would of back fire pretty bad so just put the 148 back in for the time being going riding this up coming weekend and will see how it runs
 
#4 ·
your results of excessive backfiring and running poor mid range is pointing to a very lean needle after you reduced the size of the main. everything that is metered by the needle first must pass through the main.
are you sure your A/F meter is calibrated?
are you using a wide band sensor?
is your float bowl fuel level correct?
atomizer ports or those tiny holes on the sides of the needle jet retainer may be plugged,
the air jets may be plugged, (air jets are those tiny ports and the bottom third of the main carb air intake bore)
 
#6 ·
I have a wideband installed on my 02 500 and usually my afrs are:

14.5 @ idle- warm richer when cold
10.9-11.5 @ 1/4 throttle
13-13.5 @ 1/2 & 3/4 throttle
12.2-12.5 @ wot

My 1/4 throttle circuit is rich and I've tried everything to lean it out with no success. I even tried a smaller pilot jet, adjusting the needle and the PMS but it still remained the same.
Yours looks good beside the rich WOT and imo I would lean the idle out closer to 14. 11.3 afr at idle is too rich. When your at a idle with a engjne up to temp it should be close to 14.7.
When I was tuning mine I had my idle running at 11.5-11.8 and when I would throttle aggressively it would fall flat on its face. Leaned her out and it takes off quick. I'm not too worried about my rich 1/4 circuit because I'm never really riding at 1/4 any way. I guess it would be nice to have it perfect but I gave up after trying everything. GL
 
#10 ·
you are right I forgot to mention my idle is that rich when its cold, it does lean up when its warmed up good, not as lean as yours is, though.

Carburetors are nearly impossible to get ratios flat just by changing jetting alone. You can achieve some further success by changing the slide (amount of cut-away), Slide spring, Actual needle jet and different needle tapers. That really get to become a headache trying different things and checking the results for just a little more benefit when it comes down to it, Once you've got it as close as you can get it with just jetting. you can pretty much says it's good Trouble is, most of these parts are not available as carb tuning parts for your run-of-the-mill Keihin carbs. Many sources claim 12.8 to 1 is a perfect ratio. Tell you the truth I doubt if you can feel the difference between 12.5, 13.1 and 12.8, but may make a few 100's of a second difference in a drag race???? An EFI on the other hand can be set nearly perfect through out the entire range if one sticks at it long enough.
 
#7 ·
Btw how far back from the cylinder head is the o2 bung on the exhaust pipe? You don't want it too close and I have mine about where the seat starts.
 
#11 ·
Sorry for going off a bit but I seen a dyno video of a new WC Trail and stock there running 11.4 afr at wot. Seems a tad rich to me. But I now know the stock blocks can take 9 psi all day long. Good news because that would give it roughly 120 hp without needing internals. Can't wait.
 
#13 ·
Good to hear man.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top