Hi all,

Playing with a 08 GS500F down here in Melbourne, Australia.
Local bike mech shop had a dyno day this morning so thought this would be a good chance to see how far out I am with the rejetting.

Mods so far:
Megacycle carbon slip on (cut weld)
K&N Lunch box air filter
Airfuel mixture screws at 2.5 turns out.
Rejetted to:
Pilot: 20
Mid Main: 62.5
Main: 142.5

Heres what my dyno graph looks like:


And here is a video of my dyno run:
http://www.youtube.com/watch?v=-bfjLDGhlrA
As you can see shes popping like nuts off the throttle and popping some flames aswell. Also noticed a bit of smoke at redline.

She is running rich low end and then leaning out on mid and top end as you can see in the graph.
Pulling 37.14 hp. Getting 4.2L per 100km atm for mileage.

Mechanic suggested going up 2 sizes on the main jet to 147.5 or even a 150 jet, and to play around with the needles.

What you guys reckon? 

with slip on and K&N Lunchbox you should try 147.5.
It may still pop on hard deceleration though. Mine does, but it's not an issue because it pulls nicely all the way through gears.

Yeah, in my experience, any engine that uses carburetors is going to backfire on hard deceleration when set up correctly.

Wow...your experience is completely different from mine.  A little chortling is ok but afterfiring is never acceptable, unless you want to sound like the Harley shaZam! that rolls past my house all the time.  More fuel my son.

Don't forget that these bikes have an electronic valve that allows more air through the carbs on decel and also the air pump on the exhaust.

When I took all that off mine, the popping and banging stopped, apart from the occasional bang.

Well my major concern with running this lean, would it adversely affect engine wear or damage?

Sure a little popping is ok but my exhaust on decel sounds like a popcorn machine.

haha.  Just bump it up to 150, that's basically what everyone else runs unless you're high altitude

^^^^
because 'everyone' runs it doesn't mean it's good or adequate in every situation.
Original poster has, what sounds like, custom fitted slip on which means stock headers.
150 main will be too large.
I have custom fitted bolt-on, stock headers and 147.5 is still tiny bit on a rich side. Pulls very well but like I said earlier it pops on deceleration.

Quote from: kml.krk on July 04, 2010, 12:26:13 PM
^^^^
because 'everyone' runs it doesn't mean it's good or adequate in every situation.
Original poster has, what sounds like, custom fitted slip on which means stock headers.
150 main will be too large.
I have custom fitted bolt-on, stock headers and 147.5 is still tiny bit on a rich side. Pulls very well but like I said earlier it pops on deceleration.

I've got stock header's and a custom slip-on too, and 150 is money, although I've got a '98 with the 2-circuit carbs, and I'm at sea level.

I have a jardine full system and lunch box, when I dyno tuned mine (with a lambda sensor) I ended up needing 20-62.5-152.5 jets and +1 washer, it ended up at 12.5:1 afr (stock was 13:1). with the looks of your graph and your lower power than stock (stock is 39whp) your probobly at around 16:1afr (very dangerous). With a slip-on on the stock headers a 150 main should be good.

also DJ jets/needles dont use the same units of measurment as all other mikuni jets. so a 150dj is not the same as a 150 mikuni jet. so junk all the DJ parts, use the stock needles, and buy correct mikuni jets and washers.

Hi guys,

Appreciate the feedback.
In regards to AFR its peaking at 14.5:1 on top end.
Dyno guys said it wouldn't damage the engine apparently.
But yes it does feel a little flat pulling up the revs.
And would explain my fuel economy being at 4.2L per 100km (which is great!)
but yes i might try a bigger jet.
Also forgot to mention atm it is winter in melbourne so the ambient temperature is sub 10degrees lately.

On an update i pulled out the spark plugs and they were whiteish. So replaced them. I reckon it pops more now after the fresh plug change. Weird.

Great thing about the popping though, it sure keeps those cagers away. haha

Also guys I got the air fuel mixture screws at 2.5 screws out.
Do you think I should leave it at that? Or give it some more turns out?
Does this air fuel mixture only affect low range?
Because my low range on the graph is rich.

14.5 afr is way too lean, the most power will be made with 13-13.5:1. but to be safe 12.5-12.8:1 is what I shoot for.

The mix screws only affect idle/just-off-idle.

P.S. I have my idle screws 3.5 turns out. you have to tune those by ear, how ever many turns it takes to get it to idle the best.