Bigger jets?

[dirtydog]

Seeing as I'm going to be having my carbs apart again this week, is it worth going up a jet size?

At the moment its got a bmc air filter, akrapovic system with a cut down can and some tank risers on it.
It pops quite a bit on overrun, which jambo pointed out could be that its running lean.

So is it worth upping the jets from the standard size?

[Bibio]

how does it feel when its running and what colour are the plug insulators.

[dirtydog]

Feels ok when it is running properly (sticking float/needle issues at the mo hence taking them apart again). Changed the spark plugs a few months back but didn't look at the colour of them. Just concerned about all the popping on overrun and the fact it should have more air going through but I've not upped the fuel

[Bibio]

well from what i know popping is an air leak in the exhaust system or unburnt fuel.

if you can crack the throttle open and it revs freely and the plugs are a nice tan/biscuit colour then all is well. if the plugs are white then bigger main jets.

the man to ask though is Y_C.

What the plugs look like depends on what the bike was doing when you shut it off. If it was idling, which is almost always what it's doing before shutdown, the plug color will tell you about idle mixture and only idle mixture.
If you shut it down at half throttle, you'll learn about the mid-range jets and needles (plus the idle mixture, since the idle circuit is still working). Since most normal operation is at part throttle settings, you need to have your idle mixture right, then check the mid-range and adjust/shim the needles up if needed. Only after these two are correct does it make any sense to check the wide open throttle color by shutting down after a brief full throttle run. Then you'll know if you need bigger main jets, or not.

[yorkie_chris]

Depends which BMC filter

[dirtydog]

Originally Posted by yorkie_chris

Depends which BMC filter

I think its the bmc road filter, its not got the massive hole in the top of it

[yorkie_chris]

In that case I would stick with stock jets unless you are having a specific problem that sounds lean. Did it run ok on that setup and jetting before?

Popping and farting on the overrun is more likely to be an exhaust leak that does no harm at all. Popping and a different sort of banging on the overrun is more likely an intake leak.

[dirtydog]

Yeah it ran ok with that set up on the previous sv, this one hasn't done many miles with this set up.

You can try to tune carbs by sound and feel and what works in some other engine or by somebody's recommendation of what worked for them, or you can spend lots of money on dyno time, hoping the dyno operator knows what he's doing, or, you can do what everybody did before dyno's, and tune by plug color.
It's tedious, especially when the plugs aren't easy to get to, and the idle mixture screws are not easily accessible, but, it works as good as a dyno tune, and it doesn't cost much at all, mostly time.

Start with the idle circuits. When they're right, do half throttle chops and adjust the needles until the mid-range is right, then do full throttle chops and change main jets if necessary until the carbs are right throughout the entire range and your engine runs sweet and clean.