Larger pilot jet

[james250ninja]

I have a stock 08 ninja 250s
Was wondering what would happen if i went size larger on the pilot jets only..rather than go larger on main jet.
Everything stock on my bike

[Triple Jim]

What's your goal? Pilot jets are active only down around idle, and your mixture screws should have enough range to get your idle mixture correct without changing the jets.

[DannoXYZ]

The factory main jet is actually too rich. With my Tyga exhaust, the DynoJet kit actually has a smaller-than-stock main jet for a 2-3hp gain. Remember that '60s hot-rodder slogan?

[jkv45]

Originally Posted by JacRyann

The factory main jet is actually too rich. With my Tyga exhaust, the DynoJet kit actually has a smaller-than-stock main jet for a 2-3hp gain. Remember that '60s hot-rodder slogan?

Dynojet has their own numbering system that doesn't correlate with the OEM jets, so the numbers are meaningless in comparison.

Comparing actual specs (internal measurements) would give you a comparison, but that's the only way to know how much richer or leaner it is.

That's why I prefer Factory Pro jet kits over Dynojet.

[jkv45]

Originally Posted by james250ninja

I have a stock 08 ninja 250s
Was wondering what would happen if i went size larger on the pilot jets only..rather than go larger on main jet.
Everything stock on my bike

They control opposite ends of the the fuel mixture, and have minimal effect on each other.

https://faq.ninja250.org/wiki/How_a_...arbs_explained

[Ralgha]

I have a Keihin 95 main jet in mine with an AreaP full exhaust. Stock is 98, so stock is too rich on some specimens at least.

[DannoXYZ]

Originally Posted by jkv45

Dynojet has their own numbering system that doesn't correlate with the OEM jets, so the numbers are meaningless in comparison.

Comparing actual specs (internal measurements) would give you a comparison, but that's the only way to know how much richer or leaner it is.

That's why I prefer Factory Pro jet kits over Dynojet.

I only go by the orifice size in the jet, and even then, it doesn't cross brands due to the taper going into and out of the jet. Dynojet numbering goes by orifice size in mm, so a 96 jet is 0.96mm. Easy to compare. Which is close to factory Keihin 98 @ 0.0375" or so.

Only way to know actual AFR and when to go richer or leaner is with dyno or wideband-O2. So far from our empirical data, going to leaner mixture at WOT gives more power with factory and aftermarket exhaust.

[DannoXYZ]

Originally Posted by james250ninja

I have a stock 08 ninja 250s
Was wondering what would happen if i went size larger on the pilot jets only..rather than go larger on main jet.
Everything stock on my bike

As mentioned, you can adjust low-end AFR with the mixture screws, so no need to change pilot jets. Main jets tend to be too rich and more power can be had by going smaller & leaner (and/or coupled with high-RPM air-flow increasing mods). Some threads that discusses that here:

https://www.ninjette.org/forums/showthread.php?t=50337
https://www.ninjette.org/forums/showthread.php?t=55927

[Triple Jim]

I would perform a correctly done plug chop before going to leaner main jets.